In order to produce Class A biosolids, the Oceanside Water Pollution Control Plant retrofitted its original four mesophilic anaerobic digesters into a Temperature Phased Anaerobic Digestion (TPAD) process between 2014 and 2016. At the same time the plant staff worked on addressing long term anaerobic digestion operational challenges. The initial design led to significant improvements in digestion foam monitoring and control. However, operation of the new process was challenged by grit accumulation and the system was not able to consistently produce Class A biosolids. The grit accumulation issue was later resolved by modifying the sludge recirculation patterns while not operating the mixing pump and by eliminating the use of the original dewatering feed tank. The grit does not accumulate in the system as before and there is no more need for routine cleanup. This results in a plug-flow thermophilic batch digester process capable of reliably producing Class A biosolids at a relatively low operation and maintenance cost. The new process also resulted in a 30% increase in biogas production. This paper presents the approach to develop this novel anaerobic digestion process. © 2019 Water Environment Federation