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Dehydrators & Digesters Turn Down The Volume

Most operators think long and hard about the costs that go into making meals—water for food prep, cooking and washing; electricity and gas for prep, cooking and cooling, and so forth. But how many of us think about the costs of handling the food that we don’t use, or that ends up as waste?

If you throw food waste in the garbage, you incur tipping fees on all that weight, plus you have the potential problems of trash odors and pests. At anywhere from $60 to $150 or more, plus weight charges, plus labor on the part of your staff, the cost of simply trashing food waste isn’t cheap.

To top it off, more and more municipalities are limiting the amount of food waste they’ll take in landfills, if not banning it outright due to the formation of methane, a greenhouse gas far worse than CO2 unless collected and reused. Estimates in California, for example, are that about 15% of commercially disposed waste is food, adding up to more than 6 billion lb. a year. You read that right. That’s only a fraction of the food that’s wasted, and only a small portion of that amount is diverted from landfills.

The landscape is rapidly changing. Massachusetts, for example, mandated organic waste recycling a few years ago. And as of April 1, 2015, any business in California generating more than eight cubic yards of organic waste per week must recycle it. That number goes down to four cubic yards on Jan. 1 next year and to two in 2020.

It’s clear that these trends will affect almost all operators eventually, not just volume feeders producing a lot of organic waste. The question is no longer whether you’ll have to change how you handle food waste, but when.

Some cities now have composting and/or waste-to-energy programs that convert organic matter such as food waste into compost and mulch for agricultural users, or siphon off methane gas to power turbines and generate electricity. And a number of large institutions, such as universities and hospital complexes, as well as hotels and convention centers, are able to do the same thing due to their size and location. Also more manufacturers are gearing up smaller equipment that will make it easier and more economical to implement this kind of waste-to-energy stream in smaller venues.

But where restrictions have been put in place on the type of waste that can go into landfills, or on water use and sewer effluent, more operators—even smaller ones—are turning to alternatives.

Picking Your Option
The object of any food-waste handling system is to reduce the volume of the food waste you generate. From there, you have a couple of options of how to dispose of or divert the food waste. Your three main options are pulpers, dehydrators and digesters. Like any other piece of equipment, which you choose depends on a number of factors.

First off, check your local regulations regarding food waste disposal, water usage and sewage disposal. If waste haulers offer organic waste recycling you have more options. But remember that in places like Massachusetts and California where recycling is being mandated, waste haulers know they can charge more. And typically, local governments can tack on fees to cover the cost of implementation and enforcement. All of which means your goal should be sending as little volume to recyclers as possible.

The simplest way to reduce the volume of your food waste is to grind it and press as much water out of it as possible mechanically. Pulping systems with dewatering presses reduce food volume up to 85%. While the remaining waste can be thrown away, pulping is an excellent option if organic waste recycling is offered in your area. Your disposal costs will decline significantly, since your waste hauler collects only 15% of the volume you formerly produced. And the resulting food waste ends up being used as a feedstock for a generating system that turns organic waste into compost.

Pulpers can run from about $35,000 up to $150,000 or more, but a couple of manufacturers now produce food grinding and dewatering systems on a smaller scale. These systems consist of a large disposer coupled with an undercounter dewatering press, making them suitable for even mid-size restaurants.

The Two Ds
The other two options available—dehydrators and digesters—have been around more than a decade now. The list of suppliers has grown (though some have changed hands and some companies license to others), and the units themselves have improved in terms of performance and ease of use.

Dehydrators, as the name implies, remove the moisture from food waste through evaporation. The units typically have paddles or agitators that continuously stir the waste (macerating it to some degree at the same time), and a heater raises the temperature inside to 180°F. Dehydrators reduce food weight and volume by up to 90%. The resulting end product (the consistency of coffee grounds), is sterilized and might be used as a feedstock for composting or as a soil amendment. But take note: no dehydrator produces an end product that can go directly onto your landscaping or be used as compost. The end product from a dehydrator needs to go through a second processing step to render it usable in a sustainable application. The dehydrated product could also have high levels of salt or acidity; either way, it will need further processing. Dehydrator literature does not always make this clear.

Food waste processed in a dehydrator also is odorless, as long as it’s kept dry, so it can be stored until a hauler picks it up. (Obviously, if it gets wet, the decomposition process starts immediately, and it will grow in volume and start to smell.) The only other by-product of the process is the water that’s evaporated from the food. It’s condensed in the dehydrator’s sealed environment and can go down the drain or be used as grey water in the dishroom or on landscaping. A 250-lb. load of food waste basically ends up as 25 lb. of dry waste and 25 gal. of water.

