The Milwaukee Metropolitan Sewerage District has been a pioneer in beneficial use of biosolids: For 85 years, its Milorganite organic fertilizer, made from waste activated sludge at the Jones Island Water Reclamation Facility, has been a staple for golf courses, landscapers and homeowners.
Now, the district is exploring new frontiers in generating and using digester methane at its South Shore Water Reclamation Facility. The South Shore plant processes its own sludges, and primary sludge sent by pipeline from Jones Island, in its anaerobic digesters. The gas fuels a 5-MW cogeneration system that provides much of the site’s electricity as well as heat for the digestion process and other needs.
The district is pursuing a variety of initiatives to add organic material to the digesters and so maximize gas production. One such effort is a “Food Is Fuel” public communication effort that encourages district residents to grind food waste in their garbage disposals and send it to the district instead of tossing it into the trash and having it hauled to landfills.
District public information manager Bill Graffin and director of water quality protection Pete Topczewski talked about the innovative programs in an interview with Treatment Plant Operator.
TPO:
How important is digester methane to energy management at the district?
Graffin:
Last year our anaerobic digesters at South Shore produced the equivalent of about $800,000 worth of energy, based on market prices. The year before that, when natural gas prices were a lot higher than they are now, we produced the equivalent of about $1.8 million.
We are now making some process changes that will significantly increase our production of methane and will allow us to use all of it. In years past, we had been flaring off up to 20 percent of the methane.
TPO:
How did these digester fuel initiatives get started?
Topczewski:
We are on the leading edge of efforts to increase methane production in digesters. Globally, anaerobic digestion is used a lot more than it is here in the United States.
For several years, we have been working in this area with Dr. Daniel Zitomer, an associate professor and director of the Water Quality Center at Marquette University.
He works on methane projects all over the world. He’s bringing some of his experience back home with him, and we’re putting it to work here in Milwaukee. One of the first initiatives was to take glycol used at General Mitchell International Airport for deicing planes and inject that into the digesters.
TPO:
How does that program work?
Topczewski:
The glycol program has been ongoing for about five years. After they deice the planes, they vacuum up the deicing fluid and put it into holding tanks. Later, they transport it to the South Shore plant.
The annual volume varies. The airport uses only as much as necessary, and that’s largely weather-dependent. We take everything they can give us, and it typically ranges from 250,000 to 300,000 gallons each winter. We see an increase of about 4.3 cubic feet of methane per pound of COD added to digesters from airline deicing fluid.
TPO:
What role does food waste play in methane production at the South Shore plant?
Graffin:
A few years ago we started a project in conjunction with InSinkErator that involved having two large natural food stores take all the scraps from their produce sections, grind it up and put it in a storage vessel to be trucked to our digesters.
Topczewski:
We found that it was feasible to do, but the design of the storage vessel was not correct. The program ended with the stores just chopping up the vegetable waste in a commercial garbage disposal and releasing it directly to the sewers.
The food stores happen to be in a section of the city that is served by our Jones Island treatment plant. So now those vegetable scraps are providing solids and nitrogen to help us make Milorganite fertilizer at Jones Island and keep the nitrogen level in the product above 5 percent.
TPO:
What was the impetus behind the larger food waste program directed toward consumers?
Graffin:
In the course of working with the food stores, we had discussions with people from InSinkErator and decided we should look at the bigger picture and educate district residents to send us their food scraps.
Food waste produces a tremendous amount of methane in landfills. The average family of four produces about 2,000 pounds of food scraps in a year. Our program gives people a good alternative to putting that material in the garbage. Composting is also a great alternative, of course, but not everybody wants to compost.
TPO:
What did you do initially to promote the food waste initiative?
Graffin:
In winter of 2008-2009, we worked with InSinkErator to put together some educational materials. We launched the “Food Is Fuel” program in spring 2009 by putting information up on our Web site and doing some media outreach. We did quite a bit with the media that spring.
We did a whole morning program with a local TV network affiliate down at South Shore. We also got some good radio play. We sent out a news advisory with a fruit basket to encourage them to talk about the program and call us if they had questions or wanted an interview.
We co-hosted one morning show on a popular station with a live broadcast for one of their workforce tour stops. It was a sponsored event where we could talk about anything related to MMSD and who we are. We touched on the “Food Is Fuel” campaign several times throughout the morning.
Meanwhile, InSinkErator developed some store tags about the program to hang near their garbage disposals in store displays and drive people to our Web site for more information.
TPO:
What is being done to sustain momentum for the program?
Graffin:
We kept the program placed prominently on the front page of our Web site. We kept promoting it hard for two or three months. Then we had some big rains hit in June, and that by necessity switched the focus of communications for a time.
Our educational outreach person plans to include “Food Is Fuel” information in school talks. We included program information in our basic brochure about the district, and that’s distributed at various public-speaking presentations and various events throughout the year.
We also include “Food is Fuel” in our “Sewer School” PowerPoint presentation that lays out who we are and what we do, and the facts and figures about the district. That presentation also includes various things our residents can do to help reduce the risk of sewer overflows, basement backups, flooding and polluted stormwater runoff.
We picked up “Food Is Fuel” promotion again this past spring. We began using Twitter late last year. In addition, we may create a video about it as time permits. Our videos do a tremendous amount of good for us in terms of getting the public’s attention. We put all the videos on our Web site via direct links to YouTube.
YouTube has a great platform for putting out videos and making it very easy for people to see them no matter what kind of viewing software they have. YouTube does the translation, and it comes out to be a very clear, clean, crisp presentation. That has been a fantastic communication tool.
TPO:
What results has the district seen so far in terms of methane production from “Food Is Fuel”?
Graffin:
As of now we can’t quantify the results. To see a major increase in gas production, we would need to have a very successful advertising, marketing and promotion campaign. This is a multi-year effort in getting people to think differently about what they do with their food scraps. It takes a long time to change people’s habits — to get them to understand why they should do this and why they should care.
TPO:
What other measures are being looked at to increase gas production from the digesters?
Topczewski:
We continue to work with Dr. Zitomer at Marquette. He is identifying waste high in BOD and COD that we could add to the digesters. Mostly, those include byproducts of the food-processing industry. Examples include syrup from soda bottling plants, byproducts of the brewing industry and wastes from plants that make soup bases.
Dr. Zitomer is pilot testing some of those, and this summer we plan to do some full-scale testing at South Shore. The aim is that instead of having businesses discharge these materials to the sewers, where they get diluted, we would take them in their concentrated form and put them directly into the digesters — co-digesting them with the sludges we produce at the treatment plant.
We’re also trying to find sources of high-strength waste that are not necessarily in our service area. We may be willing to take such material from the outside if people are willing to truck it to us.
TPO:
Do fats, oils and grease have a potential role in increasing methane production?
Topczewski:
Fat is good for that purpose. It has a lot of energy potential, but right now the mixing system in our digesters is not robust enough to enable us to accept grease. It turns into a blanket that smothers the microorganisms. We have a capital project going on to assess what it would take to redesign the mixing system in the digesters so that we could take the fats, oils and grease.
TPO:
All told, what impact might these initiatives have on the volume of methane produced at South Shore?
Topczewski:
We are very hopeful that we could easily see a 25 to 30 percent increase in gas production just with what Dr. Zitomer is exploring. If we can update our mixing system and start taking in some of the FOG, we could double our gas production.
