The treatment plant serving Delhi Charter Township stays green with measures from grounds maintenance to microturbine cogeneration
The first thing you’ll notice about the new wastewater treatment plant in Delhi Charter Township, Mich. is a flock of sheep tending to the grass.
What is not so evident is that you’re also looking at the state’s first integrated biomass-to-energy system — a cogeneration plant that uses microturbines to make electricity from methane and uses the recovered heat in the digesters.
Located next to the state capital of Lansing, the township has been growing over the last 10 years. The old mesophilic digesters had reached their capacity, according to Allen Bryant, environmental coordinator. In 2007 the township decided to build a self-sufficient plant with very low environmental impact. It went online in June 2009.
The plant, located in Holt, serves a population of 25,000 and has a design flow of 4.0 mgd (average 2.5 mgd). It uses an activated sludge process with tertiary treatment.
The solids process captures and uses digester methane that used to be flared. Raw sludge is pumped from the primary clarifiers to pre-feed tanks that automatically dose a set of thermophilic digesters where material is kept at 130 degrees F for about 48 hours. The sludge is then incrementally transferred to mesophilic digesters where it undergoes further mixing for about 10 days at 99 degrees F.
The methane from the digesters is processed by a gas compression skid (Unison Solutions Inc.). “After we dry and clean the resulting methane, we use it to drive two Capstone Turbine Corporation microturbines that generate 30 kW each,” says Bryant. The microturbines reduce the need for utility power, and the waste heat supplements digester heating.
“We’re happy with the methane production,” says Bryant. “The generators are running pretty much full-time off the methane we’re producing.” The annual savings is expected to be around $30,000 in electricity and $40,000 in natural gas.
Sandra Diorka, township director of public services, says the staff hasn’t calculated the carbon footprint savings, but they are obviously significant. “We were flaring the methane, so we had that carbon dioxide and the byproducts of burning going into the environment,” she says. At the same time, the plant is not using as much natural gas or electric power generated by fossil fuels.
A big step
The $9.8 million project was the result of an effort that started from a need to improve biosolids handling. While considering options about 10 years ago, the township was approached by the HESCO environmental technology firm about partnering on a grant application for a combined heat and power plant. The board was “pretty excited” about the idea, according to Diorka. “But we didn’t get the grant.”
The township still had to do something. It would have cost about $3 million to rehabilitate the old digesters or about $7 million for a new Class B biosolids plant. “The board said ‘Let’s just do the right thing and continue on with the combined heat and power,’” recalls Diorka.
Designed by Hubbell, Roth & Clark, Inc. and built by Irish Construction of Howell, Mich., the plant won a PISCES Award (Performance and Innovation in the State Revolving Fund Creating Environmental Success) from the U.S. EPA.
HESCO supplied its patented Integrated Biomass to Energy System (IBES) process using Infilco Degremont’s Two-Phase Anaerobic Digestion (2PAD) to enhance the anaerobic digestion process and produce Class A biosolids.
HESCO’s combined heat and power system is designed to offset the energy requirements needed to process the solids to a Class A waste. The company says it can produce pelletized and granular dried solids with no further energy input other than that produced from the digestion process. It can also integrate sludge gasification technology with its IBES system.
State assistance made the project more affordable. The Michigan Department of Environmental Quality provided a $500,000 grant and a $9.85 million loan at 1.65 percent interest.
Diorka adds that the project was managed with the environment in mind. All plant drawings were submitted and viewed electronically through a shared Internet site, and pay requests were paperless. Surveillance cameras allowed project engineers to monitor progress from their office instead of having to drive to the site.
Just a start
“We like to think that we’re kind of a pilot project,” says Bryant. Others have taken notice, including Michigan State University. “They’re interested in doing something similar on campus, and doing a study to see if our biosolids would be a suitable substitute in a coal-fired power plant,” Bryant says. The Lansing municipal utility is also interested in the idea of using the biomass as a fuel.
And that sheep idea is pretty intriguing, as well.