SINCE their commercialization in the 1930s, food waste disposers (FWD) have been in and out of favor with wastewater treatment system operators. Due to high concentrations of solids, fat and grease that a FWD may discharge into the sewer system, their use has been banned in some countries, such as Austria and the Netherlands, as well as in some U.S. cities.
A different version of the FWD is the pulper, which has been in use for the last 30 years. Considering that most pulpers separate significant portions of the solids from the liquid prior to discharging down the drain, many municipal wastewater treatment systems allow their use since that decreases the BOD (biological oxygen demand) loading on the plant. The business or institution using the pulper may justify the higher cost than disposers through reductions in the weight of waste for disposal. Another advantage of a pulper is that the pulp itself can be recycled at composting facilities. Harvard University’s cafeterias in Boston, the University of New Hampshire’s cafeterias in Durham, as well as the U.S. House of Representative’s cafeteria in Washington, DC, employ pulpers to convert food waste into a material that is then taken to composting facilities. Still, the cost of collecting and trucking the pulp remains.
More recently, however, FWDs are being promoted for their reduced carbon footprint when it comes to food scraps diversion, especially when compared to collection and transport to composting facilities, anaerobic digesters or landfills. Some companies promoting FWD for residential and commercial kitchens suggest that directing the organics via the municipal sewers to the local wastewater treatment plant is a sustainable approach to organics diversion, as the biosolids from the WWTP can be recycled.
New Generation of Equipment
In the last few years, a new generation of FWD technologies has come on the market, attracting interest from supermarkets and restaurants that want to implement green, sustainable practices for their waste, and save on disposal costs. With goals to eliminate hauling of solids, minimize impact on municipal sewer plants and reduce consumption of both electricity and water, one type of FWD has added a decomposition step to convert solids to liquid prior to sending it down the drain.
The Bio-X machine is an organic waste decomposition system developed in Korea by BioHiTech International. Food waste is loaded into the unit where it is mixed with proprietary wood chips and microorganisms; heat and moisture are added to attain temperatures of about 105°F. An auger mixes the material continuously until it becomes a slurry that is biologically and mechanically degraded to the point that the solids drain through a pinhole strainer and into the municipal sewer or septic system. A scale tracks the weight of material, and indicator lights tell the operator when the maximum amount has been added, and when new material can be put in. Three sizes are available to process 400, 800 and 1,200 pounds in a 24-hour period. All three units use 17 kW per 24 hours, 75 to 125 gallons/day of water, and discharge 200 to 400 gallons/day, depending on unit capacity.
The Bio-X technology has gotten the attention of a number of restaurants and supermarket chains, including the Golub Corporation’s Price Chopper supermarkets. Based in Schenectady, New York, Price Chopper has had units in operation in Burlington, Vermont and Marlborough, Massachusetts. Linda Moffett, Senior Purchasing Agent for Golub Corporation, describes the company’s conventional composting experience as problematic.
“Price Chopper has always been proactive in recycling and environmental management, and we currently recycle OCC, paper, plastic bags and shrink wrap,” notes Moffett. “As for organic materials, we were the first grocery chain to contract for composting at the now closed composting facility in Menands, New York. We also had supermarkets going to composting in Burlington and Rutland, Vermont, Hudson and Poughkeepsie, New York, as well as Great Barrington, Massachusetts. Unfortunately, many compost companies have dissolved.” She continues that odors were a problem at stores where collection was once a week or less, and that unsecure dumpsters were occasionally contaminated by unauthorized dumping. “We still have a store near Syracuse that goes to composting, but our plan is to start converting stores to the Bio-X system.”
According to Moffett, 10 to 15 Price Chopper stores will have Bio-X machines installed in the coming year, and probably more stores each year thereafter. “There will be a significant dollar savings for each store, and the return on investment is estimated to be approximately two years depending on the particular situation,” she says. “This return on investment is based primarily on avoided hauling and disposal tip fees.”
The City of Marlborough has its own municipal wastewater treatment plants, and Moffett says that the company wanted to make sure Price Chopper had all approvals before installing a unit. They met with Roland Gould, Pretreatment Coordinator for the City Department of Public Works to explain the Bio-X. “I looked at the literature, and it’s supposedly better than a grease trap, and it breaks down grease, so I said if it works it would be great,” recalls Gould. “Although I generally advise businesses to not use enzymes to break down grease in a grease trap because I don’t believe there is sufficient detention time for enzymes to work, this system holds the material and apparently breaks down grease.” Gould adds that Marlborough does not require permits for garbage disposals so the unit is exempt anyway.
