SYSTEMATIC IMPROVEMENT TO DEER ISLAND TREATMENT PLANT DIGESTER GAS SYSTEM

The Massachusetts Water Resources Authority (MWRA) has one of the largest, most extensive biosolids treatment systems in the industry. The anaerobic digester complex, consisting of twelve (12) three-million gallon “egg-shaped ”digesters, produces a vast quantity of digester gas, over four million standard cubic feet daily. The digester gas has an energy equivalent of over 20,000 gals/d of fuel oil.DITP utilizes low-pressure gas storage, and a medium pressure delivery system. It also has various gas utilization points. Because of the significant value of the gas produced and the need to have stable system pressures at the various combustion and relief processes, it was determined that system changes were necessary.A systematic program to address the many design, safety and reliability issues was carried-out over an extended period. The silver lining to this long work effort is that DITP now utilizes over 95 % of the value of digester gas being produced, saving in the order of 400,000 per month. Additionally, DITP staff now clearly understands the extent of the future work efforts required to enhance this system to approach the goal of 100 % digester gas utilization.The efforts of Deer Island Treatment Plant (DITP) staff to first get this system on-line, and then optimize the utilization of this fuel source within the on-site thermal power plant for electrical and thermal generation is the focus of this paper.