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Incorporating a variety of microalgae into wastewater treatment is considered an economically viable and environmentally sound strategy. The present work assessed the growth characteristics of Chlorella sorokiniana during cultivation in balanced synthetic media and domestic wastewater. Increasing the NH4+–N concentration to 360 mg L−1 and adding extra PO43−–P and SO42−–S (up to 80 and 36 mg L−1, respectively) contributed to an increase in the total biomass levels (5.7–5.9 g L−1) during the cultivation of C. sorokiniana in synthetic media. Under these conditions, the maximum concentrations of chlorophylls and carotenoids were 180 ± 7.5 and 26 ± 1.4 mg L−1, respectively. Furthermore, when studying three types of domestic wastewaters, it was noted that only one wastewater contributed to the productive growth of C. sorokiniana, but all wastewaters stimulated an increased accumulation of protein. Finally, the alga, when growing in optimal unsterilized wastewater, showed a maximum specific growth rate of 0.73 day−1, a biomass productivity of 0.21 g L−1 day−1, and 100% NH4+–N removal. These results demonstrate that the tested alga actively adapts to changes in the composition of the growth medium and accumulates high levels of protein in systems with poor-quality water.

Maize is one of the most important cereals in the world. It is a crop demanding in nitrogen. Therefore, alternative sources of fertilization bring agronomic, environmental and economic benefits. The objective of this study was to evaluate the biomass and productivity of maize fertigated with wastewater from swine and fish farming in different dilutions. The soil used is classified as Dystroferric Red Latosol, Cerrado phase, with clayey texture. The experimental design used was randomized blocks in 2 × 4 split plots with three replications. The treatments consisted of two sources of wastewater (fish farming and swine farming) diluted with the recommended dose of wastewater + 0, 25, 50 and 75% of its volume in water. The accumulation of dry mass (leaf, stalk and aerial parts) was evaluated at 30, 60, 90 and 110 days after sowing. The evaluation of yield variables (number of grain rows, number of grains per row, grain sizes, grain dry weight, gran yield and harvest index) occurred at 130 days after sowing. The largest accumulation of dry biomass at the end of the maize cycle and evaluated productivity variables were obtained with the application of swine farming wastewater. Wastewater from fish farming applied via an irrigation system without dilution (0%) is the most suitable for obtaining the productivity of corn grains. The two sources of wastewater have the potential to partially replace mineral nitrogen fertilizer in maize.

Concern that depletion of fertilizer feedstocks, which are a finite mineral resource, threatens agricultural sustainability has driven the exploration of sustainable methods of soil fertilization. Given that microalgae, which are unicellular photosynthetic organisms, can take up nutrients efficiently from water systems, their application in a biological wastewater purification system followed by the use of their biomass as a fertilizer alternative has attracted attention. Such applications of microalgae would contribute to the accelerated recycling of nutrients from wastewater to farmland. Many previous reports have provided information on the physiological characteristics of microalgae that support their utility. In this review, we focus on recent achievements of studies on microalgal physiology and relevant applications and outline the prospects for the contribution of microalgae to the establishment of sustainable agricultural practices.

Miscanthus, a C4 perennial rhizomatous grass, is capable of growing in varied climates and soil types in Europe, including on marginal lands. It can produce high yields with low nutrient inputs when harvested after complete senescence. Senescence induction and rate depend on complex genetic, environmental, and management interactions. To explore these interactions, we analysed four miscanthus hybrids (two novel seed‐based hybrids, GRC 3 [Miscanthus sinensis × sinensis] and GRC 14 [M. sacchariflorus × sinensis]; GRC 15, a novel M. sacchariflorus × sinensis clone; and GRC 9, a standard Miscanthus × giganteus clone) in Italy, Croatia, Germany and the UK. Over all trial locations and hybrids, the average aboveground biomass of the 3‐year‐old stands in August 2020 was 15 t DM ha−1 with nutrient contents of 7.6 mg N g−1 and 14.6 mg K g−1. As expected, delaying the harvest until spring reduced overall yield and nutrient contents (12 t DM ha−1, 3.3 mg N g−1, and 5.5 mg K g−1). At lower latitudes, the late‐ripening M. sacchariflorus × sinensis GRC 14 and GRC 15 combined high yields with low nutrient contents. At the most elevated latitude location (UK), the early‐ripening M. sinensis × sinensis combined high biomass yields with low nutrient offtakes. The clonal Miscanthus × giganteus with intermediate flowering and senescence attained similar low nutrient contents by spring harvest at all four locations. Seasonal changes in yield and nutrient levels analysed in this study provide: (1) a first step towards recommending hybrids for specific locations and end uses in Europe; (2) crucial data for determination of harvest time and practical steps in the valorization of biomass; and (3) key sustainability data for life cycle assessments. Identification of trade‐offs resulting from genetic × environment × management interactions is critical for increasing sustainable biomass supply from miscanthus grown on marginal lands. [ABSTRACT FROM AUTHOR]

