Sustainable Development of Anaerobic Digestion in the U.S.

List of Acronyms 

• RNG –– Renewable Natural Gas 

• CHP –– Combined Heat and Power 

• WWTP –– Wastewater Treatment Plant 

• AD –– Anaerobic Digester 

• SA –– Stand-Alone Anaerobic Digesters 

• GHG –– Greenhouse gases 

• OFMSW –– Organic Fraction of Municipal Solid Waste 

• NPK –– Nitrogen, Phosphorous, Potassium 

• CAFO –– Concentrated Animal Feeding Operation 

• RFS –– Renewable Fuel Standards 

• RPS –– Renewable Portfolio Standards 

I. Introduction 

Currently, natural gas is used to fuel large portions of the U.S. heat, electricity, and transportation sectors. For decades, natural gas was seen as a more environmentally friendly fuel, and more recently has been characterized as a “bridge fuel” between fossil fuel and renewable energy technologies.2In reality, new investments in natural gas infrastructure contribute to increased greenhouse gas emissions by introducing previously sequestered fossil fuel carbon into contemporary carbon cycles. With more stringent carbon regulation on the horizon, natural gas investments carry a growing risk of becoming stranded assets, yielding environmental damage and outsized costs for utilities and rate payers. The capital costs of natural gas infrastructure are very high and return on investment occurs over decades. These investments not only preclude alternative investments; they create incentives to continue using infrastructure in order to realize returns, even when it is clear the infrastructure creates continuing environmental and economic harm. 

“Path dependence” is one key concept for critiquing the current natural gas infrastructure. Path dependence “describes how the reinforcement of a given set of arrangements over time raises the cost of changing them.”3 As certain economic activities such as the natural gas sector are institutionalized, returns on investment tend to stabilize or even increase, as the market adopts technologies, skills, and expectations that are dependent upon the existing system.4Increasing returns then create self-reinforcing feedback loops, “locking in” a given path because switching costs are high, even if the existing system leads to sub-optimal outcomes such as continued fossil fuel carbon emissions.5 

Yet path dependency thinking offers insight into how societies may switch to more optimal technologies by identifying “critical junctures.” Critical junctures are “brief moments at which opportunities for major institutional reforms appear, followed by long stretches of institutional stability.”6 The climate crisis, paired with a weakening oil sector and the advent of distributed energy, provides a critical juncture where States can rethink and reorient energy policy to achieve energy sovereignty and environmental gains. However, such large-scale institutional reforms are unlikely to succeed unless they address “both the nature and the scale of the switching costs faced by internal and external actors engaged in or with these institutions.”7In some cases, beneficiaries of the institutional status quo may need to be bought out. Some switching costs associated with learning new technologies and techniques can be “mitigated by state-sponsored public education programs and by gradual processes of transition,” rather than an abrupt regime shift.8 Finally, the political economy maintaining the status quo can be rehabilitated by cultivating “a countervailing political constituency that benefits from the reforms.”9 

In the case of switching from natural gas to biogas, those countervailing beneficiaries are every local community and company that generates biomass as a byproduct of existing economic activity. Lawmakers and regulators can encourage the market to avoid the risk of stranded assets, environmental damage, and rate payer costs by incentivizing sustainable use of anaerobic digesters and the biogas they create. Anaerobic digesters provide a sustainable alternative to natural gas infrastructure, replacing fossil fuel natural gas with biogas for heat, electricity, or transportation uses. Investments in biogas eliminate new greenhouse gas emissions and can avoid the risk of stranded assets when deployed sustainably. Food waste, animal manure, municipal yard waste, wastewater, and other sources of biomass feedstock have an energy value and emissions potential regardless of how they are managed.10 

Anaerobic digesters facilitate better waste management practices and derive energy and value from existing waste streams and nutrient cycles. These additionalities can be achieved without increasing the total amount of carbon in contemporary carbon cycles. Managed properly, anaerobic digestate can also reduce the volume of mineral fertilizer needed for agriculture, or biomass needed for energy production.11In addition to eliminating waste management and energy expenses, reducing GHG emissions, and generating revenue, anaerobic digesters can also help build energy resilience by creating distributed energy production across communities. Paired with storage, anaerobic digesters can help reduce peak demand. 

II. Benefits of Anaerobic Digestion and Biogas Utilization 

A. Identical Use to Natural Gas 

Biogas can be applied to the same uses as natural gas, because it is chemically indistinguishable. These uses typically include electricity generation, heating, combined heat and power (CHP), and fuel. Some uses such as fuel may require additional processing, such as refinement, compression, and storage. 

