Contact Stabilization with Enhanced Accumulation Process for Energy Recovery from Sewage

Conventional activated sludge (CAS) system is currently the predominant technology in wastewater treatment, but its painfully energy-intensive aerobic pathway has led researchers to investigate alternative technologies. These technologies are often focused on recovery of chemical energy from sewage. In this article, we introduce the CoSEA (Contact Stabilization with Enhanced Accumulation) process, a novel upconcentration method that separates the most valuable sewage content through a modified bioflocculation-adsorption-sedimentation-stabilization process for further anaerobic treatment. Raw sewage was treated in a 1 L psychrophilic (15 degrees C) sequencing batch reactor (SBR). By using an SBR, a time-concentration gradient was applied to enhance accumulation abilities of the sludge. The reactor was operated at very low sludge age (<1 day) and with a short (1.5 h) aeration phase. We tested two initial conditions: (1) operation with inoculation by activated sludge and (2) without any inoculation. Average chemical oxygen demand removal with and without inoculation was as high as 80% and 70%, respectively. Up to 55% of incoming chemical energy was recovered as gaseous methane. This recovery was significantly higher than can be typically achieved by CAS even with optimized anaerobic stabilization. Although CoSEA effluent requires subsequent removal of nutrients (N, P), the process is a promising new approach for energy recovery in a main wastewater treatment line. The process is especially suitable for moderate climates, where direct anaerobic digestion is so far not suitable for sewage treatment.