Purpose Agronomic and environmental reasons force farmers to know the total P concentration of composted cattle manure. Laser-Induced Breakdown Spectroscopy seems proper to obtain such information. For logistic reasons (carriage, storage, field application, etc.), a dry matter characterization is also needed. Method Thirty samples of feedlot compost at different stages of stability and maturity were studied. Samples were dried at 50°C for dry matter characterization. As a reference method to determine total P concentration, wet digestion and colorimetry were employed. The area of the P I line emission obtained by laser-induced ablation of the samples was measured to estimate the total P concentration. Randomized calibrations through a modified version of the Kennard-Stone algorithm based on the Mahalanobis distance were performed. Results Dry matter varied from 40% to 90%, and no pattern was found related to compost origin, maturity, or stability. The total P concentration of the studied compost ranged from 1800 ppm up to 11200 ppm. Almost 80% of the calibration fittings have an R2 = 0.895. The mean validation error was less than 22% for about 80% of the calibrations, with a mean prediction error bound to 40%. Discarding outliers, the errors were reduced to 19% and 30%, respectively. Conclusion Water content must be considered in addition to other characterizations due to logistic implications. Calibrations with a 30 percent of prediction error were achieved, which seems enough as a first approximation to predict the total P content in compost for utilization in farms to recycle nutrients. [ABSTRACT FROM AUTHOR]

Long-term nutrient mining of soil hampers agricultural production across Africa. However, emerging sanitation technologies afford a hygienically safe and ecologically sustainable solution to this development challenge by providing fertilizers derived from human excreta that could facilitate a socio-technical transition toward a more sustainable food system. To evaluate one such technology, nitrified urine fertilizer (NUF), we conducted participatory action research to assess the potential, from both a biophysical and social perspective, of NUF to serve as a soil fertilizer to support smallholder agricultural production in Swayimane, South Africa. To achieve this objective, we formed a stakeholder group comprised of a cooperative of smallholder farmers, a local NGO (Zimele), and researchers from ETH Zurich and the University of Kwazulu-Natal. Over the course of two growing seasons (2016 and 2017) this stakeholder group assessed the potential of NUF to support smallholder vegetable production (i.e., cabbage). First, we adopted a randomized complete block design incorporating five treatments in season 1 (unfertilized control, nitrified urine, nitrified urine+bone meal, urea, and urea+diammonium phosphate (DAP) and six treatments (unfertilized control, urea, urea+DAP, DAP, nitrified urine, and nitrified urine+DAP) in season 2 to assess cabbage yield and leaf nutrient concentration (sodium, phosphorus, potassium, carbon, nitrogen). Although we observed large variability in yields, the urine-based treatments were as effective as any of the chemical fertilizers. Second, beyond the biophysical analysis, we elicited the challenges and opportunities of the smallholder farmers in our stakeholder group, as well as their attitudes toward the use of NUF as a fertilizer. Through this qualitative work, farmers indicated that their attitudes about the use of NUF as a fertilizer improved and that they would be willing to incorporate this product into their production practices if it was available at scale. Thus, we demonstrate the potential of participatory action research to co-produce knowledge and awareness around an innovative technology. In so doing, we provide evidence that this approach can support a change toward nutrient recycling-based agriculture.

