Septic tank treatment of the effluent from a small-scale commercial recycle Aquaculture system

摘要

The efficiency of a conventional domestic septic tank for primary treatment of the wastewater effluent from a small-scale commercial recycle aquaculture system (RAS) was evaluated. The aquaculture facility had five 39.2-m(3) dual-drain culture tanks and a total system volume of 249.9 m(3). The mean standing stock of fish during the study was 4,837 kg (25.6 kg/m(3)) consisting of 9.6% largemouth bass Micropterus salmoides, 32.1% walleye Sander vitreus, 17.8% hybrid striped bass (white bass Morone chrysops x striped bass M. saxatilis), and 40.5% rainbow trout Oncorhynchus mykiss. The entire RAS volume was exchanged with makeup water only once every 62 d. Inflow to the septic tank contained 25.3% total nitrogen (TN) and 55.1% total phosphor-us (TP) added to the culture system as fish feed. Relative to inflow, outflow from the septic tank reduced biochemical oxygen demand by 5.1%, TN by 59.5%, TP by 35.3%, settleable solids by 92.6%, total dissolved solids by 9.6%, and total suspended solids by 69.8%. Septic tank effluent was discharged to a subsurface drain tile that passed below a row crop field to a pond; the pond did not discharge from the operator's property during the study (i.e., zero discharge). Of the nutrients fed, 9.6% of TN and 34.5% of TP were present in the septic tank effluent. Septic tank sludge was pumped out monthly and dewatered to 14.9% moisture by air-drying. It contained 3.6% TN and 2.6% TP (percent dry weight) and was test-marketed as a soil amendment for greenhouse use.