Toward Sustainable Urban Food Production: Integrating Hydroponic Cultivation with Wastewater Reuse

The growing crisis of freshwater scarcity together with the increasing global food demand directs attention to the need for alternative water sources for agriculture. The research presented here engages this need by carrying out indoor cultivation of food crops in Nutrient Film Technique (NFT) hydroponic systems using residential wastewater. Randomized single factor experimental designs were used to investigate the physiochemical and microbiological makeup of the hydroponic nutrient solution throughout the cultivation cycle and their relationship with different plant development parameters. For agricultural wastewater reuse to be of low risk to human health there must be some advancement in pathogen monitoring methods to allow for a rapid, user-friendly, and low-cost way to quickly diagnose the presence of pathogens and thus prevent an outbreak of foodborne illness. This research also investigated the use of DNA amplification to detect the indicator organism E. coli in hydroponic nutrient solution. This work presents an iteration of development of a molecular assay based on loop-mediated isothermal amplification (LAMP) using the BioRanger device from Diagenetix Inc. to amplify and detect the malB gene of E. coli. Lettuce plants successfully grew in NFT hydroponic systems using simulated wastewater solution inoculated with low (1 CFU/mL) and high (10,000 CFU/mL) E. coli concentrations, thus demonstrating that the concept of wastewater reuse for urban agriculture is possible. The outcomes of the experiments show that lettuce grown with half-strength fertilizer supplemented with simulated wastewater contained higher levels of nitrogen, phosphorus, and potassium in the leaf tissue than lettuce grown with full-strength conventional fertilizer. A LAMP protocol was developed, and a primer set and reagent kit were chosen. The LAMP molecular assay underwent several phases of troubleshooting in an attempt to find the optimal assay conditions. Though the assay did not achieve successful DNA amplification, several key observations and recommendations are given to guide future experiments. A portable method of rapid and sensitive pathogen detection would increase the scientific and agricultural communities’ ability to conduct real-time analytical testing of irrigation water in non-laboratory settings. This work points out the current lack of wastewater reuse guidelines specific to hydroponics, an area that requires further research in order for integrated wastewater reuse and food production systems to be implemented in urban areas