Dehydrators are batch processors. Once filled and turned on, they require 12-18 hours to fully dry a batch of food waste. Since you can’t interrupt a batch in process, you need to judge capacity accurately, so you don’t have food waste sitting around waiting to be loaded into the unit. On the other hand, dehydrators are mobile, and it’s easy enough to get two and roll one into an out-of-the-way corner for processing when it’s full and keep the empty one accessible.

Digesters, or biodigesters as they’re often called, accelerate decomposition of food waste using enzymes, special microbes or micronutrients that aid bacteria in breaking food down. Unlike dehydrators, units from different manufacturers tend to be more unalike than alike. Some have grinders that break food up as it goes into the digester, so they can handle shells, bones and fruit pits. All have agitators to stir the contents and help speed decomposition, but those without grinders won’t take bones, shells or pits. Most, though not all, use water, so the units must be plumbed. Some require warm water for the process, and have heaters built in, while others only need cold water.

Biodigesters process food waste continuously so employees can keep adding scraps or food waste throughout the day. A unit’s capacity is rated at how much food it can process in 24 hours (unlike dehydrators, which may dry a particular batch of food in half that time). The liquefied matter that’s left, after the digesting media has done its work, passes through a filter and can be put down a drain into the sewer system in most locales.

At least one manufacturer still makes a “dry” biodigester. Essentially, a combination dehydrator and digester, the unit uses microorganisms to accelerate food decomposition, and heats food waste to about 285°F using a patented microwave technology. It reduces volume by 85%-90% and offers the convenience of continuous feed like a digester and the volume reduction of a dehydrator, while using no additional water. It requires no drain and the end product is finished compost.

What water boards are most concerned about in the effluent that biodigesters produce are biochemical oxygen demand (BOD), fats, oils and grease (FOG) and total suspended solids (TSS). The acidity of the effluent, if too high, can be an issue for pipes, too. Depending on the organic matter you put in the units, your local water utility might turn down effluent from a digester. What water utilities worry about are potential dead spots in waterways caused by BOD; the possibility of continued enzymatic action in their sewage plants (if your digester uses enzymes); and sewer pipes clogging from effluent that emulsifies when enzymes stop working or due to FOG. You may be able to get around objections by diluting the effluent with additional water or changing the mix of waste you put in the digester.

Size Your System
The good news is that many manufacturers make models of these units in sizes as small as 110-220 lb. in capacity, so the technology isn’t beyond the realm of a medium-sized or even small restaurant. As mentioned earlier, even grinding/dewatering systems have shrunk in size, so you don’t have to be a huge institutional operator to use what amounts to a small pulper. Of course, these other technologies come in jumbo models, too, capable of processing up to about 3,000 lb. of food per day.

The bad news is that none of these systems come cheap. A small grinding/dewatering system will set you back about $14,000 compared to $60,000 or more for a pulper. And the smallest dehydrators run about $20,000, with mega-models costing close to $400,000. Biodigesters tend to run somewhat less, with the smallest models starting at about $16,000, and larger models (up to 2,000 lb./day) costing about $45,000. Customization can send costs up to as much as $150,000.

Since most makers have models in a range of sizes, you should be able to find one that matches the amount of organic waste your operation produces in a day. But remember, batch-feed systems like dehydrators may be tied up for as long as 24 hours. You may need to purchase two or plan on how to store waste until a dehydrator is free.

Obviously, with continuous-feed systems, such as pulpers or digesters, you can simply size the unit based on the daily waste you generate. Continuous-feed systems also give you the benefit of locating either the digester or dewatering unit and receptacle remotely. (At least one dehydrator maker also lets you feed the machine from a remote grinder, but once it’s full, you have to run the cycle.)

Manufacturers have made these systems nearly foolproof. You simply load, close the lid and press a start button. All have interlocks that prevent the unit from running when the cover’s open. Most have logic boards that monitor what’s going on inside the tank and adjust the machine’s actions accordingly. All are easy to clean, usually consisting of rinsing a filter screen daily and wiping down the stainless exterior.

Add It Up
While the capital cost of these systems may shock operators used to paying nothing for trash receptacles except tipping fees, most manufacturers say in the right operations their systems have a payback of about two years. And here’s where you have to sharpen your pencil.

You’ll find ROI calculators on a lot of manufacturers’ websites to help you do the math. Weigh the costs of what you pay for trash collection and employee labor to haul trash and food waste out to the dock against what you’ll spend on electricity for a dehydrator, and electricity, water and sewer for either a pulper or a digester.

Dehydrators typically use about 3-4kW of electricity for smaller models. (Large models that process 2,400 lb. and up are rated at 27kW and up, and use about 16kW/hr.) At around 10 or 11 cents per kW, a typical cycle for a 250-lb. load will cost around $6-$7 with no additional water cost.

