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Utilization of Egg-Shaped Digesters for efficient wastewater disposal : a report submitted to the faculty of the Milwaukee School of Engineering in partial fulfillment of the requirements for the degree of Master of Science in Environmental Engineering / by Brad Holland.

by Holland, Brad., Milwaukee School of Engineering

Sewage -- Purification -- Anaerobic treatment.

Sewage sludge digestion

Wastewater -- Treatment and disposal

Sewage disposal plants

106 leaves : illustrations, some of which are in color ; 29 cm.

Introduction of project and location -- Literature review -- Methods and materials -- Data results and analysis discussion -- Conclusions and recommendations -- Appendix A: Waukesha service area -- B: Digester complex heating drawing -- C: Waukesha plant equipment -- D: Waukesha plant operating data -- E: Digester gas usage data -- F: Digester gas analysis report.

As the world's population continues to grow, the use of water resources generates larger amounts of wastewater that are collected and treated to protect public health and the environment. The municipal wastewater treatment process stabilizes collected solids, most commonly done through the process of anaerobic digestion. Anaerobic digestion is the anaerobic biological decomposition of organic solid material that concomitantly destroys harmful pathogens, thus reduces the risk of disease transmission to the public.

The objective of this research is to evaluate the impact of replacing the existing anaerobic digesters with Egg-Shaped Digesters at the Waukesha WWTP. The evaluation of ESD life-cycle performance, including capital operating and maintenance costs, is reviewed versus continued operation of a conventional anaerobic digester. Life cycle costs are defined as the overall cost of an alternative to the WWTP operation over a twenty year planning period. Capital costs include necessary structures and equipment to install ESDs at the WWTP.

This study involved analysis of data collected daily over a three-year period at an operational wastewater facility in the United States. To review the feasibility of the ESDs, a large amount of data needed to be sorted and analyzed to evaluate efficiency and effectiveness of the existing anaerobic digestion system.

Egg-Shaped Digesters are efficient in passing through sand and grit, while producing volatile solids reductions that exceed conventional digester performance. There is less need for removal of ESDs from service to be cleaned or repaired as the shape and mixing systems keep a minimal amount of build-up from occurring at the bottom of the tank and scum build-up at the surface. Data from operating ESD systems can provide guidance on which designs are the most cost effective in future use. With a draft tube assembly used to induce flow throughout the digester, and heat exchangers to assist boilers in heating the contents, a wastewater utility can reduce capital costs and construction expenses.

For Waukesha's plant, the researcher recommends not adding the Egg-Shaped Digesters at this time. Their existing conventional digesters are operating at the high end of the typical volatile solids reduction with annual maintenance and upkeep of one digester out of service each year. They have adequate storage of the final cake product and sufficient fields to apply it during the spring and fall months. The only use of their existing biogas is for the two hot water boilers that serve the digester building. Figuring that electrical and heating consumption is the same when comparing the conventional pancake digester and the ESD, it is possible to determine that the plant would not experience a payback at this time. The initial construction costs are also significantly higher for an ESD than refurbishment of the existing conventional digesters.

In order to make the addition worthwhile, and feasible, the plant would also need to add projects that would utilize the biogas, such as fuel cells, additional heating equipment for other buildings, and generators or turbines to create electricity for the plant to use. These are all upgrades that should be further analyzed along with the payback periods that they would experience.

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