Characteristics Of Treatment And Microorganism On The Cyclic Activated Sludge System Of The Foshan Municipal Wastewater Treatment Plant

The municipal wastewater treatment plant was designed and constructed with pump station, screen unit, grit chamber, CASS tanks, blower house and sludge thickener in Foshan city where 1.96 hectares land was available. The gross investment was 20,492,100 Yuan.The cyclic activated sludge system was utilized to treat 20,000 m³ wastewater per day. Residual sludge was pumped from the CASS tanks at periodic intervals and dewatered further by sludge thickener. After then, the sludge would transport and bury in sanitary landfill with a minimum of damage to the environment. When the treatment plant was completed in April 2005, all the mechanical equipment was inspected with clean water treatment in May. The cultivation of activated sludge followed this step and considered as trial-operation, which lasted about three months. During this period, several kinds of physical and chemical pollutants including pH, biochemical oxygen demand, chemical oxygen demand, suspended solids, total nitrogen, ammonia-nitrogen and total phosphorus, and the characteristics of microorganisms were detected to determine the system's efficiency and regulate the operation's parameters. The concentrations of chemical oxygen demand, biochemical oxygen demand, ammonia-nitrogen, and total phosphorus of influent were ranged from 146.7 to 841.3 mg/L, 91.3 to 312.0 mg/L, 5.39 to 50.67 mg/L, and 2.06 to 4.59 mg/L respectively. After treated, the concentration decreased to 38.0 to 269.2 mg/L, 3.3 to 38.9 mg/L, 1.67 to 12.94 mg/L, and 0.17 to 1.57 mg/L respectively. Effluent could return back into the environment with the match of discharge standard of pollutants for municipal wastewater treatment plant and local criteria in 2006. In order to figure out the relationship between treatment efficiency and the microorganisms containing in the activated sludge, the microbial amounts and microscopic morphology of the activated sludge, bacteria, yeast, mould, protozoa and metazoa were studied. The results indicated that there were large numbers of species in the sludge. For instance, the total amounts of bacteria, yeast and mould were(4.2×10¹⁰±1.8×10¹⁰, 44.2) CFU,(2.5×10⁷±1.8×10⁷, 73.1) CFU,and(3.6×10⁶±2.6×10⁶, 72.4) CFU per gram sludge respectively in the operation period. As the system became stable, several sorts of protozoa, such as Vorticella, Epistylis, Aspidisca, Amoeba and Arcella, appeared. Some Rotifers and Limnodrilus were also observed.