Anaerobic Digestion

Many would say that solids are the most critical component to handle in a digester, but water is a critical factor as well, logistically and financially.

April 13, 2017, Haverhill, MA — The city's board of health has approved a waste-to-energy digester for farm in Bradford.

April 4, 2016, Chilton, WI – DVO, Inc.’s Phosphorus Recovery system received honors at the Environmental Protection Agency’s (EPA) Nutrient Recycling Challenge Summit in Washington, DC.

The goal of the challenge was to identify technologies that not only help farmers manage nutrients from livestock manure and create valuable products, but also protect the environment.

“We are honored to be recognized for our innovative phosphorus recovery technology,” said DVO president, Steve Dvorak. “The practical ability to recover and recycle nutrients will make modern agriculture more sustainable and provide real benefits for our communities and the environment.”

The Nutrient Recycling Challenge was launched by the EPA in late 2015 in partnership with the U.S. Department of Agriculture, pork and dairy producers, and environmental and scientific experts. The EPA initially received 75 concept papers and recognized the top 10 submissions with awards. DVO received a spot in the top 10 with an Honorable Mention Award for its work on advanced phosphorus recovery.

DVO’s Phosphorus Recovery (PR) system is a fully commercialized and economical treatment process that removes up to 95 percent of the total phosphorus from large-scale farm and commercial waste streams and up to 55 percent of total nitrogen content from digested wastes. By treating these wastes first in DVO’s patented Two-Stage Mixed Plug Flow anaerobic digester and then employing the add-on PR system, valuable nutrients are conserved and natural resources are protected by reducing the likelihood of runoff and water pollution.

Doug VanOrnum, vice president of technology and strategy at DVO, accepted the award at a ceremony at the White House Eisenhower Executive Office Building in Washington, DC on March 30.

More information on the challenge can be found at


In 2013, the Canadian Biogas Association issued a study identifying the opportunities in biogas production so provinces could develop policies to support this budding industry. It also developed farm-to-fuel guides to help farmers decide whether biogas production makes sense for them.

The study determined biogas could make up three percent of Canada’s natural gas supply, Canadian Biogas Association executive director Jennifer Green told the 2016 Agricultural and Municipal Biogas Forum, held recently in Abbotsford, B.C.

She calls biogas an “overwhelming” opportunity for agriculture, saying agriculture could produce about two-thirds of the biogas, or about 1.65 million cubic meters per year.

While there are a growing number of anaerobic digesters on Ontario farms, there are only three in B.C., with one more under construction. The province’s first anaerobic digester began operation in rural Abbotsford about five years ago and is now producing gas from cull potatoes and other organic waste. Not long after, as part of its demonstration farm, Bakerview Dairy in Abbotsford put in a demonstration digester that utilizes manure from its tiny 50-cow herd to produce electricity for the farm.

In early 2015, Seabreeze Farms in Delta fired up B.C.’s second large-scale digester, using manure from its 350 milking cowherd and cooking fats and oils.

While one purpose of an anaerobic digester is to manage and create value from farm waste, it produces its own waste (digestate). The digestate includes most of the nutrients from the inputs, as they are not absorbed by the gas production process. This is a concern for both regulators and farmers as high livestock concentrations are already leading to nutrient overloading on many fields. Bringing in off-farm inputs only exacerbates the issue, leading to potentially serious environmental consequences.

As a result, the digester “is only one piece of the equation,” says Chris Bush, who built the Sumas Prairie anaerobic digester, located outside of Abbotsford.

That’s why researchers and industry are working on ways to manage the nutrients, particularly phosphate, to maximize their value while minimizing any detrimental environmental impacts.

There are a number of ways to do that, says Henno Haaring of Dorset Green Machines, based in the Netherlands. The first step is to separate the liquid and solid digestate so each can be applied separately or, in the case of the liquid, re-circulated. Cheapest is a press screen, which provides good dry matter content in the solids but has poor nutrient recovery. Another low cost option, a drum filter, provides good phosphate recovery but is not very efficient, has highly variable results and requires a lot of filter maintenance.

