Degradation of pulp and paper-mill effluent by thermophilic micro-organisms using batch systems

Abstract

Paper manufacturers produce large quantities of wastewater, which can have deleterious effects on the receiving waters; therefore there is a need to find a treatment process which can minimize these effects considerably. A suitable aerobic biological treatment process that can be used with great success involves the use of thermophilic micro-organisms. This technology has many advantages, which include rapid biodegradation rates, low sludge yields, and excellent process stability. Batch studies were conducted on two types of activated sludge (pulp-mill sludge and sewage sludge) at 40°C, 50°C and 60°C to determine the feasibility of thermophilic degradation of bleach pulp-mill effluent in terms of increasing aeration, biomass concentration and nutrient addition. Preliminary batch studies had confirmed the feasibility of thermophilic degradation, as COD removal achieved with the pulp-mill sludge was 55.2%, 37.6% and 31.4% at 40°C, 50°C and 60°C after 5d, respectively while the COD removal with sewage sludge was 50.2%, 37.3% and 27% under the same conditions. Degradation was further improved, using the same inocula in subsequent experiments and this confirmed that an acclimatization period is required, prior to degrading the bleach pulp-mill effluent. Thermophilic degradation of pulp-mill effluent occurs at temperatures of up to 60°C; however, once final degradation is obtained, it decreases significantly as temperature increases.