Distributors of Bio-X, such as Pat Griffin with Fore Green Solutions, have encountered some skepticism on the part of wastewater operators, and therefore retained Boston Environmental & Engineering Associates (BEEA) to assess the effluent from a Bio-X machine. BEEA found that, based on one test of effluent from the unit at the Marlborough store, total solids were 14,700 mg/L, or 1.5 percent, and oil and grease were 33 mg/L. The pH was 4.3, which may have been caused by citrus that was passed through the machine. Tests conducted at a different supermarket chain store showed a total suspended solids concentration of 9,290 mg/L (0.93%), pH of 3.7, 983 mg/L of oil/grease, and BOD at 21,000 mg/L. Griffin says these results do not necessarily reflect “steady state” operations since the machine was in start-up and some modifications were being made. Herschel Clopper of BEEA has recommended that the effluent be resampled after the machine modifications have been made, particularly an adjustment to the water flow rate so that the pH can be raised to 5.0 or above.
Mark Allain, President of the Massachusetts Pre-Treatment Forum, has invited Griffin to make a presentation to his organization in order to educate its members since this type of technology appears to be gaining a foothold in supermarket and restaurants in Massachusetts. Allain is one of the skeptics. “We don’t need extra solids, nutrients, enzymes, or microbes in our wastewater treatment plants,” he says. “It increases the strength of the wastewater since you will still get solid materials, and the waste has value as compost.”
Griffin says that the cost for a machine ranges from $35,000 (400 lbs) to $45,000 (1,200 lbs), plus the site preparation costs to connect to 3-phase power, a hot/cold water feed and a floor drain to the sewer. Studies at a number of stores are showing a payback of 2 to 4 years, with a 10 plus year life expectancy of each machine. For a typical Massachusetts supermarket where tipping fees are about $85/ton, they are projecting annual savings between $20,000 and $25,000 through reduced trash hauling costs. His company also requires a maintenance contract at a cost of $2,400 per year per machine, which includes quarterly recharge of microbes, maintenance by authorized service agents, and annual replacement of proprietary wood chips.
The Somat Company has been selling pulping and dewatering equipment to the food service industry for many years. More recently, it began marketing the eCorrect Waste Reducer, which dehydrates food waste “to produce a humus-rich soil amendment in less than 24 hours, without the use of enzymes, fresh water or venting, and with no other by-products, resulting in zero sewer and landfill impact,” according to the product literature. It adds that the process heats the waste to 180°F in a “decomposing chamber that uses condensate run-off to control humidity in the chamber. The system also recycles the heat energy. The end product is considered a soil amendment suitable for use in landscaping. The system is capable of reducing compostable waste weight and volume by 80 to 90 percent.”
The only discharge into the sewer is from a condensate drain, similar to the one on a home air conditioning unit, says Lin Sensenig, General Manager of Stero and Somat Companies, divisions of ITW Food Equipment Group. The eCorrect is made in Korea as well. Sensenig says that he was skeptical at first when he heard about the machine, but Somat’s investigations convinced them it had a significant potential role as a product line. “There have been 400 installations in Asia over the last 10 years, and Somat is now the sole distributor in North and South America,” Sensenig notes. “We have a couple installations in California, and a unit on the east coast at Marriott’s world headquarters.”
One installation is at the Marriott South Bay hotel in Torrance, California, which has been testing the eCorrect Model ET-100w that processes up to 220 pounds/day of organic materials. “We have had the unit running for two months and so far it is working great,” reports Silvano Merlo, Assistant General Manager of the 487-room hotel. “We are showing it to other companies who want to see one operating. The system is reducing our waste, and will save us money.” He adds that it is too soon to report on the payback period but they are tracking costs.
The biggest challenge so far has been training employees, and reminding them to use the separate bins for organic waste. “We put in all food waste except big bones which will not break down and then show up in the end product,” says Merlo. “We take out the material every day and our groundskeeper puts it in the hotel flower beds.” According to Sensenig, metal utensils will go through the system and come out in the compost product, but can then be removed. “We have found that compostable utensils do not compost in it, but come out as small pieces, but they should eventually break down in the soil product.”