Depending on the make and type, digesters will use anywhere from one gal. of water for every four lb. of food waste to one gal. per lb. of waste. One maker estimates its smallest unit (120 lb./day) uses 1.1 gal. of water per hour and its largest (2,000 lb./day) uses 15.8 gal. per hour. If you’re looking at a digester that requires warm water, tack on the cost to heat the water. And you’ll need to factor in the annual cost of microbes or enzymes that must be replenished from time to time.

Remember that a dehydrator won’t eliminate trash pickups; it will simply reduce food waste to about 10% of its volume and weight. However, if your waste hauler has a composting program, pick-up may be free or a reduced price. In some locations, you may be able to sell the product from the dehydrator as a soil or compost amendment or animal feed component.

The last thing you’ll want to factor into your calculations is the value to your business of being more sustainable and/or qualifying for LEED points. When California went through the math before passing the bill that took effect April 1, economists estimated that keeping all the state’s food waste out of landfills would save the equivalent greenhouse gases of three million cars. That’s not a bad payback.

Full Circle
When Carroll University, Waukesha, Wis., was in the market for a new dishmachine recently, it got far more than it bargained for.

“Not only was our 30-year-old machine at the end of its life,” says Matt Sirinek, Senior Director of Auxiliary Services, “it was inefficient and costing us money.” The old machine was servicing the campus’s main dining room, which serves about 1,800 meals a day.

Both the school’s and dining contractor Chartwells’ interest in saving energy and water go beyond just money, however. Sirinek and Scott Henning, Director of Dining Services, had already implemented trayless dining to save water and energy. Now, they looked for a dishmachine that would help the operation be more sustainable, too.

After researching options, they installed a Trisys system from Champion. In addition to a flight-type machine, the scrapping station feeds food waste to a relatively quiet, slow-speed grinder. The slurry then pumps to a storeroom below the dishroom where a centrifuge spins excess water out of the waste. What’s left falls directly into a dehydrator that dries the remaining waste, reducing it in volume and weight by about 90%.

“The grounds crew picks up the dried waste every day and mixes it with compost. After it’s processed into compost, it can be used on the campus,” Henning says. “To be part of an operation where we take food full circle is a rewarding experience.”

“Not only are we reducing a tremendous amount of waste, and the cost to remove it,” Sirinek adds, “but we expect to save about $10,000 a year on energy costs.”

What started as a hunt for a dishmachine ended up as a solution to the university’s sustainability challenge.

The fully-automated BioGreen360 organic food waste digester operates using a continuous-feed loading system and processes 1,500 lb. of food waste in 24 hr. The machine accelerates the decomposition process using long-lasting, proprietary microorganisms. A microbial process liquefies food waste then fast-acting patented microwave technology rapidly heats and evaporates the liquid. The end product is an immediately compostable organic matter that is 10% its original weight and 100% sterile. The system doesn’t require water intake and doesn’t discharge water; there’s no need for drain access. Operating the unit requires an electrical hook up and venting. Measuring about 56-in.W x 543/4-in.D x 791/2-in.H, the system is clean, quiet and self-contained.

The BioHiTech Eco-Safe Digester comes in three models, available to digest 400-2,500 lb. of virtually any kind of food waste—vegetables, fruits, meat, fish, poultry, grains, coffee grounds, egg shells and dairy products—within 24 hr. You can continuously add food waste throughout the day. The system uses a proprietary blend of microorganisms while agitation and water help digest the food waste into a grey-water effluent that drains into the conventional sewer system. The digester also weighs each increment of waste during the digestion process, providing data for waste-stream analysis. The Eco-Safe 4, the smallest unit, measures 453/4-in.W x 351/2-in.D x 50-in.H while the larger Eco-Safe 12 tallies 69¼-in.W x 44¼-in.D x 55 ¼-in.H.

Champion’s Phoenix Dehydrator processes organics, including produce, cut flowers, meat, fat trimmings, fish, paper napkins, coffee grounds, spoiled milk and deli products, as well as some soft plastics, reducing waste by up to 90%. The dried remnants are produced as a sterile biomass. The company’s proprietary technology features accelerated dehydration for a shorter processing time; the dehydrator can process up to 2 batches of food waste a day. (A moisture sensor illuminates LED lights to let you know when the cycle is finished.) Models are available in a range of capacities from 125-2,400 lb. The larger model PHX-1400AL measures 93-in.W x 63-in.D x 91-in.H and processes 1,400 lb. in 18-23 hr. The Phoenix dehydrator can stand alone or be part of Champion’s Trisys waste-management system.

