IMPLEMENTATION OF A CENTRIFUGE DEWATERING FACILITY FOR THE CITY OF CAMDEN, NEW JERSEY

The City of Camden's, NJ Morris Delair Water Treatment Plant has a capacity of 18 MGD and obtains water from 16 wells with iron levels ranging from 0.5 to 40.0 mg/L and manganese levels ranging from 0.4 to 4.0 mg/L. The treatment processes consist of aeration, lime and chlorine addition, solids contact clarification and filtration. Average day solids production is approximately 10,000 pounds dry solids (DS) per day and the maximum solids production is 27,000 pounds DS per day. Residuals removed from the clarifiers have historically been disposed of in a lagoon which is adjacent to environmentally sensitive areas adjoining the Delaware River. In 1999, the NJDEP ordered the City of Camden to develop a plan to stop using the lagoons by the end of 2002. In July 2002 a new centrifuge dewatering facility (CDF) was placed into operation. The heart of the CDF is two solid bowl centrifuges. Each centrifuge can consistently produce a cake of 30% solids while operating at a throughput of 3,000 pounds DS/hr.There are very few mechanical dewatering facilities in the United States dewatering iron based residuals similar to those generated at the Morris Delair Facility. The implementation process therefore consisted of a comprehensive investigation and design phase to insure that the selected dewatering process met the design objectives for throughput and cake solids. The following options were investigated: belt filter presses, plate and frame presses, vacuum diatomaceous earth dewatering, and centrifuges. Bench testing, conceptual designs and lifecycle cost estimates were prepared for each option. In addition, a qualitative ranking was developed for each option. Criteria evaluated in each ranking included: history of the technology on similar applications, equipment complexity and safety. A survey of centrifuge installations treating drinking water treatment plant residuals was conducted to independently assess the performance of centrifuges on drinking water plant residuals. The evaluation concluded that the centrifuge option had the lowest lifecycle cost and the highest qualitative ranking. The low lifecycle cost was due in part to the high throughput, resulting in fewer and smaller machines as compared to the other options. Pilot testing was conducted to confirm the results of the bench testing and to provide detailed design criteria for the full scale system. Unlike most other drinking water pilot projects that use smaller scale versions of the treatment process, the centrifuge dewatering pilot test used a full-scale machine. The use of a full-scale centrifuge eliminated the scale-up effects associated with smaller pilot systems. The pilot test demonstrated that a centrifuge with a 20-inch diameter bowl, operating at 3,500 G could produce a 30% cake at a throughput of 3,000 lbs DS/hr.The key features of the full-scale design are two gravity thickeners which concentrate a 0.5% feed to a minimum of 3%, a settling tank for filter waste washwater, and the CDF which contains sludge feed pumps, centrifuges, a screw conveyor system and a polymer feed system. The centrifuges were purchased as part of a construction contract totaling 5.6 million. The centrifuge specification was written to allow competitive bidding within the performance and size requirements developed during the pilot testing. However, in order to ensure the proper equipment was obtained, the performance test specification contained penalties for not meeting the polymer, energy and cake solids requirements. The CDF achieved all of the specified performance requirements and has been successfully operating since July 2002.