Application of Liquor Treatment to WWTPs Operating Solids Pretreatment and Advanced Digestion Processes: A Unique Set of Challenges

Over the past ten years, there has been a significant increase in the application of dedicated ammonia removal processes for treatment of solids processing liquors. Generally these processes have been applied to WWTPs that are operating mesophilic anaerobic digesters followed by dewatering. As flowsheets using alternative nitrogen removal pathways, such as nitritation/denitritation and partial nitritation/anaerobic ammonium oxidation (deammonification) were developed, WWTPs began applying these processes as sustainable alternatives. In parallel, there has been a focus on solids minimization and advanced digestion technologies to increase the net volatile solids reduction (VSR), increase production of biogas for energy recovery, and/or produce higher quality Class A residuals. WWTPs with nitrogen limits are looking for both sustainable biosolids alternatives and sustainable nitrogen removal processes. There are unique considerations associated with applying centrate treatment processes to return liquors from these solids handling schemes and limited experience to date in doing so. This paper will cover liquor treatment process selection and design considerations for three WWTPs.