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FER FOCUS: New Tools For Tackling Food Waste

If you could wave a magic wand and get rid of your organic waste, no doubt you’d brandish it fiercely. At anywhere from about $60 to more than $150 per dumpster pickup—plus any weight charges—it’s expensive. It requires labor. It’s a health and safety issue.

A growing number of jurisdictions are starting to restrict or ban some of the usual handling techniques. Some municipalities are edgy about how you use disposers and standalone pulpers, and some jurisdictions are moving toward restricting or banning food waste going to landfills. The trend is especially strong in the Northeast, such as in Connecticut and Vermont; effective July 1, Massachusetts is banning any entity that produces more than a ton per week of organic waste from sending it to the landfill. The affected group includes supermarkets, healthcare, colleges/universities, large schools, businesses, large restaurants, etc. California is studying similar limitations. New York City is imposing restrictions. The trend is pretty clear. 

So for many of you, the question isn’t whether you’re going to change how you handle organic waste—it’s how and when. 

Two Main Types, Several Suppliers 

Composting long has been—and continues to be—an option in many areas. It reduces waste going to landfills, but it’s still a hauling issue for all but the largest institutions; additionally, composting facilities aren’t available everywhere. Several technologies that reduce waste at the source have emerged over the past few years, and two in particular are gaining in the foodservice sector: food-waste dehydrators and “wet” biodigesters. 

These two categories are only about five years old in North America, and the list of suppliers still is in flux with various names coming and going. Many are from Asia, South Korea in particular. Some are made here in the U.S. as well as Australia. As we gathered information for this article, the current lineup for dehydrators included a well-known name in foodservice, Somat, plus other brands that are lesser known in foodservice circles, such as GaiaRecycle and Hungry Giant. EcoVim USA, which has a fair number of units in the field, appears only to have an active distributor for parts and maintenance support.

On the wet biodigester side, suppliers include Enviro-Pure Systems, owned by T&S Brass, as well as BioHitech America, Green Key Environmental Solutions, Totally Green/ORCA and Power Knot. 

Dehydrators, as their name indicates, remove water content from food waste. Dehydration uses heat and churning to remove about 80-90% of weight and volume, leaving a dry, sterile, odorless biomass that is “suitable for use as compost feedstock, and—after testing—in some instances may be used directly as a soil amendment,” according to a study by Northeastern University for the Massachusetts Department of Environmental Protection.*

Wet biodigesters accelerate natural decomposition. Some introduce microbes and/or enzymes to speed up the breakdown; others don’t use additives but instead use micronutrients to accelerate the action of bacteria that occur naturally in food waste. Both types add incoming water to accelerate the process. As the food disintegrates and liquefies, it passes through filters or screens into the sewer system. Generally, nothing is left to haul away. 

Each category has its pros and cons; as you go forward, you’ll be doing the usual economic math plus weighing environmental and regulatory priorities from area to area.

Systems For Your Size 

Before you start sorting through your options, you need to decide if any of them will make economic sense for you. Capital costs run all over the board, partly because these systems can be customized considerably and come in a number of capacities. Ballpark costs are $22,000-$50,000 and higher. A wet biodigester will have a lower capital cost than a dehydrator.

Like most technologies, larger applications are more cost effective at first, then smaller versions come into play. Most end users of either system type have been larger operations—supermarkets, casinos, hotels, colleges/universities, hospitals/healthcare facilities, etc.—and their systems can process as much as 2,000 lb./day or more. But smaller models are suitable for midsize, fairly busy restaurants. These units come in capacities as low as 110-220 lb. per batch; typical cycle times for a full 220-lb. batch are 12-18 hours for standard content. If your waste tends to be wetter or drier, your cycle times will be higher or lower, respectively. 

You’d have to run the numbers, but if payback is a deciding factor, midsize restaurants and larger operations generally can find a system with a payback of 24 months, maybe less.

Dehydrators & Electricity 

So if you’re in the market, how do you sort your options? First, consider the operating differences between dehydrators and biodigesters. There are more than a few.

