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Program to Upgrade Biosolids Processing Yields Unprecedented Reduction in Emissions in Hartford, Connecticut

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In 1997, The Metropolitan District embarked on a project to upgrade two multiple hearth incinerators. The 21 million, multi-task project has resulted in emission reductions of criteria pollutants from 64 to 99.9 percent.

When the Connecticut General Assembly created The Metropolitan District (MDC, the District) in 1929, one of its most important missions was to provide a quality biosolids collection, treatment and disposal system for the region. From 1938 to 1972, the end product of the primary treatment process, biosolids, was “applied” to the land, both on the grounds of the Hartford facility and off site. In the early 1970s, in conjunction with the growth of the environmental movement in America and the advent of the Federal Clean Water Act, the Hartford Water Pollution Control Facility (HWPCF) was upgraded to provide secondary treatment. These improvements enable MDC to remove 90 percent of the pollutants prior to discharging its effluent into the Connecticut River. Three multiple hearth biosolids incinerators were built to burn approximately 50 tons of dry biosolids produced each day, as part of the 30+ million upgrade to secondary treatment.

Beginning in 1997, the District embarked on a 21 million upgrade program to satisfy existing air emissions standards by simultaneously providing long-term improvements to two of their three existing multiple hearth incinerators. Addressing complex design/construction challenges, such as determining the Best Available Control Technology (BACT), use of patented processes, and maintaining uninterrupted existing operations while performing these extensive upgrades, required a focused team effort to successfully complete this program.

The specific incinerator improvements can be placed into three categories: incinerator modifications, air pollution control systems, and biosolids conveyance system. Completely reconfigured brickwork, new incinerator combustion components, variable speed center shaft drive, flue gas recirculation system and the existing instrumentation and controls system was retrofitted with a new, state-of-the-art programmable logic controller (PLC)-based monitoring and control system. Following extensive analysis of the air pollution control systems, BACT was identified as a combination of a venture scrubber with afterburners set to a nominal 1200 degrees Farenheit. A total hydrocarbon continuous emissions monitoring system (THC CEMS) was also designed and expeditiously constructed. The new biosolids conveyance system delivers material to strategically identified locations in the eleven hearth incinerators.

Through the optimization of the combustion process, these upgrades have increased throughput, improved reliability and overall operations, reduced fuel use, achieved the most effective and efficient operation possible while yielding significant, and unprecedented, reductions in stack emissions for multiple hearth incinerators. The results measured during emissions testing efforts exceeded all expectations for performance. The results of these tests, as they specifically relate to the five criteria pollutants (CO, NOx, SOx, THC, and TSP), indicate that all applicable Connecticut Department of Environmental Protection (DEP) and United States Environmental Protection Agency (EPA) regulations are being met or bettered. Stack emissions are now barely visible to both the experienced and inexperienced eye, due to optimization of the District's biosolids processing operations.

The District's multiple hearth incinerators will be able to provide the region with an environmentally effective and efficient means of processing and disposing of biosolids for many years, as a result of the approximately 21 million in improvements and upgrades.
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Document Type: Research Article

Publication date: 2002-01-01

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