Anaerobic treatment of complex wastewater and waste activated sludge — Application of an Upflow Anaerobic Solid Removal (UASR) reactor for the removal and pre-hydrolysis of suspended COD

Abstract

The application of one phase anaerobic wastewater systems for the treatment of complex wastewaters containing high amounts of suspended solids or lipids is usually limited by accumulation of these compounds in the sludge bed. This accumulation reduces the solid retention time and methanogenic activity of the sludge. The aim of the presented research was to achieve removal of suspended solids or lipids in an Upflow Anaerobic Solids Removal reactor to make higher reactor loadings possible. Raw sewage, waste activated sludge and dairy wastewater were pre-treated in an UASR reactor. When treating the raw sewage at 17°C and 3.0 h HRT 65% of the suspended COD could be entrapped in the sludge bed. Treatment of 2 g COD/l waste activated sludge at 9.6h HRT and 20°C resulted in 98% removal of the suspended COD. In both cases only 6–7% acidification of the complex wastewater took place. Dairy wastewater consists of mainly dissolved and colloidal COD. The lipids are surrounded by a protein membrane. These proteins will precipitate at pH <4.6 resulting in co-precipitation of the lipids. At 20°C and 4.5h HRT 57% of the lactose present in the wastewater was acidified, resulting in a pH of 4.0 and 98% lipids removal. It was concluded that the UASR reactor can achieve very high removal efficiencies for CODss and lipids, yet the retained COD is just partly hydrolysed. The produced sludge can be post-digested at thermophilic or mesophilic conditions to produce methane gas.