Leveraging Real-time Analytical Instrumentation for Anaerobic Digester Health Monitoring During and After Successful Startup of THP Pretreatment Process

Anaerobic digestion is nothing new in municipal and industrial solids stabilization processes. While the basic operating procedures are relatively well understood, anaerobic digesters still regularly experience costly upsets due to changing conditions. To reduce overall costs, carbon footprint, and to achieve Class A sludge the Medina County Sanitary Engineers implemented a thermal hydrolysis process (THP) at the Kenneth W. Hotz Water Reclamation Facility. This process pretreats the biosolids prior to anaerobic digestion, mesophilic anaerobic digestion in this case, using pressure and heat to achieve these improved results. The thermal hydrolysis process can increase the potential for additional variability in operation and stability, mainly through temperature and solids feed rates. Historically, anaerobic digester health monitoring has been achieved via regular grab or composite samples for laboratory analysis of volatile acids, pH and alkalinity. In an attempt to reduce the risk from the added complexity to anaerobic digester operations introduced by the THP pretreatment process, automated and real-time digester acid/alkalinity (VFA:ALK) monitoring was explored and implemented. This paper discusses the THP process and anaerobic digester startup and operating experiences and associated pros and cons of the online digester monitoring solution as a means to mitigate the risk of upsetting their anaerobic digester. The county now relies on the readings from the analyzer to maintain stable digester operations and provides them with confidence in seeking additional sources of industrial waste to increase their total energy recovery.