By Wendy Wert, Training Coordination Committee Chair
and Jon Hay, CWEA Biosolids Committee Chair
On January 27, 2009, the California Water Environment Association (CWEA) Biosolids Committee hosted a specialty conference “Reducing Solids Handling & Disposal Costs through Dewatering System Optimization” at the Carson Community Center in Carson, CA.
This one-day biosolids specialty conference, which trained 80 people, consisted of a series of technical presentations and a tour of the Los Angeles County Sanitation Districts Joint Water Pollution Control Plant (JWPCP) in Carson. During the morning session, the opening remarks were presented by the conference chair followed by seven technical presentations, orientation for JWPCP tour. During the afternoon session, conference attendees traveled by bus to JWPCP where they toured solids handling and odor control facilities, heard three technical presentations, and participated in panel discussion with the speakers.
A total of 11 speakers gave presentations that covered a wide range of relevant topics, including biosolids regulations, WERF research, dewatering theory and principles, advances in major dewatering technologies, odor control, polymer conditioning, process monitoring and control, and equipment procurement and delivery. The speakers also presented on these same topics at EBMUD in Oakland on January 28. This event trained 100 CWEA members and non-members.
The conference began with CWEA Biosolids Committee and Conference Chair, Jon Hay’s opening remarks, which highlighted the overall goal of the training: to provide practical training to the biosolids industry in order to optimize dewatering, reduce handling and disposal costs, and maintain the long term viability of biosolids recycling in California in a changing regulatory environment. He also described the specific objectives of the conference as follows: improve knowledge of dewatering practices, process enhancements, latest research, and regulatory developments, promote “Best Management Practices” for biosolids dewatering, encourage resource stewardship and environmental protection, encourage information exchange and networking and “raise the bar” for the biosolids industry. Jon’s opening remarks set the stage for technical presentations that followed; key learning points from three of these presentations are summarized below.
Speaker Bob Gillette then moved the discussion into a more technical arena with his presentation on the ABC’s of Dewatering-Theory, Principles, Design, and Operation. WEF defines sludge dewatering as the removal of a portion of the water contained in sludge by means of a filter press, centrifuge, or other mechanism. Bob then showed the exponential relationship between the percent solids in residuals and the pounds of water. For example a two percent increase in solids content results in a reduction of 500,000 lbs of water in 10 tons of sludge when you go from 3% to 5% solids. However, dewatering exhibits the phenomena of diminishing returns, a two percent increase in solids content from 23% to 25% results in a reduction of 100 pounds of water in 10 tons of sludge.
Speaker Bob Gillette emphasized planning as essential to the success of dewatering design projects and presented an example case study using planning tools such as a project goal setting sheet, a dewatering system planning checklist, and specific project task lists. Effective planning involves the development of accurate P&ID drawings that help to resolve design issues such as: establishing a controllable process, algorithm location, identification of reliable sample flow, identification of representative sample flow, sample conditioning, and process lag time.
Speaker Paul Bland then discussed industry advancements in equipment manufacturing, such as those found in the Winklepress belt filter press. These improvements were developed through ongoing research and development, equipment design, and process analysis. The presentation discussed several advancements in dewatering theory and explained how the improved technologies address current and future needs and goals of our industry. Paul explained how changes in sludge characteristics are affecting dewaterability, including: the ratio of primary / secondary biosolids (which creates less structure in treated biosolids), changes in amount of inorganic solids due to better grit removal, and added sludge age realized from additional MBR or BNR application. In general, the above changes indicate that biosolids are becoming more fragile and difficult to dewater. Innovative features of the Winklepress that enhances dewatering are a larger Dandy roller with filtrate internal scoops, increased dewatering areas, adjustment of pressure zones, enhanced hydraulic loading, higher capture rate, and cake dryness.
The program continued with Speaker Dan Buhrmaster’s presentation of Centrifuge Procurement-Lessons Learned. Dan began by introducing the typical phases of a project, which include: project definition, project delivery selection, preliminary design, equipment alternatives evaluation, manufacturer and model evaluation, detailed design, bidding/negotiations/contract, shop drawings, manufacturing, installation, start-up and testing. The centrifuge procurement process focuses on manufacturer and model evaluation, bidding/negotiations/contract, and startup and testing.
Speaker Buhrmaster continued with a present worth cost analysis from a specific project showing how sensitive long-term biosolids operating costs are to centrifuge performance. In the example given, present worth cake hauling costs were valued at $937,000 per percentage point cake solids and present worth polymer costs were valued at $446,000 per pound of polymer dose. The elements of a comprehensive procurement process were reviewed, which include pre-qualification, site visits, performance review, equipment screening, pilot testing to verify performance, detailed specifications on important features, pre-purchase, evaluated bid based on capital and operating costs, and award based on lowest life-cycle costs. It was recommended that owners include a service maintenance agreement, complete shop drawing reviews prior to the construction phase, and a performance test with associated penalties.
Other presenters covered several related topics, as follows: Layne Baroldi, biosolids regulations and WERF research developments; Dave Bachtel, advances in centrifuge dewatering technologies; Kevin Kennedy, advances in screw press technology; Jim Barry, odor control; Ken Plache, polymer conditioning; and Peter Brady, process monitoring and control.
A highlight of the event was a tour of the County Sanitation Districts of Los Angeles County’s (Districts) Joint Water Pollution Control Plant (JWPCP) in Carson. Ken Rademacher, the JWPCP Manager, provided excellent overview of the facilities prior to the tour. Innovation has long marked the biosolids management practices at the Districts. Reuse of biosolids began in 1928 via a contract with Kellogg Supply, a fertilizer company, to distribute dried solids for the JWPCP.
Today, the JWPCP serves as the centralized biosolids processing facility for the 520 million gallons per day (mgd) Joint Outfall System (JOS). The JOS has a network of six water reclamation plants, with a combined flow of 170 mgd, with return their residual solids to the sewer system for centralized processing at the JWPCP where an additional 350 mgd are treated. Biosolids are anaerobically digested and then dewatered at the JWPCP with the digester gas used as fuel for gas turbines, digester heating and internal combustion engine driven pumps. The dewatered biosolids are hauled offsite for additional processing and beneficial reuse.
Dewatering of biosolids has been the subject of much research, often using full size equipment because of the unpredictability of scale-up from small units. Unique improvements in centrifugation have greatly reduced biosolids cake production from 1,600 to 1,300 tons per day, generating a savings of about $3 million per year in hauling costs.
The panel discussion at the end of the day gave the attendees the opportunity to ask the speakers additional questions about biosolids dewatering subjects covered at the conference. Overall, the conference greatly enhanced the understanding and knowledge of state-of-the-art dewatering technologies, equipment procurement, facility operation, odor control, polymer conditioning, and process monitoring and control. This unique learning opportunity fulfilled CWEA’s mission to train and disseminate technical information to wastewater professionals.