A decanter has high phosphate recovery and leaves little dry matter in the liquid but is expensive to buy and costly to operate.

A belt press is very good at separating solids and liquids, removing enough dry matter to make the liquid treatable by filtration or reverse osmosis. However, it requires additives and a knowledgeable operator.

Haaring says Dorset’s solution is to dry the digestate, which not only reduces the volume but creates a good final product.

“We generate a product with 85 to 95 percent dry matter that is 10 to 25 percent of its original weight,” he says. Its nutrient content depends on whether the drying is done with or without first separating the digestate.

“The dry product can be used as fertilizer, bedding or even fuel,” Haaring says.

One of Dorset’s installations dries 100,000 tonnes of hog manure, producing 25,000 tonnes of solids. The solids go into a “phosphate factory” which further compresses them into 6,500 tonnes of pellets with a nutrient content of 2.1 percent N, 6.5 percent P and 1.5 percent K. The pellets are then exported from the intensive hog production area in the Netherlands to the north of France.

Trident Processes of Abbotsford has integrated some of these technologies with ideas of their own to develop a complete nutrient recovery system, which it is now being tested at Seabreeze.

The system first separates the fiber and conditions it for reuse as bedding in the barns, leaving four percent solids in the remaining wastewater. A second press removes most of the remaining water, creating a “sludge” with double the solids content and 85 to 90 percent of the phosphate, 54 percent of the nitrogen and 17 percent of the potassium, says Bush, now Trident’s operating manager. It then uses polymers to concentrate the sludge, complete with its nutrients, into a “cake” which contains 25 percent solids.

The cake can be pelletized and sold off-farm as a nutrient-rich fertilizer. The remaining wastewater, which Langley environmental farm plan advisor and consultant Dave Melnychuk calls a “digestate tea,” contains very few nutrients.

The Seabreeze dairy slurry generally contains 0.25 percent nitrogen, 0.05 percent phosphorus and 0.21 percent potassium. Once through the Trident process, the tea contains 0.16 percent N, less than 0.01 percent P and 0.12 percent K. In contrast, the bedding contains 0.40 percent N, 0.13 percent P and 0.11 percent K while the cake contains 0.68 percent N, 0.22 percent P and 0.12 percent K.

Melnychuk believes the tea offers tremendous potential as it still includes some nitrogen but almost no phosphorus.

Noting many farmers “have too much phosphorus but not enough nitrogen in their fields,” Melnychuk has started a
three-year trial to find out how corn and grass respond to the tea. Even a low application rate produced a wet yield of 29 tonnes/hectare, higher than the 25 to 28 tonne average in B.C. fields.

“We are very pleased with the initial results,” Melnychuk says. He notes there was less phosphorus in both the corn and grass fields at the end of the season than at the beginning. “If we can validate that for the next two years, it provides an option for phosphate rich soils.”

University of B.C. civil engineering professor Victor Lo is trying a different approach: treating the manure before it even gets to the digester. He has spent the past few years developing a microwave-enhanced advanced oxidation system to reduce solids in the manure by 85 percent and extract the phosphorus and crystallize it as struvite, which is 95 percent pure phosphorus.

Lo says nutrients can be captured more easily when the solids are broken down and microwave technology is the only way to do that. The system “reduces the amount of disposable solids and number of nutrients which need to be applied to the land.”

Lo says the resulting largely liquid product “reduces the processing time in the AD.”

He is now building demonstration units and conducting feasibility studies at both the UBC Dairy Education & Research Centre in Agassiz, B.C., and the James Wastewater Treatment Program in Abbotsford

Although the system may not be a money-maker because of its high capital and operating costs, Lo believes it could solve some of the environmental issues farmers and waste treatment plants face.




October 21, 2015, Boston, MA – At its third annual conference, the American Biogas Council (ABC) recognized 12 organizations for their leadership and innovation, which are helping to strengthen and grow the U.S. biogas industry.

