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Industrial by-products, such as bauxite residue, may be used to treat phosphorus (P)-enriched water and wastewater. Once fully saturated, they may be reused as P fertilisers. This study aimed to investigate the effectiveness of P-saturated bauxite residue on biomass yield of perennial ryegrass (Lolium perenne L.), identify any adverse effects on soil fauna such as Eisenia fetida L. using choice tests, and quantify any phytotoxic effects on the germination of seeds, root growth, and plant elemental uptake. Two types of spent P-saturated bauxite residue were examined: P-saturated bauxite residue, which had been modified with gypsum at a rate of 8% w/w and chemically amended bauxite residue. There was a comparable biomass yield between the plants grown on the bauxite residue nutrient source and those receiving superphosphate, indicating that there were no phytotoxic effects on the growth of L. perenne L. When examining the effect of the treatments on the soil fauna, the E. fetida L. showed a significant preference in the choice of soil treatment, the largest percentage (58± 2.1 %) of E. fetida L. favoured the control soil over the amended soils. Overall, the bauxite residue was comparable to the superphosphate fertiliser in terms of the biomass yield obtained, indicating the potential recycling of P from wastewaters using bauxite residue as a low-cost adsorbent. No phytotoxic effects on the growth of L. perenne L. were found using germination and plant uptake bioassays. Open Access funding provided by the IReL Consortium. peer-reviewed

The dairy industry produces vast quantities of dairy processing sludge (DPS), which can be processed further to develop second generation products such as struvite, biochars and ashes (collectively known as STRUBIAS). These bio-based fertilizers have heterogeneous nutrient and metal contents, resulting in a range of possible application rates. To avoid nutrient losses to water or bioaccumulation of metals in soil or crops, it is important that rates applied to land are safe and adhere to the maximum legal application rates similar to inorganic fertilizers. This study collected and analysed nutrient and metal content of all major DPS (n = 84) and DPS-derived STRUBIAS products (n = 10), and created an application calculator in MS Excel¿ to provide guidance on maximum legal application rates for ryegrass and spring wheat across plant available phosphorus (P) deficient soil to P-excess soil. The sample analysis showed that raw DPS and DPS-derived STRUBIAS have high P contents ranging from 10.1 to 122 g kg-1. Nitrogen (N) in DPS was high, whereas N concentrations decreased in thermo-chemical STRUBIAS products (chars and ash) due to the high temperatures used in their formation. The heavy metal content of DPS and DPS-derived STRUBIAS was significantly lower than the EU imposed limits. Using the calculator, application rates of DPS and STRUBIAS materials (dry weight) ranged from 0 ¿ 4.0 tonnes ha-1 y-1 for ryegrass and 0 ¿ 4.5 tonnes ha-1 y-1 for spring wheat. The estimated heavy metal ingestion to soil annually by the application of the DPS and STRUBIAS products was lower than the EU guideline on soil metal accumulation. The calculator is adaptable for any bio-based fertilizer, soil and crop type, and future work should continue to characterise and incorporate new DPS and STRUBIAS products into the database presented in this paper. In addition, safe application rates pertaining to other regulated pollutants or emerging contaminants that may be identified in these products should be included. The fertilizer replacement value of these products, taken from long-term field studies, should be factored into application rates. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 814258. peer-reviewed

With the intensification of agricultural production in many European countries, more marginal soils with elevated organic matter (OM) content are being brought into cultivation. However, little is known about the transformations in the constituent phosphorus (P) pools of organic soils receiving applications of P fertiliser. Soil P fractions were measured before and after receiving fertiliser in a controlled experiment to determine the change in the soil pools and path analysis was used to evaluate the relationships between P pools. In this study, P deficient soils ranging in OM content from 8 to 76 %, were placed in large pots, planted with ryegrass and subjected to P fertiliser applications ranging from 10 to 145 kg ha-1, and monitored over an eight-month study period. High OM soils had a diminished ability to build-up the labile pool from freshly applied P, with relatively low increases up to 200 % of the initial value, compared to mineral soils in which the labile pool increased to more than 2500 % of the initial concentration. Additionally, organic soils had higher P uptakes in the grass yield than mineral soils, indicating a higher availability of added P in the soil solution than mineral soils due to their limited sorption ability. In general, there was a reduction in the organic P pool over applications from 0 to 55 kg ha-1, which was indicative of partial mineralisation, but was followed by an accumulation of added P over applications from 55 to 145 kg P ha-1. The residual P pools did not build-up with P additions, but data indicated the occurrence of mineralisation in most of the soils with decreases of around 40 % of the initial concentrations. Organic and residual pools therefore displayed potential to supply P to more labile P pools across all soils of this study. Path analysis indicated that applied P was the only source of labile P in the soil with the highest OM content, leaving it dependant on continuous P applications to supply P for productivity, whereas in the rest of the soils there were interrelations between the non-labile and labile pools. Low pH strongly immobilised the applied P and should be corrected before the initiation of any fertilisation program, even in soils deficient in plant available P. The results demonstrated that P added as fertiliser to organic soils does not accumulate as in mineral soils, which may leave them susceptible to P losses in surface runoff. Therefore, organic soils under agricultural production located in high status catchments should receive low P applications and only during periods with low probability of precipitation to minimise the possibility of P exports to receiving waters. This work was funded by the Irish Department of Agriculture, Forestry and the Marine (project reference 13/S488) as part of the Research Stimulus Fund 2013. José L. González Jiménez was funded by the Teagasc Walsh Fellowship Scheme. The authors would like to thank the landowners for generously providing the soils used in this study, and the support and assistance of D. Brennan, L Moloney Finn and I. Marongiu for their support and advice in the use of Teagasc Johnstown Castle laboratories. We would also like to thank the editor and two anonymous reviewers for their critical and helpful comments and suggestions. peer-reviewed 2020-12-05

The use of filter media to adsorb phosphorus (P) from nutrient-rich waters is an effective, simple and low-cost method to recover and reuse P as an inorganic fertiliser replacement. Although it is assumed that the saturated filter media can be applied to cropland as a safe fertiliser replacement, there is presently a lack of information on the fertiliser replacement value (FRV) of such products and their negative effects on plants and soil. Therefore, the aims of this paper were to evaluate the (1) P removal capacity and plant response to soil application of waste media from three sectors (industry, agriculture, and construction and demolition), and natural and synthetic materials (2) potentially confounding risks arising from the reuse of media as a fertiliser replacement, and (3) factors affecting their fertilising efficiency once applied to soil. The predominant factors affecting the FRV of P-saturated media were their adsorption capacity and chemical composition, soil pH, and composition of water used for saturation. Some measures to overcome the negative impacts of the land application of P-saturated media include selecting the most appropriate soil-filter material combinations, the use of P solubilising microorganisms, and mixing with manure before land application. Despite confounding factors and a lack of information on the performance of some media under comparable study conditions, this study found that there is a significant potential for P-saturated filter media to partially replace the use of P mineral fertilisers and aid in the attainment of a circular economy in agriculture. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 675120. peer-reviewed

Peatlands are becoming recognized as important carbon sequestration centers where, through restoration projects, peatlands may stop being considered as carbon sources and become carbon neutral or p...

