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Sewage sludge management for fertilizer purposes can be a step in the circular phosphorus (P) economy. Using microbial solubilization in manufacturing fertilizers from recycled materials is an innovative approach with the potential to increase P compounds' bioavailability, and fertilizers from sewage sludge ash and P-solubilizing bacteria are promising products of this technology. In addition to P and a range of macronutrients, these fertilizers contain small amounts of micronutrients and potentially toxic elements. This paper discusses the effects of fertilizer on iron (Fe) and aluminum (Al) content in soil, test plants (spring or winter wheat; grain and straw), weeds and post-harvest residues, based on field experiments. Treatments with conventional P fertilizers (superphosphate, phosphorite) and without P fertilization provided references. The tested biofertilizers containing the Bacillus megaterium or Acidithiobacillus ferrooxidans strain had no effect on total Fe and Al content in the soil or on the concentration of these elements in plant biomass when applied at P doses up to 35.2 kg ha–1. Fe and Al levels in grain did not suggest a potential risk to consumers. [ABSTRACT FROM AUTHOR]

Autotrophs play an essential role in the cycling of carbon and nutrients, yet disease‐ecosystem relationships are often overlooked in these dynamics. Importantly, the availability of elemental nutrients like nitrogen and phosphorus impacts infectious disease in autotrophs, and disease can induce reciprocal effects on ecosystem nutrient dynamics. Relationships linking infectious disease with ecosystem nutrient dynamics are bidirectional, though the interdependence of these processes has received little attention. We introduce disease‐mediated nutrient dynamics (DND) as a framework to describe the multiple, concurrent pathways linking elemental cycles with infectious disease. We illustrate the impact of disease–ecosystem feedback loops on both disease and ecosystem nutrient dynamics using a simple mathematical model, combining approaches from classical ecological (logistic and Droop growth) and epidemiological (susceptible and infected compartments) theory. Our model incorporates the effects of nutrient availability on the growth rates of susceptible and infected autotroph hosts and tracks the return of nutrients to the environment following host death. While focused on autotroph hosts here, the DND framework is generalizable to higher trophic levels. Our results illustrate the surprisingly complex dynamics of host populations, infection patterns, and ecosystem nutrient cycling that can arise from even a relatively simple feedback between disease and nutrients. Feedback loops in disease‐mediated nutrient dynamics arise via effects of infection and nutrient supply on host stoichiometry and population size. Our model illustrates how host growth rate, defense, and tissue chemistry can impact the dynamics of disease–ecosystem relationships. We use the model to motivate a review of empirical examples from autotroph–pathogen systems in aquatic and terrestrial environments, demonstrating the key role of nutrient–disease and disease–nutrient relationships in real systems. By assessing existing evidence and uncovering data gaps and apparent mismatches between model predictions and the dynamics of empirical systems, we highlight priorities for future research intended to narrow the persistent disciplinary gap between disease and ecosystem ecology. Future empirical and theoretical work explicitly examining the dynamic linkages between disease and ecosystem ecology will inform fundamental understanding for each discipline and will better position the field of ecology to predict the dynamics of disease and elemental cycles in the context of global change. [ABSTRACT FROM AUTHOR]

This study uses a new approach for the recycling of plant nutrients by co-digesting sewage sludge with fly ash from a wood combustion. Sewage sludge and fly ash both are enriched with nutrients of the wastewater resp. wood, which makes these products an enhanced source for recycled fertilizers. The effects of the ash addition to the anaerobic digestion are studied in several lab scale experiments including effects on the gas production and microbial activity. Following that, the fertilizing qualities of the digestate are evaluated by plant growth experiments. The results show that the fertilizing qualities of the digested sludge were improved by the ash addition. Next to this, gas production results show that the methane production was not affected by the ash addition, while the total gas release was reduced. The sulphur addition by the ash stimulated sulphate reducing bacteria. The sulphate reducing bacteria did not markedly inhibit the methanogens. [ABSTRACT FROM AUTHOR]

Developmental petal senescence is a type of programmed cell death (PCD), during which the production of ethylene is induced, the expression of PCD-related genes is upregulated, and nutrients are recycled. Autophagy is an intracellular mechanism involved in PCD modulation and nutrient cycling. As a central component of the autophagy pathway, Autophagy Gene 6 (ATG6) was previously shown as a negative regulator of petal senescence. To better understand the role of autophagy in ethylene biosynthesis and nutrient remobilization during petal senescence, we generated and characterized the knockout (KO) mutants of PhATG6 using CRISPR/Cas9 in Petunia × hybrida 'Mitchell Diploid.' PhATG6- KO lines exhibited decreased flower longevity when compared to the flowers of the wild-type or a non-mutated regenerative line (controls), confirming the negative regulatory role of ATG6 in petal senescence. Smaller capsules and fewer seeds per capsule were produced in the KO plants, indicating the crucial function of autophagy in seed production. Ethylene production and ethylene biosynthesis genes were upregulated earlier in the KO lines than the controls, indicating that autophagy affects flower longevity through ethylene. The transcript levels of petal PCD-related genes, including PhATG6 , PhATG8d , PhPI3K (Phosphatidylinositol 3-Kinase), and a metacaspase gene PhMC1 , were upregulated earlier in the corollas of PhATG6- KO lines, which supported the accelerated PCD in the KO plants. The remobilization of phosphorus was reduced in the KO lines, showing that nutrient recycling was compromised. Our study demonstrated the important role of autophagy in flower lifespan and seed production and supported the interactions between autophagy and various regulatory factors during developmental petal senescence. [ABSTRACT FROM AUTHOR]

