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The objective of this review was to provide quantitative insights into algal growth and nutrient removal in anaerobic digestate. To synthesize the relevant literature, a meta-analysis was conducted using data from 58 articles to elucidate key factors that impact algal biomass productivity and nutrient removal from anaerobic digestate. On average, algal biomass productivity in anaerobic digestate was significantly lower than that in synthetic control media (p < 0.05) but large variation in productivity was observed. A mixed-effects multiple regression model across study revealed that biological or chemical pretreatment of digestate significantly increase productivity (p < 0.001). In contrast, the commonly used practice of digestate dilution was not a significant factor in the model. High initial total ammonia nitrogen suppressed algal growth (p = 0.036) whereas initial total phosphorus concentration, digestate sterilization, CO 2 supplementation, and temperature were not statistically significant factors. Higher growth corresponded with significantly higher NH 4 –N and phosphorus removal with a linear relationship of 6.4 mg NH 4 –N and 0.73 mg P removed per 100 mg of algal biomass growth (p < 0.001). The literature suggests that suboptimal algal growth in anaerobic digestate could be due to factors such as turbidity, high free ammonia, and residual organic compounds. This analysis shows that non-dilution approaches, such as biological or chemical pretreatment, for alleviating algal inhibition are recommended for algal digestate treatment systems. [Display omitted] • A meta-analysis was conducted on algal cultivation in anaerobic digestate. • Significant difference (p < 0.05) in algal growth in digestate vs. control media. • Chem/Bio pretreatment support (p < 0.05) algal productivity in digestate. • Non-dilution approaches are recommended for algae production from digestate. [ABSTRACT FROM AUTHOR]

The circular bio-based economy offers great untapped potential for the food industry as possible valuable products and energy can be recovered from food waste. This can promote more sustainable and resilient food systems in Europe in follow-up of the European Commission's Farm to Fork strategy and support the global transition to more sustainable agri-food systems with the common agricultural and fisheries policies. With its high nutrient content, waste and by-products originating from fish and seafood industry (including aquaculture) are one of the most promising candidates to produce alternative fertilising products which can play a crucial role to replace synthetic mineral fertilisers. Whereas several studies highlighted the opportunities to recover valuable compounds from fishery waste, study towards their potential for the production of fertilising products is still scarce. This study presents an extensive overview of the characteristics of fishery waste and by-products (i.e., fish processing waste, fish sludge, seafood waste/by-products), the state-of-the-art nutrient recovery technologies and recovered nutrients as fertilising products from these waste streams. The European Commission has already adopted a revised Fertilising Products Regulation (EU) 2019/1009 providing opportunities for fertilising products from various bio-based origins. In frame of this opportunity, we address the quality and safety aspects of the fishery waste-derived fertilising products under these criteria and highlight possible obstacles on their way to the market in the future. Considering its high nutrient content and vast abundance, fish sludge has a great potential but should be treated/refined before being applied to soil. In addition to the parameters currently regulated, it is crucial to consider the salinity levels of such fertilising products as well as the possible presence of other micropollutants especially microplastics to warrant their safe use in agriculture. The agronomic performance of fishery waste-derived fertilisers is also compiled and reported in the last section of this review paper, which in most cases perform equally to that of conventional synthetic fertilisers. • Fish processing waste/wastewater/sludge has high protein and lipid contents. • The choice of technology depends on the raw material and desired end-product. • Salinity and microplastics are potential critical parameters. • Fish sludge has a great potential but should be treated/refined before application. • Fishery waste-based fertilisers perform equally to commercial synthetic fertilisers. [ABSTRACT FROM AUTHOR]

