Innovative Biosolids Dewatering System Proved a Successful Part of the Upgrade to the Old Town, Maine Water Pollution Control Facility

Abstract

The City's water pollution control facility (WPCF) serves the City of Old Town and the adjacent Town of Milford. The WPCF is an RBC facility with primary clarification. The rated dry weather secondary treatment capacity of the facility is 1.7 mgd with a peak hourly rate of 4.7 mgd. All flows greater than 4.7 mgd (and up to 16 mgd) receive primary treatment and disinfection through the on-site Storm Flow treatment system. The WPCF and CSO Upgrade Project was completed in early 2004 and had a construction cost of $6.8M.The purpose of this paper is to present a case study of the biosolids dewatering aspect of the recent upgrade to the City of Old Town's WPCF. The upgrade included the installation of the RoS3 inclined screw press as manufactured by Huber Technology, Inc. (Headquartered in Germany as Hans Huber AG with U.S. offices in Huntersville, North Carolina). The Old Town project is the first permanent installation in the U.S. for this equipment; however, another unit has been installed in Utah and others are underway. The company also recently manufactured a trailer-mounted demonstration unit to be used for pilot testing throughout the U.S. and has begun to actively market the product.The inclined screw press technology consists of feeding flocculated sludge (mixture of primary and secondary solids) into an inclined screw (~20°) rotating inside a stainless steel, wedge wire screen (200 micron). As the sludge is advanced up the rotating screw (typically between 1 to 4 rpm), filtrate flows out through the screen. The frictional force at the sludge/screen interface coupled with increased pressure caused by the outlet restriction produces the dewatered sludge cake. The slow rotational speed results in less noise, vibration and overall wear, reducing anticipated long-term maintenance costs. The unit is constructed of stainless steel and is fully enclosed, reducing the corrosion potential and assisting with containing odors and improving working conditions. In addition, the operation of the unit is fully automated, reducing operational costs as compared to more traditional technologies.Through the full scale operation of the unit since October 2003, the inclined screw press has successfully met its design criteria and has demonstrated its worthiness as a viable and costeffective option to both the tried and true belt filter press and centrifuge technologies, as well as, the newer rotary press type technologies for smaller and mid-size treatment facilities. The benefits of the unit for the Old Town project included: lower capital costs, achievement of desired cake solids, lower than expected polymer usage, simplified operations, and significantly reduced solids disposal costs. 6650