chapter 18: MANAGEMENT OF INDUSTRIAL WASTEWATER
Other emerging aerobic technologies for industrial effluent are the moving bed biofilm reactor (MBBR) and the HYBACS process. In the MBBR, a biofilm grows within engineered plastic carriers that are suspended and thoroughly mixed throughout the water phase. The MBBR system is able to withstand high industrial effluent loads and has a small footprint. The HYBACS process is a combination between rotating mesh disc fixed film technology and conventional activated sludge. The result is a works that has a footprint up to 40% less than conventional AS and uses 50% less energy, with full nutrient removal.
Figure 18.4: HYBACS process for industrial effluent treatment, utilising an enhanced Bacillus culture. A fixed biofilm is established on rotating mesh discs (left) followed by activated sludge reactors (right). (Pictures courtesy of Bluewater Bio).
Another interesting variation on the conventional AS process for industrial effluent is the PACT configuration (by DuPont and Siemens), where powdered activated carbon is added to the activated sludge system to buffer the biomass against toxic organics and to adsorb certain refractory compounds. Anaerobic treatment can be effected in lagoons (where space allows) or in purpose-built reactors. For an effluent volume of 1 Ml/d and a COD of 4 000 mg/l, an anaerobic system will use 224 kWh/d versus 2240 kWh/d for an aerobic set-up (based on 80% COD removal). Sludge production for the anaerobic option is 96 kg/d versus 640 kg/d for the aerobic one. The anaerobic system will produce biogas containing about 340 kW of energy. These figures illustrate that where anaerobic treatment is practical, it has distinct advantages over an aerobic equivalent, a difference that becomes more pronounced as the effluent strength increases. It should, however, be appreciated that if the final effluent is to be discharged to a local watercourse, secondary aerobic polishing would be required. Both low and high rate anaerobic reactor configurations exist, the selection often being made based on the anticipated ease of treatment for a particular effluent, together with its biodegradability.
Figure 18.5: Different options for anaerobic reactors: high rate Internal Circulation (IC) reactor on left (nominally 20 kg COD/m3/d) and low rate Upflow Anaerobic Sludge Blanket (UASB) reactor on right (nominally 10 kg COD/m3/d). (Pictures courtesy of Paques BV).
the sUSTAINABLE Water Resource HANDBOOK
129