The award recipients were honored during the 2015 Biogas Industry Awards Reception held during BioCycle REFOR15 Conference and Expo. This year, the ABC recognized biogas industry leadership and innovation with three awards: Innovation of the Year, Project of the Year and the new Outside-the-Box award.

"The Biogas Industry Awards not only recognize excellent projects and innovations," explained Bernie Sheff, chairman of the ABC board and vice president of engineering for ES Engineering Services. "They recognize great industry achievements and creative solutions to commonly faced issues that can be held out as an example to others."

This year, the ABC expected to present six awards, one Innovation of the Year Award, one Outside the Box Award, and four Projects of the Year across four categories: agricultural, municipal, institutional and merchant. In the end, 12 were awarded.

"The quality of innovation in the biogas industry is at a fever pitch today," remarked Patrick Serfass, executive director of the ABC. "We're excited to honor our winners for their steadfast commitment to overcoming obstacles and discovering new ways to help us deploy more biogas systems in the U.S."

There are more than 2,100 operational biogas systems in the U.S. today with the potential for more than 11,000 new systems to be built.


Biogas Projects of the Year:

  • The Furrer and Martin Families' project – Green Cow Power in Goshen, IN – was named agricultural Biogas Project of the Year for their complex project which uses manure from five dairies, plus large volumes of food waste, to generate more than 3MW of electricity, heat, digested liquids for fertilizer, and digested solids for cow bedding.
  • quasar energy groups' project – Wooster Renewable Energy in Wooster, OH – was awarded the municipal Biogas Project of the Year for their project which digests biosolids, FOG and food waste at a volume that's five times the throughput of the city's original system to generate electricity in excess of the plant's needs, as well as heat and digestate used as fertilizer.
  • The City of Gresham's Cogen Expansion and FOG Receiving Station project in Gresham, OR was awarded the municipal Biogas Project of the Year for their operation of a net zero energy, 10 MGD water resource recovery facility which uses biosolids, FOG from restaurants and food waste to generate 800 kW of electricity and heat, and digestate used as a fertilizer at local farms. In addition to the notable physical plant, its creative use of a wide variety of financing tools such as RECs, transferrable tax credits, and public funds from both the city and state sets this project apart from its peers.
  • Minnesota Municipal Power Agency's project –Hometown BioEnergy in Le Sueur, MN – was awarded the municipal Biogas Project of the Year for their operation of a large Minnesota Municipal Power Agency digester which uses local manure, sweet corn silage, and FOG to generate 8 MW of electricity, heat, digested liquids for farm fertilizer and digested solids for cow bedding, burnable fuel or soil enhancement. The size of the system compared to other municipal biogas projects and its gas storage system which provides the option to only generate power during peak needs, sets it apart from its peers.
  • Univeristy of Wisconsin-Oshkosh Foundation's Rosendale Biodigester project in Pickett, WI was awarded the institutional Biogas Project of the Year for their collaborative project between the University of Wisconsin-Oshkosh and Rosendale Dairy, which uses manure from Wisconsin's largest dairy to generate electricity, heat, liquid digestate for fertilizer and digested solids that are pelletized for use as a soil amendment. Apart from the physical plant, this first of its kind learning facility serves as a teaching center for the development of technicians, scientists, engineers, and animal husbandry specialists sets it apart from its peers.
  • CleanWorld's project – UC Davis Renewable Energy Anaerobic Digester (READ) in Davis, CA – was awarded the institutional Biogas Project of the Year for their innovative system which uses manure and 50 tons per day of food waste to generate digested liquids for fertilizer and biogas which is blended with landfill gas to generate electricity from several microturbines. What sets this project apart from its peers is the combination of wide variety of feedstocks, the blending of landfill gas with digester gas and the use of microturbines to power the university's West Village Project.
  • Forest County Potawatomi Community's Renewable Generation Biogas Facility in Milwaukee, WI was awarded the merchant Biogas Project of the Year for their exemplary system that brings together many players, using food waste from local casino, grocers, the dairy, meat and beverage industries plus byproducts of pharmaceutical and methanol production to generate 2MW of electricity, heat, and digested solids for fertilizer. The successful operation of this enormously complex collection of partnered organizations and feedstocks – plus its performance, which has doubled expectations – sets this project apart from its peers.
  • South San Francisco Scavenger Company's project –Blue Line Biogenic CNG Facility in San Francisco, CA – was awarded the merchant Biogas Project of the Year for their successful operation of a dry biogas system which uses commercial and residential yard and food waste to generate 120,000 diesel gallon equivalents of renewable natural gas each year for waste hauling vehicles and organic-certified compost. This exceptional physical plant plus the integration of dry digestion and vehicle fueling, where each collection vehicle will collect enough organic material on its route to fuel the vehicle for the day, sets it apart from its peers.