Organic fertilization is a promising strategy to decrease N mineralization rates and high N losses via leaching and denitrification, thus synchronizing N application with N uptake for crops. A 230-day experiment with olive plants was realized under greenhouse conditions to compare urea and biogas digestate (BD) application on the growth, nutrient uptake, and physiological performance of Olea europaea L. plants. The following treatments were applied: (i) UREA, (ii) UREA + DCD (nitrification inhibitor), (iii) BD, (iv) BD + DCD, (v) acidified BD, (vi) acidified BD + DCD, (vii) CONTROL (typical native Marl soil type, without fertilizer application). Under BD application, significantly higher levels of organic matter, Olsen P, and exchangeable K compared to UREA were found. Significantly lower main shoot length and total plant biomass were recorded in the CONTROL soil compared to BD. Foliar N was lower in the ACID.BD and ACID.BD + DCD treatments, while leaf P was lower in UREA. The highest PSII activity was recorded in UREA + DCD, while the highest photosynthetic rate and intercellular CO2 concentration were determined in UREA. It is expected that these data will constitute a first comparative approach between urea and BD application in olive plants, which should be carefully considered, towards boosting sustainable fertilization in the frame of circular economy strategy. [ABSTRACT FROM AUTHOR]

Aquaculture has grown rapidly to play a crucial economic and social role and meet the increasing global demand for seafood. As aquaculture intensifies, there is increasing pressure to find more sustainable practices that save resources and reduce waste. Major wastes and by-products from aquaculture were quantified across a full range of farming types. Key opportunities for wastewater treatment and by-product recovery include nutrient recycling through a combination of biofilters, bioaccumulation and multitrophic systems. To support a sustainable intensification of aquaculture, improvements in by-product harvesting, accumulation and processing methods require further investigation. Likewise, energy generated from by-products can potentially support intensified production through land-based recirculating aquaculture systems (RAS). Future challenges faced by the reuse of side streams include control of food safety and gaining consumer acceptance. Combined with increases in resource use efficiency across the aquaculture sector, from feeding methodologies to product storage, nutrient recycling can enable aquaculture to contribute sustainably toward the nutritional requirements of billions of people over the next century. [ABSTRACT FROM AUTHOR]

In streams, unionoid mussels and fish form aggregations that exert bottom‐up and top‐down effects on food webs, but the magnitude and spatial extent of their effects are controlled by species traits. Sedentary mussels live burrowed in the sediment in patchily distributed dense aggregations (mussel beds) where they filter seston and provide a local, relatively constant nutrient subsidy. In contrast, fish move on and off mussel beds, and thus comprise a transient nutrient subsidy.We asked how overlap between fish and mussels influences nutrient recycling and resource distribution in streams. We conducted an 8‐week study in experimental streams where we created mussel beds (comprised of two species, Actinonaias ligamentina and Amblema plicata), manipulated the occurrence of a grazing minnow (Campostoma anomalum), and tracked nutrient (nitrogen and phosphorus) and resource (algae, detritus, and chironomids) abundance up and downstream of the mussel beds.In general, neither consumer had strong effects on the concentration or spatial distribution of nutrients. Water turnover time in our experimental streams may have diluted fish and mussel nutrient excretion effects, making it difficult to detect spatial patterns during a given sampling period.Fish controlled the abundance and productivity of algae. In treatments without fish, large mats of filamentous algae formed early in the experiment. These algae senesced, decomposed, and were not replaced. When fish were present, algae consisted of attached biofilms with consistent biomass and spatial distribution over time.Although previous work has shown that mussels can have strong, seasonal bottom‐up effects on both primary and secondary production, our results suggested that adding grazing mobile fishes, led to a more consistent and homogenous supply of algal resources. Because mussels rarely occur in the absence of fish, considering their combined influence on ecosystem dynamics is likely to be important. [ABSTRACT FROM AUTHOR]

With the general objective of optimizing internal nutrient recycling, circular multitrophic food production systems, e.g., combining fish, plant, and insect larvae production, rely on the quality and composition of sustainable nutritional inputs. Therefore, differences in dissolved and solid nutrient excretion patterns produced by Nile tilapia (Oreochromis niloticus) reared in recirculating aquaculture systems (RAS) with 5% daily water exchange and fed black soldier fly meal (BSFM), poultry by-product meal (PM), poultry blood meal (PBM) and fish meal (FM) as single protein sources were investigated to evaluate the potential for creating specific fish meal-free diets. Fish fed the FM and PM diet showed the significantly best (p < 0.05) and among each other similar (p > 0.05) growth performance (specific growth rate (SGR): 2.12 ± 0.04/2.05 ± 0.11; feed conversion ratio (FCR): 0.86 ± 0.03/0.92 ± 0.01), whereas the PBM diet caused significantly reduced performance (SGR: 1.30 ± 0.02; FCR: 1.79 ± 0.05) in comparison to the FM/PM diet as well as the BSF diet (SGR: 1.76 ± 0.07; FCR: 1.11 ± 0.05). The FM and PM diet resulted in a faster increase and significantly higher dissolved nitrogen and phosphorus levels, while the BSF diet caused faster accumulation and significantly elevated levels of dissolved potassium, magnesium, and copper. The PBM diet resulted in the feces with the significantly highest nutrient density (gross energy, crude protein, and amino acids) but overall much lower dissolved nutrient levels in the water. Results are discussed with regard to implications for developing circular multitrophic food production systems. [ABSTRACT FROM AUTHOR]

