The Anaerobic Digestion of Textile Desizing Wastewater

Anaerobic digestion is a biological process which converts the chemical oxygen demand (COD) present in wastewater to methane and carbon dioxide and thus can be used to reduce the treatment costs of industrial wastewaters. Textile desizing wastewater is a high strength wastewater (20,000mg^-1 COD) and extremely alkaline (>pH 12) and therefore is costly to discharge to sewer and will require neutralisation to a lower pH before discharge to sewer. An anaerobic treatment stage consisting of two 50m³ mesophilic upflow anaerobic sludge blanket reactors (UASB) with an activated sludge polishing stage was built and operated from August 2003. This wastewater treatment plant has contributed to a COD reduction of up to 80% and a neutralisation of the pH from pH 12 to pH 7-8. The methane present in the biogas is utilised to heat the anaerobic digesters and the CO₂ produced in the biogas is used to neutralise the alkali in the wastewater. This results in an in-house wastewater treatment process with low running costs i.e. low in energy demand and chemical usage.