Biogas Innovations of the Year:

  • Magic Dirt, LLC's product, MagicDirt Premium Potting Soil, was named product Biogas Innovation of the Year because it represents both a product innovation for creating a sustainable, saleable product from digester-derived fiber and a marketing innovation for successfully selling a consumer product through major retailers such as Walmart. The success of Magic Dirt in the marketplace demonstrates that digester co-products can gain access to national retail markets, contribute to the greenhouse emission reduction goals of major retail chains, and attain consumer acceptance-all while contributing to the bottom line of the biogas project.
  • quasar energy group's technology Phosphorus Recovery System was awarded the technical Biogas Innovation of the Year for its innovative and exemplary portable phosphorus removal system. This technical innovation, which has been proven at scale, will help farms with and without digesters plus water resource recovery facilities to remove 99 percent of phosphorus from organic material, both preventing it from entering our waterways and recovering it for use where the nutrients are needed most. The mobile and versatile qualities of the system plus the nearly complete recovery of phosphorus and proven performance make this technology stand out as an exemplary technical innovation.
  • DVO, Inc.'s technology Phosphorus Recovery was awarded technical Biogas Innovation of the Year for its exemplary and innovative phosphorus and nitrogen removal system. This technical innovation has been proven to perform at scale and ultra-low cost removing 95 percent of phosphorus and 50 percent of nitrogen from digested material both preventing the nutrients from entering our waterways and recovering them for use where they are needed most. The nearly complete phosphorus recovery, impressive nitrogen recovery, proven commercial-scale performance and all at an ultra-low cost make this technology stand out as an exemplary technical innovation.

Outside-the-Box Award:

  • Newlight Technologies was awarded the Outside-the-Box Award for development and commercialization of its AirCarbon Greenhouse to Plastic technology. The AirCarbon process combines air and biogas with Newlight's biocatalyst to create a carbon-negative polymer at ambient operating conditions-no high pressures, high temperatures, or multiple major unit operations-generating significant savings in energy, water, capital costs, and carbon emissions. Turning biogas into cell phone cases and similar products is an innovation that should soon be "in the box" for the biogas industry.

October 19, 2015, Waunakee, WI – The operator of a troubled manure digester near Waunakee has tentatively agreed to sell the facility to a California firm.

Clear Horizons, the Milwaukee-based company that has operated the facility since 2010, announced recently that it had signed a letter of intent to sell the digester to Clean Fuel Partners of San Francisco. READ MORE

August 12, 2015, Turin, Italy — On the La Bellotta farm outside of Turin, the owners are demonstrating the concept of an energy-independent farm. And part of the mix is a unique New Holland tractor that runs on biogas produced at the farm.

CNH Industrial, which owns the New Holland Agriculture brand, recently hosted a trip to Europe for a group of journalists. The trip included a demonstration at La Bellotta of the New Holland T6.175 Methane Power tractor. READ MORE

May 8, 2015 – PlanET Biogas Global has published a brand new online tool, which enables farmers to check out the energy potential of their substrates.

