Methods to Handle Organic Waste: Compost and Kilowatts

Credit: CD Enviro

In 1915, a tragic farm accident reported in The Fruit Grower and Farmer was a mere footnote of local news. Patients from the State Hospital in Athens, OH, whose job was “to tramp down the silage comprised of corn stalks and leaves” were found asphyxiated in a tower silo. The report says “. . . the silage was a little green and had settled about three feet the previous night,” and went on to describe the young men killed by a heavier-than-air gas that so efficiently depletes oxygen that “a lighted lantern lowered in its presence will almost instantly extinguish the flame.”

There was no mention of nitrogen ­dioxide, or carbon dioxide, both lethal byproducts of decaying silage.

A century ago, tower silos were a relatively new structure on the farm landscape. The threat of exposure to this gas from fermenting organic material was an accepted occupational farm hazard. Certainly there was no prediction that this decay of organic matter “anaerobic digesting,” would be a booming business that a century later this process would be induced to purposefully generate biogas as a source of energy to light homes, run tractors, and create heat.

Anaerobic Digestion Overview
The silos that create killer gas are just one example of natural anaerobic digestion (AD)—the consequence of moist plant or manure products decaying in the presence of bacteria to give off a lethal gas product.

In the European Union (EU) anaerobic digesters creating methane gas have long been in operation to comply with EU policies on emission and nutrient management bringing positive environmental and human health results: decreased runoff, less chemical and nutrient deposition from landfills, and reduction of unhealthy incineration emission byproducts.

But AD has flexibility in its technology and depending on the source material, there are two potential outputs—biogas and plant rich residue called digestate.

Ernie Ruckert, an upstate New York-based solid waste consulting specialist with “a professional career in garage,” explains an overview of the process.

“There are two general types of digesters—wet and dry. The ‘wet’ technology is employed at many wastewater treatment plants, where one of the steps in the wastewater treatment process may be an anaerobic treatment tank [Anaerobic Digester] to degrade the organics in the wastewater. Processed organic waste slurry [‘wet’] is treated in these types of anaerobic digester tanks.

“Then we have the ‘dry’ technology which is widely used in Europe where organic waste, such as food scraps, yard waste, poultry manure or other biomass is loaded into an enclosed, oxygen free chamber that has is then inoculated with the microbes necessary to perform the organic breakdown.”

Ruckert says that in the “dry” digesters you can monitor temperature, oxygen, moisture, and pH to control all the processes so it truly approaches a concept of zero waste. In other words biogas is produced, digestate is produced that can be composted, and some liquid would require treatment.

As example, Ruckert describes what happens with the organic waste from an industrial food processor. “All the peels, other food preparation scraps that cannot be delivered to a food bank, and unusable product is collected in a truck, transported, and then offloaded into the enclosed chamber. The liquids are removed and collected and the remaining solids are exposed to a heat source. As the solids and organic liquids are decomposed, the microbes generate methane gas, which can be collected and can be used in a combined heat and power [CHP] system whereby electricity can be generated.

“Then this CHP product could fuel the processing plant so it can minimize the reliance on outside energy dependence. And if heat is needed for an offsite drying or industrial process, then that heat from the biogas combustion can be diverted to that location.”

Ruckert says typically, private contractors pick up the organic waste and these collection trucks drive it to the organics processor. The waste is unloaded in an environmentally enclosed building and is conveyed to equipment that separates the organic from non-degradable items.

“You wouldn’t think of it but organic waste is not just steak bones and peels. Depending on the source, it has its fair share of plastic bags, silverware, and grit, which has to be separated out. With this separation equipment process, an organic slurry
is produced.”

At this point, the separated slurry—sometimes this is referred to as a “puree”—can go to a dedicated digester, or it can be pumped to a wastewater digesting operation to be mixed with domestic wastewater or, “it could go to a digester on a farm operation and be mixed with manure.”

The biogas produced “is an asset to any municipality” and Ruckert says collecting organic waste is another step in the recycling process to capture the potential of what we throw out.