The health of agroecosystems is subsiding unremittingly, and the over-use of chemical fertilizers is one of the key reasons. It is hypothesized that integrating biochar, a carbon (C)-rich product, would be an effective approach to reducing the uses of synthetic fertilizers and securing crop productivity through improving soil properties and nutrient cycling. The bamboo biochar at different quantities (4–12 Mg ha−1) and combinations with chemical fertilizers were tested in stevia (Stevia rebaudiana) farming in silty clay acidic soil. The integration of biochar at 8 Mg ha−1 with 100% nitrogen (N), phosphorus (P), and potassium (K) produced statistically (p ≤ 0.05) higher leaf area index, dry leaf yield, and steviol glycosides yield by about 18.0–33.0, 25.8–44.9, and 20.5–59.4%, respectively, compared with the 100% NPK via improving soil physicochemical properties. Soil bulk density was reduced by 5–8% with biochar at ≥ 8 Mg ha−1, indicating the soil porosity was increased by altering the soil macrostructure. The soil pH was significantly (p ≤ 0.05) augmented with the addition of biochar alone or in the combination of N because of the alkaline nature of the used biochar (pH = 9.65). Furthermore, integrating biochar at 8 Mg ha−1 with 100% NPK increased 22.7% soil organic C compared with the sole 100% NPK. The priming effect of applied N activates soil microorganisms to mineralize the stable C. Our results satisfy the hypothesis that adding bamboo biochar would be a novel strategy for sustaining productivity by altering soil physicochemical properties. [Display omitted] • Integration of biochar at 8 Mg ha−1 produced 25.8–44.9% higher dry leaf yield. • Biochar did not make a significant effect on the growth of stevia in the first year. • Biochar significantly (p ≤ 0.05) increased soil pH compared with control and 100% NPK. • Soil bulk density was reduced by 5–8% with the addition of biochar at ≥ 8 Mg ha−1. • Integration of biochar at 8 Mg ha−1 increased 22.7% soil OC compared with 100% NPK. [ABSTRACT FROM AUTHOR]

Urban centres acquire and accumulate many materials from their hinterland, among these are nutrient elements such as nitrogen (N). The popular North American vision of a peri-urban setting is one where urban food production, composting and re-cycling are assumed to limit urban accumulation of nutrients. This study quantifies this assumption using the Lower Fraser Valley (LFV) of British Columbia as an example, ideal because it is surrounded by mountains, ocean and an international border which collectively delimit the peri-urban boundaries. Nitrogen influxes are dominated by livestock feed imports to support dairy and poultry production (18000 tonnes N), followed by human food imports (9210 tonnes N), as well as 5410 tonnes N as fertilizer and 4690 tonnes N in atmospheric deposition. There is a transfer of 6700 tonnes N from agricultural to urban ecosystems displacing food imports, but food production contributes to the N footprint of the LFV. Nitrogen effluxes are dominated by sewage disposal (10400 tonnes N), solid waste disposal (7020 tonnes N) and atmospheric emissions (9460 tonnes N). The total influx is 15 kg N per person, the net influx is 3.1 kg N per person. Per unit land area, these are a total influx of 24 kg N/ha and a net influx of 4.7 kg N/ha. The atmospheric emissions are 4.7 kg N per person and 7.2 kg/ha. The N in soil is mobile and it is assumed soil N is at a steady state concentration, thus the surplus N is lost from the soil, probably by leaching and runoff. The Fraser River is estimated to acquire and transport 5230 tonnes N from the region into the ocean each year, in addition to 10300 tonnes N from sewage outfall. This is coupled with effluxes of phosphorus (estimated previously), and the result probably has an impact on the coastal waters. There is little reuse of imported N and current waste management practices including composting and combustion do little to improve N efficiency. • The N budget is presented for a physically isolated peri-urban region. • N influxes were dominated by livestock feed to support local dairy and poultry. • N influxes for human food were the next most important. • N effluxes were dominated by sewage, atmospheric emissions and solid waste. • The total annual influx was 15 kg N per person, the net was 3.1 kg N per person. [ABSTRACT FROM AUTHOR]

Abstract Human faeces from a dry toilet are converted via hydrothermal carbonization to obtain a sterilized carbonaceous material. During this process the original material undergoes consecutively hydrolysis, water elimination and polymerization reactions. Consequently, the oxygen content is reduced, leading to a material with a better dewaterability and an attractive higher heating value (HHV = 22–28 MJ kg−1). The influence of pH-value, set by the addition of citric acid, the reaction time and the reaction temperature are investigated. By thermogravimetric analysis it is shown that especially higher acid concentration as well as higher reaction temperatures and longer reaction times are necessary to fully convert the feedstock into a stable carbon-rich material. As pathogens are destroyed by hydrothermal carbonization, nutrient recovery becomes a relevant aspect. The analysis shows that alkali salts such as sodium and potassium are dissolved in the aqueous phase, but an important proportion of the phosphorus and nitrogen remain in the hydrochar. This finding is the basis for phosphorus recycling or to produce an organic fertilizer. Graphical abstract Image 1 Highlights • Evaluation of HTC as a waste management technique including nutrient recovery. • Successful conversion of dry toilet residues via HTC into a carbon-rich material. • Better understanding of the fate of fertilizer-relevant nutrients during HTC. [ABSTRACT FROM AUTHOR]