Electricity is one of the most common uses for biogas after its production. There are two major options that producers have when they produce biogas for electricity. Some use biogas for producing electricity that is then sold to the grid (40% of stand-alone ADs; 69% of farm; 16% WWTP).12 Others may also use the electricity for behind the meter use and self-sufficiency (30% of SA; 50% of farm; and 21% of WWTP).13 This does not necessarily require additional refinement. Heating is another common use for biogas. There are a few different heating services biogas can provide. Some use it to “loop back” to fuel boilers and furnaces to heat the digesters themselves (9% of SA; 25% of farm; and 60% of WWTP).14 Some use it to fuel boilers and furnaces to heat other spaces on-site. (30% of SA; 25% of farm; and 33% of WWTP).15 Combined heat and power (CHP) is a common use for on-site generators. 60% of stand-alone digesters used the biogas for CHP, 81% of on-farm co-digesters used biogas for CHP and 76% of co-digestion systems at water treatment facilities used biogas for CHP.16 This approach creates two opportunities to derive value from captured gas which would otherwise off-gas in landfills or be flared.17 These do not necessarily require additional refinement either. 

Finally, biogas may be refined, compressed, and stored to create “renewable natural gas” which meets industry standards for natural gas grid injection. Compressed renewable natural gas reduces GHG emissions “by up to 91% relative to petroleum gasoline.”18 Some will use biogas for mechanical power for machinery (0% SA; 6% Farm; 4% WWTP).19 Others may use biogas for compressed natural gas vehicle fueling or for fleet vehicles (5% SA digesters).20The final option is to use the biogas as renewable natural gas and inject it into the existing pipeline network (3% WWTP).21RNG can potentially provide 10% of the natural gas used in the United States,22 which could provide a sustainable pathway for phasing out fleets that use CNG. 

B. Cost-Effective, Clean, Renewable Grid Support 

Biogas can provide grid support and security because it has a high energy potential.23 The energy potential varies depending on the feedstock. Anaerobic digesters are also a cost-effective way of reducing emissions. In 2017, the California Climate Investments Annual Report found that “Advanced Technology Freight Demonstration Projects required $3,613 of funding invested per ton of CO2 equivalent (MTCO2e) GHGs reduced.”24 Their Hybrid and Zero Emission Truck and Bus Voucher Incentive Project required $329 per MTCO2e reduced.25By contrast, the California Department of Food and Agriculture’s Dairy Digester R&D program required only $7 per MTCO2e reduced, and the CalRecycle Organics Grant Program required $9 per MTCO2e reduced.26 

Biogas is already providing many communities with clean, renewable energy. In a 2016 study, the 119 respondents in an EPA survey produced 126 MW worth of biogas in 2016 which could power 79,820 homes per year.27 With about 2.5 people per home, this amounts to around 160,000 people’s energy being met through biogas. This is roughly the population of Providence, Rhode Island.28 The study found that 40 stand-alone digesters produced 10,498 standard cubic feet per minute (SCFM), which translates to roughly 33 MW.29 This could power 20,911 homes for one year. The same year, 12 on-farm digesters produced 4,053 SCFM of biogas, or 13 MW equivalent–8,246 homes per year.30 Finally, the co-digestion systems at 67 wastewater treatment plants produced 25,753 SCFM of biogas, around 80 MW. This could power 50,663 homes per year.31 EPA estimates that CHP systems can be cost effective for WWTPs treating at least 5mgd (million gallons per day), which would provide an equivalent to around 100 kW of electric power generation capacity.32 

Like natural gas, biogas can also be used “as a source of peak power that can be rapidly ramped up.”33 Whereas wind and solar power are intermittent, biogas can provide a continuous (or on-demand, with storage) high capacity source of renewable energy.34 Because anaerobic digestion can provide baseload irrespective of the time of day, it is an indispensable tool in renewable energy portfolios for policy makers concerned about mitigating the duck curve and shaving peak demand. Promoting sustainable deployment of AD (described in section III) will also allow energy developers to avoid additional siting costs, and allow the utility to save money by avoiding additional procurement costs. 

ADs can also facilitate on-site associated load reduction. Biogas is used on-site “to heat digesters and buildings/maintenance shops, to fuel boilers or kilns, and to generate heat or steam.”35 This on-site use offsets the high load use of farms, maintenance sites, commercial buildings, and more. Where sites with large loads would generally pull energy from the grid, an on-site AD system that utilizes the biogas for heat and electricity reduces peak demand on the grid. This enables large energy users such as wastewater treatment plants to become self-sustaining, perhaps even conveying excess generation to the grid.36 

C. AD Extra-credit: Associated Benefits of Clean Energy Generation 

Anaerobic digesters provide co-benefits which are not directly related to energy production or emissions reduction, but nevertheless provide substantial benefits for both natural and human-made systems. Four primary areas include creating closed-loop systems, easing burdens on wastewater treatment plants and landfills, and promoting sustainable farm nutrient management. 

1. Creating Closed-Loop Systems 

ADs have an added benefit of increasing institutional resilience to external economic factors. This is largely due to the integrative approach that reduces dependence on external goods and service providers, such as waste management, energy production and distribution, or nutrient and/or organic material sourcing. ADs allow market actors to save money on electricity and waste management bills, while also deriving value through more efficient use of existing materials on hand as part of existing activities. This helps close both financial and material loops on which institutions and firms rely, making them more financially and environmentally solvent. 

