LESSONS LEARNED FROM ASSESSMENT OF FOUR LABORATORY-SCALE SLUDGE DEWATERABILITY METHODS USED DURING AN ANAEROBIC DIGESTION PILOT PERFORMED AT THE ROBERT W. HITE TREATMENT FACILITY

摘要

Efficient biosolids dewaterability is an operationally and financially important goal for Water Resource Recovery Facilities (WRRF). Experiences at the Metro Wastewater Reclamation District corroborate what has been observed elsewhere; enhanced biological phosphorus removal negatively affects dewaterability and results in nuisance struvite scaling and deposits. Pilot tests on waste activated sludge pretreatment technologies were conducted at the Robert W. Hite Treatment Facility in 2017 with focus on both struvite control and the impact on dewaterability. Four different methods (limit dryness test, modified centrifugal technique, pneumatic press, and thermogravimetric cake solids analysis coupled with polymer demand determined electrophoretically) were used to assess the changes in dewaterability. The key lessons from this evaluation are: (A) Consistency in pilot operations and bench dewaterability assessment methods is critical. (B) Polymer demand determined externally at Bucknell University and Klaranlagen Beratung Kopp is higher than the polymer demand determined on-site, which speaks to the importance of assessing dewaterability with fresh sludge. (C) Conventional total solids analysis for cake can be skewed by the presence of struvite, which partially volatizes above 70°C. This is not the case for when cake solids are determined thermogravimetrically. (D) Cake solids determined by Modified Centrifugal Technique by two different laboratories was consistent despite the differences in conditioning. All of the methods evaluated provide more information on dewaterability indicators of cake solids and polymer dose compared to typically used rate assessments such as Capillary Suction Time and Specific Resistance to Filtration. As more WRRF are implementing biological phosphorus removal as a sustainable alternative to reduce effluent phosphorus, it is critical to both understand its impact on dewaterability and have the ability to easily and quickly assess changes in dewaterability.