Sludge Heating and Anaerobic Digestion - Mesophilic

There are two general types of digestion processes known as aerobic and anaerobic digestion. Aerobic uses oxygen and anaerobic is an oxygen free environment. Anaerobic digestion is a biological process that breaks down for organic solids. In this process wastewater sludge is stored in large vessels, referred to as digesters that range from 0.5 - 3.0 million gallons of storage capacity. One of the other key differences in anaerobic digestion is that heat is added to stimulate the biological activity which accelerates the process. In the mesophilic stage, temperatures are typically maintained around 96 °f. Historically heat has been added through the use of heat exchangers. Heat exchangers can face the following challenges when heating sludge: * Wastewater sludge is scorch sensitive. Live steam used to provide heat for heat exchangers creates hot spots where sludge can burn and build-up in the heat exchanger tubes. As the buildup increases on the tube walls, a thermal barrier is created which requires additional heat to be added thus accelerating the problem. * Build-up problems can lead to plugging and fouling in the heat exchanger. This plugging and fouling increases maintenance costs and an increase pressure drop across the heat exchanger. * Increased pressure drop adds demand to the sludge pumps thus increasing energy usage.