2. Wastewater Treatment: Burdens and Additionality 

ADs can ease the burden on wastewater treatment facilities by reducing the organic load or pathogen population in water entering the system. This eliminates contamination of local waterways through leaching and reduces costs for wastewater treatment facilities by allowing them to continue processing existing loads without increasing capacity. Processing and capturing organic material prior to wastewater treatment facilities also reduces the volume of landfill sludge, as this organic material is often deemed too contaminated for agricultural reuse after treatment. 

ADs not only reduce costs for wastewater treatment plants; it can also reduce costs significantly for upstream market actors by providing an integrative alternative. For instance, ADs can be used to manage wastewater associated with livestock waste, reducing pathogen levels by “up to 99% compared to undigested manure.”37 This creates important environmental benefits for local communities and ecosystems in addition to reducing liability for the livestock farmer. ADs can also enable industrial pre-treatment of wastewater for the food and beverage industry. Producers such as breweries may be charged fees based on the biochemical oxygen demand (BOD) of their discharge, while ADs can significantly reduce or eliminate these charges by reducing the BOD of their wastewater on site.38 

3. Reducing Landfill Waste 

“Municipal solid waste generation is expected to increase to about 2.2 billion tonnes globally with the associated management cost of USD 375.5 billion by 2025.”39 Currently the organic fraction of municipal solid waste (OFMSW) generated by European households accounts for around 65% of their total municipal solid waste.40 When OFMSW is properly segregated, it can produce digestate with few impurities.41 Notwithstanding additionalities achieved by utilizing OFMSW prior to the end of its lifecycle, merely processing OFMSW with AD reduces the GHG potential by about 75%.42 

There are several applications for digestate derived from OFMSW. Some applications sequester carbon long-term. For instance, digestate can be used for landscape alteration or restoration, road construction,43 or bioremediating contaminated soil.44 Pyrolysis converts organic matter in digestate into char, bio-oil, and syngas, though this comes with additional processing costs.45 Another option is to use the digestate as a cover at sanitary landfills.46While this option still places organic material in a landfill at the end of its lifecycle, it does make productive use and minimize GHG emissions prior to disposal. Finally, incinerating the solid digestate can reduce the volume of organic matter.47 This method can allow some elements to be captured from the bottom ash, such as phosphorous, potassium, and calcium.48 

4. Farm Nutrient Management 

ADs can assist in farm nutrient management programs as well. Conventional management systems dispose of nutrients in livestock waste such as nitrogen and phosphorus in wastewater treatment systems directly, or indirectly into waterways through leeching and leaking. ADs concentrate these nutrients, diverting them from waterbodies and redirecting them toward beneficial uses.49 This benefits the waterway and wastewater systems, while also capturing nitrogen and phosphorus on site in a stable, usable form. ADs reduce the total nutrient input for agricultural operations, as digestate provides liquid fertilizer and the organic material provides bedding and compost. 

ADs not only produce energy from waste, but also displace energy, emissions, and environmental harm associated with sourcing mineral fertilizer.50 A 1998 study estimated that mineral fertilizer production consumes ”approximately 1.2% of the world’s energy and is responsible for approximately 1.2% of the total GHG emissions.”51 Judicious use of digestate can displace or eliminate emissions across the lifecycle of mineral fertilizer by avoiding extraction, transportation, and production.52 Digestate typically contains large amounts of mineralized nitrogen, as well as other minerals which vary based on inputs.53In some cases, digestate has a higher NPK value than undigested manures because digestion stabilizes the compounds, increasing bioavailability.54 Some studies suggest that digestate properly rendered can be used as fertilizer without additional treatment.55 Others are more cautious, pointing to possible phytotoxicity, viscosity, odor, transportation, and application challenges.56 Nevertheless, several studies have shown that digestates yield similar or greater crop yields than undigested manures.57 Some studies show that digestate decreases the need for input of chemical fertilizers as well, as the organic material improves soil texture and retention.58 

However, using the digestate for agricultural applications comes with its own set of challenges. When properly processed, AD keeps valuable nutrients while removing pathogens and stabilizing volatile substances.59 Yet suboptimal processing or inappropriate use of digestate may result “in disease transmission through the food chain, if appropriate and stringent controls are not enforced.”60 Suboptimal processing and application techniques could promote eutrophication in fresh water reservoirs or oversaturate some soils with excess nutrients.61 Additionally, ”the agriculture demand for nutrient supply can fluctuate during peak crop.”62 Thus, timing of application is an important factor,63in some cases making storage necessary.64 Finally, because of the high moisture content, digestate has a high transportation cost which may restrict large scale application.65 

III. Sustainable Development of Biogas 

A. Path-Dependent Deployment of ADs 

Turning back to the concept of path dependence, not all biogas development promotes sustainable practices. In some cases it can further entrench unsustainable models by providing additional revenue streams and apparent compliance with environmental regulation. Consider the case of ADs installed in CAFOs, where ADs may effectively “green wash” an otherwise environmentally insolvent enterprise. AD investments there work to justify the economics of the CAFO, and returns are dependent upon continued “factory farming” to achieve the volume of organic material for which the AD was designed. 

