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Biosolids Improvements Roger Road Wastewater Reclamation Facility (RRWRF) Pima County Regional Wastewater Reclamation Department (PCRWRD) Tucson, Arizona

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The 41 million gallon per day (MGD) wastewater reclamation facility at RRWRF in Tucson, Arizona faced a major challenge when it was believed that one of the primary anaerobic igesters may require repair, but the lack of digester capacity prevented removing it from service without violating the Arizona Department of Environmental Quality (ADEQ) requirements for 15 days hydraulic retention time (HRT) in order to produce class B biosolids. Moreover, high ummertime ambient temperatures caused the thickening efficiency of the gravity thickeners to egrade by approximately 25%, further exacerbating the problem. Potential damage could nclude catastrophic release of undigested biosolids to the environment, significant nvironmental fines, millions of dollars of construction and operation costs and years of disruption to treatment during construction.

A collaborative innovative approach undertaken by the plant staff, engineers, contractors and ounty officials produced a very cost effective, environmental friendly solution which was mplemented within in a record time. The solution entailed separating the sludge into primary nd secondary components, thickening the secondary sludge in a new gravity belt thickener GBT), and increasing the digestion capacity by converting an existing secondary storage igester to a primary digester. No unauthorized releases of biosolids occurred, no fines were ncurred, objectives were accomplished at a fraction of the time and cost to construct a new igester, the annual cost of operation was reduced by about 200,000/year, and the plant did not xperience any operational disruptions. In addition, while not a goal of the original project, the roject achieved all the applicable objectives “Sustainable Action Plan for County Operations” hich Pima County subsequently implemented in August 2008.

Keywords: Job Order Contractor (JOC); Pima County Regional Wastewater Reclamation Department (PCRWRD); Roger Road astewater Reclamation Facility (RRWRF); Sustainable Action Plan for County perations; anaerobic digestion; beneficial reuse; class B biosolids; gravity belt thickeners; gravity hickeners; hydraulic retention time (HRT); primary sludge; secondary sludge

Document Type: Research Article


Publication date: January 1, 2009

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