Building on WERF Energy Research to Achieve Net-Zero with Incineration

This paper builds on results from the Water Environment Research Foundation’s (WERF’s) latest research into energy efficiency and production for “water resource recovery facilities” (WRRFs), in the area of energy recovery from incineration. As part of the WERF research, energy balances were developed for WRRF multiple hearth and fluid bed incinerators with and without heat recovery (steam generation) boilers; gasification; and Organic Rankine Cycle (ORC) heat recovery from incineration. For the newer, more innovative technologies – gasification and ORC heat recovery, profiles were prepared for full scale operating facilities to validate the energy balances and capture “lessons learned” for others to benefit from in evaluating and pursuing these technology options. As a means of improving energy production and strive for energy “net zero”, energy balances were developed with anaerobic digestion paired with incineration. Adding in anaerobic digestion with Combined Heat and Power (CHP) into a facility with incineration and steam turbine energy recovery has the potential to be near electrical energy neutral. The addition of digestion does, however, increase the supplemental fuel requirements for incineration so additional outside fossil fuel is required. This is the result of the reduction in energy content resulting from conversion of a substantial portion of the energy contained in the volatile solids in the feed to biogas.The study team found that this inherent trade-off could be overcome through a combination of (a) Thermal Hydrolysis Pretreatment (THP) prior to anaerobic digestion to improve volatile solids destruction/biogas production, and improve the dewaterability of the digested biosolids to achieve a near-neutral autogenous burn in spite of the reduced energy content; and (b) using the additional anaerobic digestion capacity created by the addition of THP to co-digest Fats, Oils and Grease and other high strength organic wastes available in a WRRF service area to yield a truly net-zero facility with no imported power or fossil fuel.