Repurposing poultry effluents for irrigation in controlled environment agriculture

Abstract

Rapid global population continues to drive increased demand for food production, placing significant pressure on water resources and nutrient availability. The poultry processing industry, which reflects this growth, produces approximately 901 billion liters of nutrient-rich wastewater globally each year. Although nutrients in poultry processing wastewater (PPW) holds significant potential for reuse in hydroponic systems, current industry practices treat PPW predominantly as waste. Concurrently, the agricultural sector is increasingly constrained by freshwater scarcity, rising fertilizer costs, and food safety concerns, necessitating innovative and circular resource-efficient solutions. However, there is a critical knowledge gap on the impacts of wastewater reuse such as: maintaining system performance in real-world, pilot-scale operations; crop productivity and nutrient utilization; and food safety. This dissertation introduces and validates “Poultryponics”, a novel bioponics system that integrates the biological treatment of PPW with hydroponic lettuce production, by assessing pilot-scale system performance, nutrient dynamics, plant yields, and food safety. Microalgae enhance organics removal and nitrogen transformation in wastewater treatment via photosynthetic oxygenation to heterotrophic and autotrophic bacteria. The first objective therefore, assessed the impact of microalgae on treatment performance and fate of food pathogens during long-term (>220 days) continuous pilot-scale operation (~115 L d-1). The bioreactors achieved >80% soluble chemical oxygen demand (sCOD) removal but exhibited limited nitrification due to short hydraulic retention times (HRT), high organic loading, and oxygen limitation due to heterotrophic out competition. However, significant nitrification occurred in downstream hydroponic grow beds, driven by CO₂-supplemented pH modulation. UV disinfection showed approximately 40% and 30% reductions in total coliforms and aerobic plate counts respectively, with no Salmonella and Campylobacter detection in bioreactor effluents. The second objective of this research evaluated the effect of treated PPW on lettuce yields and plant nutrient status. Lettuce cultivated on treated PPW exhibited 58% lower shoot biomass and deficiencies in K, Mg, Ca, and Cu compared to mineral fertilizer controls. However, lettuce growth inhibition with treated PPW was mitigated through pH control (pH=7.0) and nutrient supplementation (N, P, K and micronutrients). A nitrogen mass balance revealed that although nitrogen was not limiting for plant growth, nitrogen use efficiency (nitrogen assimilated by lettuce) ranged between 3.7 and 6.3% of input nitrogen, while 65.4 – 83.0% remained in effluents. This highlights the importance of balancing nitrogen supply with targeted nutrient supplementation to enhance lettuce growth on treated PPW. The third objective of this study addressed a critical food safety concern by evaluating the system's response to high exogenous Salmonella influxes (3 and 5 log₁₀ CFU mL⁻¹) under simulated worst-case contamination scenarios and its implications for hydroponic lettuce. The bioreactors achieved 97.5 – 99.6% Salmonella removal, with no Salmonella detection in lettuce at the 3 log₁₀ CFU mL⁻¹ dosage. At the 5 log10 CFU mL -1 dosage, Salmonella removal in bioreactor effluent reduced to 68.4%, with Salmonella detection after UV treatment but not in grow beds or lettuce. Although these Salmonella dosages exceeded typical concentrations found in PPW, the results demonstrate the system’s capacity to manage extreme Salmonella contamination by maintaining non-detection in hydroponic lettuce. To expand on the treatment performance observed in Poultryponics, the fourth objective involved a comprehensive microbial community analysis to determine the impact of bioreactor conditions (illumination, CO₂ supplementation, and pH control) on dominant microbial taxa involved in organics removal, nutrient transformation, plant growth promotion and food safety. The results demonstrated that Proteobacteria (<83.0% of prokaryotes) and Bacteroidetes (<20.6% of prokaryotes) dominated in all bioreactors, consistent with high sCOD removal efficiencies (>80%). Illumination and CO₂ sparging promoted Desmodesmus (<45.8% of eukaryotes) in the algal bioreactors but had no impact on nitrification. Relative abundance of total nitrifying genera remained low in all bioreactors (<0.03%) but were increased in hydroponic grow beds (<4.31%) due to pH-modulating effects of CO2. Sulfuric acid-based pH control suppressed nitrifier and denitrifier abundance while enriching dissimilatory nitrate reduction to ammonium-associated taxa. Hydroponic grow beds enriched diverse plant growth-promoting bacteria with siderophore activity of approximately 0.6 ng L⁻¹ deferoxamine mesylate equivalence in the algal system. The absence of nitrification in bioreactors presented a bottleneck due to incompatible pH requirements between nitrifiers and lettuce. Therefore, the last research objective was to establish a continuous multistage bioreactor configuration to promote upstream nitrification and to assess the impact of bioreactor HRT on treatment efficiency, nitrogen dynamics and microbial communities. The bioreactors achieved organics removal (80 – 96%) and complete nitrification (>70% of TN) at 72-hr HRT. However, nitrogen losses reached 43% of total nitrogen (TN) at 48-hr HRT, aided by denitrifier proliferation (Zoogloea and Hydrogenophaga) and the presence of carbon sources (VFAs, and amino acids). This dissertation advances the practical implementation of bioponic systems for sustainable food production. It is the first body of work to demonstrate continuous long-term PPW treatment for safe hydroponic irrigation. The results provide a foundation for broader wastewater reuse applications across meat processing industries and field-scale agriculture within a circular bioeconomy.