Removal of organics and calcium hardness in liner paper wastewater using UASB and CO_2 stripping system

摘要

An upflow anaerobic sluge blanket (UASB) reactor showed fairly good COD removal efficiency for the wastewater from a liner paper factory. Over 70% of COD removal efficiency were obtained even at 18 g COD/l day loading. A considerable amount of alkalinity was produced in the reactor when sulphate was reduced to hydrogen sulphide by sulphate reducing bacteria (SRB). Calcium was efficiently removed in CO_2 stripping unit where excess alkalinity was consumed to form calcium carbonate. No additional chemical such as caustic soda was necessary to facilitate the formation of calcium carbonate since the degassing of CO_2 increased the pH level in the CO_2 stripping unit. Calcium removal efficiency approached about 80% and the level of effluent calcium ranged from 80 to 150 mg/l. Since this system (UASB+CO_2 stripping unit) used biologically produced alkalinity for the formation of calcium carbonate, it can be called a biosoftening process. Wastewater treatment using both an UASB reactor and a CO_2 stripping unit showed favourable properties for the papermaking process.