“We have the technology to make everything repurposed and eventually, who knows, there may come a day when landfills are a thing of the past.”

Bigger Chicken, Drier Air
Sometimes the unintended consequences of one policy reap benefits totally unexpected. The eastern shore of Maryland, for example, is home to a huge poultry production of more 7.5 billion chickens. But this produces 1.2 million tons of manure that after decades of spreading as fertilizer has created a soil that literally “can’t take it anymore.”

One option to handling manure is AD. The process of treating manure before use as a fertilizer is generally considered ­positive, since the resulting digestate product has higher proportions of mineralized ­plant-available nutrients than the untreated poultry manure, and there is significant odor reduction.

But beyond compost/fertilizing are a host of new technologies to repurpose manures that offer multiple benefits to production, industry, and the environment.

Enter the Maryland Animal Waste Technology Fund (AWTF), authorized in 1998 as part of the Water Quality Improvement Act that was under the State Department of Budget and Economic Improvement. With new mandates for nutrient management for the Chesapeake Bay, the program later became part of the Maryland Department of Agriculture (MDA) administered through its Office of Resource Conservation (ORC).

Louise Lawrence, who heads up ORC, says the ATWF is now part of a suite of grant programs that assist farmers to manage nutrients and use best management practices—from manure management to cover crops and more.

She explains that the poultry manure is a huge organic waste output and has tremendous potential beyond spreading in fields, but that new technologies that are “economically sound and would benefit the environment are needed to repurpose this manure.”

One option to handling manure is AD. The process of treating manure before use as a fertilizer is generally considered positive, since the resulting digestate product has higher proportions of mineralized plant-available nutrients than the untreated poultry manure, and there is significant odor reduction.

But beyond compost/fertilizing are a host of new technologies to repurpose manures that offer multiple benefits to production, industry, and the environment. “Our objective is to make sure that technologies answer business and conservation needs by aligning the economies that make sense for different farmers with different farm situations. But the technologies have to be reasonable, so that farmers who invest can realistically pay them off. This means that the developers must not only be creative, but demonstrate their commitment to efficient operation and maintenance as well.”

In the UK and the European Union (EU), making sense of organic waste has been an ongoing process for much longer and in a more widespread business arena than in the US, says Declan O’Connor, co-founder and innovator of BHSL Energy Centre from Limerick, Ireland. He describes how his technology was successful in demonstrating to the MDA the many requisite parameters of commitment, efficiency, and economy, which won his company, and a local Maryland poultry producer, a million dollar grant to prove the process. O’Connor explains the evolution of his technology.

“More than a decade ago, our family poultry farm was threatened with closure due to the strict regulations on ground water pollution. My brother, Jack O’Connor went to work to solve the problem and developed a fluidized-bed technology that answers the manure disposal issue through a unique patented combustion process. This creates enough energy to not only heat the chicken houses but allows excess to be sold as electricity back to the power grid.”

Fluidized bed technology is not new and is commonly used in coal-fired power generation.

O’Connor adds that after perfecting the process and attending an organic waste conference where he met US poultry producers, he invited several Maryland state Senators to visit Ireland and learn first hand what this could do to address multiple production and environmental issues.

After their visit he recalls how the policymakers said, “We’ve seen the future, and we need this.” BHSL was then connected to the AWTF and to a local poultry farmer, Bob Murphy, whose farm was awarded a technology grant to test the process, with the additional commitment of another 3 million by BHSL.

Credit: BHSL
Irish agri-tech company BHSL welcomed Governor of Maryland Larry Hogan to the launch of a $3m pilot project that is demonstrating the powerful role BHSL’s technology can play in addressing the environmental challenges the State faces from its large poultry industry. Pictured are Governor Larry Hogan, poultry farmer Bob Murphy and Denis Brosnan, Chairman, BHSL (both on the Governor’s immediate right).