Photo-activated sludge (PAS) systems are an emerging wastewater treatment technology where microalgae provide oxygen to bacteria without the need for external aeration. There is limited knowledge on the optimal conditions for enhanced biological phosphorus removal (EBPR) in systems containing a mixture of polyphosphate accumulating organisms (PAOs) and microalgae. This research aimed to study the effects of substrate composition and light intensity on the performance of a laboratory-scale EBPR-PAS system. Initially, a model-based design was developed to study the effect of organic carbon (COD), inorganic carbon (HCO3) and ammonium-nitrogen (NH4-N) in nitrification deprived conditions on phosphorus (P) removal. Based on the mathematical model, two different synthetic wastewater compositions (COD:HCO3:NH4-N: 10:20:1 and 10:10:4) were examined at a light intensity of 350 µmol m−2 sec−1. Add to this, the performance of the system was also investigated at light intensities: 87.5, 175, and 262.5 µmol m−2 sec−1 for short terms. Results showed that wastewater having a high level of HCO3 and low level of NH4-N (ratio of 10:20:1) favored only microalgal growth, and had poor P removal due to a shortage of NH4-N for PAOs growth. However, lowering the HCO3 level and increasing the NH4-N level (ratio of 10:10:4) balanced PAOs and microalgae symbiosis, and had a positive influence on P removal. Under this mode of operation, the system was able to operate without external aeration and achieved a net P removal of 10.33 ±1.45 mg L−1 at an influent COD of 100 mg L−1. No significant variation was observed in the reactor performance for different light intensities, indicating the EBPR-PAS system can be operated at low light intensities with a positive influence on P removal.

Trichloroethylene (TCE) is a human carcinogen that is commonly found in landfill leachate as a result of anthropogenic activities. Contaminated leachate plumes may be intercepted prior to reaching groundwater and treated in situ using permeable reactive barriers (PRB). This study used a packed column system containing herbal pomace and spruce biochar, previously shown to have TCE adsorptive capabilities, to investigate the feasibility of using pyrolysed waste as a fill material in a PRB. Influent containing raw or autoclaved landfill leachate was used to investigate the potential for environmental micro-organisms to establish a TCE-dechlorinating biofilm on the biochar, in order to prolong the operational life span of the system. TCE removal ≥ 99.7 was observed by both spruce and herbal pomace based biochars. No dichloroethylene (DCE) isomers were present in the column effluents, but cis-1,2 DCE was adsorbed to the biochar treating raw landfill leachate, indicating that dechlorination was occurring biologically in these columns. Known microbial species that are individually capable of complete dechlorination of TCE to ethene were not detected by 16S rRNA gene sequencing, but several species capable of partial TCE dechlorination (Desulfitobacterium spp., Sulfurospirillium spp. and Desulfuromonas spp) were present in the biofilms of the columns treating raw landfill leachate. These data demonstrate that biochar from waste material may be capable of supporting a dechlorinating biofilm to promote bioremediation of TCE. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Actions grant agreement No 748106. The authors would like to acknowledge assistance with column installation from Edward Kilcullen, NUI Galway; biochar contributions from Caspar von Ziegner, NovoCarbo, Germany and Timo Ferdinand, HerbaCarbo, Germany; and supply of landfill leachate from Barry Cormican, East Galway Landfill. peer-reviewed

Rapid small-scale column tests (RSSCTs) have been previously used to predict the effluent concentration of a single nutrient in large filters with good accuracy. However, in drainage waters originating from heavy textured soils, where there is a need for in-ditch filters to retain both dissolved reactive phosphorus (DRP) and ammonium (NH4) simultaneously, the suitability of a RSSCT approach to model both parameters must be proved. In this study, a decision support tool was used to identify appropriate media that may be placed in filters for the removal of DRP and NH4. The selected media for this study were sand and zeolite. Both media were placed in acrylic tubes each with an internal diameter of 0.01 m and with lengths ranging from 0.1 to 0.4 m, and their performance for simultaneous removal of DRP and NH4 (1 mg DRP and NH4-N L-1) from water was evaluated. The data generated from the RSSCTs were used to model DRP and NH4 removals in 0.4 m-long laboratory columns of internal diameter 0.1m, which had the same media configuration as the small columns and were operated using the same influent concentrations. The developed model successfully predicted the effluent concentration of both the DRP and NH4-N from the large columns. This indicates using RSSCTs to model the performance of filters will produce substantial savings in operational, financial and labour costs, without affecting the accuracy of model predictions. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 675120. peer-reviewed

Understanding source elements of the ocean plastic crisis is key to effective pollution reduction management and policy. The ubiquity of microplastic (MP) fibres in the oceans is considered to derive primarily from clothing fibres released in grey water. Microplastic fibres degraded from widely flushed personal care textile products (wet wipes and sanitary towels) have not been clearly identified in aquatic systems to date. Unregulated personal hygiene and sanitary product labelling fails to identify textile materials. This study demonstrated that white MP fibres in sediments adjacent to a wastewater treatment plant (WWTP) are comparable with white fibres from sewage-related waste and commercially available consumer sanitary products. Commercially available non-flushable wipes are manufactured from either polyethylene terephthalate (PET), polypropylene (PP), or a combination of PET and cellulose. Fifty percent of brands labelled flushable that were tested were comprised of a mixture of PET and cellulose and the remainder of cellulose alone. Sanitary towels are made from PP, PE, or a combination of high-density polyethylene (HDPE) and PP. The accumulation of large quantities of washed-up sewage-related macro-debris (including wet wipes and sanitary towels) intermingled with seaweed biomass adjacent to the WWTP was associated with a combined sewer overflow. Microplastic fibres extracted from this waste were similar to those extracted from intertidal sediments in close proximity to the WWTP over a ten-month period. In comparison, fibres extracted from locations spatially removed from the WWTP were primarily comprised of ABS, PP and polystyrene. The results confirm that wet wipes and sanitary towels flushed down toilets are an underestimated source of white MP fibres in the environment. Given the global distribution and projected growth of the non-woven textile industry, there is a need for increased public awareness of MP pollution in the marine environment from the inappropriate disposal of sanitary products down the toilet, instead of diversion to alternative land-based waste management. This project (Grant-Aid Agreement No. PBA/ME/15/03) is carried out with the support of the Marine Institute and funded by the Marine Research Programme of the Irish Government under the framework of JPI Oceans (PLASTOX). The authors wish to thank Dr. Anne O’ Shaughnessy for drawing the graphical abstract, and Dr. Kieran Craven, Sean Cullen, Niall Finn, Eoin MacCraith, Dr. Gerard McCarthy, Dr. Emma McDermott, Xavier Monteys, Dr. Audrey Morley and Heather Stewart for technical advice and assistance. Finally, a special thanks to Sharon Shannon and the Claddagh beach clean-up group. peer-reviewed

Globally, peatlands experience water storage fluctuations. Seasonality was once the sole contributor of this natural water table variation, however, for many years, freshwater drainage of peatlands for agriculture, afforestation, and energy production has been prevalent. With constant changes in storage, there exists a measurable connection between subsurface water levels and solute transport in the deep layers of peatland material. Traditionally, water level modelling has benefitted environmental protection schemes with the identification of critically important areas and by implementing relevant hydraulic structures for optimal protection. Restoration and rehabilitation efforts occurring in the last several decades have occasionally highlighted results of miscalculation, whereby a peatland’s capacity to alleviate water flux effects was overestimated in degraded regions. Once a peat layer becomes dry and aerated, it decomposes, releasing nitrogen and other nutrients into the environment. Conversely, if a peatland is inundated beyond its storage capacity, aggregates of peat and vegetation become suspended within the excess water, signifying the potential for an increased methane flux.In spite of an ideal water level, one that satisfies a degraded condition while preventing excess flooding, research must continue to expand upon land use and management activities and how they affect hydrology and water quality parameters across a given peatland. To quantify geochemical and hydrological properties given the scale of highly variable peat parameters, many studies have relied on single point data to represent peatlands. Since water chemistry has a strong control on geophysics in peatland environments, a remote sensing technique was used in this study to qualitatively describe the surface of a cutaway peatland. Qualitative analysis of the study site describes soil moisture and peat depth through a geophysical interpretation and an ability to detect gamma radiation.Remote sensing data, acquired by the Geological Survey Ireland, was used to capture radiometric variation at the study site. The airborne survey data was used to identify suitable locations on the study site in which to collect representative soil cores, which were then brought to the laboratory for analysis. The results from laboratory-based hydrological testing of these cores will be used to quantify the impacts of various water management regimes on site. By combining geophysical analysis with laboratory measurements of soil and water chemistry, there is an opportunity for improving upon the development of suitable mitigation measures.

