Progress of Waste-to-Energy in the USA

Rising rates of consumption necessitate an improved approach to resource management. Around the world, from Europe to Asia, governments have adapted their practices and policies to reflect renewability. They’ve invested in facilities that repurpose waste as source of energy, affording them a reliable and cheap source of energy.

This seems like progress, given the impracticality of older methods. Traditional sources of energy like fossil fuels are no longer a realistic option moving forward, not only for their finite nature but also within the context of the planet’s continued health. That said, the waste-to-energy sector is subject to scrutiny.

We’ll detail the reasons for this scrutiny, the waste-to-energy sector’s current status within the United States and speculations for the future. Through a concise analysis of obstacles and opportunities, we’ll provide a holistic perspective of the waste-to-energy progress, with a summation of its positive and negative attributes.

Status of Waste-to-Energy Sector

The U.S. currently employs 86 municipal waste-to-energy facilities across 25 states for the purpose of energy recovery. While several have expanded to manage additional waste, the last new facility opened in 1995. To understand this apparent lack of progress in the area of thermochemical treatment of MSW, budget represents a serious barrier.

One of the primary reasons behind the shortage of waste-to-energy facilities in the USA is their cost. The cost of construction on a new plant often exceeds $100 million, and larger plants require double or triple that figure to build. In addition to that, the economic benefits of the investment aren’t immediately noticeable.

The Palm Beach County Renewable Energy Facility is a RDF-based waste-to-energy (WTE) facility.

The U.S. also has a surplus of available land. Where smaller countries like Japan have limited space to work within, the U.S. can choose to pursue more financially viable options such as landfills. The expenses associated with a landfill are far less significant than those associated with a waste-to-energy facility.

Presently, the U.S. processes 14 percent of its trash in waste-to-energy (WTE) plants, which is still a substantial amount of refuse given today’s rate of consumption. On a larger scale, North America ranks third in the world in the waste-to-energy movement, behind the European nations and the Asia Pacific region.

Future of WTE Sector

Certain factors influence the framework of an energy policy. Government officials have to consider the projected increase in energy demand, concentrations of CO2 in the atmosphere, space-constrained or preferred land use, fuel availability and potential disruptions to the supply chain.

A waste-to-energy facility accounts for several of these factors, such as space constraints and fuel availability, but pollution remains an issue. Many argue that the incineration of trash isn’t an effective means of reducing waste or protecting the environment, and they have evidence to support this.

The waste-to-energy sector extends beyond MSW facilities, however. It also encompasses biofuel, which has seen an increase in popularity. The aviation industry has shown a growing dedication to biofuel, with United Airlines investing $30 million in the largest producer of aviation biofuel.

If the interest of United Airlines and other companies is any indication, the waste-to-energy sector will continue to expand. Though negative press and the high cost of waste-to-energy facilities may impede its progress, advances in technology promise to improve efficiency and reduce expenses.

Positives and Negatives

The waste-to-energy sector provides many benefits, allowing communities a method of repurposing their waste. It has negative aspects that are also important to note, like the potential for pollution. While the sector offers solutions, some of them come at a cost.

It’s true that resource management is essential, and adapting practices to meet high standards of renewability is critical to the planet’s health. However, it’s also necessary to recognize risk, and the waste-to-energy sector is not without its flaws. How those flaws will affect the sector moving forward is critical to consider.

A Primer on Waste-to-Energy

Waste-to-Energy (also known as energy-from-waste) is the use of thermochemical and biochemical technologies to recover energy, usually in the form of electricity, steam and fuels, from urban wastes.These new technologies can reduce the volume of the original waste by 90%, depending upon composition and use of outputs.

Energy is the driving force for development in all countries of the world. The increasing clamor for energy and satisfying it with a combination of conventional and renewable resources is a big challenge. Accompanying energy problems in different parts of the world, another problem that is assuming critical proportions is that of urban waste accumulation.

The quantity of waste produced all over the world amounted to more than 12 billion tonnes in 2006, with estimates of up to 13 billion tonnes in 2011. The rapid increase in population coupled with changing lifestyle and consumption patterns is expected to result in an exponential increase in waste generation of upto 18 billion tonnes by year 2020.

Waste generation rates are affected by socio-economic development, degree of industrialization, and climate. Generally, the greater the economic prosperity and the higher percentage of urban population, the greater the amount of solid waste produced. Reduction in the volume and mass of solid waste is a crucial issue especially in the light of limited availability of final disposal sites in many parts of the world. Millions of tonnes of household wastes are generated each year with the vast majority disposed of in open fields or burnt wantonly.

