In keeping with a national push to bring greater energy efficiency to wastewater treatment plants, a Pennsylvania facility used data loggers to analyze motor utilization, a first step toward cutting energy costs and meeting environmental rules.
This article explains why the Cumberland County wastewater facility decided to improve its efficiency, and how its contractor, Reynolds Energy Services, employed data loggers to gather preliminary information.
Importance of upgrades
The decision to improve the plant’s efficiency reflects a national movement to reduce consumption at energy-hungry wastewater facilities. After labor, energy is the highest expense at the 15,000 publicly-owned wastewater treatment plants, which serve about 70% of the US population, according to the Consortium for Energy Efficiency (CEE). The facilities account for as much as 35% of the energy used by some municipalities.
As a result, several towns and cities are directing funds from the American Recovery and Reinvestment Act (ARRA) toward wastewater treatment improvement. Upper Allen Township applied for a portion of the $2.2 million in ARRA funds received by Cumberland County, but was unsuccessful in securing funds due to the overwhelming number of requests the county received for funding.
In addition to reducing energy, planned improvements at Upper Allen Township’s Grantham wastewater treatment plant will help Pennsylvania meet federal standards established to protect the Chesapeake Bay. Located about two hours west of Philadelphia, the Upper Allen Township wastewater system treats between 500 and 700 thousand gallons of wastewater on average daily. The treatment plant was most recently expanded and upgraded in 1990 and uses a Sequencing Batch Reactor (Aqua SBR) system with aerobic digester(s). The facility is scheduled for additional improvements in 2010-11 to meet anticipated new NPDES Permit discharge requirements in connection with the Chesapeake Bay Tributary Strategy.
Streams in Cumberland County flow into the Susquehanna River, which in turn feeds into the Chesapeake Bay. The river has been deemed a major source of nitrogen, phosphorous, and sediment found in the bay. As a result, the US Environmental Protection Agency has devised a “pollution diet” for the bay. To that end, Pennsylvania wastewater treatment plants must cap their nutrient flow into Susquehanna tributaries to win approval as their permits come up for renewal.
Data loggers reveal inefficiencies
Studies estimate that potential exists to reduce energy use 15% to 30% at US wastewater plants. The extent of savings depends upon the facility size, type, technology and regional operating conditions. Motor replacement might reduce energy use about 2%, while modifications in process control might cut consumption 30%, according to CEE.
The aeration process, which uses fans and motors, consumes the most energy. Gaining maximum efficiency in the aeration process is particularly important because it is a peak load operation, meaning the plant consumes large amounts of power when electricity prices are highest. Reynolds Energy Services, of Harrisburg, conducted a detailed audit of the Upper Allen facility, with an eye toward installing improved aeration technology that reduces energy use and meets environmental permitting requirements.
Equipment does not always perform as efficiently as manufacturers estimate for a variety of reasons. So the auditors attached Onset HOBO® U9 Motor On/Off data loggers on existing equipment at the treatment plant and pumping stations to “see how equipment is actually operating,” said Michael Conchilla, Reynolds’ Project Development Manager.
The project focused on motor loads, particularly for the larger equipment -- aerators and pumps at pumping stations. “We had a dozen different motors being logged. We were looking for runtime patterns and how many hours per day they’re being used. Many of the motors run on/off, on/off in small intervals. We wanted to see what those patterns are, what the collective hours are, and extrapolate that out on an annual basis,” he said.
Reynolds left the data loggers on site for about four weeks. This was easy to do since the loggers are portable and rugged standalone devices that operate independent of any other apparatus or connection. The data loggers monitor the alternating current field generated by the motors.
“I got great results from tying the loggers to feeders in electrical cabinets rather than deploying them only on the motors. Some of the motor casings were too large to get a good field reading. I’ll probably do this more in the future,” Conchilla said.
After retrieving the data loggers, Reynolds downloaded the information, and graphed and analyzed the data using HOBOware® software, which allows quick readout and plotting of information, with export to spreadsheets.
“We needed to understand the run time patterns for each individual motor. If you can extrapolate that out for a year you know how many kilowatt hours each motor is using,” Conchilla said. “The township collects amp readings on a regular basis. This is used to estimate electrical draw on the motors. We use this and the runtime data to estimate actual kilowatt hour usage for each motor.”
He added: “As long as you have the amperage data and run time you can make the calculation. We used Microsoft Excel to do those calculations. I would export all the run time data from HOBOware to an Excel file, tabulate hours based on the period and extrapolate that out for the year.”
Reynolds will use the information to help Upper Allen determine where upgrades to the system are necessary and where the expense can be avoided. After the new equipment is installed, the energy services company will continue to use data loggers to confirm results, a necessity since Reynolds is operating under an energy services performance contract.
Thanks to the data loggers, Upper Allen now can move forward with its efficiency improvements, assured that any guesswork has been removed. “You can’t argue with the data. They tell you what’s going on 24 hours a day,” Conchilla said.