Spent hydroprocessing catalysts are known to contain a variety of potentially toxic metals and therefore studies on the bioavailability and mobility of these metals are critical for understanding the possible environmental risks of the spent catalysts. This study evaluates the different chemical fractions/forms of aluminium (Al), nickel (Ni), and molybdenum (Mo) in spent hydroprocessing catalyst and the changes they undergo during bioleaching with Acidithiobacillus ferrooxidans. In the spent catalyst (prior to bioleaching), Al was primarily present in its residual form, suggesting its low environmental mobility. However, Ni comprised mainly an exchangeable fraction, indicating its high environmental mobility. Molybdenum was mainly in the oxidizable form (47.1%), which indicated that highly oxidizing conditions were required to liberate it from the spent catalyst. During bioleaching the exchangeable, reducible and oxidizable fractions of all the metals were leached, whereas the residual fractions remained largely unaffected. At the end of bioleaching process, the metals remaining in the bioleached sample were predominantly in the residual fraction (98.3-99.5%). The 'risk assessment code' (RAC) and IR analysis also demonstrated that the environmental risks of the bioleached residue were significantly lower compared to the untreated spent catalyst. The results of this study suggest that bioleaching is an effective method in removing the metals from spent catalysts and the bioleached residue poses little environmental risk.

peer-reviewed The use of biosolids as a fertiliser may be an indirect route for contaminants into the food chain. One of the main concerns regarding the spreading of biosolids on agricultural land is the potential uptake of contaminants into plants which may bio-transfer into grazing animals that supply the food chain directly (e.g. meat and milk) and hence are subsequently consumed. The aim of this project was to create a quantitative risk assessment model to estimate the fate and translocation of triclosan (TCS) and triclocarban (TCC) into the feed (grass) and food chain with subsequent human exposure. The model's results indicate that TCS and TCC have low potential to transfer into milk and beef following the ingestion of contaminated grass by dairy cows. Mean estimated TCS and TCC residues in milk and beef show that TCC had the greatest concentration (mean values of 7.77 × 10− 6 mg kg− 1 in milk and 1.36 × 10− 4 mg kg− 1 in beef). Human exposure results show that TCC was greater for milk consumption in infants (1–4 years) (mean value 1.14 × 10− 7 mg kg− 1 bw d− 1) and for beef consumption by teens (12–17 years) (mean value 6.87 × 10− 8 mg kg− 1 bw d− 1). Concentrations of TCS and TCC were well below the estimated acceptable daily intake (ADI). Human health risk was estimated by evaluation of the hazard quotient (HQ), which used the NOAEL as a toxicity endpoint, combined with milk and beef human exposure estimates. HQ results show that all values were < 0.01 (no existing risk). A sensitivity analysis revealed that the Kow and initial concentration in biosolids as the parameters of greatest importance (correlation coefficients 0.91 and 0.19, respectively). This highlights the importance of physio-chemical properties of the compounds and their detection in biosolids post wastewater treatment along with their persistence in soil following application. This model is a valuable tool in which to ascertain the potential transfer of contaminants in the environment into animal forage with knock on consequences for exposure through the human food chain.

Given the current decline of natural wetlands worldwide and the consequent negative impacts on amphibians, wetlands constructed for the treatment of wastewaters have the potential to play a role in the protection of these animals. However, there is a paucity of information regarding the value of constructed wetlands (CWs) to amphibians, particularly relating to the terrestrial phase of their life-cycle. This study compares the terrestrial habitats of natural wetlands (NWs) and CWs as refuges for the smooth newt (Lissotriton vulgaris, [L., 1758]) with the aim of developing recommendations for CWs (both new and existing) to enhance their usefulness as newt friendly habitats. Terrestrial habitats surrounding NWs and CWs were mapped using ArcGIS. Potential barriers to newt movement in addition to the presence of features such as wood or stone which could act as potential newt refuges were also mapped. Natural wetlands had significantly more terrestrial habitat types than CWs and while woodlands at both wetland types were most likely to contain features of benefit to newts, terrestrial habitats of NWs contained more features compared to those of CWs. The application of a Habitat Suitability Index, which assesses the likelihood of the presence of newts, resulted in seven of eight NWs compared to only two of eight CWs receiving good scores, the lower scores for CWs being due primarily to the presence of a barrier to newt movement. Recommendations for enhancing the design and management of CWs for smooth newts include less intensive ground maintenance, reduction of barriers to newt movement, judicious planting of suitable trees or shrubs and the provision of additional refuges such as wood or stone. The authors acknowledge funding from the Irish Environmental Protection Agency (EPA) (Project number 2013-B-PhD-12). peer-reviewed 2019-06-22

In Ireland, the land application of biosolids is the preferred option of disposing of municipal sewage waste. Biosolids provide nutrients in the form of nitrogen, phosphorus, potassium and increases organic matter. It is also an economic way for a country to dispose of its municipal waste. However, biosolids may potentially contain a wide range of pathogens, and following rainfall events, may be transported in surface runoff and pose a potential risk to human health. Thus, a quantitative risk assessment model was developed to estimate potential pathogens in surface water and the environmental fate of the pathogens following dilution, residence time in a stream, die-off rate, drinking water treatment and human exposure. Surface runoff water quality data was provided by project partners. Three types of biosolids, anaerobically digested (AD), lime stabilised (LS), and thermally dried (TD)) were applied on micro plots. Rainfall was simulated at three time intervals (24, 48 and 360 h) following land application. It was assumed that this water entered a nearby stream and was directly abstracted for drinking water. Consumption data for drinking water and body weight was obtained from an Irish study and assigned distributions. Two dose response models for probability of illness were considered for total and faecal coliform exposure incorporating two different exposure scenarios (healthy populations and immuno-compromised populations). The simulated annual risk of illness for healthy populations was below the US EPA and World Health Organisation tolerable level of risk (10−4 and 10−6, respectively). However, immuno-compromised populations may still be at risk as levels were greater than the tolerable level of risk for that subpopulation. The sensitivity analysis highlighted the importance of residence time in a stream on the bacterial die-off rate. The authors acknowledge the Irish EPA for the funding of this project under the STRIVE Programme (2007–2013). peer-reviewed 2019-03-06

Bioleaching is considered to be a low-cost, eco-friendly technique for leaching valuable metals from a variety of matrixes. However, the inherent slow dissolution kinetics and low metal leaching yields have restricted its wider commercial applicability. Recent advancements in bio-hydrometallurgy have suggested that these critical issues can be successfully alleviated through the addition of a catalyst. The catalyzing properties of a variety of metals ions (Ag+, Hg++, Bi+++, Cu++, Co++ etc.) during bioleaching have been successfully demonstrated. In this article, the role and mechanisms of these metal species in catalyzing bioleaching from different minerals (chalcopyrite, complex sulfides, etc.) and waste materials (spent batteries) are reviewed, techno-economic and environmental challenges associated with the use of metals ions as catalysts are identified, and future prospectives are discussed. Based on the analysis, it is suggested that metal ion-catalyzed bioleaching will play a key role in the development of future industrial bio-hydrometallurgical processes. This work was financially supported by a grant from the Irish Research Council (GOIPD/2015/589). peer-reviewed 2019-01-06