Benthic consumers profoundly impact nutrient regeneration in coastal marine ecosystems. The concurrent nutrient imbalance and warming of our coastal seas will change the nutritional requirements and metabolic demands of these consumers, which may affect their ability to recycle nitrogen and phosphorous. Here we explore whether nutrient excretion rates of two benthic consumers, the Baltic clam (Macoma balthica) and the invasive spionid polychaete (Marenzelleria spp.) can be quantified with basic biological traits across seasons using allometric and stoichiometric relationships. We found species-specific N and P excretion rates that positively link to allometric traits, i.e., per individual rates increased with body mass and temperature; thus, high mass-specific excretion rates characterized small relative to large macrofaunal individuals. Interestingly, our body size scaling coefficients diverge from predictions by the metabolic theory of ecology (MTE) and the universal model of excretion. Furthermore, stoichiometric traits and stable isotope signatures (δ 13C and δ 15N) explained a minor additional proportion of variability in excretion rates among species. The excretion rates also varied strongly seasonally, with the highest nutrient recycling rates during summer months, when community NH4-N and PO4-P excretion clearly exceeded net sediment efflux. The seasonal pattern emphasized that changes in temperature and food availability drove metabolic processes and thus excretion rates of the benthic consumers, and indicated that these effects could outweigh the importance of animal biomass. Our results highlight the benefits of using allometric and stoichiometric traits when quantifying species-specific contributions to nutrient recycling in coastal marine environments, and in predicting alteration of function in response to environmental change.

Two nutrient–phytoplankton–zooplankton (NZP) models for a closed ecosystem that incorporates a delay in nutrient recycling, obtained using the gamma distribution function with one or two degrees of freedom, are analysed. The models are described by systems of ordinary differential equations of four and five dimensions. The purpose of this study is to investigate how the mean delay of the distribution and the total nutrients affect the stability of the equilibrium solutions. Local stability theory and bifurcation theory are used to determine the long-time dynamics of the models. It is found that both models exhibit comparable qualitative dynamics. There are a maximum of three equilibrium points in each of the two models, and at most one of them is locally asymptotically stable. The change of stability from one equilibrium to another takes place through a transcritical bifurcation. In some hypotheses on the functional response, the nutrient–phytoplankton–zooplankton equilibrium loses stability via a supercritical Hopf bifurcation, causing the apparition of a stable limit cycle. The way in which the results are consistent with prior research and how they extend them is discussed. Finally, various application-related consequences of the results of the theoretical study are deduced.

The sustainable management of forest plantations by keeping the harvest residues on site improves the soil’s chemical, physical and biological properties while constituting an important nutrient reserve. Our objectives were: (a) to identify and quantify the characteristics of Eucalyptus dunnii, Eucalyptus grandis and Eucalyptus globulus that affect the decomposition rates of harvest residues, as well as indicators that can explain the process and (b) to quantify the potential recycling of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) to the soil from residue decomposition and the quantitative and qualitative differences between the species. We analyzed the information of five commercial plantations of Uruguay. At the harvest, the biomass of leaves, thin and thick branches, bark and their respective N, P, K, Ca and Mg contents were quantified. At each site, bags with samples of the different residues were left to decompose and were periodically collected throughout 24 months. Eucalyptus dunnii presented the largest amounts of residues of all parts. The decomposition rates of the different residues depended on their chemical constitution, part size and the species. Eucalyptus dunnii leaves showed the shortest half-life (0.94 years), while the bark of the same species presented the longest (5.62 years). Total nitrogen and carbon (total and soluble) contents, which can be easily determined, emerged as good predictors for half-life estimation. The release patterns of nutrients depended more on their dynamics in the plant and their parts than on the species itself. The results highlight the importance of nutrient recycling to ensure the sustainability of the productive system in the medium and long term.

