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Metropolitan Wastewater Management Commission Capital Improvement Program <br />projects. These design projects are now scheduled for FY 03-04 with construction to follow in <br />FY 04-05. <br />'; j The Predesign Study is now scheduled for completion in FY 02-03. Included in the study will be <br />a process temperature evaluation and a nutrient removal evaluation to address new dischazge <br />permit requirements. <br />i <br />Digester Gas Filter -Cogeneration <br />FY 02-03 Capital Budget = $300,000 <br />This project includes the design and construction of a filter system to remove siloxane from <br />digester gas. Electricity is generated at the Regional WPCF by burning digester gas in lazge <br />engine generators. The presence of siloxane in the digester gas causes severe weaz on the <br />internal working components of the Jenbacher engine. Siloxane is a silicon compound that <br />crystallizes under heat and pressure conditions. in engine operation. Siloxane weazs heavily on <br />engine components such as the pistons, cylinders, and turbochazgers. The result has. been <br />frequent engine rebuilds, mechanical breakdowns, and reduced electrio power generation due to <br />maintenance downtime. Premature weaz on engine components has also caused high oil <br />consumption that translates to higher emissions of air pollutants. <br />The solution to this problem is the installation of a digester gas filter system. The filter system <br />will include a condenser and a carbon media filter. A filter system is anticipated to extend the <br />frequency of upper engine rebuilds that cost about $60,000 each from 1 year to 2.5 years. The <br />filter will also be effective to remove hydrogen sulfide that is another corrosive fuel contaminant. <br />Recent increases in electric power rates have reduced the payback period to make this capital <br />project a reasonable investment. The cost analysis for this project indicates the payback period <br />will be five years or less. The filter system will be sized to handle the full capacity of all digester <br />gas burning equipment: This will provide an additional benefit at minimal cost for the operation <br />and maintenance of other siloxane-affected equipment such as the boiler and heat exchangers.. <br />Biosolids Management Facility -Force Main Access Vaults <br />~.__ j FY 02-03 Capital Budget = $100,000 <br />This project includes the design and construction of additional access vaults on the Biosolids <br />~ force main between the treatment plant and the Biosolids Management Facility in order to <br />~ •_~ ~ - .. <br />provide better access for inspection and line cleaning. The single, five-mile force main has only <br />-,, five access vaults. The force main is becoming blocked with struvite, a crystal precipitate of <br />magnesium ammonium phosphate, which adheres to surfaces such as pipe walls and is a • <br />common problem in sludge handling and treatment systems. The build-up of struvite has <br />~ -, restricted the capacity of the force main, and the most recent efforts to clean the pipe by pigging <br />!_ '' were unsuccessful. No further attempts have been made to pig the line because of the high risk <br />of indefinitely plugging the line. The lack of vaults prevents access for physical cleaning. <br />'~, Additional vaults will provide access for visual inspection with TV camera, access for pipe <br />' ' cleaning, and may facilitate chemical cleaning. Physical removal by pressure jetting is effective, <br />but the maximum distance that can be cleaned from any access point is only 800 feet. Physical <br />~ !, cleaning of the entire force main could require up to 21 additional vaults. The actual number of <br />access vaults required at this time may depend upon the success of an initial effort to acid clean <br />the line in FY 01-02. The capital program includes $100,000 in each of FY 02-03 and FY 03-04 <br />as a safety net to address this problem. <br />Page 27 FY 02-03 BUDGET <br />