Safe and effective circulation of nutrient-rich meat and bone meal (MBM) could become a carbon-based alternative to limited chemical fertilizers (CFs). Therefore, MBM biochars (MBMCs) were produced at 500, 800, and 1000 °C to evaluate their effects on plant growth, nutrient uptake, and soil characteristics. The results revealed that MBMC produced at 500 °C (MBMC500) contained the maximum amount of C, N, and phytoavailable P. All additional MBMC doses with recommended CF increased sorghum shoot yield (6.7–16%) and significantly improved P uptake. Additional experiments were conducted with decreasing doses of CF (100–0%) with or without MBMC500 (7 t/ha) to quantify its actual fertilizing value. MBMC500 showed the capability to reduce CF requirement by 20% without compromising the optimum yield (by 100% CF) while increasing pH, CEC, total-N, available-P, Mg, and microbial population of post-harvest soil. Although a δ15N analysis confirmed MBMC500 as a source of plant N, a reduction in N uptake by MBMC500 + 80% CF treatment compared to 100% CF might have limited further sorghum growth. Thus, future studies should concentrate on producing MBMC with better N utilization capability and achieving maximum CF reduction without negative environmental impacts. [Display omitted] • Effective nutrient recycling capacities of different MBM biochars were compared. • While the P content increased with production temperature, availability decreased. • N-rich MBM biochar proved to be a direct source of plant N. • Co-application of MBMC and chemical fertilizer imparts numerous agronomic benefits. • Greater utilization of MBMC-N might completely replace synthetic fertilizers. [ABSTRACT FROM AUTHOR]

Improving environmental protection and finding sustainable and renewable resources of nutrients are core issues in circular bioeconomy. Thus, this study evaluated the efficiency of recovering struvite, MgNH 4 PO 4 ·6H 2 O, from different agro-industrial wastewaters (four highly loaded reject waters of anaerobically co-digested agro-industrial waste and a raw swine slurry) and assessed the quality of recovered struvite crystals and their reusability as fertilizer. The efficiency of crystallization (E c 40–80%) and amount of struvite in the precipitate (P p 55–94%) highly varied due to the characteristics of influent wastewaters, particularly to the content of competing elements, such as alkaline and heavy metals and total solids (TS). In particular, E c (94, 75, 61%) and P p (76, 66, 48%) decreased at increasing TS (0.57, 0.73, 0.99%), demonstrating the hindering effect of solid content on struvite recovery and quality. According to X-ray diffraction analysis, the structure of all isolated samples corresponded to crystalline, orthorhombic struvite, which exhibited high purity (32–48 g/kg d N, 114–132 g/kg d P, and 99–116 g/kg d Mg) containing only a few foreign elements, whose amount depended on the characteristics of the influent wastewater. All struvite contained other plant macronutrients (K, Ca) and many micronutrients (Fe, Na, Cu, Mn, Co, Zn) that further enhance its agronomic value. Therefore, this study showed that struvite can be successfully recovered from a wide range of highly loaded agroindustrial wastewaters, and that the quality of the recovered struvite could be suitable for reuse in agriculture. [ABSTRACT FROM AUTHOR]

