Anaerobic treatment of the high strength wastes from the yeast industry

This paper presents the full-scale anaerobic treatment results from a fermentation plant producing baker's yeast from sugar beet molasses. The process of baker's yeast production generates high strength industrial effluents with a chemical oxygen demand (COD) of 10 000-30 000 mg/liter. In addition to the sugar containing substances sulphur and nitrogen containing substances are added to the batch processes to promote cell growth and to control pH. This results in rather high concentrations of sulphate (1000-2700 mg/l) and ammonia (400-900 mg/l) in the wastewater. The treatment plant at Pakmaya limit Factory has two different processes: anaerobic first-stage treatment and aerobic second stage treatment. The anaerobic first-stage treatment system includes a buffer tank, an acid reactor, two methane reactors, lamella separators, a gas storage tank and gas burning facilities. The anaerobic reactors were constructed as upflow anaerobic sludge blanket reactors (UASBR) with internal sludge recirculation facilities. The anaerobic reactors have been operating m series mode at mesophilic temperature ranges. Long term Organic Loading Rates (OLR) in the acid, the first and the second stage methane reactors have been averaging 9.8, 8.6 and 3 kg COD/m³.d respectively. Average COD removal is 75 percent in the anaerobic pretreatment stage. Average biogas production is 8000 m³/d, corresponding to a biogas conversion yield of 0.6 m³ per kg COD removed and it is equivalent to a net bioenergy recovery of 40 000 kWh/d.