For instance, C2e Renewables NC was completed in 2017. Prior to completion, C2e y signed contracts to supply 100 percent of the plant's output of biomethane to the utility giant Duke Energy and a second, unnamed Fortune 500 company.66 The $100-million facility, located on 82 acres in southeastern North Carolina, is the first in a pipeline of large-scale anaerobic digestion and biogas treatment facilities planned by Carbon Cycle Energy (C2e), the renewable energy development company based in Colorado.67 This facility processes in excess of 750,000 tons of organic waste per year. It produces enough fuel annually to generate approximately 290,000 MWH of electricity (enough to power 32,000 homes), far surpassing the capacity of any other standalone facility in the U.S., according to C2e CEO James Powell.68 

At full capacity, the plant generates 6,500 dekatherms of biomethane per day, equivalent to roughly 50,000 gallons of diesel fuel.69 While this project captures impressive additionalities and could be touted as ”carbon neutral,” it does not account for upstream or downstream lifecycles. Future environmental and animal welfare regulation could strand this asset when the system upon which the AD relies is disassembled. 

B. Sustainable Deployment 

Defining the sustainability of anaerobic digesters is somewhat difficult, as there are many variations in technology, complexity, and scale that can achieve the desired result of methane emission reduction. Determining what constitutes sustainable deployment of anaerobic digesters (AD) to create renewable natural gas (RNG) requires site-specific analyses. However, this framework identifies four critical factors that guide the AD design process toward sustainability: independence from natural gas transmission infrastructure, reliance on local feedstock and consumption of RNG, adding value to existing waste streams, and integration into efficient energy systems. 

First, “independence from natural gas transmission infrastructure” encourages financially sustainable deployment of ADs by encouraging designs that do not rely on assets likely to be stranded by future regulatory pressure. This independence further diminishes operational risk because developers will rely less on external energy markets to justify the economics of projects. 

Second, “reliance on local feedstock and consumption of biogas” encourages environmentally sustainable deployment by requiring projects to perform an energy solvency analysis in sourcing biodegradable materials, effectively defining a “service area” for source materials in need of more efficient management. “Local,” on-site, or community feedstock contextualizes the AD project in broader socio-economic activities, ensuring that projects do not rely on source materials whose collection requires more energy than it produces. This criterion also reinforces non-reliance on secondary markets to justify project finance, making design and scale contingent on existing, available material flows within a given context. This criterion requires projects to map feedstock assets and identify related applications for RNG prior to construction. Where AD is utilized to manage manure on small scale farms, it may also contribute to gains in animal welfare as well. 

Third, “adding value to existing waste streams” encourages socially sustainable deployment by constraining source materials to existing waste streams, discouraging development of energy crops or other sources of organic waste solely for the purpose of providing AD feedstock. This criterion reduces the economic and environmental cost of current waste management practices, as well as the volatility and volume of non-organic outputs. It also adds value to waste streams by creating new commodities: renewable natural gas, liquid digestate, and solid fertilizer. This criterion can encourage designs that accrue other related values, such as increased water quality where AD systems reduce biomass in landfills or eliminate manure lagoons. Finally, “integration into efficient energy systems” encourages deployment that maximizes the characteristics of biogas.

Most of the energy produced by conventional combustion energy generation systems is lost to heat. Therefore, combined heat and power systems are preferable. Some less desirable (but still environmentally beneficial) applications of RNG include heating alone, electricity generation alone, and fueling closed-loop transportation systems. Where ADs are located further than 16-32 km from land application, incineration or pyrolysis of digestate may be necessary to ensure economic feasibility, as digestate transportation costs can be quite high due to moisture content.70 These criteria envision firms, institutions, and municipalities that create closed-loop energy systems by managing organic waste with ADs, and distribute the heat and power within the same service area. This may include utilizing the heat in existing production processes, or distributing the heat through a district energy system. By incorporating ADs into existing operations, municipalities and institutions can grow more resilient and self-sufficient while reducing their carbon footprint and reducing costs. The following case studies provide examples of RNG capture/ADs deployed in various settings, including organics-intensive industry such as food and beverage processing, agricultural production, and wastewater treatment. 

C. Case Studies 

The following case studies highlight anaerobic digester installers and the companies they are working with to incorporate waste management into their workflow. These projects exemplify many or all of the sustainable development criteria enumerated above in § 3(A). 

i. Sistema Biobolsa 

Sistema Biobolsa is promoting low-tech continuous flow biodigesters for homestead and small-scale agricultural use in Mexico, Colombia, Kenya, and India.71 On one such homestead, María and Nicolas are using a single continuous flow bag to manage pig manure and other organic materials from production.72 The AD reduces flies and odor near their home, and improves water quality by reducing run-off. María and Nicolas are saving money by providing their own cooking gas, rather than buying natural gas. 

On the small-scale production side, Los Pinos farm produces pork “through 100% of the supply chain,” from birthing piglets to processing and selling meat and other pork products.73 After consulting with Sistema Biobolsa, Los Pinos uses three continuous flow bags to manage manure and other animal byproducts. The ranch requires gas to process the pork to provide value-added products like stew and lard. Los Pinos increased profitability by becoming more cost-effective. By incorporating an AD into the operation, Los Pinos reduced the amount of gas it bought, saving MEX$2500/month in 2015. 