Don’t Fight It, Burn It
Bob Murphy talks about the success and positive impact the BHSL Energy Centre is having on his 160,000-bird farm that now makes a new use for the more than 3,600 tons of litter created each year.

“I was looking down the road at what we were going to have to do. We can’t apply this to the land anymore; the soil is already oversaturated with phosphorous. When the MDA connected me with the BHSL people they said ‘We’ve got a plan. We’re going to generate electricity, heat the chicken houses, and burn this poultry litter efficiently, and you’ll have some leftover to sell on the grid.'”

“Prior to that we were trucking this to other
farms and industries who could use this, but I knew we couldn’t do this forever and we had to find new options,” says Murphy.

He says birds get graded on efficiency, a good feed conversion and good heat conversion and so far he is very pleased at the outcomes.

With this process, the fluidized bed technology takes the manure collected in a separate shed and delivers it by conveyer belts to the BHSL unit. It passes into a chamber with superheated sand where it burns and creates the energy used to either heat water for the poultry houses, or to be sold on the grid. And the small percentage of leftover ash is useful fertilizer additive.

“The system is similar to a radiator system,” says Murphy.

“There are heated pipes in each chicken house that have fans that blow on them to deliver dry heat. Immediately we noticed a ­difference in humidity and odor, which means no ammonia. And the benefit of a lowered ammonia from the litter in each house from the dry heat helps increase production so we have larger, more healthy birds for market.”

The BHSL has put an end to the farm using costly propane, creates a smaller carbon footprint, and has made Murphy an evangelist to the process with his local producers. “I tell them don’t fight this manure issue. We are only going to see more restrictive measures on how we dispose of this organic waste. I tell them you need to get on board with this, this is the ticket.”

Murphy adds he applauds how the system is also helping them to keep the Chesapeake Bay clean.

Credit: Marie Keating
Brothers Jack O’Connor (Left–founder and chief technology officer) and Declan O’Connor
(Right–chief executive officer) stand in front of the BHSL Energy Centre prior to it being shipped to Maryland. Irish agritech business BHSL has agreed a $3 million pilot project with the State of Maryland to trial its pioneering manure-to-energy
technology, which is aimed at transforming the environmental impact of the global poultry industry. BHSL employs 28 people at its headquarters in Ballagh, County Limerick.

Not Every Wastestream Is the Same
Maximizing their customer’s energy potential of organic waste is all in a day’s work, says Aaron Zahn, CEO of Florida-based BCR Environmental Corporation and NuTerra Management, LLC.

“The company goals are to develop technologies that convert organic waste into environmentally responsible products. Our public -private partnerships in Florida alone have completed $180+ million in organic waste recycling facilities. Plus, BCR is the only company in the 30-year history of the US Environmental protection Agency [EPA] to develop and obtain national regulatory approval for new technologies that convert human waste to recycled usable materials. All other options are based on legacy technologies invented in the early 1900s or before.”

Contemplating how and where human waste, or what is known as “biosolids,” will be used might suggest a bit of “do you really want to really see how the sausage is made?” for the more squeamish, but Zahn emphasizes that their processes “totally transforms the waste to a product indecipherable from fertilizers purchased in home improvement stores.”

According to the Composting Council about 96% of food scraps are sent to landfills with only 4% being recovered for AD or recycling. While there are techniques to limit the amount of methane from the waste decomposition it is not the exact science that exists in an AD. The Council also reports that each person produces 60–80 pounds of biosolids each year which is treated by wastewater plants and half of this goes either to grow food or crops and the rest is incinerated or goes to landfills which adds greenhouse gases of carbon dioxide or nitrous oxide to our atmosphere. They cite nitrous oxide as being 298 times more warming to the atmosphere than carbon dioxide.

“Every town has a wastewater treatment plant and whether you are a small 5,000 person rural town or a city of multi-millions, we’ve perfected our processes to be economically viable solutions to harvesting and using these biosolids for beneficial purpose that is environmentally responsible,” says Zahn.

