Effluent Water Characterization of Intensive Tilapia Culture Units and its Application in an Integrated Lettuce Aquaponic Production Facility

Abstract

In an intensive aquaculture project, effluent water characterization from three systems were evaluated (biofloc, polygyser and opposing flows). There were no differences in the mineral additions to the water per unit of feed while comparing the polygyser and opposing flow systems, both of which are bead bio-filter based systems. When both were compared to the biofloc system which lacks a bio-filter, the latter provided approximately 50 to 300% more mineral content in the water which varied based on the component discussed. This study suggests that the biofloc system provides a higher mineral content (and hence a higher nutrient value) for integrated applications such as a hydroponic grow bed. Characterizing the mineral content and feed nutrition value of effluent sludge indicates that the polygyser and opposing flow systems would be better than biofloc systems for organic fertilization purposes in an on land application due to a higher mineral value in the sludge since it had a longer time to mineralize. The proximate analysis trials showed that all three effluent sludge sources were a potentially excellent source of feed; they were not different and ranged around 17 to 24% crude protein among other variables tested. Lettuce trials showed that using settled fish water or unsettled fish water produced the same results and growth parameters. Lettuce grown in a commercial hydroponic solution produced better quality lettuce unless the fish effluent water being exchanged on a daily rate had nitrate, soluble phosphorus, potassium and calcium at 27 mg/L, 21 mg/L, 33 mg/L and 21 mg/L, respectively. It is only at these levels that the quality and growth of the lettuce produced by the fish effluent water was comparable to that of the commercially produced hydroponic lettuce. Tissue analysis of lettuce grown under three different treatments (fish effluent with solids, fish effluent without solids and commercial hydroponic solution) showed no differences, indicating that mineral uptake in lettuce was limited by the lowest mineral component found in the nutrient solution.