During storage of urine, urea is biologically decomposed to ammonia, which can be lost through volatilization and in turn causes significant unpleasant smell. In response, lactic acid fermentation of urine is a cost-effective technique to decrease nitrogen volatilization and reduce odour emissions. Fresh urine (pH = 5.2–5.3 and NH 4 + -N = 1.2–1.3 g L −1 ) was lacto-fermented for 36 days in closed glass jars with a lactic acid bacterial inoculum from sauerkraut juice and compared to untreated, stored urine. In the lacto-fermented urine, the pH was reduced to 3.8–4.7 and the ammonium content by 22–30%, while the pH of the untreated urine rose to 6.1 and its ammonium content increased by 32% due to urea hydrolysis. The concentration of lactic acid bacteria in lacto-fermented urine was 7.3 CFU ml −1 , suggesting that urine is a suitable growth medium for lactic acid bacteria. The odour of the stored urine was subjectively perceived by four people to be twice as strong as that of lacto-fermented samples. Lacto-fermented urine induced increased radish germination compared to stored urine (74–86% versus 2–31%). Adding a lactic acid bacterial inoculum to one week old urine in the storage tanks in a urine-diverting dry toilet reduced the pH from 8.9 to 7.7 after one month, while the ammonium content increased by 35%, probably due to the high initial pH of the urine. Given that the hydrolyzed stale urine has a high buffering capacity, the lactic acid bacterial inoculum should be added to the urine storage tank of a UDDT before urine starts to accumulate there to increase the efficiency of the lactic acid fermentation. [ABSTRACT FROM AUTHOR]

Excess phosphorus (P) in peri-urban regions is an emerging issue, whereas there is global depletion of quality mined supplies of P. The flow of P across the landscape leading to regional surpluses and deficits is not well understood. We computed a regional P budget with internal P flows in a fairly discreet peri-urban region (Lower Fraser Valley, BC) with closely juxtaposed agricultural and non-agricultural urban ecosystems, in order to clarify the relationship between food production, food consumption and other activities involving use of P (e.g. keeping pets and horses and using soaps). We hypothesized changes that might notably improve P efficiency in peri-urban settings and wider regions. Livestock feed for the dairy and poultry sectors was the largest influx of P: the peri-urban land is too limited to grow feed grains and they are imported from outside the region. Fertilizer and import of food were the next largest influxes of P and a similar amount of P flows as food from the agricultural to urban ecosystems. Export of horticultural crops (berries and greenhouse crops) and poultry represented agricultural effluxes that partially offset the influxes. P efficiency was lower for horticultural production (21%) than animal production (32%), the latter benefited from importing feed crops, suggesting a regional advantage for animal products. There was 2.0, 3.8, 5.7 and 5.6 tonnes imported P per $ million farm cash receipts for horticulture, dairy, poultry meat and eggs. Eliminating fertilizer for corn and grass would reduce the ratio for the dairy industry. The net influx, dominated by fertilizer, animal feed and food was 8470 tonnes P per year or 3.2 kg P per person per year, and of this the addition to agricultural soils was 3650 tonnes P. The efflux in sewage effluent to the sea was 1150 tonnes P and exported sewage solids was 450 tonnes P. Municipal solid waste disposal was most difficult to quantify and was about 1800 tonnes P, 80% of which was partly reused in the urban regions and partly sequestered in landfill, which may be considered an efflux or a surplus. Reuse of rendering waste for feeding poultry significantly reduced P importation, but no rendering waste is used for cattle due to health concerns. Sensitivity analysis showed that variation in human population and the amount of P consumed per person in chicken and dairy products had the most influence on the total movement of P from agricultural to urban-ecosystems. There are current farm practices that mitigate P surpluses and new technologies are being developed to further reduce farm imbalances. However, current waste management policies that promote practices such composting of home wastes and exporting of poultry manure and biosolids to semiarid rangeland do little to enhance overall P cycling because the P is not returned to the farms producing feed and food for the peri-urban region. Sequestering in landfills may be a better solution until better ways are found to return surplus P. [ABSTRACT FROM AUTHOR]

Sludge generation during wastewater treatment is inevitable even with proper management and treatment. Yet proper handling and disposal of sludge are still challenging in terms of treatment cost, presence of recalcitrant contaminants of concern, sanitary issues, and public acceptance. Conventional disposal methods (i.e. landfilling, incineration) have created concerns in terms of legislative restrictions and community perception, incentivizing consideration of substitute sludge management options. Furthermore, with proper treatment, biosolids from sludge, rich in organic materials and nutrients, could be utilizable as fertilizer. Despite the challenges of dealing with sludge, no review has dealt with integrated source reduction and reuse as the best sustainable management practices for sludge treatment. In this review, we present two main approaches as potentially sustainable controls: (i) pretreatment for minimizing extensive sludge treatment, and (ii) recycling and reuse of residual sludge. Drawing on these approaches, we also suggest strategies for efficient pretreatment mechanisms and residual reuse, presenting ideas for prospective future research. [ABSTRACT FROM AUTHOR]

