Written by Josh DiValentino
The city of Waianae, HI, operates a wastewater treatment plant that processes roughly three million gallons per day. The plant produces anaerobically digested biosolids that are mechanically dewatered for hauling to disposal. The Waianae plant was operating a centrifuge dewatering system, and as the system began to reach the end of its useful life, several technologies were evaluated as potential replacements.
The Waianae team selected Screw Press dewatering technology as the preferred technology, not only from a performance standpoint, but also considering ease of use, maintenance needs, and energy requirements. Considering the high cost of electricity on the Islands, a dewatering system with the same throughput requiring 10% of the HP was a welcome improvement.
Following a direct bid and evaluation, Schwing Bioset Screw Press equipment was chosen as the best overall value to replace the existing dewatering equipment. The Schwing Bioset FSP703 machine was installed to dewater anaerobically digested biosolids at a rate greater than 1,000 dry #/hr, per unit. The Schwing Bioset machine stood out from other bids because of its dewatering capacity for footprint. It was the only machine to offer capacity in excess of 1,000 dry #/hr while still fitting within a similar footprint as the outgoing centrifuge space.
Plant staff were also impressed with the quality of construction and the ease of use of the machine. The new Screw Press dewatering system, consistently producing cake of 24% dryness, will reduce disposal costs and the amount of labor required by city staff.