Effects of the Main Activated Sludge Process Configuration on Wastewater Solids Minimization Technology

Due to increasing costs in solids handling and disposal/reuse, land availability for biosolids application, and wastewater solids toxicity issues, interest in solids minimization technologies has continued to grow. The Cannibal® solids reduction process by Siemens Water Technologies uses the existing natural microbiology from the process train to condition the mixed liquor suspended solids (MLSS) in such a way as to create a growth/destruction mechanism in the plant. This mechanism is developed by systematically conditioning solids in a side stream bioreactor and subsequently interchanging this material into the main activated sludge process (ASP). It has been observed through field studies and research and development (R&D) efforts that the configuration of the main ASP also contributes to the ability of the growth/destruction mechanism to function optimally.The Cannibal solids reduction process has been integrated into a number of ASP configurations including multiple variations of oxidation ditches, multi stage fine bubble aeration, sequencing batch reactors (SBR) and membrane bioreactor (MBR) configurations. A majority of these treatment schemes were designed for nutrient removal including ammonia (NH3), total nitrogen (TN), and total phosphorous (TP). Biological yield reductions were observed at each of the types of ASPs, with certain process configurations resulting in superb performance.Specifically, both field studies and research efforts have demonstrated that the configuration of SBR and multi-stage ASPs with dissolved oxygen (DO) control to be the most conducive configuration for solids minimization. In contrast, conventional systems with two or fewer stages have been observed to provide a smaller improvement in solids reduction. The results also indicate that multi-staged activated sludge configurations can be modified and operating conditions optimized, in order to improve solids minimization.