Phosphorus (P) loss from intensive dairy farms is a pressure on water quality in agricultural catchments. At farm scale, P sources can enter in-field drains and open ditches, resulting in transfer along ditch networks and delivery into nearby streams. Open ditches could be a potential location for P mitigation if the right location was identified, depending on P sources entering the ditch and the source-sink dynamics at the sediment-water interface. The objective of this study was to identify the right location along a ditch to mitigate P losses on an intensive dairy farm. High spatial resolution grab samples for water quality, along with sediment and bankside samples, were collected along an open ditch network to characterise the P dynamics within the ditch. Phosphorus inputs to the ditch adversely affected water quality, and a step change in P concentrations (increase in mean dissolved reactive phosphorus (DRP) from 0.054 to 0.228 mg L-1) midway along the section of the ditch sampled, signalled the influence of a point source entering the ditch. Phosphorus inputs altered sediment P sorption properties as P accumulated along the length of the ditch. Accumulation of bankside and sediment labile extractable P, Mehlich 3 P (M3P) (from 13 to 97 mg kg-1) resulted in a decrease in P binding energies (k) to This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 675120. peer-reviewed 2021-12-19

Trichloroethylene (TCE) is an Environmental Protection Agency priority pollutant associated with cancer in humans. With numerous industrial applications and regular landfill disposal, TCE is a common landfill leachate pollutant. In situ treatment barriers use costly fill materials such as granular activated carbon (GAC). Here, we show that while a range of untreated waste materials had little ability to adsorb TCE, waste-derived biochar showed excellent capacity for TCE adsorption. TCE removal efficiencies by spruce and oak-derived biochars were > 99.5 %, outperforming GAC (95 %) and herbal pomace biochar (93 %). A contact time of at least 32 h was required to reach equilibrium for all of these media. Assessment of pollution swapping potential revealed release of phosphate by all biochars. Analysis of media surface characteristics by Fourier Transform Infrared Spectroscopy (FTIR) predicted that GAC should have the highest ability to adsorb TCE, followed by Oak Biochar, Herbal Pomace Biochar 1, and Spruce Biochar 2, which was not in agreement with the experimental adsorption data. These data demonstrate the potential for pyrolysed waste material to be used as an alternative fill material for in situ remediation applications, thereby also addressing the European Circular Economy Strategy. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Actions grant agreement No 748106. The authors would like to acknowledge laboratory assistance from Tatiana Kelley, NUI Galway and RPS, FTIR analysis by Pól Mac Fhionnghaile, School of Chemistry, NUI Galway, and biochar contributions from: Prof JJ Leahy, University of Limerick, Ireland; Caspar von Ziegner, NovoCarbo, Germany; Timo Ferdinand, HerbaCarbo, Germany, and Thomas Fleming, Brooko GbR, Germany. peer-reviewed 2021-12-17

Land spreading of dairy soiled water (DSW) may result in pollution of ground and surface waters. Treatment of DSW through sludge-supernatant separation using chemical coagulants is a potential option to reduce the negative environmental impacts of DSW. The aims of this study were to (1) assess the effectiveness of three chemical coagulants poly-aluminium chloride (PACl), ferric chloride (FeCl3) and alum in improving effluent quality, and (2) assess the properties of the sludge that is generated as by-product from the process for its suitability for land application. Taking into consideration optimum doses to minimize pollutants (turbidity, chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), and E. coli), optimum mixing times and cost, FeCl3 was the best performing coagulant. Generated sludges had higher nutrient content and fewer E. coli than raw DSW, and did not display any evidence of phytotoxicity to the growth of Lolium perenne L. using germination tests. The study discussed the results in a sustainable farm management context, and suggested that the effluent (supernatant) from the treatments may be recycled to wash farm yards, saving water. In parallel, the sludge portion can be applied to amend soil properties with no adverse impacts on the grass growth, providing an agronomic value as an organic fertilizer, and reducing the risk of nutrient losses. This management approach could minimize the overall net cost compared to land application of raw DSW. The authors are grateful to Teagasc for the award of a Walsh Fellowship to the first author. The authors appreciate the help of technical staff: John Paul Murphy (Teagasc Moorepark), Denis Brennan, Gareth Gillen (Teagasc Johnstown Castle), and James Feighan (NUI Galway). peer-reviewed 2022-04-29

With more than 40 countries currently proposing to boost their national bioeconomies, there is no better time for a clarion call for a "new" bioeconomy, which, at its core, tackles the current disparities and inequalities in phosphorus (P) availability. Existing biofuel production systems have widened P inequalities and contributed to a linear P economy, impairing water quality and accelerating dependence on P fertilizers manufactured from finite nonrenewable phosphate rock reserves. Here, we explore how the emerging bioeconomy in novel, value-added, bio-based products offers opportunities to rethink our stewardship of P. Development of integrated value chains of new bio-based products offers opportunities for codevelopment of "P refineries" to recover P fertilizer products from organic wastes. Advances in material sciences are exploiting unique semiconductor and opto-electrical properties of new "two-dimensional" (2D) P allotropes (2D black phosphorus and blue phosphorus). These novel P materials offer the tantalizing prospect of step-change innovations in renewable energy production and storage, in biomedical applications, and in biomimetic processes, including artificial photosynthesis. They also offer a possible antidote to the P paradox that our agricultural production systems have engineered us into, as well as the potential to expand the future role of P in securing sustainability across both agroecological and technological domains of the bioeconomy. However, a myriad of social, technological, and commercialization hurdles remains to be crossed before such an advanced circular P bioeconomy can be realized. The emerging bioeconomy is just one piece of a much larger puzzle of how to achieve more sustainable and circular horizons in our future use of P.

The nitrate nitrogen (NO3-N) and ammonium (NH4-N) and/or dissolved reactive phosphorus (DRP) load in drainage water from farms can be managed by reactive or biological media filters. The nutrient content of the drainage water can be obtained directly from water analysis, which immediately focuses attention on filter media selection. There are many factors that may be important before choosing a medium or media e.g. nutrient removal capacity, lifetime, hydraulic conductivity, the potential for pollution swapping , attenuation of non-target contaminants (e.g. pesticides, organic carbon, etc.), and local availability and transportation cost of media to site. In this study, a novel decision support tool (DST) was developed, which brought all these factors together in one place for five nutrient scenarios. A systematic literature review was conducted to create a database containing 75 media with an associated static scoring system across seven criteria (% of nutrient concentration reduction, removal of other pollutants, lifetime, hydraulic conductivity, negative externalities) and a dynamic scoring system across two criteria (delivery cost and availability). The DST was tested using case studies from Ireland, Belgium and USA with different agricultural practices and nutrient scenarios. It was then validated by SWOT (strength, weakness, opportunities and threats) analysis. The DST provided a rapid, easily modifiable screening of many media-based treatments for specific dual or single nutrient-based water drainage problems. This provides stakeholders (farmers/regulators/advisors) with a versatile, flexible and robust yet easy-to-understand framework to make informed choices on appropriate media-based mitigation measures according to users relevant technical, economic and logistical factors. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 675120. peer-reviewed 2021-07-26

Freshwater ecosystems worldwide are at risk of becoming degraded as a result of excessive inputs of phosphorus (P) associated with terrestrial activities. This study describes a novel methodology to rapidly assess the potential of low-cost adsorbents which might be used to combat this issue. The ability of aluminum drinking water treatment residual (Al-WTR) and crushed concrete (CC) to remove P from dairy wastewater (DW) and forestry runoff (wastewaters representative of point and nonpoint P pollution sources, respectively) was assessed. In addition to predicting the longevity of these media in large-scale filters, potential risks associated with their use were also examined. The results indicate that both CC and Al-WTR show promise for use in removing P from forestry runoff, however the raised pH of effluent from CC filters may pose an environmental concern. Al-WTR showed greater promise than CC for the treatment of DW due to its higher adsorption capacity at high concentrations. Small releases of aluminum (13.63-96.17 µg g-1) and copper (5.25-31.9 µg g-1) were observed from both media when treating forestry runoff, and Al-WTR also released a small amount of nickel (0.16 µg g-1). Approximately 50% of total metal loss occurred during the first 25% of total filter loading, indicating that pre-washing of the media would help prevent metal release. These results indicate that field-scale tests are warranted for the treatment of both wastewaters with Al-WTR; CC is likely to be unsuitable for either forestry runoff or DW due to its effects on pH and its short lifespan. The first author would like to acknowledge the Irish Research Council (GOIPG/2013/75) for funding. peer-reviewed 2021-07-02