Dianahi Queso Aculquense also incorporates Sistema Biobolsa ADs to manage manure, bedding, and dairy waste.74 Dianahi is an organic cheese producer that raising dairy cattle and processes the milk directly.75 Dianahi uses natural gas to cook their products, and reduced the amount of natural gas they purchased by 50% in 2015 by installing an AD. This reduces production costs for maintaining the pasture as well as pasteurizing by providing compost and energy. 

ii. Impact Bioenergy 

Impact Bioengery worked with Crooked Shed Farm to incorporate an AD into a small-scale poultry processing plant.76 Crooked Shed financed this project through the USDA‘s Rural Energy for America Program grant. Crooked Shed processes chicken, duck, turkey, and rabbit from their own operation and several other farms. This AD primarily processes animal byproducts. This system includes an electric generator, and is connected to the grid for net metering. This system has a maximum output of .15 therms per hour (around 4 

kWh), and 16 gallons per day of digestate, which is sold as liquid fertilizer. By using this system, Crooked Shed is leveraging a waste problem to ”create greater benefits,” such as reduced waste costs and creation of two new income streams.77 

Microsoft Corporation is utilizing Impact Bioenergy ADs on their main corporate campus to work toward zero waste in their cafeteria and catering operations.78 Using an intermodal microdigester, Microsoft is adding value to 40 tons of food waste per year. This system provides up to 5.6 therms per day (around 165 kWh). This system produces 164 gallons per week of liquid digestate used to fertigate the campus landscape, as well as compost which is returned to local farms that supply the catering operation.79 

Vashon Bioenergy Farm worked with Impact Bioenergy to develop a “community-scale bioenergy system.”80 This system is strategically located at the Island Spring Organics tofu factory to eliminate organic material transportation costs, and is capable of receiving additional organic waste from the community. This model generates one gasoline gallon equivalent (GGE) for every 60-80 pounds of food waste it upcycles. Vashon can handle up to 8,000 pounds of food waste per day, with the capacity to generate enough heat and power for more than 40 homes. This model provides up to 125 GGE of compressed natural gas vehicle fuel per day for fleet vehicles which collect additional biomass, creating a closed loop system. Vashon also reclaims over 2000 pounds of nutrients and 300,000 gallons of water annually, which is helping the island close carbon and nitrogen loops in their broader effort to work locally ”to reduce carbon use and increase resilience to a changing climate.”81 

iii. Native Energy 

In Washington, Native Energy and Rainier Farm created a biogas project that manages manure from three neighboring family farms.82 This project would not have been possible without a partnership between the three farms, which manage around 1,200 cows all together. Two of the farms pipe manure directly to the AD, while the third trucks manure a short distance to the digester. The Rainier Farm project includes a 1 MW generator, and the electricity is sold to the grid, making this project self-sustaining. This project avoids more than 4,000 metric tons of CO2 emissions per year, in addition to protecting two vulnerable watersheds from manure lagoon runoff and seepage. The farmers also save thousands of dollars per year by using the organic material outputs as bedding, rather than importing sawdust. 

In Vermont, Native Energy worked with the Essex Junction municipal wastewater treatment plant to develop a biogas generator.83 This project produces methane through anaerobic digestion of municipal sewage sludge. Previously, the methane was either used to heat the sludge, or simply flared to reduce methane emissions. Native Energy assisted in redesigning to create a combined heat-and power system, incorporating two 30 kW electricity-generating turbines. Now the same methane generates 350,000 kWh/year, which powers on-site pumps, grinders, and other processing equipment – in addition to heating sludge.84 This not only reduces the draw from the grid, but eliminates transmission costs by providing an on-site source of power. 

iv. Purpose Energy 

Purpose Energy worked with Magic Hat Brewery to create an AD that produces energy and pretreats wastewater.85 This brewery produces 21 tons of grain waste, 30,000 gallons of wastewater, and 10,000 gallons of yeast per day. Before the AD, the brewery paid significant electricity rates and wastewater discharge fees, with BOD discharge limits halting expansion. Now the grain waste, wastewater, and yeast are all processed by the AD, saving the company discharge fees as well as gas and energy costs. This 492,000-gallon AD is located in the parking lot behind the brewery, and the gas is used in a combined heat-and-power system to heat brewery boilers and sell power to the grid. 

v. Vanguard Renewables 

A few smaller AD programs have become a part of the Vanguard cooperative program, including Crescent Farm, which combines 10 tons of cow manure with 100 tons of pre-consumer organic waste in Haverhill, Massachusetts.86 The AD facility here produces over 7,700 MW of renewable energy every year. The RECs from this project are sold to the City of Haverhill. This clean electricity production offsets 5,500 lbs. of CO2 emissions each day for the municipality’s operations. 

Stahlbrush Farm in Oregon represents a fully closed loop agricultural AD system that utilizes a feedstock of vegetables, fruits, corn husks and cobs for its AD system. The electricity from the AD system generates electricity for the produce processing plant while the steam that is created during this operation dries the farm’s pumpkin seeds; the digestate that is leftover is used as fertilizer. Between 2009 and 2014, the Stahlbrush AD system processed 141,512 tons of agricultural feedstock. 

