Applying European Experience To Screen And Select A Sustainable Dewatering System For Green Bay

In the Green Bay Solids Management Facility Plan (2011), for cost estimating and building sizing purposes, it was assumed that high-solids centrifuges would be used for dewatering, but it was agreed that other dewatering methods would be considered during design. A key decision criterion for selecting dewatering equipment discussed during facility planning was the ability to achieve cake solids concentration of at least 25 percent to produce a material that would combust autogenously; that is, no supplemental fuel would be required in the fluid bed incinerator (FBI) that will follow the dewatering process.Bench-scale centrifuge testing results from five centrifuge manufacturers for anaerobically digested Green Bay Facility (GBF) biosolids produced from bench-scale digesters at Marquette University show that a cake solids concentration of 19 to 23 (average of 21) percent is predicted. This predicted cake solids concentration is lower than the 25 percent solids concentration previously assumed. Also, because the volatile solids content of the solids has decreased due to a change in the projected industrial waste contributions since the Solids Management Facility Plan was completed in 2011, the point of autogenous combustion in the FBI has been increased from 25 to 27 percent solids.Since the completion of the facility plan, several new technologies have been identified that can effectively be used for dewatering anaerobically digested biosolids. This presentation will include information on the evaluation of the highsolids centrifuges as compared to high-solids centrifuges combined with belt and disc dryers and newer technologies in the market, such as hydraulic piston presses and thermal vacuum dewatering/dehydration units. All these technologies (except centrifuges alone) will achieve a cake solids concentration of at least 27 percent for autogenous incinerator combustion. The comparison is based on monetary criteria and a review of nonmonetary advantages and disadvantages, including proven experience on similar feed solids, ease of operation, space requirements, and performance (cake solids concentration, solids capture and polymer consumption). Installed capital equipment cost estimates as well as operation and maintenance (O&M) cost estimates and net present worth estimates will be presented.The alternative with three high solids centrifuges with disc dryer was recommended for the Green Bay NEW Water Resource Recovery and Electrical Energy (R2E2) Project for the following main reasons: 1) one of the lowest present worth cost, 2) lowest capital cost, 3) autogenous incineration, 4) 100% of thermal dryer energy provided by waste heat, and 5) compact, enclosed and proven facilities.