He explains that energy, how much you use, and how much you can harvest to make it a worthwhile investment is key to using biosolids. He says that their system uses 90% less energy to process biosolids than traditional wastewater systems.

“Wastewater plants consume 3 to 4% of all energy produced in the US, incredibly, they use 40% of the entire municipal budget, and are the single largest consuming group of energy.

“Our technology helps municipalities save a huge portion of their wastewater treatment budget by reducing their operating costs, energy consumption, and improving the local community environmentally with less noise, dust, and odor that are all inherent to the transportation of waste through neighborhoods.”

Zahn adds that at the end of the process “The municipality benefits financially from the output as the wastewater solids can be recycled into high value biosolids. For any municipality facing nutrient runoff issues, erosion, and emissions issues at landfills and other disposals, we have the perfect solution as we harvest the nitrogen, phosphorous, and potassium, and essentially create a high quality, valuable ‘new dirt’.”

Municipalities whose existing wastewater treatment plant systems cost them valuable cash, time, real estate, and resources need to think about a complete change of mindset. In a world where new technologies are available that are cheaper and better rather than trying to upgrade their existing systems with outdated legacy approaches, he suggests.

“We are offering a scalable solution that all runs right on your property. Here’s how it works. After the raw sewage is separated from the water, we pick up the solids into our facility and using a basic chemistry recipe in our facility convert the waste to usable sterile fertilizer. Because the process is recipe driven it works the same every time. Our facilities are a more cost-effective, energy-efficient, simple, odor-free, and environmentally-responsible approach than the traditional aerobic digesters, anaerobic digesters, and thermal dryers that have been used over the last century.”

“Our facilities disinfect, deodorize, and reduce the mass so when it comes out you couldn’t tell that product from a load of high quality topsoil. It looks and smells just like dirt.”

By improving the carbon footprint through 90% energy reductions and capturing the valuable nutrients to reuse, the process keeps those nutrients from “going down the drain” literally, and leaching into the soil. Municipalities can sell the biosolids to agriculture, to turf grass users like golf courses or sports fields. The recycled fertilizer can also supplement sandy soils as Zahn says “they are about 50% organic matter with a beneficial chemical content of 6% Nitrogen, 2% Phosphorous, and 1% Potassium.

There are few sustainable solutions to reusing wastewater biosolids, particularly at the smaller levels, Zahn says. NuTerra’s process is the same at a large or small facility, it is only a matter of building the modular processing unit to size, using the consistent technology, rather than trying to shoehorn one inflexible model size into diverse settings to “make it work.”

“This means we can deliver an economically viable and environmentally responsible solution anywhere in the world—a small town in the US or a provincial capital in India—it’s totally suitable in either place. And it’s like giving low cost, clean water to the market, and who doesn’t want that these days,” says Zahn.

Credit: Ecoverse
The Ecoverse Tiger depackager

Feeding the Tiger
Audiences watching nature videos of a tiger making short work of prey for dinner can hardly fail to be astonished at the big cat’s speed and efficiency of the job at hand. William Kish, director of business development at Ecoverse, maker of the Tiger depackager, says customers watching their unit at work are equally astounded.

“When we say there is nothing like it, truly there isn’t. This is really an all-in-one unit, manufactured in Italy where it is use in Europe. Ecoverse was awarded the North American (US and Canada) contract for distribution. The Tiger takes packaged—and also unpackaged—organic waste in literally any form, and renders each component both the food and packaging, as separate commodities ready for recycling, digesting, or another repurpose.”

Kish explains that with nearly 100 million tons of food that is discarded in the US, the headache to separate the organic from the packaging is overwhelming for the food waste brokers who collect everything from unsold packaged retail foods, grocery items, and restaurant organics. He explains how the food chain, literally the fate of discarded, packaged food items, works.

First, tractor-trailers collect the discards on a regular basis, “and the next step—separating the packaging like cardboard boxes that contain eggs in Styrofoam containers—is a huge challenge.”