The biogas project calculator is free of charge and provides its users a first impression regarding a suitable mix of substrates for an efficient biogas production. The new online calculator is available on the PlanET Biogas Global website now:

"During my daily consultant work I have realized that most farmers are interested in the energy potential of their available substrates, especially in the beginning of any planning,” said Hanna Garbert, international sales consultant from PlanET Biogas Global. "Everyone who considers developing a biogas project is now able to quickly check out, if and in which size a biogas production is possible on his farm."

The experienced sales consultant hopes the biogas calculator is helpful for interested farmers.

"This biogas calculator is a rough guideline for our clients, certainly we carry out concrete feasibility calculations in a following step in which country-specific regulations such as feed in tariffs are being considered.”

May 8, 2015, New Rochelle, NY – Based on a comprehensive life cycle analysis comparing the environmental impacts and economic outcomes for managing manure and food waste produced on a dairy farm, researchers found that anaerobic co-digestion of the waste products had substantial cost, energy, and environmental benefits compared to digestion of manure but disposal of food waste in a landfill.

A detailed discussion of the potential for bioenergy production, increased profitability, and reductions in global warming and smog is presented in an original research article in Industrial Biotechnology, a peer-reviewed journal from Mary Ann Liebert, Inc., publishers. The article is available free on the Industrial Biotechnology website until June 1st, 2015.

Rui Che, M. Melissa Rojas-Downing, Yuan Zhong, Christopher Safron, and Wei Liao, Michigan State University, East Lansing, report that a calculated 25-year net value of more than $8.4 million for co-digestion of dairy farm manure and food waste, which greatly exceeds a loss of $7.5 million if only the manure undergoes anaerobic digestion and food waste is landfilled. The authors report the results of their economic analysis and the effects on global warming and air and water quality based on co-digestion at a hypothetical dairy farm in the article "Life Cycle and Economic Assessment of Anaerobic Co-digestion of Dairy Manure and Food Waste."

The article is part of an in depth special research section on anaerobic digestion led by guest editor Wei Liao, PhD. The issue also includes an overview by Dr. Liao entitled "Anaerobic Digestion: A Potential Energy and Environmental Solution" and two review articles: "Anaerobic Digestion-Based Biorefinery for Bioenergy and Biobased Products" by K.C. Surendra et al.; and "Anaerobic Digestion Potential of Coproducts Associated with Ethanol Production from Sweetpotato: A Review," by W.A. Mussoline and A.C. Wilkie.

"Efforts to take organic waste materials and find added value creates exciting opportunities for industrial biotechnology innovation and commercialization even when applying existing and familiar technology," says co-editor-in-chief Larry Walker, PhD, Biological and Environmental Engineering Department, Cornell University, Ithaca, NY.

April 1, 2015, Tulare, CA – An 18-acre, city-owned property located next to the sewer plant may have a new, environmental-friendly, energy-producing tenant.

The Tulare Board of Public Utilities is considering approving a lease with Colony Energy LLC., a Southern California-based company seeking to build an anaerobic digester and heat and power facility to produce renewable energy. READ MORE


An Internet search for manure-related spills can lead to an exhausting list of news articles and images of damage.

In Wisconsin alone, the volume of reported manure spilled during 2013 was the most since pre-2007, indicating the problem is not on a downward trend. With each and every manure spill comes increased scrutiny by the public on manure management – this perception also affects the anaerobic digestion (AD) industry in both positive and negative ways. As the number of manure spills on both large farms and those without digesters increases, so does favorability of the AD industry.

The AD industry is an established solution for nutrient management that also provides energy production in ways that are much less detrimental than conventional energy production. Positive mentality towards AD on farms is mainly due to the added manure storage onsite that comes with an installation, as well as the control over manure volume and flow. Anaerobic digestion systems help solve manure treatment issues by removing some of the biological oxygen demand of the waste stream which is the main contributor of downstream eutrophication. Because of this, it is plausible to say a spill of digester treated effluent would be less harmful to the environment than raw manure. The fertilizer value is not lost through the digestion process and effluent is still suitable for land application. In addition, anaerobic digestion systems produce biogas as a useful energy source that can be combusted to create electricity or heat.