Bauxite residue, the by-product produced in the alumina industry, is a potential low-cost adsorbent in the removal of phosphorus (P) from aqueous solution, due to its high composition of residual iron oxides such as hematite. Several studies have investigated the performance of bauxite residue in removing P; however, the majority have involved the use of laboratory batch tests, which may not accurately estimate its actual performance in filter systems. This study investigated the use of rapid small-scale column tests to predict the dissolved reactive phosphorus (DRP) removal capacity of bauxite residue when treating two agricultural waters of low (forest run-off) and high (dairy soiled water) phosphorus content. Bauxite residue media was successful in the removal of DRP from both waters, but was more efficient in treating the forest run-off. The estimated service time of the column media based on the largest column studied was 1.08 min g-1 media for the forest run-off and 0.28 min g-1 media for the dairy soiled water, before initial breakthrough time, which was taken to be when the column effluent reached approximately 5% of the influent concentration, occurred. Metal(loid) leaching from the bauxite residue, examined using ICP-OES, indicated that aluminium and iron were the dominant metals present in the treated effluent, which were both above the EPA parametric values (0.2 mg L-1 for both Al and Fe) for drinking water. The authors would like to acknowledge the financial support of the Environmental Protection Agency (EPA) (2014-RE-MS-1). peer-reviewed 2021-04-19

During laboratory assessment of the soil water characteristic curve (SWCC), determining equilibrium at various pressures is challenging. This study establishes a methodological framework to identify appropriate experimental duration at each pressure step for the construction of SWCCs via centrifugation. Three common temporal approaches to equilibrium – 24-, 48- and 72-h – are examined, for a grassland and arable soil. The framework highlights the differences in equilibrium duration between the two soils. For both soils, the 24-h treatment significantly overestimated saturation. For the arable site, no significant difference was observed between the 48- and 72-h treatments. Hence, a 48-h treatment was sufficient to determine ‘effective equilibrium’. For the grassland site, the 48- and 72-h treatments differed significantly. This highlights that a more prolonged duration is necessary for some soils to conclusively determine that effective equilibrium has been reached. This framework can be applied to other soils to determine the optimum centrifuge durations for SWCC construction.

Journal article This review examines the utilisation of waste products from three sectors (industry, agriculture, and construction and demolition) in filters for the removal of contaminants from water. Sand is commonly used in drinking water filtration in water treatment plants. However, the use of alternative, low-cost materials could address the limitations of sand, particularly for the removal of emerging contaminants, and address European legislation which fosters the development of a circular economy, in which materials are used effectively. This review assesses the suitability of potential media by quantifying their adsorption potential across a variety of common drinking water contaminants. The media investigated were fly ash, Bayer residue, ground granular blast furnace slag, coconut shell, tea/coffee waste, rice husk, crushed concrete, masonry waste, and wood waste. There is a potential for the use of these media in the water treatment sector, although certain precautions must be taken to ensure any concerns are mitigated, such as release of metals into water. Recommendations, following this review, include testing the media in large-scale applications, and also constructing filters so as potential media are placed in layers to harness their contrasting adsorptive potentials. Environmental Protection Agency (EPA) (​Grant no: 2012-W-PhD-5) peer-reviewed 2018-07-21

Journal article Land application of dairy soiled water (DSW) is expensive relative to its nutrient replacement value. The use of aerobic filters is an effective alternative method of treatment and potentially allows the final effluent to be reused on the farm. Knowledge gaps exist concerning the optimal design and operation of filters for the treatment of DSW. To address this, 18 laboratory-scale filters, with depths of either 0.6 m or 1 m, were intermittently loaded with DSW over periods of up to 220 days to evaluate the impacts of depth (0.6 m versus 1 m), organic loading rates (OLRs) (50 versus 155 g COD m-2d-1), and media type (woodchip versus sand) on organic, nutrient and suspended solids (SS) removals. The study found that media depth was important in contaminant removal in woodchip filters. Reductions of 78% chemical oxygen demand (COD), 95% SS, 85% total nitrogen (TN), 82% ammonium-nitrogen (NH4-N), 50% total phosphorus (TP), and 54% dissolved reactive phosphorus (DRP) were measured in 1 m deep woodchip filters, which was greater than the reductions in 0.6 m deep woodchip filters. Woodchip filters also performed optimally when loaded at a high OLR (155 g COD m-2 d-1), although the removal mechanism was primarily physical (i.e. straining) as opposed to biological. When operated at the same OLR and when of the same depth, the sand filters had better COD removals (96%) than woodchip (74%), but there was no significant difference between them in the removal of SS and NH4-N. However, the likelihood of clogging makes sand filters less desirable than woodchip filters. Using the optimal designs of both configurations, the filter area required per cow for a woodchip filter is more than four times less than for a sand filter. Therefore, this study found that woodchip filters are more economically and environmentally effective in the treatment of DSW than sand filters, and optimal performance may be achieved using woodchip filters with a depth of at least 1 m, operated at an OLR of 155 g COD m-2 d-1. Teagasc peer-reviewed 2017-01-31

Journal article Slow sand filers are commonly used in water purification processes. However, with the emergence of new contaminants and concern over removing precursors to disinfection by-products, as well as traditional contaminants, there has recently been a focus on technology improvements to result in more effective and targeted filtration systems. The use of new media has attracted attention in terms of contaminant removal, but there have been limited investigations on the key issue of clogging. The filters constructed for this study contained stratified layers comprising combinations of Bayer residue, zeolite, fly ash, granular activated carbon, or sand, dosed with a variety of contaminants (total organic carbon (TOC), aluminium (Al), ammonium (NH4+-N), nitrate (NO3--N) and turbidity). Their performance and clogging mechanisms were compared to sand filters, which were also operated under two different loading regimes (continuous and intermittently loaded). The study showed that the novel filter configurations achieved up to 97% Al removal, 71% TOC removal, and 88% NH4+-N removal in the best-performing configuration, although they were not as effective as sand in terms of permeability. Deconstruction of the filters revealed that the main clogging mechanism was organic matter build-up at the uppermost layer of the filters. The clogging layer formed more quickly on the surface of the novel media when compared to the sand filters, but extended further into the sand filters, the extent dependent on the loading regime. The study shows the potential for an alternative filtration configuration, harnessing the adsorption potential of industrial waste products and natural media. EPA Grant Number 2012-W-PhD-5 peer-reviewed 2018-05-20

This study investigated a novel method of predicting the long-term phosphorus removal performance of large-scale adsorption filters, using data derived from short-term, small-scale column experiments. The filter media investigated were low-cost adsorbents such as aluminum sulfate drinking water treatment residual, ferric sulfate drinking water treatment residual, and fine and coarse crushed concretes. Small-bore adsorption columns were loaded with synthetic wastewater, and treated column effluent volume was plotted against the mass of phosphorus adsorbed per unit mass of filter media. It was observed that the curve described by the data strongly resembled that of a standard adsorption isotherm created from batch adsorption data. Consequently, it was hypothesized that an equation following the form of the Freundlich isotherm would describe the relationship between filter loading and media saturation. Moreover, the relationship between filter loading and effluent concentration could also be derived from this equation. The proposed model was demonstrated to accurately predict the performance of large-scale adsorption filters over a period of up to three months with a very high degree of accuracy. Furthermore, the coefficients necessary to produce said model could be determined from just 24 hours of small-scale experimental data. peer-reviewed