Human urine can be used as fertilizer and technologies, such as alkaline-urine treatment, are being developed to enable easier re-use. There is, however, a risk of pathogens being present in the urine. This hygiene assessment examined inactivation of three model organisms, one parasite (Ascaris suum) and two viruses (coliphages MS2 and ΦX174), during 1) alkaline-urine treatment and 2) drying of the alkalized-urine (A. suum only). Fresh human urine was mixed with calcium hydroxide (10 g Ca(OH)2 L−1 urine) and divided into three fractions (Mixed liquor, Supernate, Precipitates). The factions were inoculated with the model organisms and then subjected to three treatments (Drying-storage, Stored and Thermal treatment) at temperatures between 20 and 50°C. For Ascaris, drying (moisture content (MC) 13–33%) the alkaline-urine proved effective in shortening the time required for a 3 log10 reduction in viable eggs at 20°C, but only Partially drying (MC 73–82%) the urine led to longer inactivation times compared with Wet (MC >90%) or Dry conditions. While virus inactivation took place during the initial addition of Ca(OH)2, the viruses that were embedded in feces survived longer compared to the free viruses. At pH 11.5, contact times of 1.5 and 90.7 min were required to achieve a 4 log10 decay of phages in solution and phages embedded in feces respectively. In areas prone to parasites, Thermal treatment (≥42°C) and/or Storage (111 days at 20°C or 79 days at 35°C) is recommended in order to meet the WHO and USEPA guidelines for unrestricted fertilizer use. Drying (MC 73–82%) can also be used in combination with thermal treatment and/or storage, to accelerate the process.

Developmental petal senescence is a type of programmed cell death (PCD), during which the production of ethylene is induced, the expression of PCD-related genes is upregulated, and nutrients are recycled. Autophagy is an intracellular mechanism involved in PCD modulation and nutrient cycling. As a central component of the autophagy pathway, Autophagy Gene 6 (ATG6) was previously shown as a negative regulator of petal senescence. To better understand the role of autophagy in ethylene biosynthesis and nutrient remobilization during petal senescence, we generated and characterized the knockout (KO) mutants of PhATG6 using CRISPR/Cas9 in Petunia × hybrida ‘Mitchell Diploid.’ PhATG6-KO lines exhibited decreased flower longevity when compared to the flowers of the wild-type or a non-mutated regenerative line (controls), confirming the negative regulatory role of ATG6 in petal senescence. Smaller capsules and fewer seeds per capsule were produced in the KO plants, indicating the crucial function of autophagy in seed production. Ethylene production and ethylene biosynthesis genes were upregulated earlier in the KO lines than the controls, indicating that autophagy affects flower longevity through ethylene. The transcript levels of petal PCD-related genes, including PhATG6, PhATG8d, PhPI3K (Phosphatidylinositol 3-Kinase), and a metacaspase gene PhMC1, were upregulated earlier in the corollas of PhATG6-KO lines, which supported the accelerated PCD in the KO plants. The remobilization of phosphorus was reduced in the KO lines, showing that nutrient recycling was compromised. Our study demonstrated the important role of autophagy in flower lifespan and seed production and supported the interactions between autophagy and various regulatory factors during developmental petal senescence.

Alkaline earth hydroxides are widely used in water and wastewater treatment. Within the emerging niche of source-separating sanitation, these chemicals have found a new application—to prevent urease-catalysed degradation of urea present in freshly excreted human urine. However, little is known about the dissolution behaviour of these hydroxides in biological fluids like human urine. Herein, we investigate the solubility of Mg(OH)2 and examine factors that govern its dissolution in different types of urine (real fresh urine, synthetic fresh urine, synthetic dephosphatised fresh urine and real fresh urine concentrated by CO2-free drying). We report experimentally determined as well as thermodynamically simulated data on Mg(OH)2 solubility, dissolution kinetics, and chemical speciation in urine. We find that it takes between 6 and 16 min for Mg(OH)2 to dissolve and the average solubility in real fresh urine at 25°C to be 650 mg L−1. We show that solubility is influenced mainly by concentration of organic compounds, soluble phosphate, and magnesium excreted in fresh urine. When fresh urine is supersaturated with Mg(OH)2, the pH increases to >10.5 and urease-catalysed degradation of urea is inhibited for >14 days. Removing 95% water present in urine increases the solubility of Mg(OH)2 to 16,240 mg L−1 but reduces pH to < 10. Because relative increase in Mg(OH)2 solubility decreases as more water is removed and the solubility is retrograde with respect to temperature, to increase the urine pH to >10 and prevent enzymatic ureolysis, the temperature must be kept < 29°C at 75% water removal and < 22°C at 95% water removal. We find this dissolution behaviour of Mg(OH)2 in concentrated urine solutions to be unlike other alkaline earth hydroxides. These findings have significant implications for the design of new sanitation systems that separately collect and recycle plant-essential nutrients present in human urine.

Purpose Reuse of landfill leachate is an effective alternative for their nutrients to mitigate decrease in freshwater. On the other hand, the growth of vegetation in the final disposal areas provides many benefits such as improving the visual impact, controlling of hydric erosion, etc. The purpose of this work was to evaluate landfill leachate as irrigation water and source of nutrients for growth of Tagetes erecta L., an ornamental plant with phytoremediation capacities. Method Vegetal growth, physiological responses and mineral elements uptake of the ornamental plant Tagetes erecta L. were studied with different levels of landfill leachate irrigation. The landfill leachate was provided by the municipal waste treatment. Experimental period covered 34 days of daily watering between the beginning and end of the flowering stage. Three different irrigation treatments were used: T1: 10% leachate; T2: 25% leachate; T3: 50% leachate. Hoagland's solution served as the control treatment. Results The irrigation treatment with a dose of 50% leachate causes a clear deterioration in the plant and its flowers. In lower doses, the plant responds favorably to both the production of flowers and the main features of them. Also, the water-use efficiency (WUE) is diminished in those plants irrigated with the major dose of leachate. Conclusion Maintaining controlled doses, landfill leachates can be used as an alternative source of water and nutrients. Irrigation with leachates of these characteristics should be done in dosages not higher than 25% to avoid possible damage of Tagetes erecta L. growth.