Microalgae biomass (MB) is a promising source of renewable energy, especially when the cultivation is associated with wastewater treatment. However, microalgae wastewater technologies still have much to improve. Additionally, microalgae biomass valorization routes need to be optimized to be a sustainable and feasible source of green bioenergy. Thus, this paper aimed to evaluate the environmental impacts of the production of briquettes from MB, cultivated during domestic wastewater treatment. Also, it was evaluated how much the drying of the MB affected the life cycle and the environment. Improvements in the life cycle to mitigate the environmental impacts of this energy route were proposed. Cradle-to-gate modeling was applied to obtain a life cycle assessment (LCA) from cultivation to the valorization of MB, through its transformation into a solid biofuel. With LCA, it was possible to identify which technical aspect of the process needs to be optimized so that environmental sustainability can be achieved. Two scenarios were compared, one with the microalgae growth in a high-rate algal pond (HRAP) (scenario 1) and the other in a hybrid reactor, formed by a HRAP and a biofilm reactor (BR) (scenario 2). LCA highlighted the electric power mix, representing, on average, 60% of the total environmental impacts in both scenarios. The valorization of MB in briquettes needs to consume less energy to offset its yield. The environment suffered pressure in freshwater eutrophication, due to the release of 3.1E-05 and 3.9E-05 kg of phosphorus equivalent; in fossil resources scarcity, with the extraction of 1.4E-02 and 4.5E-02 kg of oil equivalent; and in climate change, by the emission of 1.0E-01 and 1.9E-01 kg of carbon dioxide (CO 2) equivalent, in scenarios 1 and 2, respectively. Scenario 1 was highly damaging to terrestrial ecotoxicity, with the release of 3.5E-01 kg of 1,4 Dichlorobenzene, coming from the CO 2 used in MB growth. This category was the one that most negatively pressured the environment, differing from scenario 2, in which this input was not required. This was the only impact category in which scenario 2 had a better environmental performance when compared to scenario 1. Cotton, required in scenario 2, represented up to 87% of emissions in some of the evaluated categories. Despite the impacts that occurred in the two modeled scenarios, the environmental gains due to the use of wastewater for microalgae growth, replacing the synthetic cultivation medium, stood out. In the sensitivity analysis, two alternative scenarios were proposed: (i) electricity consumption for drying has been reduced, due to the natural decrease of MB humidity, and (ii) MB briquettes were considered a substitute for coal briquettes. Results indicated that pressures on climate change and fossil resource scarcity were eliminated in both scenarios and this also occurred for freshwater eutrophication in scenario 2. This paper contributes to the improvement and development of converting MB routes into more sustainable products, causing less pressure on the environment. Also, the study contributes to filling a gap in the literature, discussing methods and technologies to be improved, and consequently making microalgae biotechnology environmentally feasible and a potential renewable energy alternative. [Display omitted] • Environmental impacts of microalgae biomass briquette were obtained. • The environment was stressed on terrestrial ecotoxicity, by CO 2 supplementation. • The net energy of the process was negative due to drying. • Optimizing biomass drying improved energy and environmental performance. • Microalgae biomass briquettes to replace coal benefit the environment. [ABSTRACT FROM AUTHOR]