Since 2009, Gill Onions has used an AD to deal with its 300,000 pounds of onion skins and trimmings.87 They process 1 million pounds of onions per day. The biogas displaces 112,000 cubic feet of natural gas, and provides 100% of the electricity on-site. They save $700k/year in annual electrical costs and $400k in hauling disposal costs. This has also eliminated a pest problem that the former method of storage had created. 

IV. Complementary Policy Needs 

A. Digestate Quality Standards 

In order for ADs to be sustainable, local communities must make use of the digestate. However, impurities in digestate “can lead to negative public perception about the anaerobic digestion technology, cause aesthetic damage to the environment, increase the operational costs and affect operational stability…”88In the UK, source segregation regulations and restricting agricultural applications to on-farm digestate help encourage better waste management practices.89 Additionally, after processing the quality of the digestate must be declared in order to be a useful resource in agricultural nutrient management. Many countries require digestate processing that eliminates pathogens and seeds, and declaration of nutrient load, storage capacity, and spreading season.90 

B. Application Guidelines 

Local communities should work with agricultural extension offices to develop application guidelines for digestate use. “Inappropriate handling and spreading of digestate may cause environmental risk, either due to leakage of nitrate into recipient soil or water or due to potential gaseous losses of ammonia, methane and nitrous oxide.”91 Because appropriate handling is contingent upon local weather, soil, nutrient, and water conditions, local communities are in the best position to regulate and advise. Other regulations may prevent land application in some places and times, and storage may diminish the value of the digestate. Therefore, ADs should cultivate alternative applications. These include microalgae for biorefinery, solid fuel, solid fuel after densification, ethanol production, co-combustion for power generation, pyrolysis for char, bio-oil, and syngas.92 

C. Proper Valuation 

ADs stand at the intersection of energy production, waste management, nutrient sourcing, and environmental protection. As such, proper valuation of the resources they produce can be tricky. With respect to digestate, the value depends on whether the analysis includes avoided landfill costs, displaced mineral fertilizer costs, efficiency gains in mineral fertilization with complementary organic fertilization, and environmental gains with fertilizer applied in more stable states. The avoided cost of mineral fertilizer may not reflect the actual value to local communities in terms of water quality benefits or landfill diversion. 

Currently, Renewable Fuel Standards create incentives for pipeline injection and off-site consumption of RNG by creating RINs at the point of injection. This precludes proper valuation of RNG in stand-alone contexts, where the resource is integrated into the operation that produces the biogas. Thus, current RFSs incentivize pipeline-dependent AD development, which requires substantial fuel handling, cleaning, and upgrading. This could be partially alleviated by creating RFS/RPS carve outs for biogas, allowing ADs to create RINs at the point of production, and creating rate adders for net-metered AD energy generators. A uniform carbon fee would also level the playing field for more pure competition. 

D. Contract Facilitation 

Facilitating contract formation for ADs is essential to promote widespread acceptance. One way of streamlining the process is to create an integrated waste management/ power purchase agreement. Stand-alone digesters or ADs with excess receiving capacity can contract to take or purchase organic material, selling the energy, gas, or heat back to the same client. This would potentially allow the client to make green claims in both waste management and energy production. It would also put the AD in a better negotiating position when seeking financing. 

E. Permitting and Planning 

As with many environmental challenges, the onus for sustainably deploying ADs will fall on local government. Optimal levels of AD, biogas, and digestate use will only be attained if regional planners identify opportunity zones for nutrient reclamation and digestate markets. Local government may benefit from focusing on streamlining siting processes and should create subdivision standards that incorporate ADs into developed landscapes when a minimum volume of organic waste is anticipated. Rather than continuing to “retrofit” existing facilities with ADs, local policy can ensure that institutions begin to incorporate ADs in new builds where feasible.

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1 Upon request from directing attorney, time not spent perfecting citations, as this product is meant to inform comprehensive research by the team. 

2 For a brief history of natural gas in the U.S., see: https://www.directenergy.com/learning 

center/energy-choice/history-of-natural-gas-industry 

3 Mariana Prado and Michael Trebilcock, Path Dependence, Development, and the Dynamics of Institutional Reform, University of Toronto Law Journal, 2009. P. 350. 

4Id. at 351. 

5Ibid. 

6Id. at 358. 

7Ibid. 

8Id. at 370. 

9Ibid. 

10 https://www.epa.gov/sites/production/files/documents/Why-Anaerobic-Digestion.pdf 

11 “Anaerobic digestion of organic waste has significant potential to reduce global warming and climate change as it promotes enhanced cycling of nutrient resources through nutrient-rich end products... and presents an alternative to the energy-demanding generation of mineral fertilizers.” 

12 https://www.epa.gov/sites/production/files/2019-09/documents/ad_data_report_v10_- _508_comp_v1.pdf 13 Ibid. 