Sustainable food production has become increasingly important. Soilless cultivation systems offer several advantages, such as water and nutrient use efficiency, and can be implemented where traditional agriculture is impossible. Bioponic systems use locally or regionally available nutrient sources from organic waste streams (either fluid or solid) and can thus contribute to closing nutrient cycles locally. Bioponics harnesses the metabolic processes of microorganisms which release nutrients from organic matter. This study aimed to set up a bioponic system, by using biogas digestate concentrate and biochar as nutrient sources, and promoting nutrient release from the organic sources by including a biofilter in the system. The development of water quality, plant growth, and quality was monitored extensively. In addition, the influence of either the fungal biocontrol agent Trichoderma atrobrunneum or UV-C treatment of the nutrient solution on plant health and growth was investigated. Three cultivation cycles with Lactuca sativa (“HAWKING” Salanova®) in bioponic (BP), hydroponic (HP), and soil (SO) cultivation were performed. The study showed that healthy lettuces could be produced in BP systems, using a biogas digestate concentrate and biochar as nutrient sources, despite salt accumulation in the nutrient solution. In plant sap analyses, lettuces cultivated in BP systems contained less nitrate but more ammonium and chloride. The yield of the lettuces grown in the BP systems was intermediate, compared to the HP and the SO. The fungus, T. atrobrunneum, strain, T720, survived in soil and soilless cultivation systems. Compared to the HP and the SO systems, the shoot height of lettuces grown in the BP system, with the application of Trichoderma, was significantly increased. In SO systems with Trichoderma application, a significantly higher chlorophyll and flavonoid content, but significantly lower shoot height was observed. The fresh weight of lettuce roots was significantly higher in HP systems with Trichoderma treatment. Cultivating plants by using organic waste streams requires commitment and experience from producers. In BP systems, a biofilter (either within the system or externally, to increase nutrient levels) can help to rapidly convert the ammonium-rich fertilizer to plant-available nutrients. Unlike conventional HP systems, in BP systems, nutrients are released slowly over time, requiring close monitoring and adjustments. In conclusion, healthy lettuces for human consumption can be produced in BP systems, and the application of the biocontrol agent used has some beneficial influence on plant growth.

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]

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]

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.

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.

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]

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.

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.

Insect protein production is considered a sustainable alternative to livestock protein which furthermore utilizes waste streams. Its production can have positive but also potentially negative environmental effects, which require evaluation. Frass, the byproduct of insect production, is regarded an efficient organic fertilizer or soil amendment. However, several studies report negative frass effects on plant growth and nitrogen (N) cycling. Therefore, a pot trial was carried out which sought to understand N release from frass and subsequent growth and nutrient uptake of Italian ryegrass. Mealworm frass (MWF) or buffalo worm frass (BFW) was applied at two rates (1.5 and 3% w/w) to a soil-sand mix. To evaluate N release processes, frass was applied alone, with a nitrification inhibitor (NI), a urease inhibitor (UI), or both (NI+UI). Plant N, nutrient uptake and soil inorganic N were measured at the experiment's end. To gauge whether altered N fluxes induced changes in the microbial community, soil microbial biomass, bacterial/archaeal abundances and ergosterol content as a fungal biomarker, were determined. Both frass types and application rates stimulated microbial growth and N mineralization. The 3% rate inhibited seed germination, possibly due to salinity or ammonia toxicity. At the 1.5% rate, both frass types were effective fertilizers. MWF led to higher biomass and nutrient uptake, owing to its higher extractable nutrient concentrations. The 3% rate caused nitrite accumulation in the absence of NI. NI improved plant biomass, nutrient uptake, stimulated archaeal and bacterial abundances and prevented nitrite accumulation. UI reduced N mineralization, showing that a substantial fraction of frass organic N is ureic. UI enhanced fungal contribution to the microbial biomass, revealing the importance of bacteria in frass N mineralization processes when UI is not applied. NI and UI combined, induced greater N release from frass than UI or NI alone. Our study demonstrated the usefulness of NI and UI in studying N release from frass. NI can improve plant N uptake and minimize N losses following frass application, reducing its potentially negative effects. UI can retard N release from frass, allowing its application as a slow-release fertilizer, but should not be used concurrently with NI.