Creating an ecologically sustainable circulation of nutrients requires local solutions with commitment from all participating parties. Due to vast differences between various regions, it is very complicated, if not impossible, to create fair, simple, and applicable legislation that can consider all of these differences in a meaningful way. Thus, there is a need for clear and easy ways of developing sustainable and viable solutions locally, as well as communicating them with local community and all the way up to the supervising governmental representatives. To meet this need, we developed a simulation tool that allows the user to explore the effectiveness and impact of a local biorefinery in waste management. As an iterative model based on state machine agents, it can easily be modified for a multitude of scenarios with changes taking place over time, while considering the viewing points of all involved. In this article, we report the first version of this tool and demonstrate its usefulness in estimating suitable biogas reactor size in a biorefinery.

• >150 organic metabolites are oxidised over chloride and urea in unconcentrated, non-hydrolysed urine acidified to pH 3.0. • Heat-activated peroxydisulphate removed >50% TOC and degraded >40% ΣOMs with <10% nitrogen loss. • Heating real, unconcentrated urine acidified to pH 3.0 at 90 °C for 1 h activated >90% of 60 mM peroxydisulphate. • Concentrated urine had lower persulfate activation but higher chloride & urea degradation compared to unconcentrated urine. The human urine metabolome is complex, containing a wide range of organic metabolites that affect treatment of urine collected in resource-oriented sanitation systems. In this study, an advanced oxidation process involving heat-activated peroxydisulphate was used to selectively oxidise organic metabolites in urine over urea and chloride. Initial experiments evaluated optimal conditions (peroxydisulphate dose, temperature, time, pH) for activation of peroxydisulphate in unconcentrated, non-hydrolysed synthetic urine and real urine acidified to pH 3.0. Subsequent experiments determined the fate of 268 endogenous organic metabolites (OMs) and removal of COD from unconcentrated and concentrated real urine (80–90% mass reduced by evaporation). The results revealed >90% activation of 60 mM peroxydisulphate in real unconcentrated urine heated to 90 °C for 1 h, resulting in 43% ΣOMs degradation, 22% COD removal and 56% total organic carbon removal, while >94% of total nitrogen and >97% of urea in real unconcentrated urine were recovered. The mechanism of urea degradation was identified to be chemical hydrolysis to ammonia, with the rate constant for this reaction determined to be 1.9 × 10−6 s−1 at pH 3.0 and 90 °C. Treating concentrated real urine resulted in similar removal of COD, ΣOMs degradation and total nitrogen loss as observed for unconcentrated urine, but with significantly higher chloride oxidation and chemical hydrolysis of urea. Targeted metabolomic analysis revealed that peroxydisulphate treatment degraded 157 organic metabolites in urine, of which 67 metabolites were degraded by >80%. The rate constant for the reaction of sulphate radicals with oxidisable endogenous organic metabolites in urine was estimated to exceed 108 M−1 s−1. These metabolites were preferentially oxidised over chloride and urea in acidified, non-hydrolysed urine treated with peroxydisulphate. Overall, the findings support the development of emerging urine recycling technologies, including alkaline/acid dehydration and reverse osmosis, where the presence of endogenous organic urine metabolites significantly influences treatment parameters such as energy demand and product purity. [ABSTRACT FROM AUTHOR]

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]

Microalgae are capable of assimilating nutrients from wastewater (WW), producing clean water and biomass rich in bioactive compounds that need to be recovered from inside the microalgal cell. This work investigated subcritical water (SW) extraction to collect high-value compounds from the microalga Tetradesmus obliquus after treating poultry WW. The treatment efficiency was evaluated in terms of total Kjeldahl nitrogen (TKN), phosphate, chemical oxygen demand (COD) and metals. T. obliquus was able to remove 77% TKN, 50% phosphate, 84% COD, and metals (48–89%) within legislation values. SW extraction was performed at 170 °C and 30 bar for 10 min. SW allowed the extraction of total phenols (1.073 mg GAE/mL extract) and total flavonoids (0.111 mg CAT/mL extract) with high antioxidant activity (IC50 value, 7.18 µg/mL). The microalga was shown to be a source of organic compounds of commercial value (e.g., squalene). Finally, the SW conditions allowed the removal of pathogens and metals in the extracts and residues to values in accordance with legislation, assuring their safety for feed or agriculture applications.

This study focuses on the feasibility of the dry anaerobic digestion of solid agricultural biomass for efficient renewable-energy production and nutrient recycling. Methane production and the amount of nitrogen in the digestates were measured in pilot- and farm-scale leach-bed reactors. In the pilot scale, with a digestion time of 133 days, the methane production of a mixture of whole crop fava bean and horse manure corresponded to 94% and 116%, respectively, of the methane potentials of the solid substrates. The mono-digestion of fava beans resulted in relatively low methane production (production/potential ratios of 59% and 57%). In two full-scale experiments, the methane production of mixtures of clover-grass silage, chicken manure, and horse manure corresponded to 108% and 100% of their respective methane potentials with digestion times of 117 and 185 days. In co-digestion, the production/potential ratios were similar in the pilot and farm experiments. High nitrogen loss was observed in the farm scale when the digestate was stored in a stack covered with a tarpaulin during summertime. Thus, although the technology seems promising, attention needs to be paid to management practices to minimise nitrogen losses and greenhouse gas emissions.