Anaerobic digestates from sewage sludge (SSADs) are a by-product of the wastewater treatment process that still preserves a certain agronomic interest for its richness in plant nutrients and organic matter. Fertilizing properties of two liquid and two dewatered SSADs were tested on tomato plants (Solanum lycopersicum L.). Pot experiments were performed on sandy soil and peat substrate under greenhouse conditions with a SSADs application rate of 170 kg N/ha over a period of three months. Beneficial effects of SSADs were reported on different growth parameters, revealing an increase in biomass and height up to 37.5 and 6-folds over untreated control. No phytotoxic effect occurred on SSAD-exposed plants. Chemical analysis of soils treated with SSADs showed enrichment of macro- and micro-nutrients as well as organic matter. In some cases, the chemical characterization of leaves revealed an enhancement of uptaken macronutrients. This study contributed in general to deepen the knowledge on the short-term growing season fertilizing effects of SSAD. Despite the treatment dosage was calculated only on nitrogen requirements, the study highlighted the importance of the other nutrients and organic matter on plant growth. Image 1 • Anaerobic digestates from sewage sludge increased plant biomass up to 37.5-folds. • No phytotoxic effect occurred on plants exposed to anaerobic digestates. • Digestates application induced soil enrichment in nutrients and organic matter. [ABSTRACT FROM AUTHOR]

Microbial contamination of vegetables due to irrigation with wastewater-polluted streams is a common problem around most cities in developing countries because wastewater is an available source of water and nutrients but wastewater treatment is often inadequate. On-farm treatment of polluted water is a feasible option to manage microbial risks in a multi-barrier approach. Current evidence indicates good suitability of biochar filters for microbe removal from wastewater using the hydraulic loading rate (HLR) designed for sand filters, but their suitability has not been tested under on-farm conditions. This study evaluated the combined effect of several variables on removal of microbial indicators from diluted wastewater by biochar filtration on-farm and the correlations between removal efficiency and HLR. Columns of biochar with three different effective particle diameters (d 10) were fed with diluted wastewater at 1x, 6x, and 12x the design HLR and two levels of water salinity (electrical conductivity, EC). Influent and effluent samples were collected from the columns and analyzed for bacteriophages (ɸX174 and MS2), Escherichia coli , Enterococcus spp., and Saccharomyces cerevisiae. Microbe removal decreased with increasing HLR, from 2 to 4 to 1 log 10 for bacteria and from 2 to 0.8 log 10 for viruses, while S. cerevisiae removal was unaffected. Effective particle diameter (d 10) was the main variable explaining microbe removal at 6x and 12x, while EC had no effect. Correlation analysis showed removal of 2 log 10 bacteria and 1 log 10 virus at 3x HLR. Thus biochar filters on-farm would not remove significant amounts of bacteria and viruses. However, the design HLR was found to be conservative. These results, and some technical and management considerations identified, can assist in the development of a scientific method for designing biochar filters for on-farm and conventional wastewater treatment. Image 1 • Biochar filters for on-farm wastewater treatment were studied for microbial removal. • Influent and effluent samples were taken weekly under four loading regimes. • Studied microbes were reduced in 1 log 10 at 6X design HLR and 1.4 mm grain diameter. • Microbial removal rates were found to be similar at 1X and 3X the design HLRs. • On-farm implementation is context-dependent, but promising for treatment plants. [ABSTRACT FROM AUTHOR]

Sewage sludge is a valuable source of nutrients and organic matter, which are beneficial for plant growth. The use of sewage sludge for agricultural purposes can be limited by the potential content of heavy metals and toxic organic compounds that pose a threat to the environment. The characterisation of sewage sludges from 11 Polish wastewater treatment plants (WWTPs) in terms of their fertilizing properties and heavy metal contents are presented in the study. Based on the chemical composition of sewage sludge from the WWTP in Żywiec, the compositions of organo-mineral fertilizers dedicated for rapeseed crop was developed. Alternative raw materials such as poultry litter ash and biomass ash were considered as components for fertilizer production. The production process of organo-mineral fertilizers included mixing sewage sludge with poultry litter ash/biomass ash and mineral fertilizers and granulation with mineral acids. The final products contained 24–34% of total NPK and fulfilled the requirements regarding heavy metal content according to Polish legislation. Using sewage sludge for fertilizer production is a promising solution for sewage sludge management, allowing the recycling of 82–140 tonnes of phosphorus (as P 2 O 5) and 42–73 tonnes of nitrogen (N) annually in the WWTP in Żywiec. • Sewage sludge from Polish WWTPs were analysed. • Fertilizers with high NPK content based on 48–52% of waste were produced • Final products fulfil the requirements related to heavy metal content. [ABSTRACT FROM AUTHOR]