The use of liquid waste as a feedstock for cultivation of microalgae can reduce water and nutrient costs and can also be used to treat wastewater with simultaneous production of biomass and valuable products. This study applied strategies to treat diluted anaerobic digester effluent (ADE) as a residue of biogas reactors with moderate (87 ± 0.6 mg L−1; 10% ADE) and elevated NH4+-N levels (175 ± 1.1 mg L−1; 20% ADE). The effect of ADE dilution on the acclimatization of various microalgae was studied based on the analysis of the growth and productivity of the tested green algae. Two species of the genus Chlorella showed robust growth in the 10–20% ADE (with a maximum total weight of 3.26 ± 0.18 g L−1 for C. vulgaris and 2.81 ± 0.10 g L−1 for C. sorokiniana). The use of 10% ADE made it possible to cultivate the strains of the family Scenedesmaceae more effectively than the use of 20% ADE. The growth of Neochloris sp. in ADE was the lowest compared to other microalgal strains. The results of this study demonstrated the feasibility of introducing individual green microalgae into the processes of nutrient recovery from ADE to obtain biomass with a high protein content.

A stochastic nutrient–phytoplankton–zooplankton model with instantaneous nutrient recycling is proposed and analyzed in this paper. When the nutrient uptake function and the grazing function are linear and the ingested phytoplankton is completely absorbed by the zooplankton, we establish two stochastic thresholds R0S and R1S, which completely determine the persistence and extinction of the plankton. That is, if R0S<1, both the phytoplankton and the zooplankton eventually are eliminated; if R0S>1 and R1S<1, the phytoplankton is persistent in mean but the zooplankton is extinct; while for R1S>1, the entire system is persistent in mean. Furthermore, sufficient criteria for the existence of ergodic stationary distribution of the model are obtained and the persistent levels of the plankton are estimated. Numeric simulations are carried out to illustrate the theoretical results and to conclude our study. Our results suggest that environmental noise may cause the local bloom of phytoplankton, which surprisingly can be used to explain the formation of algal blooms to some extent. Moreover, we find that the nonlinear nutrient uptake function and grazing function may take credit for the periodic succession of blooms regardless of whether they are in the absence or presence of the environmental noises.

The objective of this study was to verify the feasibility of using biochar, functionalized with layered double hydroxides, as a fertilizer after its use in phosphate treatment (P-BC-LDHs). It was conducted with several levels of P-BC-LDHs using seed germination and early growth assays of lettuce (Lactuca sativa L.). The application of P-BC-LDHs resulted in successful seedling emergence, with an excellent germination capacity of over 96% for all treatments. However, compared to the controls, P-BC-LDHs did not provide favorable seedling traits. In contrast, in the latter experiments, lettuce cultivated under mixtures with P-BC-LDHs, particularly at an application rate of 2.5% (w/w), displayed superior growth quality to those under non-treated conditions. The length of lettuce shoots and roots from this optimal dosage were increased by at least 24% compared to untreated samples. A 17% reduction in biomass yield was observed for the samples from non-supplemented substrates. The nutrient release profiles showed that P-BC-LDHs were capable of slowly supplying phosphorus, thereby increasing the long-term nutrient availability for plants. The findings reported here provide important insights into these materials and confirm that P-BC-LDHs can be used for agricultural purposes after phosphate remediation applications. The results of this study provide constructive information to facilitate the implementation of biochar-based LDH composites for sustainable phosphate removal and recovery. [ABSTRACT FROM AUTHOR]

