Site Energy Management Plan Helping Wastewater Plant
Reduce Carbon Footprint

In the mid 1990s, the neighboring townships of Marion, Howell, Oceola and Genoa, Michigan, formed the MHOG (using the first four letters of the township names) Sewer and Water Authority to provide water services to the four townships. The Authority – whose townships each encompass approximately 36 square miles – has managed an increase in the number of water and wastewater service connections averaging 13.6 percent per year since 2001, with a high of more than 21 percent in 2002. Relying on a private operator to manage the treatment facilities through a public-private partnership, this growth has led to increased power consumption.

That's no surprise, given that energy costs are the second largest expense for treatment facilities – 11 percent for water utilities, 28 percent for wastewater utilities. Reducing power consumption is one way utilities are generating savings and minimizing their carbon footprint.

In 2008, Severn Trent Services, the Authority's private operator, undertook a program to identify additional areas of energy reductions at facilities the company operates. Targeting five facilities geographically dispersed across the United States, the company rolled out its pilot Site Energy Management Program (SEMP). Process/plant optimization models were developed by the company's Technical Services Group, with additional opportunities being identified by on-site personnel.

One of the five original targeted facilities, the Genoa Oceola Sewer and Water Authority's 1.2-mgd oxidation ditch wastewater treatment facility, achieved a 21 percent energy reduction by an improved utilization of sequencing batch reactors (SBRs), upgrading to HVAC systems and a continuous improvement in process control to save power.

Establishing a benchmark
To ensure the quality and reliability of the treatment process, the formal SEMP:

• evaluates site energy consumption
• challenges current practices
• identifies opportunities for energy reduction
• produces priority actions for increasing energy efficiency

The Genoa Oceola facility's baseline energy usage for the benchmark period (October 2007 – September 2008) was measured in kilowatt hours (kWh). The Genoa SEMP committee, composed of Severn Trent operators, managers, technical services personnel and MHOG's utility director, identified the following opportunities to improve savings and increase efficiency at the facility:

• decommissioning the SBR system
• optimizing the sludge handling system
• upsizing/improving the sludge thickening system
• precise metering of sludge
• upgrades to the HVAC systems
• data collection to identify and correct pump run times
• reducing effluent filters in operation
• reducing mixed liquor suspended solids in aeration basins

The committee's preliminary target was to provide a savings of 10 percent of power usage and sludge handling costs.

Beginning in 2007, baseline energy usage was measured and process/plant optimization models were developed. Then, an energy analysis model was developed to determine optimal operating parameters for each facility, ensuring other process variables (sludge production, chemical use) were not adversely impacted.

Baseline energy usage was 1,425,410 kWh.

Priority actions
During the evaluation period (October 2008 – September 2009), the SEMP committee implemented priority actions based on the opportunities identified during the benchmark year, including:

• decommissioning the Genoa Oceola SBR system once proven it could be brought back on line without difficulty
• thickening of sludge; on-site sludge volumes and concentrations were monitored, as were volumes and concentrations of sludge transported off site
• rebuilding and refining the sludge handling system through capital investment
• repair of heating thermostats in several buildings at the facility
• analysis of data to identify grinder pumps for repair and lift station pumps not operating properly in lead/lag mode
• cost/benefit analysis of removing on-line effluent filters
• exploration of reduced mixed liquor concentrations

Evaluation
After demonstrating the SBRs could return to operation if required, Severn Trent operators took the system off line as planned at the beginning of the evaluation period, reducing power consumption by not having the system idled and in stand-by mode. Comparing total kWH usage for the two periods showed a reduction of 252,520 kWH (21.5 percent).

Energy Usage

At eight cents a kWH, the savings realized was more than $20,000.

Addressing the sludge issue involved using an existing drum thickener and adding polymer at the outset of the evaluation period. Analysis of seasonal hauling figures (gallons hauled) showed a reduction of 817,700 gallons (34 percent).

Sludge Volume

Accounting for variations in per-gallon hauling costs, fuel surcharges and polymer expenses, the savings realized for sludge reduction totaled more than $26,000.

The SEMP committee deemed removing effluent filters would not prove to be cost effective, and tabled reducing mixed liquor concentrations for a later date.

Conclusion
After analyzing the savings from reducing energy usage and sludge volume through the formal SEMP, Genoa Oceola WWTP surpassed the SEMP committee's preliminary target of 10 percent savings, realizing a total savings of $46,461 over the evaluation period.

According to Bob Lugar, Severn Trent Services senior area manager, "The SEMP process demonstrates a sound partnership between Severn Trent Services and Genoa Township. The process proves we can collectively find ways to improve operating efficiency and take an active role in reducing Genoa Township's carbon footprint."

Bill Gramlich, Severn Trent Services area manager, concurs. "The Genoa Oceola SEMP delivered measurable results that benefit Genoa Township, our environment and our Great Lakes."

For more information, e-mail info@severntrentservices.com.

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