Integrated hydroponics systems with anaerobic supernatant and aquaculture effluent in desert regions: Nutrient recovery and benefit analysis.

Hydroponics is a resource-efficient system that increases food production and enhances the overall sustainability of agricultural systems, particularly in arid zones with prevalent water scarcity and limited areas of arable land. This study investigated zero-waste hydroponics systems fed by agricultural waste streams as nutrient sources under desert conditions. Three pilot-scale systems were tested and compared. The first hydroponics system ("HPAP") received its nutrient source internally from an aquaponic system, including supernatant from the anaerobic digestion of fish sludge. The second system ("HPAD") was sourced by the supernatant of plant waste anaerobic digestion, and the third served as a control that was fed by commercial Hoagland solution ("HPHS"). Fresh weight production was similar in all treatments, ranging from 488 to 539 g per shoot, corresponding to 5.7 to 6.0 kg total wet weight per m2. The recovery of N and P from wastes and their subsequent uptake by plants was highly efficient, with rates of 77 % for N and 65 % for P. Plants that were fed using supernatants demonstrated slightly higher plant quality compared with those grown in Hoagland solution. Over the duration of the full study (3 months), water was only used to compensate for evapotranspiration, corresponding to ~10 L per kg of lettuce. The potential health risk for heavy metals was negligible, as assessed using the health-risk index (HRI < 1) and targeted hazardous quotient (THQ < 1). The results of this study demonstrate that careful management can significantly reduce pollution, increase the recovery of nutrients and water, and improve hydroponics production.

Carbon dynamics and energy recovery in a novel near-zero waste aquaponics system with onsite anaerobic treatment.

Aquaponics is gaining renewed interest to enhance food security. This study aimed to investigate the performance of a novel off-grid aquaponics system with near-zero water and waste discharge, focusing on the carbon cycle and energy recovery that was achieved by the addition of onsite anaerobic treatment of the solid waste streams. Following a stabilization stage, the system was closely monitored for four months. Fish tank water was recirculated via solid and nitrification reactors, from which 66% was recycled to the fish tank directly and 34% indirectly through the hydroponically grown plants. Fish solid waste was anaerobically treated, energy was recovered, and the nutrient-rich supernatant was recycled to the plants to enhance production. Plant waste was also digested anaerobically for further recovery of energy and nutrients. Fish stocking density was 15.3 and over time reached approximately 40 kg/m3 where it was maintained. Feed (45% protein content) was applied daily at 2% of body weight. Typical fish performance was observed with a survival rate >97% and feed conversion ratio of 1.33. Lettuce production was up to 5.65 kg/m2, significantly higher than previous reports, largely because of high nutrients reuse efficiency from the anaerobic supernatant that contained 130 and 34 mg/L N and P, respectively. Of the feed carbon, 24.5% was taken up by fish biomass. Fish solid wastes contained 38.2% carbon, of which 91.9% was recovered as biogas (74.5% CH4). Biogas production was 0.84 m3/kg for fish sludge and 0.67 m3/kg for dry plant material. CO2 sequestration was 1.4 higher than the feed carbon, which reduced the system's carbon footprint by 64%. This study is the first to demonstrate highly efficient fish and plant production with near-zero water and waste discharge and with energy recovery that can potentially supply the system's energy demand.

Advanced near-zero waste treatment of food processing wastewater with water, carbon, and nutrient recovery.

A near-zero waste treatment system for food processing wastewater was developed and studied. The wastewater was treated using an anaerobic membrane bioreactor (AnMBR), polished using an outdoor photobioreactor for microalgae cultivation (three species were studied), and excess sludge was treated using hydrothermal carbonization. The study was conducted under arid climate conditions for one year (four seasons). The AnMBR reduced the total organic carbon by 97%, which was mostly recovered as methane (~57%) and hydrochar (~4%). Microalgal biomass productivity in the AnMBR effluent ranged from 0.25 to 0.8 g·L-1·day-1. Nitrogen (N) and phosphorous (P) uptake varied seasonally, from 18 to 45 mg·L-1·day-1 and up to 5 mg·L-1·day-1, respectively. N and P mass balance analysis demonstrated that the process was highly efficient in the recovery of nitrogen (~77%), and phosphorus (~91%). The performance of the microalgal culture changed among seasons because of climatic variation, as a result of variation in the wastewater chemistry, and possibly due to differences among the microalgal species. Effluent standards for irrigation use were met throughout the year and were achieved within two days in summer and 4.5 days in winter. Overall, the study demonstrated a near-zero waste discharge system capable of producing high-quality effluent, achieving nutrient and carbon recovery into microalgae biomass, and energy production as biogas and hydrochar.

Holistic approach for evaluation of landfill leachate pollution potential - From the waste to the aquifer.