“But with the Tiger, every bit of these are reusable. It’s just a matter of separating the paper, Styrofoam, and eggs into discrete collections.”

Using the eggs as an example Kish describes how the Tiger makes short and efficient work of anything you put into it, at the rate of up to 30 tons an hour.

After the delivery to the Tiger site, a front end loader with a 6-yard bucket picks up a the cardboard boxes containing the styrofoam packaged eggs and dumps it into an 8-cubic-yard hopper. This is the first step.

“The augers in the hopper go to work where one auger is feeding, the other auger is reversing—this prevents the food waste from bridging,” says Kish.

“This creates a backward movement so you can continually keep feeding. Cardboard boxes are pushed around, and the boxes are opened. Now it’s feeding all this broken-down material into a mill that is attached to the hopper.”

Kish describes the Tiger’s mill as 8 feet wide and 20 feet long and spinning at 1,000 revolutions per minute (RPMs). This visual blur of motion is a speed resembling a high-end electric electric drill, operating at top speed. As the product from the hopper comes in at the bottom of the mill, which is outfitted with stainless steel paddles bolted onto it in a set pattern, it then forces the material from the bottom to the top.

“What happens while this mill is spinning is amazing. The bolt on paddles break open the food boxes and the food is directed by centrifugal force to spin out through the side holes. This organic material drops down below where it is collected and augured as a solid for compost or made into a slurry for AD. If the product is dry, like dog food, we can add water to turn it into a compressed cake at the final processing point.

“So now, the food is out and the packaging is spinning around and forced up through the mill and out into a 30-cubic-yard hopper where this can be collected for recycling purposes.”

And while eggs are a soft job, Kish says the Tiger can take on the toughest challenges, like tons of stainless steel cans from vegetables. “It’s a rugged unit, all solid stainless, which it has to be to withstand the low pH of soft drinks, fruits, and vegetables whose acidity would soon eat through other metals. We can take on anything except food in glass bottles as the process would incorporate glass in digestate or compost, and that would be an unwanted mix.”

Kish says there is an incredible quantity of drink items that are discarded and the food value is lost in typical recycling where plastic bottles or aluminum cans of unopened water, fruit juices, or soft drinks are simply crushed.

“Think about the water that can be recycled or the sugars that can feed a digester to turn all that carbon into methane gas. And another benefit is that the spinning action of the mill is like a dryer, so when the cans are collected, at the end they are all dry, residue-free, and shiny, and can be baled up for recycling.”

And the Tiger handles all kinds of messy jobs “like the 150 pound blocks of cheese, plastic containers of yogurt, desserts, and recalled frozen vegetables we’ve done.” But the amount of discarded and in many cases perfectly good food, is a disconcerting aspect.

“We did a load of unsold sandwiches from a high-end coffee retail marketer and processed 20 tons of these sandwiches that still had their price tags of $5.95 on them. It’s good for business but nonetheless difficult to reconcile all this waste.

“If you stop to consider all of the energy to produce the food, the livestock produced but left uneaten, the labor to manufacture, then package and distribute these to retail outlets, and then it is all unsold and discarded, it’s a source for concern. However, the good piece of this is that it’s not going to waste in the traditional sense because it is going to organic waste processing. So all the breads and fillings and paper wrappings can be reused for positive purpose—maybe compost fertilizer, or digestate for energy,” notes Kish.

He adds that the incredible amount of US food waste “when four out of ten children go to bed hungry,” is discouraging and the company has talked with suppliers to consider how it might be distributed for human or animal consumption.

“We’re not there yet in terms of making better use of this organic commodity that could feed people in need. But the transport and distribution process is the next big hurdle to overcome. At least we are now reusing these unused products, and preventing them from sitting in a landfill giving off bad odor and air-polluting gases.”

Currently, the Tiger is in operation across the US and as Kish says “more to come.” The latest unit is helping the Fresh Kills AD site on Staten Island, New York to process more than 20 tons an hour of organic waste in plastic bags, delivered from the city. The facility anticipates processing 100,000 tons of organic waste a year, and creating a sustainable source of energy.