However, because farms with AD are more closely monitored, a spill occurrence results in highly touted, bad press that significantly impacts the public’s perception. Photos and images can provide lasting impact on brands or digester types that leave readers or viewers with the thought that AD causes more environmental damage than assistance. This article aims to provide a better understanding of the levels of prevention, detection, and control that are in place for manure handling on farms and AD facilities.

Determining the cause of previous manure spills or leaks is the first level of understanding. Evaluation of spills in Iowa by the Iowa Environmental Council and Iowa Farm Bureau found most spills occur during transportation of manure and are caused by human error or equipment failure. The development of manure spills is affected by numerous factors, including, but not limited to: snow fall, cold temperatures, storage volume, farm size, and conveyance method. Wisconsin’s 2013-2014 winter was filled with especially harsh temperatures and snowfall, putting more strain on piping and liquid storage.

The first level of protection against manure spills is prevention. Manure spills are preventable with proper design, operation, and upkeep. However, as a factor of safety, multiple levels of protection should be used. Prevention can be as simple as minimizing water use and addition to manure supply; this will decrease total volume of manure as well as the likelihood of the manure to flow. Treatment of runoff or wash water in a separate area will help minimize the volume of high-strength wastewater. In addition to volume reduction, farm managers should strive for minimal transportation from production to enduse. Doing so limits the duration inside piping and vehicles and will decrease the potential impact area. Regardless of manure transport type, manure must be stored in some manner. Storage units should be professionally designed and evaluated on a regular basis for performance. When it comes to anaerobic digestion, manure is most often stored in constructed tanks.

Properly constructed tanks should be visually inspected on a regular basis to ensure structural integrity. Commonly, tank levels will vary as manure is treated during an anaerobic digestion process. Using level sensors with redundancy or backup will help keep readings accurate in the event of a unit failure. Today’s technology allows operators to receive immediate updates on AD process output and function. Plant errors and warnings can be connected to phone dial-outs or on site-displays to notify changes in process performance. These readings can provide the following key information:

• High-level readings – may indicate pumping or addition to the tank is occurring too rapidly and the outlet to the tank is blocked or malfunctioning. Control logic should be set in place to shutdown feeding to the tank if this occurs. Some examples of sensors that work well for high level readings are float sensors or capacitance probes set at the correct height.

• Low-level readings – may indicate pumping or removal of material from the tank is occurring too rapidly and the inflow is not working properly. It could also indicate a leak in the tank at some location. Some examples of sensors that work well for low-level readings are float sensors or capacitance probes set at the correct height.

• Continuous level transmitters – this type of measurement displays height or change in height of the storage vessel. Radar, sonar, pressure, or capacitance sensors may be used to obtain liquid height within the tank. Monitoring the level change over time will show how rapid the level is increasing or decreasing and could help pinpoint the type of error.

Liquid manure is often conveyed via pumps, drag hose, or piping. Since this step involves transport of manure underground or in exposed conditions – and sometimes long distances – the risk of leakage remains high. Simple flow and pressure sensors can be installed on suction and discharge sides of pumps to detect piping and pump performance; this helps indicate pipe blockages or leaks as a leak on the discharge side can be detected by a zero gauge pressure or a lack of flow in a down stream flow meter. Control logic can be setup to immediately shutdown this type of situation, preventing large spill volumes.

Proper control and operation of manure handling systems is the first line of defense against large manure spills. Operators should be equipped with safety plans and emergency procedures. However, with today’s advancements in facility controls and software, operators can be notified of plant errors by dial-out and can control the plant remotely via phone or Internet connection. This is a unique feature with the potential to decrease leak time through proper and immediate response to isolate areas.