Leachate contamination from uncontrolled landfills is a long-lasting environmental hazard that threatens groundwater resources worldwide. We developed a holistic site-characterization approach that incorporates leachate data from the waste body, unsaturated zone, and groundwater with information on landfill geomorphology and climatic conditions. An advanced vadose-zone monitoring system was used to characterize the percolation patterns and chemical properties of the leachates in the waste body and underlying unsaturated zone; a set of observation wells was used to characterize the contaminants' distribution in the groundwater. Multivariate analysis of the chemical composition overcame multiparameter complexity, and pinpointed the dominant factors controlling contaminant migration dynamics. The landfill's mound morphology, constructed with steep slopes, led to runoff generation, limited water infiltration through the waste, and enhanced infiltration of contaminated water at the landfill margins. Aerated conditions in the unsaturated zone under the margins induced leachate degradation and oxidation processes. The chemical composition of leachates under the center of the landfill remained typically anaerobic (high DOC, NH4+, Fe2+) despite the low water penetration. The limited water-percolation rates through the waste body and substantial mixing of the leachates with the oxidizing aquifer water led to almost complete degradation of the organic matter and significant nitrogen attenuation in the groundwater. Bromide release from decomposing waste served as an effective tracer for leachate distribution in the subsurface. The holistic approach implemented in this study provides robust and valuable insights into the factors that control landfill contamination potential and can be implemented in other sites with different climatic and geomorphological features.

Phosphorous recovery from a novel recirculating aquaculture system followed by its sustainable reuse as a fertilizer.

Phosphorus (P) is an essential element for life that is introduced through feed in modern aquaculture-the fastest growing food production sector. P can also be a source of environmental contamination and eutrophication if mistreated. Fish assimilate only 20-40% of the applied P; the rest is released into the water. The goals of this research were to study the fate of P in a novel intensive near-zero discharge (<1%) recirculating aquaculture system (RAS). We also tested means to recover and reuse the removed P. Water, sludge and the microbial communities in the different treatment units of the system were analyzed. The treated sludge was tested as a potential substitute for P fertilization in a planter experiment. Of the applied P, 29.5% was recovered by fish, 69.8% was found in the fish sludge and 3.8% was released into the water as soluble reactive P. The P concentration in the fish tank remained stable, likely due to its uptake by denitrifying polyphosphate-accumulating organisms and its precipitation in the RAS's anaerobic reactor. Thus, only 1.5% of the applied P was discharged as effluent, and 69% recovered. The dominant minerals were from the apatite group, followed by the struvite family. Differences in mineral abundance between thermodynamic prediction and actual findings were most probably due to biomineralization by bacteria. Similar plant biomass was recorded for the commercial and digested-sludge fertilization treatments. Biological P removal and recovery from RAS was successfully studied and demonstrated.

Potential environmental impact resulting from biased fish sampling in intensive aquaculture operations.

Aquaculture contributes to global food security, producing over 70 million tons of fish and aquatic products annually. Protein rich fish feeds, together with labor costs are the most expensive component costs in aquaculture. Feed application is given as percent of fish weight and therefore, reliable biomass assessment is essential for profitable and environmentally sound aquaculture. Fish biomass estimates are typically based on sampling <2% of the fish population. The goals of this research were to estimate potential biases associated with fish sampling in recirculating aquaculture systems (RAS), and the potential economic and environmental implications of such biased estimations. The size of the biased sampling-based estimates of fish biomass in two cultured species was shown to be larger than what the confidence interval suggests, even after >20% of the population was sampled. Such biases, if indeed common, will most likely result in over/underfeeding, both entailing negative economic and environmental consequences. We advocate conducting similar studies with major cultured fish to generate "bias correction tables" for adjusting fish feeding rate to bias-corrected biomass. These will help reduce the potential economic losses and negative environmental impacts of aquaculture practice.

Nitrous oxide emissions from near-zero water exchange brackish recirculating aquaculture systems.

The development of intensive recirculating aquaculture systems (RAS) with low water exchange has accelerated in recent years as a result of environmental, economic and other concerns. In these systems, fish are commonly grown at high density, 50 to 150kg/m3, using high-protein (30%-60%) feeds. Typically, the RAS consists of a solid treatment and a nitrification unit; in more advanced RAS, there is an additional denitrification step. Nitrous oxide (N2O), a byproduct during nitrification and denitrification processes, is a potent greenhouse gas that destroys the ozone layer. The aim of this study was to measure and assess N2O emissions from a near-zero discharge land-based saline RAS. N2O flux was monitored from the RAS's fish tank, and moving-bed nitrification and activated-sludge (with intrinsic C source) denitrification reactors. N2O emission potential was also analyzed in the laboratory. N2O flux from the denitrification reactors ranged between 6.5 and 48mg/day, equivalent to 1.27±1.01% of the removed nitrate-N. Direct analysis from the fish tank and nitrification reactors could not be performed due to high aeration, which diluted the N2O concentration to below detection limits. Thus, its potential emission was estimated in the laboratory: from the fishponds, it was negligible; from the nitrification reactor, it ranged between 0.4 and 2.8% of the total ammonia-N oxidized. The potential N2O emission from the denitrification reactor was 3.72±2.75% of the reduced nitrate-N, within the range found in the direct measurement. Overall, N2O emission during N transformation in a RAS was evaluated to be 885mg/kg feed or 1.36g/kg fish production, accounting for 1.23% of total N application. Consequently, it is estimated that N2O emission from aquaculture currently accounts for 2.4% of the total agricultural N2O emission, but will decrease to 1.7% by 2030.