Environmental Engineering Science Seminar
Lopata 101
Friday, February 24, 2006
Time: 11 am
Dan Zitomer
Associate Professor, Civil and Environmental Engineeirng
Marquette University, Milwaukee, WI
Temperature-phased anaerobic digestion (TPAD) of municipal wastewater solids is often implemented in an effort to increase volatile solids (VS) destruction, methane production, and pathogen inactivation. However, the benefits of temperature phasing that can be achieved in comparison to a mesophilic digester in full-scale are not clear. Better mixing, increased total solids retention time (SRT), and up-grading may contribute to benefits observed in some field comparisons. Although thermophilic temperatures can lead to more rapid fecal coliform inactivation, the holding time and mixing regime of the thermophilic digester are also critical. Short-circuiting must be minimized or eliminated so that a high percentage of sludge is held at the required temperature to achieve the necessary inactivation . The study to be described was performed to compare mesophilic and temperature phased/staged digesters with identical SRT values side-by-side. Draw-and-fill operations were performed only once a day to reduce particle short circuiting and obtain low effluent fecal coliform counts. The daily slug feeding resulted in low thermophilic digester pH values and elevated volatile fatty acid concentration. Therefore, alkalinity addition, trace nutrient supplementation, and a batch staged temperature anaerobic digester (B-STAD) were investigated. The VS destruction values observed for the mesophilic and temperature-phased systems were not statistically different, but TPAD and B-STAD resulted in higher fecal coliform inactivation than the control. During a three-month start-up phase, the TPAD system required nutrient addition to increase pH in the thermophilic digester and reduce final VFA concentrations. Recycling of mesophilic biomass to the thermophilic digester, as performed in the B-STAD configuration, and trace nutrient supplementation were also also observed to help maintain near-neutral thermophilic pH values and reduce VFA concentrations during start-up of the slug-fed systems.
He will also provide a brief overview of the "Engineers without Borders" program
at the end of his talk.
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