For many years, the Village of New Lenox, Ill., was a fast-growing community. Wastewater treatment plant operators and municipal manager spent a lot of time on the expansion of the collection system and wastewater treatment plants to accommodate the increasing population. 

Three wastewater treatment plants (Plant 1, Plant 2, Plant 3) make up the New Lenox system. When plant expansions were no longer necessary, plant staff members had more time to evaluate how they could improve operations. Energy savings, becoming more “green” and saving residents money were the driving factors. In 2009, staff members at Plant 1 started looking at ways to save money at the 2.5 mgd activated sludge treatment facility. 

Plant 1 had two incoming power feeds and two separate electric meters. It was built to maximum capacity, so with no major changes planned, staff members figured any savings they could find should pay back year after year. 

The first thing they did was look at major energy costs. They realized most of the energy costs were electricity, and that gas and fuel costs were minimal. Staff members looked at which equipment used the most power and evaluated the amount of time the  equipment operated. They also learned about the effects of electric peaking on electrical costs. 

Major electrical costs 

The evaluation showed that the two major electrical costs were pumps and blowers. The next step was to see what could be done to reduce costs on those items. Other smaller electric and natural gas uses were evaluated to see if operational changes could help reduce costs, but the focus was on evaluating the following: 

Major pump costs	Major blower costs
Raw wastewater pump	Hoffman & Lamson aeration blowers (Gardner Denver)
Raw wastewater excess flow pump	Kaeser digester blowers
Primary sludge pump	Sutorbilt digester blowers (Gardner Denver)
Return activated sludge (RAS) pump
Sludge thickener pump
Sludge storage mixer

Three 1,950 cfm Hoffman & Lamson aeration blowers used the most electricity and ran the most, so operators turned down the air intake valve as much as possible to reduce motor amp draw. They also plugged about 20 percent of the aeration tank spargers to reduce air supply needed. They found that in winter they sometimes could use one aeration blower at full speed instead of running two blowers at low speed. They lowered the air feed to aeration channels and installed power factor correction capacitors from KVAR on individual aeration blowers. The capacitors were put on all the blowers and greatly reduced electrical demand.

Three 1,600 cfm Kaeser blowers and two 680 cfm Sutorbilt blowers (Gardner Denver) were the second major energy consumer. In the summer, two blowers could not supply enough air so the plant had to run all three and then had more air than necessary. Each of the two smaller blowers could supply half of the air produced by one of the large blowers. The plant can run two large blowers and one small blower, lowering electricity costs in warm weather. In the winter, the plant sometimes can run one large blower and one small blower and save on electricity costs. 

Pumps were the third major consumer of electricity. Pumps 1 and 2 are 1,066 gpm KSB pumps, pump 3 is a 1,250 gpm KSB pump, and pump 4 is a 1,866 gpm PX pump. Pumps 1 and 2 are used as lead pumps in dry weather and operators sometimes switch to pump 3 as the lead pump during higher flows. By rotating the pumps based on plant flow, pump starts and stops are minimized, reducing electrical costs. The 1,866 gpm pump is put in lead during rain events.

After evaluating the excess flow pumps, staff members found leaking flanges and pipes. These were repaired to reduce run times and save electricity. Operators also have worked to reduce inflow and infiltration in the collection system, reduce wet-weather flows and subsequently lower pumping costs. They evaluated the sludge mixing pumps and reduced the time to mix the storage tanks, which saved electrical costs.

Plant staff could not put capacitors on the RAS pumps because they were on variable-frequency drives and the technology was not compatible.

By implementing these major changes, the New Lenox plant successfully reduced electrical usage and saved money.

Savings breakdown

Building 20 and building 55 are the main power centers for Plant 1. In building 20, the plant installed the first capacitors on the aeration tank blowers. Building 20 powers the raw pumps and aeration blowers. Building 55 powers the digester blowers and RAS pumps.

Monthly costs analysis 

Plant 1 Electric: Building 20               

Month	2009	2010	2011	2012
January	$15,636	$11,620	$9,284	$13,916
February	$16,010	$11,672	$9,872	$10,241
March	$16,228	$10,738	$10,570	$12,564
April	$13,872	$12,835	$10,258	$12,299
May	$14,305	$10,640	$9,697	$10,154
June	$14,273	$13,123	$14,516	$8,098
July	$12,001	$12,880	$11,524	$8,266
August	$12,579	$11,805	$12,108	$8,103
September	$13,185	$11,232	$12,801	$8,812
October	$13,722	$12,622	$12,491	$8,190
November	$13,397	$12,611	$14,431	$9,267
December	$14,975	$11,358	$13,439	$9,825
Total	$170,243	$143,136	$140,991	$119,736
Average month	$14,186	$13,110	$11,749	$9,978

Plant 1 Electric: Building 55               

Month	2009	2010	2011	2012
January	$13,068	$8,939	$7,299	$11,053
February	$12,611	$11,672	$7,621	$9,879
March	$12,966	$10,152	$8,394	$10,210
April	$11,016	$12,098	$7,044	$10,210
May	$11,100	$10,968	$8,504	$7,419
June	$9,974	$11,431	$7,679	$5,842
July	$11,068	$8,851	$8,446	$6,272
August	$10,726	$9,700	$8,656	$6,556
September	$8,920	$8,201	$9,536	$7,481
October	$11,494	$9,394	$9,617	$5,505
November	$11,198	$7,863	$10,706	$6,756
December	$11,092	$8,513	$10,293	$6,633
Total	$135,233	$117,782	$103,795	$88,370
Average month	$12,100	$9,815	$8,649	$7,364

Plant 1 Total Electric Costs

Year	2009	2010	2011	2012
Total	$305,476	$260,918	$244,786	$208,106

The electrical cost reduction of building 20 went down $27,107 in 2010. The electric bill for building 55 dropped $13,987 from 2010 to 2011 after capacitors were installed on the digester blowers. The capacitors account for $40,000 of the $60,000 savings from 2009 to 2011. The capacitors cost $17,000 installed.

The plant negotiated a lower electric rate, switching from Exelon to Constellation in 2012, which had a major impact on total cost. Problems with grit buildup in the digesters made it necessary for operators to use more air to keep the dissolved oxygen level up and ensure proper mixing because the spargers were not working as efficiently. That temporarily hampered efficiency and the warmer winter made going to one blower for aeration impossible. The 2012 electrical costs might not have decreased if not for the lower electric rate.

Electrical costs at Plant 1 were $97,370 less in 2012 than in 2009 when the evaluation began, which is a 31 percent reduction. Even if the plant finds no other ways to reduce electrical costs, a $97,370 annual savings translates into about $2 million in savings over the next 20 years, with $800,000 of that due to the capacitors.

An efficient staff that was willing to find ways to save money and make modifications to achieve success made the changes possible. Without staff buying into the project, the plant would not have been as successful with such a small capital investment.

For a complete profile on the New Lenox plant, visit www.tpomag.com/editorial/2011/04/forward_thinking.

About the Author
Mike Turley is supervisor of Waste Water Reclamation for the Village of New Lenox, Ill., overseeing three treatment plants with a combined 3.6 mgd flow.