Each unit is constructed of 304 stainless and the decomposition chamber uses heat and mechanical agitation to break down waste. The system is capable of reducing compostable waste weight and volume by 83%-93% depending on the waste input. Units come in sizes to process from 66-6,600 lb. per cycle. The chamber has an oil jacket with substantial insulation and well-sealed inlet and outlet doors to minimize energy consumption. The system is equipped with an odor management device to control odors associated with decomposition. The utility requirements are an electrical source and a condensate line; no venting or fresh water connections are required. The decomposing chamber is capable of producing 180°F during the processing to ensure that the end product is essentially odor free.

EnviroPure’s EPW Systems are self-contained, continual-feed organic-food-waste elimination systems that convert food waste into water. The technology uses a combination of mechanical processing, heat, oxygen and all-natural additives (EPW-BioMix) to accelerate the natural aerobic decomposition process. Organic waste quickly reduces to a grey-water effluent that can be safely disposed of into existing sewer systems. The EPW Systems handle virtually any kind of food waste, from vegetables and fruits to dairy products and bones. Depending on the model, the GTSeries processes 240-3,000 lb. (750-9,000 meals) per day and consumes between 2-19 gal. of water per hr. The smallest unit measures 48-in.W x 78-in.D x 80-in.H while the largest unit is 100-in.W x 130-in.D x 110-in.H.

Hungry Giant systems heat and kill all bacteria and pathogens reducing food waste weight and volume by up to 93% without using water. Hungry Giant Australian engineers have developed a proprietary turbo-charged condensing/cooling system that will dehydrate food waste 20%-25% faster than its competitors saving significant energy costs over the 10-plus-year life span, according to the company. This liquid coolant system pulls water out of the food waste in the form of steam and then converts that steam into sterile condensate much faster than air-cooled-only dehydrators. The company offers 7 models that process from 220-2,400 lb./day. Larger units include hydraulic garbage tote lifter. Prices list from $25,900 to $150,000.

Managed by InSinkErator, Grind2Energy food waste recycling systems comprise a three-step process—grind, transport and transform—to turn waste into renewable energy. First, the system grinds food waste into a slurry. High-density shredding elements grind as fast as you can feed it; dry-grind technology minimizes the amount of water used. A sealed, enclosed tank at your facility stores the slurry. Once fluid levels in the tank reach a certain point, a sensor notifies a transportation team, who hauls the material in a truck to a local anaerobic digestion facility. Here, captured emitted gases (methane) convert into electricity or natural gas and the remaining bio-solids become fertilizer. Grind2Energy makes sense for facilities that produce at least 1 ton of food waste per week. The system requires a 3-phase power supply, water hookup and a tank-holding area.

LFC models process anywhere from 110-4,000 lb. of food waste in 24 hr. Water injects into the machine to maintain equilibrium for the microorganisms, to rapidly decompose the food waste and to then flush the resulting grey water safely into the sewer system. The machine’s rotating arm slowly churns waste to enhance the decomposing function; a proprietary mixture of microbes and enzymes accelerates the digestion. The continuous process enables you to add food at any time; the machine doesn’t need to be emptied. The LFC securely sends data through an Ethernet port to a cloud server maintained by Power Knot. Studying data (waste amounts, door openings, etc.) helps you better manage your facility’s waste. Machines range in size from 34-in.W x 27-in.D x 40-in.H to 102-in.W x 56-in.D x 69-in.H.

The Somat DH-100 dehydrator handles food waste and compostable disposables for medium- to large-scale facilities. The machine processes 110-220 lb. in 12-18 hr. through a multistage indirect heat and dry dehydration processes; no enzymes or additives required. An added bonus: dryness-sensing technology ensures proper processing time regardless of the batch size. Easy to install and maintain, the standalone machine doesn’t require a fresh water connection. Paddles macerate the food waste heated by the unit’s decomposing chamber to kill any bacteria and reduce matter by 83%-93%. A new cold weather package allows the dehydration process to occur at temperatures down to 15°F. The DH-100 footprint measures 45-in.W x 371/2-in.D x 441/2-in.H.

The ORCA organic food processing system offers a sustainable food waste disposal solution that allows customers to dispose of organics at the source. The ORCA uses an aerobic digestion process that converts food waste into an effluent safe for discharge into the municipal wastewater system where high-value renewable fuels and natural fertilizers can be economically produced and recovered. The unit accelerates the breakdown of food waste through a combination of proprietary microorganism solution and Bio Chips, oxygen and water. The ORCA can divert up to 600, 1,200 or 2,400 lb. per day, depending on food waste composition and model size. Model dimensions range between 48-in.W x 34-in.D x 49-in.H and 115-in.W x 34-in.D x 49-in.H. The ORCA is service based with no capital outlay.

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