Chlorine demand and bacteria of low salinity shrimp pond sediment treatedwith different chlorine doses

摘要

An experiment was conducted to determine the chlorine demand and the efficacy of three chlorine doses to disinfect indigenous bacteria in the sediment of a shrimp (Penaeus monodon Fabricius) pond. Sediment cores were collected by inserting 48 PVC tubes 20 cm into the pond and these tubes were planted vertically into four circular concrete tanks containing clay soil. Sediment in those tubes were treated with active chlorine in overlying water at 300, 1200 and 2400 mg l(-1) as treatments. The residual chlorine concentration in each tube was determined at 0, 6, 24, 48, and 144 h and the chlorine demand of the sediment was calculated by the, difference between initial dose and total residual chlorine. Chlorine efficacy to bacteria resided in the sediment was determined at a depth of 0-0.3, 0.9-1.2 and 1.9-2.1 cm in each core. Organic carbon, pH, and total Kjedhal nitrogen (TKN) in sediment were analyzed at the initial and end of experiment. Chlorine demand of sediment was 0.48 kg m(-2). Both organic carbon and TKN contributed to the loss of chlorine in the sediment. Chlorine at a dose of 300 mg l(-1) did not completely inactivate bacteria despite its free and residual chlorine in overlying water at the end of experiment still remained at 20 mg l(-1). Chlorine at a dose of 1200 and 2400 mg l(-1) inactivated 100% bacteria within 2 days of contact time. With high chlorine dose, chlorination was effective to inactivate bacteria only to a depth of 2.1 cm.