Abstract
A full-scale anaerobic digester receiving a mixture of primary and secondary sludge was monitored for one hundred days. A chemical oxygen demand, COD, and volatile solids (VS), and mass balance were conducted to evaluate the stability of the digester and its capability of producing methane gas. The COD mass balance could account for nearly 90% of the methane gas produced while the VS mass balance showed that 91% of the organic matter removed resulted in biogas formation. Other parameters monitored included: pH, alkalinity, VFA, and propionic acid. The values of these parameters showed that steady state had occurred. At mesophilic temperature and at steady state performance, the anaerobic digester stability was defined as a constant rate of methane produced per substrate of ?VS (average rate=0.40 L/g). This constant rate can be used as the stability index to determine the anaerobic digester stability in an easy and inexpensive way.
Highlights
Producing renewable energy is a challenge for the world today because it is often more costly than the harvesting of fossil fuels
The chemical oxygen demand (COD) mass balance could account for nearly 90% of the methane gas produced while the volatile solids (VS) mass balance showed that 91% of the organic matter removed resulted in biogas formation
Percent volatile solids (VS%), which is the percentage of the total solids that can be volatilized at 550°C, was measured by taking the total solids sample and placing it in a muffle furnace set at 550°C for two hours (EPA, 2012)
Summary
Producing renewable energy is a challenge for the world today because it is often more costly than the harvesting of fossil fuels. Use of the anaerobic digestion of sludge may represent a cost-effective approach to generate a sustainable and renewable energy source. The methane produced from the anaerobic digestion of municipal sludge, animal and crop wastes can cover up to 20% of the natural gas consumption in the US (McCarthy, 1973). Central Weber Sewer Improvement District (CWSID) is located at 2618 West Pioneer Road, Ogden, Utah, 84404. It provides service for approximately 200,000 people in Weber and Davis counties. Project upgrades completed in 2011, included construction of a new parallel 30-MGD activated sludge treatment plant, a new headwork’s facility and a new raw sludge pump station. Focus was placed on value engineering directed at emerging areas of design where improvements could be made to reduce construction costs without affecting the process design or overall finished product
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