Monday 3:00 PM
[Presentation PDF]

Room: Diamond

Rehabilitation and Optimization of Anaerobic Digester Mixing Systems

Many of the anaerobic digestion facilities in Illinois and Indiana were originally constructed with a combination of sludge gas mixing and sludge pumping recirculation systems. These sludge gas mixing systems are currently either providing inefficient digester mixing, have reached the end of their useful life or are no longer in use. A properly mixed digester will result in increased solids destruction and in turn produce greater sludge gas production, reducing sludge volume. Sludge gas, a renewable energy source, can be used for digester and plant heating needs, power generation and fuel for prime movers such as engine-driven pumps and blowers. An evaluation of the different type of digester mixing systems will be presented including both quantitative and qualitative factors based upon the evaluation of mixing systems from three different wastewater treatment plants that range in size from 20 to 48 mgd on a daily flow basis.

Moderator:  Lou Kollias


Joe Gorgan - Greeley and Hansen

Mr. Gorgan has thirty years of experience in the design and construction of new and rehabilitated wastewater treatment facilities.  He leads the firm’s Technical Services Center (TSC), which leads the firm’s initiatives in seeking out and identifying new technologies and identifying and managing project risk for clients.  He has served as project manager providing facilities planning, preliminary and final design, preparation of projected cost opinions, O&M manual preparation and office construction services.

Mr. Gorgan is also the Project Director for the replacement of existing preliminary treatment facilities at the Metropolitan Water Reclamation District of Greater Chicago’s 720 mgd Westside Plant which is part of the 1,440 mgd Stickney Water Reclamation Plant, Stickney, Illinois.

Mr. Gorgan received his M.S. in Environmental Engineering and B.S. in Civil Engineering from Illinois Institute of Technology, Chicago.

Rebecca Schaefer - Greeley and Hansen

Ms. Schaefer has over seven years of experience in the planning and design of wastewater treatment plant (WWTP) upgrades and expansions and collection system long term control planning.  She is currently a project manager at Greeley and Hansen, a leading environmental consulting engineering firm dedicated to the water and wastewater industry.

Ms. Schaefer has served as project manager for a wide variety of wastewater engineering planning and design projects.  Recently she managed a comprehensive digester upgrade evaluation study, a biosolids master plan and a preliminary design for a digester upgrade.

She has been a member of the Water Environment Federation since 2004.

Ms. Schaefer received a Bachelor’s Degree and a Master's Degree in Environmental Engineering from Purdue University. She is a registered professional engineer is the state of Indiana.