14 Ibid. 

15 Ibid. 

16 Ibid. 

17 Paolini et al., 2018, “Environmental impact of biogas: A short review of current knowledge”, Journal of Environmental Science and Health, Part A, vol. 53, no. 10, pp 899-906. 

18 https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy 

19 https://www.epa.gov/sites/production/files/2019-09/documents/ad_data_report_v10_- _508_comp_v1.pdf 20 Ibid. 

21 Ibid. 

22 Ibid. 

23 Paolini et al., 2018, “Environmental impact of biogas: A short review of current knowledge”, Journal of Environmental Science and Health, Part A, vol. 53, no. 10, pp 899-906. 

24 https://www.act-news.com/news/anaerobic-digesters-clean-transportation/ 

25 Ibid. 

26 Ibid. 

27 Ibid. 

28 http://worldpopulationreview.com/us-cities/providence-population/ 

29 EPA, Anaerobic Digestion Facilities Processing Food Waste in the United States (2016), Survey Results, 2019 30 Ibid. 

31 Ibid. 

32 https://www.cwwga.org/documentlibrary/121_EvaluationCHPTechnologiespreliminary[1].pdf p. 1-2 33 https://www.eesi.org/papers/view/fact-sheet-biogasconverting-waste-to-energy 

34 https://www.epa.gov/sites/production/files/2015-12/documents/biogas-roadmap.pdf. 

35 https://www.epa.gov/sites/production/files/2015-12/documents/biogas-roadmap.pdf. 

36 https://www.aceee.org/files/proceedings/2016/data/papers/11_228.pdf 

37 EPA, USDA, and USDOE, 2014, “Biogas Opportunities Roadmap”, 

https://www.epa.gov/sites/production/files/2015-12/documents/biogas-roadmap.pdf. 

38 https://www.biocycle.net/2012/01/12/digester-in-magic-hats-sustainability-mix/ 

39 Mohanakrishnan Logan and Chettiyappan Visvanathan, Management Strategies for Anaerobic Digestate of Organic Fraction of Municipal Solid Waste: Current Status and Future Prospects, Waste Management & Research, 2019. p. 27. 

40 https://www.royaldutchkusters.com/blog/what-is-the-organic-fraction-of-municipal-solid waste-ofmsw 

41 Mohanakrishnan Logan and Chettiyappan Visvanathan, Management Strategies for Anaerobic Digestate of Organic Fraction of Municipal Solid Waste: Current Status and Future Prospects, Waste Management & Research, 2019. p. 29. 

42 Id. at 37. 

43 Wei Pen and Alberto Pivato, Sustainable Management of Digestate from the Organic Fraction of Municipal Solid Waste and Food Waste under the Concepts of Back to Earth Alternatives and Circular Economy, Waste Biomass Valor p. 7. 

44 Id. at 6. 

45 Id. at 2. 

46 Id. at 2. 

47 Id. at 9. 

48 Mohanakrishnan Logan and Chettiyappan Visvanathan, Management Strategies for Anaerobic Digestate of Organic Fraction of Municipal Solid Waste: Current Status and Future Prospects, Waste Management & Research, 2019. p. 37. 

49 EPA, USDA, and USDOE, 2014, “Biogas Opportunities Roadmap”, 

https://www.epa.gov/sites/production/files/2015-12/documents/biogas-roadmap.pdf. 

50 “Accounting for emissions of CO2, N2O, and CH4 from agricultural practices has become increasingly important. Emissions of these gases may occur either directly during agricultural activities (eg. cultivation and harvesting), or indirectly during the production and transport of required inputs (eg. herbicides, pesticides and fertilisers).” 

51 Cite needed. 

52 “During the life cycle of fertiliser products, GHG emissions may arise during extraction of resources, the transport of raw materials and products, and during fertiliser production processes.”52 “Biogas residue, which commonly contains large amounts of mineralized N and low concentrations of heavy metals, presents a promising alternative to mineral fertilizers that require substantial energy input at production.” 

53 “Biogas residue, which commonly contains large amounts of mineralized N and low concentrations of heavy metals, presents a promising alternative to mineral fertilizers that require substantial energy input at production.” 

54 “Essential nutrients (N, P, K, Mg), including trace elements required by plants, are conserved in the residue. However, nutrients are present in inorganic plant-available forms at a markedly higher extent in digested residue, compared to untreated waste, due to the large input of organic nutrients that are mineralized during the digestion process. For instance, digested residue contains 25% more accessible ammonium (NH4+-N) than untreated liquid manure.” 

55 “Digestate can be used as fertilizer without any further treatment after removal from the digester. However, in such a case, the storage, transport, handling and application of digestate as a fertilizer result in significant costs to farmers compared with its fertilizer value, due to the large volume and low dry matter. The costs increase further with investment in slurry storage, when required by environmental regulations in countries such as Denmark, Germany and France, where the period of fertilizer application is limited to the growing season and the amount of nutrients applied per unit of agricultural land is restricted by pollution control regulations.” 