In the Amazonian periphery, there are sources of numerous disservices, including deforestation, loss of wildlife habitat and biodiversity erosion. However, there are great opportunities to adopt appropriate agricultural management practices to take advantage of the benefits of ecosystem services for sustainable agricultural intensification. Thus, the aim of this work was to evaluate the effects of certain ecosystem services provided by combined use of legumes with residue of low- and high-quality on soil quality indicators, nitrogen use efficiency and sustainability of maize grain yield in infertile tropical soil. The overarching objective is to determine how ecosystem services can contribute to the improvement of land-use policy to ensure the sustainability of cultivated lands, in such a way that forest can be preserved by avoiding deforestation of other new areas through shifting cultivation systems. Four leguminous tree species were used, two with high-quality residues Leucaena leucocephala (leucaena) and Gliricidia sepium (gliricidia) and two with low-quality residues Clitoria fairchildiana (clitoria) and Acacia mangium (acacia). Maize grain yield was evaluated between 2011 and 2017 in these treatments. In 2018, to assess how ecosystem services affect crop performance, the treatments were divided into ten treatments with and without urea. We conclude that increased uptake of inorganic and organic N by maize resulting from improvement of the soil quality indicators may allow agricultural intensification. This improvement can help meet the challenges of sustainability and feasibility of agroecosystems of the Amazonian periphery by making the agroecosystem more productive year by year. Therefore, our results confirm that the utilization of an ecosystem services style approach can help meet the challenges of sustainability and feasibility in agrosystems of the Amazonian periphery. In addition, these results can contribute to the development of land-use policy in the Amazonian periphery, aiming for the intensification of agriculture in cropped areas to avoid deforestation of new areas from shifting cultivation systems.

Sustainability assessments can be a powerful tool in decision-making regarding technical innovations. In this study, a sustainability assessment of technical systems for recovering nutrients and carbon from domestic wastewater is presented. Multi-criteria analysis was used to calculate a sustainability score of three different technical systems compared to a baseline in two case-studies: the Fyriså river catchment in Sweden and the Słupia river catchment in Poland. Two participatory workshops with local stakeholders were held in each case-study, the first to co-develop the system alternatives and sustainability criteria and the second to collect stakeholder weighting of the criteria. Although the systems assessed in both case studies were similar, the resulting sustainability scores were different. In Fyris, although the differences in scores was small, the preferred alternative was introduction of source-separation followed by a large redesign of the treatment and phosphorus extraction from incinerated sludge was the least sustainable alternative. For the Słupia systems the scores varied more, and the preferred system was a large redesign of the wastewater treatment followed by ammonia stripping of the reject water and the source-separation alternative received the lowest score. In both case-studies, the more costly system received highest sustainability score indicating the large potential benefits of enhancing resource recovery from domestic wastewater. Stakeholders did not prioritize technical aspects over the other sustainability criteria, yet most of research on resource recovery interventions is focused on technical performance.

In regions with intensive agricultural production, large amounts of organic waste are produced by livestock animals. Liquid digestate from manure-based biogas production could potentially serve as fertilizer if integrated with closed horticultural irrigation systems. The aim of this experiment was to investigate how fertilizer based on liquid biogas by-products of pig manure digestion can affect the growth and production of tomato plants. Integration of a nitrification bioreactor presumes a significantly lower concentration of nutrient solutions and a higher level of oxygenation than classical mineral cultivation. Therefore, additional controls were included. We compared plant growth and fruit quality traits of tomato plants grown in a hydroponic solution with organic fertilizer with two levels of mineral fertilizer. The tomatoes grown with organic waste-based liquid fertilizer showed reduced growth rates but increased mean fruit size, resulting in no significant change in total yield compared with high-mineral cultivation. The growth rate was similarly reduced in plants cultivated with low-mineral fertilizer. Plants cultivated with organic waste-based fertilizer had high Cl− concentration in xylem sap, leaves, and, ultimately, fruits. The leaves of plants cultivated with organic waste-based fertilizer contained higher concentrations of starch and soluble carbohydrate and low concentrations of phosphorous (P) and sulfur (S). The plants grown with organic waste-based or low-mineral medium showed significantly poorer fruit quality than the plants cultivated with the high-mineral solution. The low-mineral treatment increased xylem sap contribution to fruit weight because of higher root power. The organic waste-based fertilization did not change the root power but increased fruit size. In conclusion, organic waste-based cultivation is a possible solution for sustainable plant production in greenhouses. However, additional adjustment of nutrient supply is required to improve fruit quality.