Landfill leachate is the product of water that has percolated through waste deposits and contains various pollutants, which necessitate effective treatment before it can be released into the environment. In the last 30years, there have been significant changes in landfill management practices in response to European Union (EU) Directives, which have led to changes in leachate composition, volumes produced and treatability. In this study, historic landfill data, combined with leachate characterisation data, were used to determine the impacts of EU Directives on landfill leachate management, composition and treatability. Inhibitory compounds including ammonium (NH4-N), cyanide, chromium, nickel and zinc, were present in young leachate at levels that may inhibit ammonium oxidising bacteria, while arsenic, copper and silver were present in young and intermediate age leachate at concentrations above inhibitory thresholds. In addition, the results of this study show that while young landfills produce less than 50% of total leachate by volume in the Republic of Ireland, they account for 70% of total annual leachate chemical oxygen demand (COD) load and approximately 80% of total 5-day biochemical oxygen demand (BOD5) and NH4-N loads. These results show that there has been a decrease in the volume of leachate produced per tonne of waste landfilled since enactment of the Landfill Directive, with a trend towards increased leachate strength (particularly COD and BOD5) during the initial five years of landfill operation. These changes may be attributed to changes in landfill management practices following the implementation of the Landfill Directive. However, this study did not demonstrate the impact of decreasing inputs of biodegradable municipal waste on leachate composition. Increasingly stringent wastewater treatment plant (WWTP) emission limit values represent a significant threat to the sustainability of co-treatment of leachate with municipal wastewater. In addition, the seasonal variation in leachate production poses a risk to effective co-treatment in municipal WWTPs, as periods of high leachate production coincide with periods of maximum hydraulic loading in WWTPs.

Bauxite residue, the by-product produced in the alumina industry, is being produced at an estimated global rate of approximately 150 million tonnes per annum. Currently, the reuse of bauxite residue is low (∼2%), due to limitations associated with its alkalinity, salinity, low solid content, fine particle size and potential leaching of metal(loid)s. It has been identified as a potential secondary source for critical raw materials such as vanadium, gallium and scandium, which currently have an associated supply risk and high economic cost within Europe. However, there is an uncertainty regarding the possible variation in these and other physico-chemical, elemental and mineralogical parameters within bauxite residue disposal areas. This paper aimed to address this knowledge gap by examining the variation of these parameters in a bauxite residue disposal area (BRDA) over a twelve-year period. The general composition did not vary greatly within the bauxite residue examined, with the exception of pH and electrical conductivity, which ranged from 10 ± 0.1 to 12.0 ± 0.02 and from 0.4 ± 0.01 to 3.3 ± 0.2 mS cm−1, respectively. The bauxite residue contained critical raw materials, of which the amount of vanadium, gallium and scandium did not vary significantly over time. The vanadium and gallium were present in larger amounts compared to other European bauxite residues. On average the vanadium, gallium and scandium content measured in the bauxite residue samples were 510 ± 77.8, 107 ± 7.3 and 51.4 ± 5.4 mg kg−1, respectively. This shows promise for the potential reuse of bauxite residue as a secondary source for critical raw materials and also indicates that BRDAs may be potential mines for critical raw material extraction. The authors would like to acknowledge the financial support of the Environmental Protection Agency (EPA) (2014-RE-MS-1). peer-reviewed 2020-10-09

peer-reviewed The removal efficiency of carbon (C) and nitrogen (N) in constructed wetlands (CWs) is very inconsistent and frequently does not reveal whether the removal processes are due to physical attenuation or whether the different species have been transformed to other reactive forms. Previous research on nutrient removal in CWs did not consider the dynamics of pollution swapping (the increase of one pollutant as a result of a measure introduced to reduce a different pollutant) driven by transformational processes within and around the system. This paper aims to address this knowledge gap by reviewing the biogeochemical dynamics and fate of C and N in CWs and their potential impact on the environment, and by presenting novel ways in which these knowledge gaps may be eliminated. Nutrient removal in CWs varies with the type of CW, vegetation, climate, season, geographical region, and management practices. Horizontal flow CWs tend to have good nitrate (NO3−) removal, as they provide good conditions for denitrification, but cannot remove ammonium (NH4+) due to limited ability to nitrify NH4+. Vertical flow CWs have good NH4+ removal, but their denitrification ability is low. Surface flow CWs decrease nitrous oxide (N2O) emissions but increase methane (CH4) emissions; subsurface flow CWs increase N2O and carbon dioxide (CO2) emissions, but decrease CH4 emissions. Mixed species of vegetation perform better than monocultures in increasing C and N removal and decreasing greenhouse gas (GHG) emissions, but empirical evidence is still scarce. Lower hydraulic loadings with higher hydraulic retention times enhance nutrient removal, but more empirical evidence is required to determine an optimum design. A conceptual model highlighting the current state of knowledge is presented and experimental work that should be undertaken to address knowledge gaps across CWs, vegetation and wastewater types, hydraulic loading rates and regimes, and retention times, is suggested. We recommend that further research on process-based C and N removal and on the balancing of end products into reactive and benign forms is critical to the assessment of the environmental performance of CWs. The research was funded by Irish Research Council and Department of Agriculture, Food and Marine in Association with The University of Dublin, Trinity College.

Organic soils have low sorption capacities for phosphorus (P), and may pose a risk of P loss to water if P applications to these soils coincide with runoff events. Little is known about the magnitude of exports of P in overland flow following application of P fertiliser onto these soils, or on the influence of the frequency on P losses and persistence. The number of P fertiliser applications was surveyed across 39 commercial farms to assess current practice and inform the design of a rainfall runoff experiment to evaluate the effect of frequency of P applications on losses and persistence across time. Superphosphate (16 % P) was applied in single (equivalent to 30 and 55 kg P ha-1 applied at day 0) and split (equivalent to 15 and 27.5 kg P ha-1 applied in two doses at days 0 and 55) applications to an organic soil inclined at a slope of 6 % in a rainfall simulator experiment. The surface runoff of dissolved reactive phosphorus (DRP) was measured in controlled 30-min rainfall simulations conducted intermittently over an 85-day period. The DRP loads in surface runoff from the soil that received single applications of 30 and 55 kg ha-1 were exponentially greater than those receiving the same amounts applied in two doses, indicating that single P applications had disproportionately bigger impacts on losses than split applications. This supports the idea that frequent, but smaller, P applications can minimise the impact of fertilisation on waters. Dissolved reactive P concentrations remained significantly higher than those from the control samples until the end the experiment for almost all the P treatments, highlighting the long-lasting effects of added P and the elevated risk of P losses on organic soils. For climates with frequent rainfall events, which are likely to coincide with fertiliser applications, smaller but more frequent P applications can reduce the risk of P transfer as opposed to one single application. This work was funded by the Irish Department of Agriculture, Forestry and the Marine (project reference 13/S488) as part of the Research Stimulus Fund 2013. The authors would like to thank the landowner for generously providing the soil used in this study. We would also like to thank D. McDermott, E. Kilcullen, M. B. O'Shea, S. Letonnelier and N. Guichonnet for their valuable advice and support in the use of NUI Galway laboratories and facilities. We would also like to thank the editor and four anonymous reviewers for their critical and helpful comments and suggestions. peer-reviewed 2021-04-24