Leaf decay in seagrasses is enhanced in some seasons since large green senescent beach-cast seagrass leaves are frequently recorded during autumn and winter seasons. Here, we explore if senescence is operating in seagrass leaf decay or if hydrodynamic stress is responsible for the seasonal leaf abscission. A seasonal study on the temperate seagrass Cymodocea nodosa was carried out in four locations with contrasting hydrodynamic regimes. The morphological, biomechanical and material properties of C. nodosa were measured. The force required to break the ligule was always lower than that required to break the blade. This could be considered an adaptive strategy to reduce acute drag forces and thus lessen the chance of plant uprooting. The absolute force needed to dislodge the blade at the ligule level varied with season and location, with the lowest forces recorded in autumn. This may indicate that senescence is operating in this species. On the other hand, the minimum estimated failure velocities for leaf abscission were also recorded in autumn. Consequently, this may cause the premature shedding of leaves in this season before the senescence process has finished and can probably explain the occurrence of green beach-cast seagrass leaves usually found during autumn and winter.

The massive amounts of nutrients that are currently released into the environment as waste have the potential to be recovered and transformed from a liability into an asset through photosynthesis, industry insight, and ecologically informed engineering design aimed at circularity. Fast-growing aquatic plant-like vegetation such as microalgae and duckweed have the capacity to enable local communities to simultaneously treat their own polluted water and retain nutrients that underlie the productivity of modern agriculture. Not only are they highly effective at upcycling waste nutrients into protein-rich biomass, microalgae and duckweed also offer excellent opportunities to substitute or complement conventional synthetic fertilizers, feedstocks in biorefineries, and livestock feed while simultaneously reducing the energy consumption and greenhouse gas emissions that would otherwise be required for their production and transport to farms. Integrated systems growing microalgae or duckweed on manure or agricultural runoff, and subsequent reuse of the harvested biomass to produce animal feed, soil amendments, and biofuels, present a sustainable approach to advancing circularity in agricultural systems. This article provides a review of past efforts toward advancing the circular nitrogen bioeconomy using microalgae- and duckweed-based technologies to treat, recover, and upcycle nutrients from agricultural waste. The majority of the work with microalgae- and duckweed-based wastewater treatment has been concentrated on municipal and industrial effluents, with <50% of studies focusing on agricultural wastewater. In terms of scale, more than 91% of the microalgaebased studies and 58% of the duckweed-based studies were conducted at laboratory-scale. While the range of nutrient removals achieved using these technologies depends on various factors such as species, light, and media concentrations, 65% to 100% of total N, 82% to 100% of total P, 98% to 100% of NO3 -, and 96% to 100% of NH3/NH4+ can be removed by treating wastewater with microalgae. For duckweed, removals of 75% to 98% total N, 81% to 93% total P, 72% to 98% NH3/NH4+, and 57% to 92% NO3 - have been reported. Operating conditions such as hydraulic retention time, pH, temperature, and the presence of toxic nutrient levels and competing species in the media should be given due consideration when designing these systems to yield optimum benefits. In addition to in-depth studies and scientific advancements, policies encouraging supply chain development, market penetration, and consumer acceptance of these technologies are vitally needed to overcome challenges and to yield substantial socio-economic and environmental benefits from microalgae- and duckweed-based agricultural wastewater treatment. [ABSTRACT FROM AUTHOR]

Residue management is one of the most difficult tasks in the modern-mechanized agriculture with the intensification of cropping systems, which leads to reduced sowing window between two crops and farmers prefer in-situ burning of crop residues. Therefore, the present study was conducted to assess the effect of zero tillage (ZT) based residue management on soil health parameters in maize (Zea mays L.)–chickpea (Cicer arietinum L.) rotation in black soils of central India. After 4 years of study, the soil bulk density was reduced by 3.0–10.2% and volumetric moisture content was improved by 10.2–19.3% at 0–10 cm soil depth in ZT with residue over conventional tillage (CT). The soil organic carbon and labile carbon were increased by 13.6–61.7% and 6.0–22.0%, respectively, at 0–10 cm soil depths. Similarly, ZT with residue increased the KMnO4-N, Olsen-P and NH4OAc-K, and total fungal and actinomycetes density in surface soil as compared to CT. Thus, our study advocates that ZT with residue retention (1.8–5.4 Mg ha–1 maize and 0.8–2.4 Mg ha–1 chickpea residue) should be implemented for sustainable soil health in Vertisols (Typic Haplustert) of central India and other similar agro-ecological systems. [ABSTRACT FROM AUTHOR]

Wastewater reuse from fertirrigation has become a new strategy for sustainable crop production, especially because there is a need to save fresh water. It can also reduce fertilizer costs and environmental pollution. This work aimed to evaluate the production of tomato and eggplant seedlings irrigated with wastewater reuse from fertirrigation. The experiment was carried out in a completely randomized design in a 2 × 4 factorial scheme with four replicates, where each replicate was represented by 25 seedlings. Treatments were represented by two crops (tomato and eggplant) and four concentrations of fertirrigation wastewater leachate (Treatment 1 (T1): 25%; Treatment 2 (T2): 50%; Treatment 3 (T3): 75% and Treatment 4 (T4): 100%). Seedlings were evaluated for the following parameters: number of leaves, seedling height, basal stem diameter, leaf area, total dry mass, and relative water content. With the exception of the basal stem diameter, eggplant seedlings were affected by leachate concentrations for all the other parameters evaluated, while tomato seedlings presented significant responses for all variables. It was observed that the use of concentrations between 50 and 75% of fertirrigation wastewater leachate can be a possible alternative to reduce the use of chemical fertilizers in the production of tomato and eggplant seedlings. [ABSTRACT FROM AUTHOR]