In regions with intensive agricultural production, large amounts of organic waste are produced by livestock animals. Liquid digestate from manure-based biogas production could potentially serve as fertilizer if integrated with closed horticultural irrigation systems. The aim of this experiment was to investigate how fertilizer based on liquid biogas by-products of pig manure digestion can affect the growth and production of tomato plants. Integration of a nitrification bioreactor presumes a significantly lower concentration of nutrient solutions and a higher level of oxygenation than classical mineral cultivation. Therefore, additional controls were included. We compared plant growth and fruit quality traits of tomato plants grown in a hydroponic solution with organic fertilizer with two levels of mineral fertilizer. The tomatoes grown with organic waste-based liquid fertilizer showed reduced growth rates but increased mean fruit size, resulting in no significant change in total yield compared with high-mineral cultivation. The growth rate was similarly reduced in plants cultivated with low-mineral fertilizer. Plants cultivated with organic waste-based fertilizer had high Cl− concentration in xylem sap, leaves, and, ultimately, fruits. The leaves of plants cultivated with organic waste-based fertilizer contained higher concentrations of starch and soluble carbohydrate and low concentrations of phosphorous (P) and sulfur (S). The plants grown with organic waste-based or low-mineral medium showed significantly poorer fruit quality than the plants cultivated with the high-mineral solution. The low-mineral treatment increased xylem sap contribution to fruit weight because of higher root power. The organic waste-based fertilization did not change the root power but increased fruit size. In conclusion, organic waste-based cultivation is a possible solution for sustainable plant production in greenhouses. However, additional adjustment of nutrient supply is required to improve fruit quality. [ABSTRACT FROM AUTHOR]

An electrical conductivity (EC)-based closed-loop soilless culture system is practical for in-field deployment. Literature on the closed-loop soilless culture nutrient management premise the limitations in managing recycled nutrients under dynamic changes in individual nutrient uptake concentrations. However, recent systems analysis studies predicting solutions for nutrient fluctuation stabilization in EC-based closed-loop soilless culture systems suggest that the system may have a deterministic side in nutrient variation. This study aims to derive a nutrient control principle in an EC-based nutrient recycling soilless culture system by theoretical and experimental analyses. An integrated model of solutes such as K+, Ca2+, and Mg2+ and water transport in growing media, automated nutrient solution preparation, and nutrient uptake was designed. In the simulation, the intrinsic characteristics of nutrient changes among open-, semi- closed-, and closed-loop soilless cultures were compared, and stochastic simulations for nutrient control were performed in the closed-loop system. Four automated irrigation modules for comparing nutrient changes among the soilless culture systems were constructed in the greenhouse. Sweet pepper plants were used in the experiment. In the experimental analysis, nutrient concentration conversion to the proportion between nutrients revealed distinctive trends of nutrient changes according to the treatment level of drainage recycling. Theoretical and experimental analyses exhibited that nutrient variations in open-, semi- closed-, and closed-loop soilless culture systems can be integrated as a function of nutrient supply to the system's boundary areas. Furthermore, stochastic simulation analysis indicated that the nutrient ratio in the soilless culture system reveals the nutrient uptake parameter-based deterministic patterns. Thus, the nutrient ratio in the closed-loop soilless culture could be controlled by the long-term feedback of this ratio. We expect that these findings provide theoretical frameworks for systemizing nutrient management techniques in EC-based closed-loop soilless culture systems. [ABSTRACT FROM AUTHOR]

• In UV-free controls, urease activity in water and synthetic urine was similar, and higher than in real urine. • No urease activity was detected in water, synthetic urine and real urine after UV treatment. • Electrical energy demand to inactivate urease in real urine was 25-fold higher than synthetic urine. • Organic metabolites in real urine absorbed radiant flux and inhibited urease inactivation. In source-separating sanitation systems, inhibiting urease activity prevents enzymatic urea hydrolysis and volatilisation of ammonia when urine is concentrated by evaporation. This study tested UV-based photoinactivation as a novel alternative to existing methods of inactivating urease that require dosing urine with acid, base or oxidants. The enzymatic activity of jack bean (Canavalia ensiformis) urease in water, synthetic fresh urine and real fresh urine was investigated, with and without a 15 W low-pressure UV lamp that emitted 185 nm and 254 nm radiation. In UV-free controls, urea was hydrolysed at a rate of 3.2 × 10−3 mmol mg urease −1 min−1, 3.3 × 10−3 mmol mg urease −1 min−1 and 2.0 × 10−3 mmol mg urease −1 min−1 in water, synthetic urine and real urine, respectively. In the presence of UV, no urease activity was detected in any matrix. A UV irradiation time of 1.3 and 3.3 min was needed for inactivating urease in water and synthetic urine, respectively, whereas an irradiation time of 71 min was needed for inactivating urease in real urine. Overall, the electrical energy demand for photoinactivation of urease in real human urine was estimated to be 29.1 kWh m−3. Photolysis and photo-oxidation of amino acid residues at the active site of the enzyme were likely reasons for inactivation. Organic metabolites in real urine affected photoinactivation by (i) absorbing radiation between 190 nm and 400 nm, which reduced incident radiant flux; and (ii) scavenging hydroxyl radicals, which impeded oxidative damage to the enzyme. Overall, the findings demonstrate the feasibility of on-site treatment using a low-pressure UV lamp for inactivating urease in freshly excreted urine. [ABSTRACT FROM AUTHOR]