Bauxite residue (red mud), the by-product produced in the alumina industry, is being produced at an estimated global rate of approximately 150Mt per annum. Due to its highly alkaline nature, many refineries use neutralisation techniques such as mud farming (atmospheric carbonation), direct carbonation using carbon dioxide or reactions with seawater, to treat the bauxite residue and reduce its alkalinity prior to disposal in the BRDA (bauxite residue disposal area). Applying a treatment can render the bauxite residue non-hazardous and may also prepare the bauxite residue for reuse, particularly as an adsorbent. In this study, gypsum and seawater treatments were applied to the various bauxite residue samples obtained and the effects on its mineral, elemental and physiochemical properties were examined, as well as the effect on its phosphorus (P) adsorption capacity. It was found that in addition to reducing the alkalinity of all bauxite residue samples used, the P adsorption capacity was also enhanced following amendment with seawater or gypsum, particularly with gypsum. A positive correlation was detected between P adsorption and both Ca and CaO. A negative correlation was detected between the P adsorption and pH of the media. Fitting the data obtained from a batch adsorption experiment to the Langmuir adsorption isotherm, the maximum adsorption capacity was estimated to range from 0.345 to 2.73 mg P per g bauxite residue, highlighting the re-use potential for bauxite residue as an adsorbent for P. The authors would like to acknowledge the financial support from the Irish Environmental Protection Agency (EPA) (2014-RE-MS-1) and the UK Natural Environment Research Council (NE/L01405X/1). The authors would also like to thank Rusal Aughinish Alumina and Alteo Gardanne, who provided the bauxite residue sand and mud samples. peer-reviewed 2020-01-20

Treated municipal sewage sludge ("biosolids") and dairy cattle slurry (DCS) may be applied to agricultural land as an organic fertiliser. This study investigates losses of nutrients in runoff water (nitrogen (N) and phosphorus (P)), metals (copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr)), and microbial indicators of pollution (total and faecal coliforms) arising from the land application of four types of treated biosolids and DCS to field micro-plots at three time intervals (24, 48, 360 h) after application. Losses from biosolids-amended plots or DCS-amended plots followed a general trend of highest losses occurring during the first rainfall event and reduced losses in the subsequent events. However, with the exception of total and faecal coliforms and some metals (Ni, Cu), the greatest losses were from the DCS-amended plots. For example, average losses over the three rainfall events for dissolved reactive phosphorus and ammonium-nitrogen from DCS-amended plots were 5 and 11.2 mg L(-1), respectively, which were in excess of the losses from the biosolids plots. When compared with slurry treatments, for the parameters monitored biosolids generally do not pose a greater risk in terms of losses along the runoff pathway. This finding has important policy implications, as it shows that concern related to the reuse of biosolids as a soil fertiliser, mainly related to contaminant losses upon land application, may be unfounded.

A quantitative risk ranking model was developed for human exposure to emerging contaminants (EC) following treated municipal sewage sludge (“biosolids”) application to Irish agricultural land. The model encompasses the predicted environmental concentration (PEC) in soil, surface runoff, groundwater, and subsequent drinking water ingestion by humans. Human exposure and subsequent risk was estimated for 16 organic contaminants using a Monte Carlo simulation approach. Nonylphenols ranked the highest across three environmental compartments: concentration in soil (PECsoil), runoff (PECrunoff), and groundwater (PECgroundwater), which had mean values of 5.69 mg/kg, 1.15 × 10−2 µg/l, and 2.22 × 10−1 µg/l, respectively. Human health risk was estimated using the LC50 (chemical intake toxicity ratio, (RR)) as a toxicity endpoint combined with PECrunoff and PECgroundwater. NP ranked highest for LC50 combined with PECrunoff and PECgroundwater (mean RR values 1.10 × 10−4 and 2.40 × 10−3, respectively). The mode...

Forestry harvesting on peats is known to result in significant losses of soil phosphorus (P) to adjacent waters, and the issue is becoming an increasingly serious concern as peatland forest stocks mature and reach harvestable age. One potential solution could be the use of low-cost P recovery techniques based on the chemical precipitation and/or adsorption of the dissolved fraction of soil P, which would otherwise be lost. Such recovery techniques have shown promise in similar applications on mineral soils. However, the interaction of peat with P adsorbing materials can significantly alter their adsorptive characteristics, and it is consequentially not known what materials might be suitable for this application. This study compared the performance of six potential soil amendments (aluminum water treatment residual (Al-WTR), crushed concrete, gypsum, magnesium hydroxide, magnesium oxide, and steel wool) in removing P from aqueous solution in the presence of a typical forest peat soil. Comparison of adsorption isotherms plotted from these batch adsorption studies showed that the observed P adsorption maxima of Al-WTR and steel wool were increased by the presence of peat, from 10.6 mg g-1 and 20.4 mg g-1, to 11.8 mg g-1 and 52.5 mg g-1, respectively. In contrast, the observed P adsorption maxima of crushed concrete, gypsum, and magnesium oxide were reduced in the presence of peat, by 44%, 87%, and 37%, respectively. The maximum P adsorption achieved by magnesium hydroxide was increased from 29.8 mg g-1 to 59 mg g-1 at an amendment to peat-solid ratio of 1:4, but decreased from 73.9 mg g-1 to 23.6 mg g-1 at an amendment to peat-solid ratio of 1:10. It was concluded that Al-WTR, in particular, shows considerable promise for use as a soil amendment for P immobilization in a peat environment. The first author would like to acknowledge the Irish Research Council for funding. peer-reviewed 2017-10-18

Denitrification bioreactors, typically containing woodchips, are artificial sinks used to remediate nitrate (NO 3 − ) losses on agricultural landscapes. Analysis of these bioreactors frequently considers their efficacy in terms of only a single contaminant (for example, NO 3 − ), but does not consider other losses – ammonium (NH 4 + ), phosphorus (PO 4 3− ), methane (CH 4 ), carbon dioxide (CO 2 ) and nitrous oxide (N 2 O). In this study, laboratory-scale denitrifying bioreactors operated at hydraulic retention times (HRTs) ranging from 4 to 22 d, containing either lodgepole pine woodchips (LPW), lodgepole pine needles (LPN), barley straw (BBS) or cardboard, were investigated to elucidate operational optima considering three scenarios using: (1) only NO 3 − net fluxes; (2) NO 3 − , NH 4 + and PO 4 3− combined fluxes and (3) all fluxes (water and gaseous) combined. At the end of the experiment, after up to 745 days of operation, the bioreactors were destructively sampled for microbial analysis. In scenario 1, there was a net removal in the bioreactors, which generally performed best at shorter HRTs. In scenario 2, there was a net release of contaminants from all bioreactors, which substantially increased in scenario 3. Total greenhouse gas emissions were highest for the cardboard bioreactors (296 g CO 2 -eq m −2 d −1 ) at the longest HRT, and were dominated by CH 4 emissions. Highest N 2 O emissions emanated from LPN and LPW bioreactors, which also had a greater proportion of denitrifiers than the other bioreactors. Overall, considering all three scenarios, LPN bioreactors were the best performing at all HRTs. However, the long-term availability of its carbon source may be limited, as there was an 80% reduction over a 560 d period.

peer-reviewed This study aimed to quantify leaching losses of nitrogen (N), phosphorus (P) and carbon (C), as well as carbon dioxide (CO2) and methane (CH4) emissions from stored slurry, and from packed soil columns surface applied with unamended and chemically amended dairy and pig slurries, and dairy soiled water (DSW). The amendments to the slurries, which were applied individually and together, were: polyaluminum chloride (PAC) and zeolite for pig and dairy slurry, and liquid aluminium sulfate (alum) and zeolite for DSW. Application of pig slurry resulted in the highest total nitrogen (TN) and nitrate-nitrogen (NO3-N) fluxes (22 and 12 kg ha 1), whereas corresponding fluxes from dairy slurries and DSWwere not significantly (p < 0.05) higher than those from the control soil. There were no significant (p < 0.05) differences in leachate N losses between unamended and amended dairy slurries, unamended and amended pig slurries, and unamended and amended DSW. There were no leachate P losses measured over the experimental duration. Total cumulative organic (TOC) and inorganic C (TIC) losses in leachate were highest for unamended dairy slurry (82 and 142 kg ha 1), and these were significantly (p < 0.05) reduced when amended with PAC (38 and 104 kg ha 1). The highest average cumulative CO2 emissions for all treatments were measured for pig slurries (680 kg CO2-C ha 1) followed by DSW (515 kg CO2-C ha 1) and dairy slurries (486 kg CO2-C ha 1). The results indicate that pig slurry, either in raw or chemically amended form, poses the greatest environmental threat of leaching losses and gaseous emissions of CO2 and CH4 and, in general, amendment of wastewater with PAC, alum or zeolite, does not mitigate the risk of these losses.