The waste rock dumps (WRD) in mining operations and post-mining activities pose environmental challenges unless rehabilitated with vegetation. The optimal planting density for the re-vegetation of WRD with forest tree species is unknown. This study determined the effective planting density for a native forest species Acacia mangium. Acacia seedlings were in-situ established on a WRD of a mining site at planting densities 3 m × 3 m, 2.5 m × 2.5 m, and 2 m × 2 m with an unplanted plot. The treatments were assigned to plots in a Completely Randomized Design and replicated six times. The pre-plant and post-planting physicochemical properties of the soil on the WRD were assessed. The experimental site had very low organic C content (0.07–0.95%), slight to strongly acidic reaction (pH, 2.82–6.65), moderate levels of exchangeable Mg (0.34–1.44 cmol/kg), and K (0.03–0.32 cmol/kg) in the top 30 cm of the WRD. WRD material also had appreciable amounts of toxic elements such as Al, Cu, Fe, Mn, and Cd. The post-planting results indicated that rehabilitation of WRD with Acacia at a density of 2.5 m × 2.5 m significantly (p < 0.05) increased organic C (100%), exchangeable K (124%), and Mg (55%) contents and enhanced extractable Cu contents (by 5-folds) compared to unplanted WRD. Other physicochemical characters of WRD such as pH, exchangeable Ca content, extractable P and toxic metals such as extractable Al, Fe, and Mn, and total Cd concentrations were unaffected by the planting density. The study recommended the Acacia mangium re-vegetation of WRD at a planting density of 2.5 m × 2.5 m to potentially improve the chemical fertility, nutrient recycling, and re-establishment of microbial ecosystem services. [ABSTRACT FROM AUTHOR]

Integrating a combination of organic matter management (OMM) practices can increase soil fertility, biomass, and nutrient recycling, but evidence of this potential is limited. This study tested the impact of integrating a combination of OMM practices on soil fertility, biomass, and nutrient recycling on smallholder farms. Following a randomised complete block design, a four-season experiment was conducted in 2018-2019 on 10 farms. The treatments (T) included T1: cowpea-maize-bean-maize rotation; T2: cowpea-maize-bean-maize rotation + farmyard manure; T3: Faidherbia albida alleys + cowpea-maize-bean-maize rotation; T4: F. albida alleys + cowpea-maize-bean-maize rotation + farmyard manure; and T5 (control): maize monocrop with diammonium phosphate application at 50 kg/ha application rate. T1-T4 are the OMM practices. The maize in T2-T4 was undersown with Mucuna pruriens. Soil fertility parameters (i.e. pH, water holding capacity, nitrogen, phosphorus, and potassium), biomass, and nutrients in the biomass were determined. There were no differences in soil fertility parameters among all treatments (P > 0.05). From the second to the fourth season, biomass was consistently higher under T3 and T4 than in other treatments. Moreover, the nutrients in biomass were higher in T3 and T4 than in other treatments, an indicator that OMM practices with alley crops can increase nutrient recycling. [ABSTRACT FROM AUTHOR]

Twelve concrete ponds were stocked with pacific white shrimp (Penaeus vannamei) each weighing about 0.1g and grown for 77 days. The effects of autotrophs, floating beds of water spinach (Ipomoea aquatica) and microalgae (Chlorella pyrenoidosa) on water purification and shrimp growth were assessed. The results showed that the water quality of aquaculture water with water spinach (S1), aquaculture water with chlorella (S2), and aquaculture water with water spinach and chlorella (S3) were significantly better than that of Aquaculture water without vegetation and chlorella (S0). The combination of water spinach and chlorella (S3) was able to keep ammonia and nitrite nitrogen levels below 1.0 mg/L and 0.1 mg/L, respectively. These low levels were not lethal or detrimental to the growth of the white shrimp. The roots of the water spinach were the vital organs for the removal of N and P. Sixty percent of the removed portion of N and P accumulated in the roots of the water spinach. The survival rate and mean harvest weight of shrimp from S1, and S3 was significantly higher than that from S0, and S2. In addition, in S3 the immunity of the shrimp was improved due to the formation of similar biological floccules around the roots and thus increasing their survival rate. The present study indicates that a vegetable-microalgae-shrimp system has a good potential for practical application in commercial shrimp production. [ABSTRACT FROM AUTHOR]

Microalgae can produce biofuels, nutriceuticals, pigments and many other products, but commercialization has been limited by the cost of growing, harvesting and processing algal biomass. Nutrients, chiefly nitrogen and phosphorus, are a key cost for growing microalgae, but these nutrients are present in abundance in municipal wastewater where they pose environmental problems if not removed. This is not a traditional review article; rather, it is a fact-based set of suggestions that will have to be investigated by scientists and engineers. It is suggested that if microalgae were grown as biofilms rather than as planktonic cells, and if internal illumination rather than external illumination were employed, then the use of microalgae may provide useful improvements to the wastewater treatment process. The use of microalgae to remove nutrients from wastewater has been demonstrated, but has not yet been widely implemented due to cost, and because microalgae derived from wastewater treatment has not yet been demonstrated as a commercial source for value-added products. Future facilities are likely to be called Municipal Resource Recovery Facilities as wastewater will increasingly be viewed as a resource for water, biofuels, fertilizer, monitoring public health and value-added products. Advances in photonics will accelerate this transition. [ABSTRACT FROM AUTHOR]

A completely randomized factorial experiment was conducted to evaluate the growth and biomass production of single- and mixed crop species inoculated with mycorrhizae. Radish, (R), safflower (SF), pearl-millet (PM), mustard (M), field peas ((FP), faba-bean (FB), common vetch (CV), and berseem clover (BC) and their blends as R-SF-PM-M, FP-FB-CV-BC, R-SF-PM-M-FP-FB-CV-BC, R-SF-M-FP-FB-CV-BC, and PM-FP-FB-CV-BC were planted in a pot culture. The mycorrhizal inoculum significantly influenced the cover crops growth and biomass production under sterilized soils than that of non-sterile soils. While the safflower produced the highest total biomass, the pearl millet and field peas produced the lowest total biomass. Generally, in sterile and mycorrhizal conditions plant grown better and have high total C fixation. Within non-sterile and mycorrhizal inoculation, Safflower (1383.1 g C m−2) and Berseem Clover (1235.5 g C m−2) as a single species have fixed highest amount of carbon as biomass. Mycorrhizae inoculated BC+CV+FB+FP+SF+PM blends had a return of 1365.0 g C m−2 in non-sterile soil. Our results suggested that cover crops in single or mixed stands with mycorrhizal inoculations are expected to provide a significantly greater amount of biomass, which would contribute to soil organic matter and nutrient recycling for crop production.

