Development of Small-scale Integrated Hydroponics—Animal Waste Bioreactor (AWB) for Romaine Lettuce (Lactuca sativa L. var. longofolia) Production

As improper processing and disposal of animal waste cause negative impacts on the environment, the animal industry sector must shift to more sustainable practices to lessen these effects. Recently, the application of the circular economy concept in agriculture, using animal waste as part of nutrient cycling, has emerged as a sustainable approach. The study aims to develop and test the small-scale integrated hydroponics-animal waste bioreactor (AWB) for romaine lettuce production using chicken manure tea (CMT) derived from dried chicken manure as a primary nutrient source. Three integrated hydroponics-AWB systems, with varying concentrations of CMT at 1,000 ppm, 1,200 ppm, and 1,400 ppm total dissolved solids (maintained within an upper and lower bound of 50 ppm), were constructed, tested, and compared to conventional hydroponics that used a nutrient solution maintained at 1,000 ppm TDS. The test result suggests that the ideal concentration of CMT in the system is 1,000 ppm. Within the optimum manure tea concentration, the small-scale integrated hydroponics-AWB produced romaine lettuce with growth parameters comparable to conventional hydroponics. In addition, increasing the CMT concentration to 1,400 ppm negatively impacts the plant growth parameters of romaine lettuce. The developed small-scale integrated hydroponics-AWB system provides a viable approach for growing lettuce using animal waste as the major source of nutrients. The developed production system could help mitigate the negative environmental effects of improper handling and disposal of animal waste and dependence on chemical-based nutrient solutions in hydroponic crop production.