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.

Cities consume the majority of proteins produced globally but have unsustainable, linear food systems from production to consumption to disposal, resulting in significant nutrient losses. The industrial rearing of insects is a promising strategy for converting otherwise lost nutrients back into protein-rich animal feed and fertilizer, particularly to supplement local food production. The black soldier fly (BSF), Hermetia illucens, has been identified as a candidate for industrial rearing. BSF has a superior feed conversion ratio and cycle-time compared to other edible insects and can convert and recover nutrients from a vast variety of organic materials to protein, oil and chitin making it an attractive solution for the management of urban organic solid waste. With an increasing awareness of the environmental urgency and interest in the economic potential of the technology, this review discusses the technological factors confounding the upscaling of insect farming in urban and peri-urban contexts using BSF as a case study. These include the challenges of feed homogenisation and pre-treatment, of integrating insect life-cycle factors (e.g. mating) with bioprocess engineering concepts (which complicates automation), of meeting the nutritional requirements of the larvae at different stages of growth in order to maximize bioconversion and product quality, and of elucidating the impact of microbiome on complex behaviours and bioconversion. A multidisciplinary effort is therefore required to lead urban insect farming to full development to ultimately contribute to future food security.

Nickel, a micronutrient essential for plant growth and development, has been recognized as a metallic pollutant in wastewater. The concentration of nickel ions in the water course, exceeding the maximum tolerable limit, has called for an alarming attention, due to the bioaccumulative entry in the water–plant–human food chain, leaving a burden of deteriorative effects on visible characteristics, physiological processes, and oxidative stress response in plants. In this work, the renewable utilization of nickel electroplating industrial wastewater effluent (0, 5, 10, 25, 50, and 100%) as a viable source of irrigation water was evaluated using a hydroponic cultivation system, by adopting Lablab purpureus and Brassica chinensis as the plant models, in relation to the physical growth, physiological and morphological characteristics, photosynthetic pigments, proline, and oxidative responses. The elongation of roots and shoots in L. purpureus and B. chinensis was significantly inhibited beyond 25 and 5% of industrial wastewater. The chlorophyll-a, chlorophyll-b, total chlorophyll, and carotenoid contents, accompanied by alterations in the morphologies of xylem, phloem, and distortion of stomata, were recorded in the industrial wastewater-irrigated groups, with pronounced toxicity effects detected in B. chinensis. Excessive proline accumulation was recorded in the treated plant models. Ascorbate peroxidase (APX), guaiacol peroxidase (POD), and catalase (CAT) scavenging activities were drastically altered, with a profound upregulation effect in the POD activity in L. purpureus and both POD and APX in B. chinensis, predicting the nickel-induced oxidative stress. Conclusively, the diluted industrial wastewater effluent up to the optimum concentrations of 5 and 25%, respectively, could be feasibly reused as a renewable resource for B. chinensis and L. purpureus irrigation, verified by the minimal or negligible phytotoxic implications in the plant models. The current findings have shed light on the interruption of nickel-contaminated industrial wastewater effluent irrigation practice on the physical and biochemical features of food crops and highlighted the possibility of nutrient recycling via wastewater reuse in a sustainable soilless cultivation.