Regarding compatibility of certified biodegradable utensils with this new line of food waste processors, Steven Mojo, Executive Director of the Biodegradable Products Institute (BPI) says it is important to look at the components of each technology. “If there is a screen system up front, then the biodegradable materials will be pulled out prior to composting, or if parameters for composting are not sustained in the unit, the utensils will not be able to break down in the time they are in the machine,” he notes. “BPI has not evaluated any of these systems but is interested in learning how certified materials are processed in them.”
According to Sensenig, the soil product is “peat-moss like, and can be mixed 1:1 with soil for use on the site where it is produced.” He adds that it does not have any viable seeds due to the heating and drying process. Will Brinton, at Woods End Laboratories, who has done studies with the product from food pulpers, cautions that, “based on my experience with food waste pulp, once the dehydrated compost gets wet it may bloom with fungus, which can be a concern for some uses of the material.”
Somat is finding great interest in the system from schools. The company highlights the unit’s low energy usage – about 48 kW/hr per cycle of 12 to 16 hours to process 250 pounds of waste. At electrical rates of 12 cents per kWh, Sensenig says that is about $158/month to process 3 to 4 tons, or $40/ton. “If you look at the alternative costs of tipping fees at $75 to $80/ton, plus transportation, this is a more cost-effective approach,” he explains. “Also, no permits are required by the local government since there is no discharge to the sewer system.” Customers already using a pulper can add an eCorrect to process the pulp on a continuous basis rather than as a batch process, greatly increasing the processing capacity of the machine.
A similar product on the market is the Liquid Waste Extractor (LWE), which is distributed in North America by Sustainable Innovations LLC of Boise, Idaho. Over the past four years, the machine has been installed at 90 Albertsons supermarkets across the country. “Now that Albertsons has concluded their contract with the European manufacturer of the Liquid Waste Extractor, we are free to further tell the story of how it facilitates diversion of organics from landfill to composting operations,” reports John Bernardo of Sustainable Innovations.
Bernardo explains that the LWE is similar to a pulper, but “more compact, more enclosed, less messy and self-cleaning.” After shredding the waste to reduce particle size and increase surface area, “it uses hot water to dissolve fats and keep them from coagulating,” he says. “A press then removes liquid, which is discharged to the sewer, and the machine discharges a compostable product into a plastic bag-lined container so it can be collected and taken to composting sites. The product looks just like salsa and has a 20 percent moisture content.”
He adds that the Albertsons store in Boise has had a unit for four years, and a worm farmer picks up the material at no charge. “For composters, it’s a better product than straight food waste or pulp since it is much drier, which saves on hauling costs,” he points out.
Bernardo says he has presented the machine to the Northwest organization of wastewater pretreatment officials, and many have approved the unit since it diverts solids from the sewer system. “The City of Boise does not allow garbage disposals, but approved the LWE after reviewing effluent data on COD, BOD, TSS directly from the extractor, as well as where the supermarket sewer line entered the City collection system,” he reports, adding that the return on investment for a Liquid Waste Extractor is about two years where it can divert 50 percent of the trash.
Pulp and Composting Considerations
POTENTIAL operational challenges for composters of pulp from food waste disposers include low pH, low total solids and high volatile fatty acids (VFA) due to the concentration of highly putrescible food waste, and the acidic content of many fruits. In research conducted for a food waste pulper manufacturing company, in which food pulper samples from across America were examined, Will Brinton of Woods End Laboratories (Mt. Vernon, Maine) found that the pulp typically had pH values in the 4 to 5 range, which is a concern for many types of composting recipes.
“If you mix food pulp with leaf and yard waste with a lower pH to start with, there may be an adverse impact on the biological process,” explains Brinton. “Since the pulp may also be loaded with VFAs, it can have high odor potential, so the promptness of handling the pulp, and the recipes used for composting it, are very important. Through careful operation of a pulper, by processing soiled cardboard and paper along with the food scraps, it was possible to produce an ideal pulp for composting, with a 30 percent solids content, and a C:N ratio of 25:1.”
Brinton points out that the low pH was still an issue, but advises that a good pulped mix that takes off rapidly in composting can swing from pH 5 to 8.5 in a matter of days, due to the very rapid breakdown of proteins. Currently, Brinton’s lab is focusing on the potential to recover the high energy content in food pulp via methanogenic processes, although pH control is “still a daunting issue,” he says.