Blazing a Green Trail
At CDENviro, “green” is more than a turn of phrase. Headquartered in Cookstown, Northern Ireland, the Emerald Isle, long known for its sparkling green landscape is the perfect backdrop to creativity, innovation, and a corporate vision founded in preserving natural resources.

John Irwin, CDEnviro Business Development Executive says they offer solutions across four markets: landfill diversion, recycling of wastewater, environmental remediation, and energy derived from waste. The goal of managing these diverse wastestreams is “to design technology and processes that can achieve zero waste.”

“For example we have developed techniques to separate components that clog sewage processing such as grit, sand, rag, and other inorganics that clog lines. And we can help recover and separate the detritus from street sweeping and storm inlet/catch basins. You may not think about it, but there’s value in the captured grit, sand, and aggregate that can be used for fill purposes, and all those plastics and papers can be recycled.”

One unique application keeps cows in comfort. “Cattle farmers, particularly the latest ‘super dairies,’ are increasingly switching to sand bedding, which is proven to be more comfortable, cleaner, and healthier for cattle over organic bedding such as straw. In these large dairies it only makes sense to reduce any potentially harmful factors that affect production, such as disease or lameness. But when manure gets mixed in with sand, it’s hard to clean out. By using a CDEnviro treatment process, we can remove manure and return and reuse 85% of the sand, and the manure can be harvested for use in compost or anaerobic digesting.”

The corporate goal as Irwin describes is pursuing multiple waste streams that harvest different wastes—sewage and wastewater, manures, road-sweepings—anything that is potentially destined for a landfill that can be collected, sorted, separated, and reused for energy, or recycled and repurposed.

He explains how organic treatment is part of that picture even before there is any organic waste byproduct.

“Even during the food production process there is an overlooked potential for recycling,” says Irwin.

He describes how the water used to clean and prepare food for processing such as potatoes, and sugar beets for example, becomes saturated with soil, grit, and sand. “This material collects in tanks, pipes, lines, and requires more fresh water to clean, and disposing of all this dirty water downstream is not a good use of resources. We can come in with with our G:MAX technology that removes and recovers the grit.”

This serves multiple purposes. By pre-screening the wastewater from food cleaning the recovered grit can be reused in construction for road fill, landscaping, and pipe-bedding, and the end product wastewater is much cleaner as it goes downstream. Both processes meet their goal of reducing environmental impact.

In the UK, Irwin cites biogas production a “clean energy,” from sewage sludge through efficient AD, and is widely used to produce heat and/or electric energy. “About 66% of the UK’s sewage sludge is treated in AD plants, and while these wastewater digesters are efficient they still need regular cleaning to optimize their performance.”

He adds that as much as 50% of AD capacity can be lost when sludge solids collect. However, the problem can be solved by using a pre-screening processing of waste from tanker waste collection such as their MSU:10.

This portable pre-screening unit “with the footprint of a parking space,” removes larger debris, sludge, and grit and provides an odor treatment of the solids. The mobile D:Max, which removes “problem causing solids like dirt, and rags from the wastestream,” helps increase waste efficiency destined for AD processing, before it has even reached the treatment plants.

“In the US, the USDA has a challenge to reduce food waste by 50% in the next 13 years to meet their 2030 goals. Urban areas, like the MidAtlantic for example where space is at a premium, will see decline in landfills that take energy to build, operate, and maintain. Anaerobic digesters are the answer since they can pretty much run on their own—bacteria is its own source of energy.

“We will work with the digester people to optimize their process. With our equipment we help ensure that no inert materials are introduced into the AD process. It’s important that all these potential sources of energy that keep waste out of landfills run as efficiently as possible, and our suite of equipment is the perfect cost-effective answer to increase capacity across several market sectors.” MSW_bug_web

  • Barry Tonning.

    Excellent articles on anaerobic digestion – I really appreciate the details, and links to real world applications.


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