The efficacy of water quality policies aiming to reduce or prevent nitrate contamination of waterbodies may be constrained by the inherent delay or Btime lag^ of water and solute transport through unsaturated (soil) and saturated (groundwater) pathways. These delays must be quantified in order to establish realistic deadlines, thresholds and policy expectations, and to design effective best management prac- tices. The objective of this review is to synthesise the current state of research on nitrate-related time lags in both the European and North American environmental and legislative contexts. The durations of time lags have been found to differ according to climatic, pedological, landscape and manage- ment scenarios. Elucidation of these driving factors at a wa- tershed scale is essential where water quality is impaired or at risk. Finally, the existence of time lags is increasingly being acknowledged at a policy level and incorporated into the development of environmental legislation. However, the full impact of these time lags is not yet fully understood or appreci- ated, and continued outreach and education in scientific, public and policy venues is still required. peer-reviewed 2018-08-14

© 2017 Elsevier B.V. An understanding of the seasonal variation in the standing stock of metals and nutrients in emergent vegetation of constructed wetlands (CWs), as well as the amounts present in aboveground (AG) and belowground (BG) biomass, is crucial to their design and management. Given that biomass harvesting is a labour and time consuming operation, a paucity of information currently exists on accumulation and standing stocks in biomass in CWs, in particular in North Western European countries. To address this knowledge gap, this paper examined the seasonal variations of metals and nutrients in Phragmites australis (Cav.) Trin. ex Steudel in a CW treating municipal wastewater, with a view to identifying an optimal time for biomass harvesting of the AG vegetation. Although the AG biomass was greatest in August (1636 ± 507 g m −2 ), the maximum concentrations and accumulations of metals and nutrients occurred at different times throughout the duration of the study (April to November). Furthermore, with the exception of zinc and nitrogen, metals and nutrients measured in BG biomass ranged from 66% (phosphorus) to greater than 80% (nickel and chromium) of the AG biomass. This indicates that analysis of only the emergent shoots may significantly underestimate the metal and nutrient uptake and capacity of the plant. In order to effectively target the bulk of metals and nutrients, an AG harvest in late August or September is suggested.

The phenomenon of adsorption is widely exploited across a range of industries to remove contaminants from gases and liquids. Much recent research has focused on identifying low-cost adsorbents which have the potential to be used as alternatives to expensive industry standards like activated carbons. Evaluating these emerging adsorbents entails a considerable amount of labor intensive and costly testing and analysis. This study proposes a simple, low-cost method to rapidly assess the potential of novel media for potential use in large-scale adsorption filters. The filter media investigated in this study were low-cost adsorbents which have been found to be capable of removing dissolved phosphorus from solution, namely: i) aluminum drinking water treatment residual, and ii) crushed concrete. Data collected from multiple small-scale column tests was used to construct a model capable of describing and predicting the progression of adsorbent saturation and the associated effluent concentration breakthrough curves. This model was used to predict the performance of long-term, large-scale filter columns packed with the same media. The approach proved highly successful, and just 24-36 hours of experimental data from the small-scale column experiments was found to provide sufficient information to predict the performance of the large-scale filters for up to three months. The first author would like to acknowledge the Irish Research Council (GOIPG/2013/75) for funding. peer-reviewed 2018-01-05

Journal article Engineered remediation technologies such as denitrifying bioreactors target single contaminants along a nutrient transfer continuum. However, mixed contaminant discharges to a water body are more common from agricultural systems. Indeed, evidence presented herein indicates that pollution swapping within denitrifying bioreactor systems adds to such deleterious discharges. The current paper proposes a more holistic approach to contaminant remediation on farms, moving from the use of denitrifying bioreactors to the concept of a permeable reactive interceptor (PRI). Besides management changes, a PRI should contain additional remediation cells for specific contaminants in the form of solutes, particles or gases. Balance equations and case studies representing different geographic areas are presented and used to create weighting factors. Results showed that national legislation with respect to water and gaseous emissions will inform the eventual PRI design. As it will be expensive to monitor a system continuously in a holistic manner, it is suggested that developments in the field of molecular microbial ecology are essential to provide further insight in terms of element dynamics and the environmental controls on biotransformation and retention processes within PRIs. In turn, microbial and molecular fingerprinting could be used as an in-situ cost-effective tool to assess nutrient and gas balances during the operational phases of a PRI. Department of Agriculture, Food and the Marine - Research Stimulus Fund (RSF 07 525) peer-reviewed

peer-reviewed The effectiveness of chemical amendment of pig slurry to ameliorate phosphorus (P) losses in runoff is well studied, but research mainly has concentrated only on the runoff pathway. The aims of this study were to investigate changes to leachate nutrient losses, soil properties and greenhouse gas (GHG) emissions due to the chemical amendment of pig slurry spread at 19 kg total phosphorus (TP), 90 kg total nitrogen (TN), and 180 kg total carbon (TC) ha-1. The amendments examined were: (1) commercial grade liquid alum (8% Al2O3) applied at a rate of 0.88:1 [Al:TP] (2) commercial-grade liquid ferric chloride (38% FeCl3) applied at a rate of 0.89:1 [Fe:TP] and (3) commercial-grade liquid poly-aluminium chloride (PAC) (10% Al2O3) applied at a rate of 0.72:1 [Al:TP]. Columns filled with sieved soil were incubated for 8 mo at 10oC and were leached with 160 ml (19 mm) distilled water wk-1. All amendments reduced the Morgan’s phosphorus and water extractable P content of the soil to that of the soil-only treatment, indicating that they have the ability to reduce P loss in leachate following slurry application. There were no significant differences between treatments for nitrogen (N) or carbon (C) in leachate or soil, indicating no deleterious impact on reactive N emissions or soil C cycling. Chemical amendment posed no significant change to GHG emissions from pig slurry, and in the cases of alum and PAC, reduced cumulative N2O and CO2 losses. Chemical amendment of land applied pig slurry can reduce P in runoff without any negative impact on nutrient leaching and GHG emissions. Future work must be conducted to ascertain if more significant reductions in GHG emissions are possible with chemical amendments. Irish Research Council for Science, Engineering and Technology (IRCSET)- EMBARK scholarship

The application of biochar produced from wood and crop residues, such as sawdust, straw, sugar bagasse and rice hulls, to highly weathered soils under tropical conditions has been shown to influence soil greenhouse gas (GHG) emissions. However, there is a lack of data concerning GHG emissions from soils amended with biochar derived from manure, and from soils outside tropical and subtropical regions. The objective of this study was to quantify the effect on emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) following the addition, at a rate of 18 t ha−1, of two different types of biochar to an Irish tillage soil. A soil column experiment was designed to compare three treatments (n = 8): (1) non-amended soil (2) soil mixed with biochar derived from the separated solid fraction of anaerobically digested pig manure and (3) soil mixed with biochar derived from Sitka Spruce (Picea sitchensis). The soil columns were incubated at 10 °C and 75% relative humidity, and leached with 80 mL distilled water, twice per week. Following 10 weeks of incubation, pig manure, equivalent to 170 kg nitrogen ha−1 and 36 kg phosphorus ha−1, was applied to half of the columns in each treatment (n = 4). Gaseous emissions were analysed for 28 days following manure application. Biochar addition to the soil increased N2O emissions in the pig manure-amended column, most likely as a result of increased denitrification caused by higher water filled pore space and organic carbon (C) contents. Biochar addition to soil also increased CO2 emissions. This was caused by increased rates of C mineralisation in these columns, either due to mineralisation of the labile C added with the biochar, or through increased mineralisation of the soil organic matter.