Phosphorus (P) is an essential plant macro-nutrient applied to soil in agriculture, mainly sourced from non-renewable mined phosphate-rock, of which readily accessible reserves are currently under pressure, while global food demand continues to grow. Meanwhile, an abundance of P is lost in waste-streams. Hence, bio-based fertilizers are increasingly produced using nutrient-recovery technologies and evaluated as a sustainable fertilizer alternative. However, there is little knowledge of how these products affect soil microorganisms. In this study, four new phosphate bio-based fertilizers (two struvite and two incinerator ashes) were assessed in permanent grassland-plots to understand their impact on soil bacterial, fungal, and nematode community responses. The experiment consisted of 40 plots (each 6 × 2 m2) of 8 treatments (2 struvite, 2 ash, cattle slurry, 100% mineral fertilizer, zero P fertilizer, and a control without fertilization) with 5 replications arranged in a randomized complete block design. Community data were obtained by amplicon sequencing of DNA extracted from soil samples and subsequent analysis of community composition, diversity, structure and influencing environmental variables. Diversity of the soil microorganisms was maintained by all bio-based fertilizer treatments. Results showed that soil bacterial, fungal, and nematode communities of the struvite-treatments were similar to those in 100% mineral treatment. Communities in ash-treatments were more disturbed in their compositions, abundances and structures, possibly due to their high pH and heavy metal content. From canonical correspondence analysis, available P, K, and Mg, as well as plant P uptake and biomass yield, were identified as factors significantly influencing bacterial and nematode communities across different treatment groups. In particular, the abundance of environmental disturbance sensitive nematodes (e.g., Dorylaimida) was significantly reduced by one of the ash products. Overall, results indicate that both struvites are benign to soil bacterial, fungal, and nematode communities and can be safely applied as a source of renewable P to meet crop nutrition requirement. The ash products require further investigations before recommending their regular application as fertilizer. As the application of novel bio-based fertilizers will increase in the foreseeable future, the findings of this study would be valuable to feed into developing environmental risk assessment protocols.

[Display omitted] • Sewage sludge can be used as substitute for conventional fertilizer resources; • Organo-mineral fertilizers optimized for maize and sunflower crops were produced; • The share of waste materials in organo-mineral fertilizers was 49–54%; • Fertilizer production based on waste allows for organic matter and nutrient recycling. The depletion of natural resources, energy consumption and environmental issues relating to fertilizer production processes are driving a move towards a more sustainable use of resources and the recycling of nutrients. With regard to the fertilizer industry, this gives the opportunity to use the fertilizing potential of alternative raw materials. This paper evaluates the possibility of using dried sewage sludge in the manufacture of organo-mineral fertilizers. Fertilizers based on sewage sludge with an addition of poultry litter ash and mineral fertilizers were developed and characterized in the study. It was possible to produce multicomponent organo-mineral fertilizers with optimized compositions for maize and sunflower crops, characterized by total nutrient content over 20%. Moreover, they contained beneficial secondary nutrients and micronutrients originated from waste materials. The fertilizers were free of pathogens and fulfilled the requirements related to heavy metal content according to Polish legislation. The method of manufacturing organo-mineral fertilizers based on waste materials is a simple waste management solution offering organic matter and nutrient recycling in line with the circular economy and reducing reliance on imported raw materials. [ABSTRACT FROM AUTHOR]

This study presents a conceptual framework of buffering through storage and recycling of elements in terrestrial ecosystems and reviews the current knowledge about storage and recycling of elements in plants and ecosystems. Terrestrial ecosystems, defined here as plant-soil systems, buffer inputs from the atmosphere and bedrock through storage and recycling of elements, i.e., they dampen and delay their responses to inputs. Our framework challenges conventional paradigms of ecosystem resistance derived from plant community dynamics, and instead shows that element pools and fluxes have an overriding effect on the sensitivity of ecosystems to environmental change. While storage pools allow ecosystems to buffer variability in inputs over short to intermediate periods, recycling of elements enables ecosystems to buffer inputs over longer periods. The conceptual framework presented here improves our ability to predict the responses of ecosystems to environmental change. This is urgently needed to define thresholds which must not be exceeded to guarantee ecosystem functioning. This study provides a framework for future research to explore the extent to which ecosystems buffer variability in inputs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Morphology of P-rich ash particles were analysed with X-ray micro-tomography. • Discrete and open pores were distinguished on a micrometre scale. • High porosity where 72–99 vol% was open pores connected to the surrounding volume. • Thin particle walls and open pores may promote weathering upon soil application. • Pore openings over 200 µm provides an opportunity for root and microbe interaction. Combustion of phosphorus-rich residual streams can produce nutrient-rich ashes and these can be used either in further processing or as materials for direct nutrient recycling. The latter requires knowledge on morphological parameters of such ash particles that may impact plant growth, nutrient availability, and soil physical properties. The present work aims to determine the porosity, pore size, and specific surface area of ash particles, and discuss these properties in light of literature concerning interaction with soil water and plant roots. Bottom ash particles from combustion of sewage sludge and wheat straw and their co-combustion were analysed with X-ray microtomography. Image analysis provided information on morphology, specific surface area, porosity, and pore structure on a micrometre scale resolution. Co-combusting sewage sludge with wheat straw resulted in differences in ash particles' porosity and pore structure compared to combustion of pure fuels. Pure wheat straw ash displayed 62 vol% porosity while there was no apparent difference between 10 wt% or 30 wt% mixtures of sewage sludge, with a porosity of 29–31 vol%. Open pore volume comprise the largest part of the porosity (72–99 vol%) enabling interaction between surrounding pore water and nutrients. Overall, the ash particles display large open volume fractions and thin particle walls which may lead to rapid weathering and extensive interaction with soil water. The particles generally contained pore openings over 200 µm towards the surroundings, which provide opportunities for interaction with microbes and roots from a variety of plant species in addition to nutrient transport by soil water. [ABSTRACT FROM AUTHOR]

