Modern Approaches to Enhance Biosolids Composting

The Town of Fairfield has the only remaining wastewater treatment plant biosolids composting facility in Connecticut. Fairfield has committed to continue the beneficial use of wastewater treatment biosolids and yard waste by implementing a major upgrade to their agitated bin compost facility.The original compost facility became operational in 1989 and included six agitated bins with a design capacity of 40 wet tons per day. The system included a positive aeration system with thirty separate blowers installed below grade in ten blower pits, five exhaust ventilation blowers, a biofilter odor control system, vintage computer compost process control system, and a pre-engineered steel painted building with structural steel support system and stainless steel roll up doors. Digested sludge is composted with wood chips from the Town's yard waste facility to produce the compost mix.From the initial process start up, the steel building was subject to significant corrosion problems, with periodic odor complaints due to fugitive emissions and an incompletely stabilized compost end product. Lack of heat and limited cross flow ventilation exhaust contributed to poor atmospheric conditions and concerns for operator safety. The corrosive atmosphere also contributed to deterioration of mechanical and electrical equipment, compromising the reliability of the compost operations. There were several interim upgrades to improve atmospheric conditions with limited success.In 2007, a major upgrade was completed which incorporated a variety of modern innovations to address these concerns. A new stainless steel core lined building was provided to withstand the corrosive atmosphere. The new building includes a stand alone electrical room providing complete separation of all electrical components from the composting area. The upgrade also included the installation of rapid speed mylar roll up doors to minimize release of fugitive emissions. The supply and exhaust ventilation system was upgraded to improve the atmosphere and reduce operator safety concerns. The waste heat from a new 200 kw fuel cell is used to provide heated make up air to the compost building in winter conditions to minimize fogging, further reducing poor atmospheric conditions while also maximizing the cogeneration capabilities of the fuel cell. The new building roof is designed to support the load of a planned 45 kw photovoltaic system. Improvements to the composting process included: new aeration blowers mounted on the walls in a more convenient location to facilitate maintenance; new thermocouples configured to facilitate maintenance; a moisture irrigation system to maintain optimal composting conditions; a new compost turner; modern computer hardware and software; composting and ventilation control systems; repairs to the turner rails; structural supports and aeration headers; replacement of the support media; and replacement of the biofilter media.The overall project was implemented through several different separate contracts, along with some portions performed by Town staff.