First, dehydrators. You load your food waste—pulped, shredded or ground is recommended to speed the dehydration process—into the unit and close the door. It’s pretty straightforward. Dehydrators do not require incoming water. They use a heater, blower and paddle-agitating system to stir the food waste and evaporate the moisture. Typically they heat to about 180°F, and cycle times generally run 12-18 hours as mentioned previously, although those times can vary depending on content. Also, some models are faster than others, so this is a detail you’ll want to check. Every menu and operation will be a little different. 

At the end of a cycle, evaporated moisture has condensed and gone down the drain. What remains is about 10-15% of the original volume and weight, a product the consistency of sawdust or coffee grounds that you can toss in the dumpster, divert for composting and/or use as a soil amendment.

Incremental water costs are zero. The system does not use incoming water, and unless your sewer load is metered, the water dehydrated from the food waste is a non-issue. (Plus, the water is potable, so the sanitation system does not experience any additional load.) 

The energy needed for this size and type of system is 3-4kW, depending on the model. For estimating purposes, a cycle time of 18-24 hours and an average rate of 10-11 cents per kW works out to about $6-$7 for a 200-250-lb. batch. Compare that with what 200-250 lb. would have cost you if it went straight into your dumpster for hauling. With a dehydrator, you still have to pay to get rid of the remaining biomass, but it’s a tenth of the volume and weight.

As for operational considerations, the only issue that might come up is overcrowding. Once a dehydrator cycle begins, you really need to allow it to finish. So if you have new waste coming in, you’ll need to be able to store it somewhere until the next batch cycle begins. 

Biodigesters & Supplies 

Wet biodigesters have a different checklist. First, they’re not batch systems. They run when they are on, and the process is continual. You can open the door and add new food waste as it arrives. When the waste is fully processed, there’s nothing—or nearly nothing—left to haul or divert.

Where dehydrators use electricity, biodigesters use water. Water consumption varies from model to model, but the Northeastern University study says you can figure: “1 gal. of fresh water is pumped in for every 4 lb. of food added to the system at the low end [of the consumption scale], with approximately 2 gal. of effluent discharged. On the higher end of the scale, about 1 gal. is pumped in for every 1 lb. of food waste.” You’ll want to figure in the cost of the additional water consumption as well as the sewer charges, which often tend to be two to four times the water charge, depending on your locale. If you choose a system that requires heated water, include heating energy in your calculations.

With biodigesters, the consumable substances come into play as well. If you use an environmentally simpler (nonenzyme) system like EnviroPure’s, you’ll need to replenish the nutrient/medium material from time to time. 

If you use an enzyme system, you’ll need to replenish the enzymes periodically.

Downstream 

All of this information gives rise to a couple of environmental questions. These technologies are so new in the U.S. that good, solid environmental information is hard to come by. There are so few systems in the field that most water utilities really have not looked into them yet, as Bio-Cycle magazine notes in its October 2013 issue. But some water authorities are wary about enzyme systems.

The BioCycle article, “Analysis of Biodigesters And Dehydrators To Manage Organics On-Site,” reports: “Specifically, the authorities responsible for a city or town’s sewer system want to prevent wastewater with excessive levels of biochemical oxygen demand (BOD). When BOD is too high … the microorganisms that decompose the pollution use too much of the oxygen, depriving other aquatic life.”

The article notes another concern about enzyme systems, saying one wastewater enforcement officer expressed concern that they may only “break down the waste temporarily, with much of the FOG congealing again downstream.” 

To date, we don’t know of any test data confirming these concerns, and they may not be founded. But the water industry is beginning to study such issues, which means regulations on enzyme systems may be in flux. Make sure you have the latest information before you buy.

*On-Site Systems for Processing Food Waste, A Report to the Massachusetts Department of Environmental Protection, Isaac Griffith-Onnen, Zak Patten and Jennifer Wong, Northeastern University, 4/26/2013.

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