56 “The residue may not be a suitable soil improver in its basic form, owing to possible phytotoxicity, viscosity and odor, difficult handling, and expensive soil application approaches. Therefore, further treatment is essential to enhance its applicability as a crop fertilizer before use as an acceptable saleable product, such as composting (i.e., aerobic degradation) and/or air drying... On the other hand, upon drying, up to 90% of NH4+ may be lost as ammonia (NH3), which would dramatically reduce the benefits of biogas residue as a crop fertilizer.” 

57 “With respect to field performances, many authors have shown that anaerobic digestates have similar or greater crop performance than corresponding undigested animal manures and slurries which factually demonstrates their high fertilizer value.” 

58 “...the input of chemical fertilizers should decrease with the use of anaerobically digested residues, whereas soil texture is improved.” 

59 Mohanakrishnan Logan and Chettiyappan Visvanathan, Management Strategies for Anaerobic Digestate of Organic Fraction of Municipal Solid Waste: Current Status and Future Prospects, Waste Management & Research, 2019. p. 28. 

60 Id. at 29. 

61 Wei Pen and Alberto Pivato, Sustainable Management of Digestate from the Organic Fraction of Municipal Solid Waste and Food Waste under the Concepts of Back to Earth Alternatives and Circular Economy, Waste Biomass Valor p. 2. 

62 Ibid. 

63 “The application time needs to be taken into account to match nutrient availability with the needs of crops and avoid leakage of mineralized N into the soil and subsequently, groundwater.” 

64 “The solid manures should be–whenever possible–applied to the fields as soon as possible, as the main emissions take place in the first weeks of storage, especially during the warmer season due to the temperature dependency of the emission rates. If storage is unavoidable, anaerobic conditions should be maintained.” 

65 Ibid. 

66 https://www.prnewswire.com/news-releases/carbon-cycle-energy-breaks-ground-on-100- 

million-biogas-facility-in-north-carolina-300377611.html 

67 Ibid. 

68 Ibid. 

69 Ibid. 

70 Wei Pen and Alberto Pivato, Sustainable Management of Digestate from the Organic Fraction of Municipal Solid Waste and Food Waste under the Concepts of Back to Earth Alternatives and Circular Economy, Waste Biomass Valor p. 10. 13

71 ” Sistema Biobolsa (Sistema.bio) is a biodigester package that produces biogas for the generation of thermal and mechanical energy, and organic fertilizer (biol). A biodigester allows farms to transform what was once a waste problem into opportunities to increase productivity. ” www.sistemabiobolsa.com 

72 https://youtu.be/33oEM2dA_rU 

73 https://www.youtube.com/watch?v=tECplqFSCts 

74 https://www.youtube.com/watch?v=mGjds4Tyr4c&feature=youtu.be 

75 https://quesoaculquense.com.mx/ 

76 http://impactbioenergy.com/wp-content/uploads/2018/06/Factsheet-AD-25-2017-2-Crooked Shed-Farm-Microdigester.pdf 

77 Lainey Piland, ”WSDA Poultry Processing at Crooked Shed Farm,” SnoValley Tilth, Nov. 15, 2017. https://www.snovalleytilth.org/wsda-licensed-poultry-processing-at-crooked-shed-farm/ 

78 http://impactbioenergy.com/wp-content/uploads/2018/06/Factsheet-AD-25-2017-1- Corporate-Campus-Microdigester.pdf 79 http://impactbioenergy.com/wp-content/uploads/2018/06/Factsheet-AD-25-2017-1- Corporate-Campus-Microdigester.pdf 80 http://impactbioenergy.com/wp-content/uploads/2019/06/Vashon-Bioenergy-Farm-Island 

Spring-Organics-NAUTILUS-overview.pdf 

81 Paul Rowley, ”Island Anaerobic Digester Unveiled,” Vashon-Maury Island Beachcomber. April 18, 2019. https://www.vashonbeachcomber.com/news/island-anaerobic-digester-unveiled/ 

82 https://nativeenergy.com/project/rainier-farm-biogas-projecthb/ 

83 https://nativeenergy.com/project/essex-junction-municipal-biogas-generatorhb/ 

84 While this project importantly derives additional benefits from wastewater, the organic material is ultimately landfilled. This highlights another important, related issue of contamination. 

85 Molly Farrell Tucker, ”Digester in Magic Hat’s Sustainability Mix,” Biocycle. January 2012. 

https://www.biocycle.net/2012/01/12/digester-in-magic-hats-sustainability-mix/ 

86 https://vanguardrenewables.com/haverhillmassfarmpoweredanaerbobicdigester/ 

87 https://www.mass.gov/info-details/anaerobic-digestion-case-studies#industrial 

88 Mohanakrishnan Logan and Chettiyappan Visvanathan, Management Strategies for Anaerobic Digestate of Organic Fraction of Municipal Solid Waste: Current Status and Future Prospects, Waste Management & Research, 2019. p. 29. 

89 Ibid. 

90 Ibid. 

91 Mohanakrishnan Logan and Chettiyappan Visvanathan, Management Strategies for Anaerobic Digestate of Organic Fraction of Municipal Solid Waste: Current Status and Future Prospects, Waste Management & Research, 2019. p. 31. 

92 Id. at 36.