Projects are used in large numbers as a method to steer societal development, especially in contemporary Western societies. This so‐called projectification has relevant socio‐political effects on sustainability transitions, especially from the policy perspective. The aim of this paper is to analyse how projects and policy framework programmes can accelerate transition processes. The paper introduces the concept of a 'projectified transition policy process' by synthesising research on projectified governance, transitions and policy processes. The concept's empirical relevance is addressed with a case study analysis focussing on a framework programme that supports nutrient recycling technologies and practices via project funding. The framework programme was the first measure to actualise transition‐driven nutrient recycling policy in Finland, which has been ongoing since 2010. The conceptual exploration and case analysis in this paper show that projects and framework programmes can accelerate transition processes by mobilising actors, creating synergies between them with intermediary actions and producing project outcomes that can be turned into effective transition inputs. [ABSTRACT FROM AUTHOR]

Chinese agriculture is seeking a sustainable production increase in order to solve the food problem for its population. The traditional “high input, high pollution” agricultural production mode has led to a large burden on resources and on the environment. At present, China is promoting the transformation of its agricultural production modes in the direction of resource conservation and green development. In recent years, the crayfish–rice integrated system of production (CRISP) has been developed intensively in China due to its important economic benefits. Evaluating this new agricultural model comprehensively and guiding the related green sustainable development are urgent issues. Here, we used statistical data and literature to review the origin and development of CRISP in China and to compare the Chinese CRISP with similar models in other parts of the world. We reviewed studies on the ecological and social effects of CRISP for its objective evaluation and drew three main findings. First, although the crayfish initially introduced were sourced from the USA, the extensive application of CRISP led China to rapidly become the largest crayfish producer worldwide — accounting for over 90% of the crayfish production — and a leader in crayfish processing and catering industries. Second, the specific Chinese CRISP culture model promotes a green transformation towards a high-quality rice production system. Finally, CRISP affected positively soil quality, water and nutrient recycling, pest limitation, and biodiversity development in the paddy field system. CRISP reveals a good example of the effective application of green revolution in China’s agricultural production. We analyze for the first time the specific ecological foundation and management model for the sustainable development of CRISP. These observations provide a reference for the development of other agriculture–livestock integrated systems worldwide. [ABSTRACT FROM AUTHOR]

Gonyostomum semen is a bloom-forming freshwater raphidophyte that is currently on the increase, which concerns water managers and ecologists alike. Much indicates that the recent success of G. semen is linked to its diel vertical migration (DVM), which helps to overcome the spatial separation of optimal light conditions for photosynthesis at the surface of a lake and the high concentration of phosphate in the hypolimnion. I here present data from a field study conducted in Lake Lundebyvannet (Norway) in 2017-2019 that are consistent with the idea that the DVM of G. semen also allows for a hypolimnetic uptake of ammonium. As expected, microbial mineralization of organic matter in a low-oxygen environment led to an accumulation of ammonium in the hypolimnion as long as G. semen was absent. In contrast, a decreasing or constantly lower concentration of hypolimnetic ammonium was found in presence of a migrating G. semen population. In summer of 2019, a short break in the DVM of G. semen coincided with a rapid accumulation of hypolimnetic ammonium, which was equally rapidly decimated when G. semen resumed its DVM. Taken together, these data support the idea that G. semen can exploit the hypolimnetic pool of ammonium, which may be one reason for the recent success of the species and its significant impact on the structure of the aquatic food web.

Secondary fertilisers are becoming an important alternative to conventional mined fertilisers. For the first time, the struvite "relative" hazenite (KNaMg2(PO4)2∙14 H2O) has been artificially synthesised. A pot trial assessed whether hazenite-fertilised ryegrass had comparable potassium (K), magnesium (Mg), or phosphorus (P) uptake and shoot yields with treatments receiving conventional K (muriate of potash), Mg (kieserite) or P (triple superphosphate, TSP) fertilisers. Ryegrass shoot biomass production and K/Mg uptake in replicates receiving hazenite were as good as or superior to those amended with conventional fertilisers. Phosphorus uptake of plants whose P source was TSP was significantly higher than that of the hazenite-amended replicates without significantly higher shoot biomass, indicating luxury P uptake. Hazenite's constituent sodium (Na) makes it a potentially useful soil amendment for forage grasses or natrophilic crops such as sugar beet. Its component Mg would also be desirable in forage grasses to pre-empt ruminant hypomagnesemia or in crops with a relatively high Mg demand, for example, maize. Furthermore, hazenite represents a good alternative to KCl for chlorophobic crops such as potatoes. However, given its unusual ratio of Mg, P, and K, the ideal application of hazenite would probably be in combination with other fertilisers.