Laboratory Scale Septic Tanks

Laboratory studies of on-site wastewater treatment systems require a dependable supply of septic tank effluent. The goal of this study was to produce a daily supply of septic tank effluent of approximately 140 mg/l BOD sub(5), 75 mg/l TSS, and 30 mg/l NH sub(3)-N for use in laboratory studies. The laboratory tank had to be easy to operate, and emulate a septic tank by producing some fluctuation in effluent quality, have the ability to maintain sludge and scum layers, and operate with minimal maintenance. Nine replicates of laboratory septic tanks were developed and tested for twelve weeks. Tanks were constructed from 114 l cylindrical polyethylene containers with lids, a floating baffle, and discharge pipe. The tanks received a daily mixture of primary sludge, ammonium chloride, and tap water. The resulting septic tank effluent averaged 161 mg/l BOD sub(5), 75 mg/l TSS, and 25 mg/l NH sub(3)-N.