Psychrophilic (6-15 degrees C) high-rate anaerobic treatment of malting wastewater in a two-module expanded granular sludge bed system

Psychrophilic (6-15 degrees C) anaerobic treatment of malting wastewater wa s investigated. A two-module expanded granular sludge bed reactor system wi th a total volume of 140 dm(3) was used to treat malting wastewater having a soluble and total chemical oxygen demand (COD) between 233 and 1778 mg dm (-3) and between 317 and 4422 mg dm(-3), respectively. The removal efficien cies at 6 degrees C were 47 and 71% of the soluble and volatile fatty acids (VFA) COD, at organic loading rates (OLR) ranging between 3.3 and 5.8 kg o f COD m(-3) day(-1). The removal efficiencies at 10-15 degrees C were 67-78 and 90-96% of the soluble and VFA COD at an OLR between 2.8 and 12.3 kg of COD m-3 day-l. The specific methanogenic activity of the sludge present in each module increased 2-3-fold during system operation for 400 days. The r elatively high concentration of suspended solids in the influent (25% of th e total GOD) caused a deterioration of the sludge bed in the first reactor module. This was aggravated by excessive growth of acidifying biomass, whic h persisted in the first module sludge bed and resulted in granular sludge flotation. However, the second module could accommodate the increased OLR, thus providing a very high effluent quality (soluble COD < 200 mg dm(-3)) o f the total system. The stability of module I concerning suspended solids c ould be restored by presettling the wastewater.