Unfortunately, no matter how efficient plant operations may be, structural failure is always a possibility. For this reason, each state will inspect and require a containment zone. This level of inspection will typically be handled by the natural resources permitting agency and will require all storage structures to be properly lined to prevent groundwater leakage, be surrounded by a secondary containment structure that can hold all the liquid within the vessel in the event of a rupture, and provide a safe spillway to reroute excess contaminated water away from environmental habitat. Manure storage tanks or anaerobic digestion reactors can be equipped with overflow piping to convey spills to properly sized and constructed storage ponds. Overflows can be equipped with simple flow sensors to provide operators alerts that an extraordinary event has occurred.

There are numerous manure spill response plans established by each state’s Natural Resources Department, a list of guidelines from the United States Geological Survey - Natural Resources Conservation Services (USGS NRCS), and other organizations to help keep these organized. However, the best response plan starts with manure spill prevention.

Steven Sell is a biologist and application engineer with BIOFerm Energy Systems






Gas production and energy potential typically dominate the spotlight in the anaerobic digestion (AD) technology world, while benefits of residues and nutrient management from AD are overshadowed. However, utilizing AD residues and considering the value of properly managing nutrients, such as phosphorus, may make-or-break projects considered uneconomical based on energy production value alone.

Nutrient management benefits from digestion should be considered to help keep residuals on the positive side of the balance sheet. For example, agricultural waste management is typically not considered a profit center. Monetizing the benefits in terms of removal and cleanup cost or value as fertilizer is vital, but can be challenging. A full spectrum of valuable nutrients and minerals can be captured from AD residues, such as phosphorus (P).

Phosphorus is an essential element for all cellular growth and demand for it is growing in the U.S.; only 28 years of phosphate deposits remain in the U.S. assuming a two percent market growth, unless more recovery is developed. Still, until scarcity and increased production costs drive phosphorus prices higher, incentives such as cost savings and reduced hauling are sought for implementing phosphorus recovery.

When compared to the aerobic organic treatment processes, anaerobic digestion retains nutrients throughout the process, transforming complex, organically bound phosphorus into a more biologically- available form.

The management of phosphorus levels post-digestion can save farmers time and cut hauling costs. Phosphorus levels in manure limit the allowable amount that can be applied in a season, and many soils are already at their maximum phosphorus levels. Manure may be applied to help meet the nitrogen needs of a crop growing in soils with concentrations up to 50 mg/kg of P; however, the P applied is not to exceed the amount taken up by the crops over a rotation cycle. If a field’s P levels exceed 100 mg/kg, then no P additions in manure or fertilizer are permitted. Nutrient planners encourage phosphorus removal from digestate slurries in these areas in efforts to allow more nitrogen requirements to be met by digestate, rather than supplementing nitrogen from other sources.

Controlled application is the key factor in proper nutrient management. Solid nutrient capture is valuable in reducing hauling costs, according to Sara Walling, section chief with Wisconsin DATCP Nutrient Management and Water Quality. For example, if a farmer pays a contractor one to two cents per gallon to haul and spread manure, the material could be separated into two streams where more concentrated material can be taken to further fields, while the lower concentration can be applied by drag-hose nearer the farm.

Phosphorus recovery processes

  • Fluidized bed crystallization-struvite
  • Dissolved Air Flotation/decanter
  • Phase separation/clarifier
  • Mechanical separation/centrifuge
  • Membrane separation
  • Polymer/belt press/dryer
  • Biological uptake-managed wetland or aquatic growth

Although phosphorus and other nutrients are valuable to farmers, excess nutrients carried in wastewater pose a serious threat to waterways. Decades of management practice and regulatory efforts have been established to combat the growth of oxygen-depleting algae as a result of phosphorus runoff. Unfortunately, both prevention and recovery of nutrients from waterways is difficult and expensive. When watershed protection is mandated by regulatory compliance, nutrient recovery technology is deployed for concern of fines or operational shutdown. For example, phosphorus cleanup from a body of water can cost from $5/pound to $100/pound; the present nutrient market value is about $0.53/pound for phosphorus pentoxide (P2O5). It is important to note that reduction of nutrients in discharge is not a linear function. The cost of reducing the first 90 percent of phosphorus in a waste stream may cost $5/pound, however, it may cost $50/pound to reach 90 to 99 percent reduction.

