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The Wooten Company was awarded a 2000 Honors Award for Engineering Excellence by the Consulting Engineers Council of North Carolina for this project.The Town of Smithfield operates a 6 mgd maximum production conventional water treatment plant with a run-of-river intake on the Neuse River. Aluminum sulfate is used for coagulation. Due to a change in local conditions in 1994, the method of sludge disposal used by the town was abandoned. In July of that year N. C. Public Water Supply changed its water filter backwashing policy. This policy change dictated the need for greater hydraulic capacity in the residuals handling facilities. The town retained The Wooten Company to evaluate this problem and recommend a solution.

The Wooten Company reviewed several water treatment residuals alternatives for Smithfield. For filter backwash water, full scale testing of backwash and rewash water quality revealed that only the first ten minutes of the backwash water required treatment before discharge. Therefore, the technology of choice was primary sedimentation of the first ten minutes of backwash, followed by NPDES discharge, and direct NPDES discharge of all water following this first ten minutes. This was an innovative approach never before permitted in North Carolina until now and resulted in reducing the cost of the primary sedimentation facilities by about one third.

Smithfield's preferred alternative for alum sludge disposal was mechanical dewatering and disposal in a landfill. Several mechanical dewatering methods were investigated: belt press, membrane filter (plate) press, and vacuum drum. Of these three units, the vacuum drum filter was chosen as the preferred method due to a significantly lower initial capital investment and due to its being a more "robust" piece of equipment. The unit had a lower operation and maintenance cost, appeared to be easier to repair, and appeared to be able to handle changes in liquid sludge characteristics with ease, thereby requiring little operator attention.

Though originally patented in 1872, very little detailed design information was available for using the precoat rotary vacuum drum filter for dewatering alum sludge. An exhaustive literature review was performed on the use of this technology on all types of sludge. Both practical and theoretical literature was reviewed in detail. From this review, design equations and parameters were developed. Results of calculations using these equations and parameters were then compared to laboratory and field trials conducted on Smithfield's sludge. Conclusions reached verified the efficacy of this technology on Smithfield's alum sludge and were used to develop the final design parameters and present worth cost analysis for comparison with other technologies. This extensive and complex analysis determined that the precoat rotary vacuum drum filter was the most economical and robust dewatering technology available for Smithfield.

The original total estimated project cost (from the study phase) was $1.02 million. The final total project cost was $1.193 million. The original completion date was November 1997. Initial start-up was performed in early February 1998. The facility performs well and as originally intended.