The Delhi Charter Township POTW has been in operation since 1962. The wastewater treatment plant currently provides influent flow equalization, grinding and grit removal, primary clarification, secondary treatment using activated sludge with final clarifiers, nitrification using a nitrification tower and chlorination/dechlorination of the final effluent prior to its discharge to the Grand River. Solids are anaerobically digested prior to being stored and applied on farmland.
To meet the needs of future growth in the Township HRC prepared a project plan, completed design, and construction is well underway for a State Revolving Fund (SRF) loan funded project for improvements and expansion to the digestion system. The Township also received a $500,000 S2 grant through the SRF program to fund the preliminary project and design engineering costs.
The digestion system will be improved to provide Class A biosolids and will generate electrical power for use within the plant. Class A biosolids meet the most stringent United States Environmental Protection Agency (USEPA) requirements for stabilization of the biosolids. This allows more options for ultimate use of the biosolids than farmland application, the typical use of less stringent Class B biosolids.
The anaerobic digestion system will be a Two Phase Anaerobic Digestion (2PAD™) system process by Infilco Degremont, Inc. The process will use two thermophilic anaerobic digester tanks with 2 days of retention time operating at a temperature of 131°F, and two mesophilic anaerobic digester tanks with 10 days of retention time operating at a temperature of 98°F.
The anaerobic digestion system improvements also include the provision of a Combined Heat and Power (CHP) system. The CHP system will use the methane gas produced during anaerobic digestion as a fuel to power microturbines. The microturbines will create electrical energy for use at the wastewater treatment plant. Initially, 60 kilowatt (KW) of electrical energy will be created with up to 120 KW available in the next 10 to 20 years. The operation of the microturbines also creates a significant amount of heat which will be used to heat the thermophilic and mesophilic anaerobic digester tanks thus eliminating or significantly reducing the amount of natural gas used for heating the digester tanks.
The new anaerobic digestion system is sized for an average wastewater treatment plant flow rate of 4.87 mgd.
The benefits of the 2PADTM with CHP system include:
- Direct savings in electrical and natural gas energy costs.
- Small volume of biosolids generated through more efficient Class A biosolids process.
- Potential savings in electrical energy through reduced peak loading costs.
- Potential for further flexibility in final use of Class A biosolids compared to Class B biosolids.