One method of meeting nutrient reduction requirements is through Nutrient Credit Trading (NCT) or Water Quality Trading, which focus greatly on phosphorus. NCT’s are earned by capture of nutrients from non- point sources by virtue of base conservation activities, such as strip farming, no-till farming, and contour farming. Capture techniques such as these can be as effective in nutrient planning as recovery of P from AD liquid and manures. With proper documentation, phosphorus removed from AD effluent can qualify for NCTs.

Some nutrient recovery techniques manipulate pH and require the addition of minerals to optimize recovery from the solution. Phosphorus recovery is aided by anaerobic digestion as the process converts and homogenizes inputs into more available form.

The management of organic material through anaerobic digestion has many offerings outside the gas and energy production. There are a multitude of uses for residues from anaerobic digestion: animal bedding, compost, fertilizer, fiber, and biochar to name a few; this material recovery component distinguishes renewable biogas from solar, wind and hydro energy. High product standards for residuals management enhance overall digester value and benefit sustainable agriculture by replacing depleted resources.

Douglas Renk is a biological commissioning engineer with BIOFerm Energy Systems






Servicing biogas plants is challenging. Methane leaks are particularly problematic – from a security, a technical, an economic as well as an environmentally friendly perspective. Researchers are working on a technique that helps to better detect leaks. In this process, a laser discovers the leaks from several meters away.

The requirements for the operation and maintenance of gas plants are high. Leakage is particularly problematic. Even small leaks from the joints of the gas lines or fermenters can have consequences. Escaping methane can result in fires, economic damage and a worsening of the carbon footprint of the gene-rated electricity.

In a project funded by the German Federal Ministry of Food and Agriculture (BMEL), researchers and a measuring equipment manufacturer are now addressing this issue. After 18 months, the experts have developed a demonstrator that, without making contact, detects biogas or natural gas escaping from leaks through the use of a laser.

The technology developed at the Fraunhofer Institute for Physical Measurement Techniques IPM in Freiburg, Germany, is based on optical emission and backscattering spectroscopy. In the process, the light of a strong laser beam detects escaping methane. Simultaneously, the gas irradiates part of the light back. The scientists analyze this proportion and determine the gas concentration from the absorption spectrum of the escaping substance. Since the gas spectrum is very precise, only methane is very selectively measured, and not any other gases. The technology is located in a box-shaped demonstrator. It stands on a three-legged tripod and is directed at the part of the equipment that is to be inspected. The optical portion of the measurement system comprises the laser, detector, camera and range finder. A connected tablet PC collects the data and evaluates it. The screen displays the graphically edited information concerning the escaping methane and the exact position of the leak. Measurements from up to 15 meters of distance are possible.

Dr. Johannes Herbst, measurement technology expert at the Fraunhofer IPM, expects the technology to be ready for the market in the next three to five years.

“In the future, the measurement team will be able to easily check the entire system from the ground. It used to be necessary to climb ladders and identify the leaks on the spot,“ said Herbst.




January 12, 2015, Sennett, NY – The methane digester in Sennett has been temporarily shut down while the Cayuga County Soil and Water Conservation District figures out a new plan of operation for it.

According to soil and water executive director Doug Kierst, the main operations of the digester were shut down in November. The digester operations have run into difficulties both from the cost of transporting manure and a lack of interest from restaurants and other food waste producers in the composting program. READ MORE

November 26, 2014, Salem, OR — Oregon wants to scale back the tax incentives that currently go to more than half a dozen projects across the state that generate power from manure.

The Oregon Department of Energy included the change in a proposed bill it hopes lawmakers will take up in the 2015 legislative session to extend the biomass energy tax credit program that also covers wood scraps and other fuels. READ MORE

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