The main categories of waste-to-energy technologies are physical technologies, which process waste to make it more useful as fuel; thermal technologies, which can yield heat, fuel oil, or syngas from both organic and inorganic wastes; and biological technologies, in which bacterial fermentation is used to digest organic wastes to yield fuel.

The three principal methods of thermochemical conversion are combustion in excess air, gasification in reduced air, and pyrolysis in the absence of air. The most common technique for producing both heat and electrical energy from wastes is direct combustion. Combined heat and power (CHP) or cogeneration systems, ranging from small-scale technology to large grid-connected facilities, provide significantly higher efficiencies than systems that only generate electricity.

Biochemical processes, like anaerobic digestion, can also produce clean energy in the form of biogas which can be converted to power and heat using a gas engine. In addition, wastes can also yield liquid fuels, such as cellulosic ethanol, which can be used to replace petroleum-based fuels. Cellulosic ethanol can be produced from grasses, wood chips and agricultural residues by biochemical route using heat, pressure, chemicals and enzymes to unlock the sugars in biomass wastes.

Waste-to-energy plants offer two important benefits of environmentally safe waste management and disposal, as well as the generation of clean electric power.  The growing use of waste-to-energy as a method to dispose of solid and liquid wastes and generate power has greatly reduced environmental impacts of municipal solid waste management, including emissions of greenhouse gases.

Pyrolysis of Municipal Wastes

Pyrolysis is rapidly developing biomass thermal conversion technology and has been garnering much attention worldwide due to its high efficiency and good eco-friendly performance characteristics. Pyrolysis technology provides an opportunity for the conversion of municipal solid wastes, agricultural residues, scrap tires, non-recyclable plastics etc into clean energy. It offers an attractive way of converting urban wastes into products which can be effectively used for the production of heat, electricity and chemicals.

Pyrolysis-MSW

Pyrolysis of Municipal Wastes

Pyrolysis process consists of both simultaneous and successive reactions when carbon-rich organic material is heated in a non-reactive atmosphere. Simply speaking, pyrolysis is the thermal degradation of organic materials in the absence of oxygen. Thermal decomposition of organic components in the waste stream starts at 350°C–550°C and goes up to 700°C–800°C in the absence of air/oxygen.

Pyrolysis of municipal wastes begins with mechanical preparation and separation of glass, metals and inert materials prior to processing the remaining waste in a pyrolysis reactor. The commonly used pyrolysis reactors are rotary kilns, rotary hearth furnaces, and fluidized bed furnaces. The process requires an external heat source to maintain the high temperature required.

Pyrolysis can be performed at relatively small-scale which may help in reducing transport and handling costs.  In pyrolysis of MSW, heat transfer is a critical area as the process is endothermic and sufficient heat transfer surface has to be provided to meet process heat requirements.

The main products obtained from pyrolysis of municipal wastes are a high calorific value gas (synthesis gas or syngas), a biofuel (bio oil or pyrolysis oil) and a solid residue (char). Depending on the final temperature, MSW pyrolysis will yield mainly solid residues at low temperatures, less than 4500C, when the heating rate is quite slow, and mainly gases at high temperatures, greater than 8000C, with rapid heating rates. At an intermediate temperature and under relatively high heating rates, the main product is a liquid fuel popularly known as bio oil.

Wide Range of Products

Bio oil is a dark brown liquid and can be upgraded to either engine fuel or through gasification processes to a syngas and then biodiesel. Pyrolysis oil may also be used as liquid fuel for diesel engines and gas turbines to generate electricity.

Bio oil is particularly attractive for co-firing because it can be relatively easy to handle and burn than solid fuel and is cheaper to transport and store. In addition, bio oil is also a vital source for a wide range of organic compounds and specialty chemicals.

Syngas is a mixture of energy-rich gases (combustible constituents include carbon monoxide, hydrogen, methane and a broad range of other VOCs). The net calorific value (NCV) of syngas is between 10 and 20MJ/Nm3. Syngas is cleaned to remove particulates, hydrocarbons, and soluble matter, and then combusted to generate electricity.

Diesel engines, gas turbines, steam turbines and boilers can be used directly to generate electricity and heat in CHP systems using syngas and pyrolysis oil. Syngas may also be used as a basic chemical in petrochemical and refining industries.

The solid residue from MSW pyrolysis, called char, is a combination of non-combustible materials and carbon. Char is almost pure carbon and can be used in the manufacture of activated carbon filtration media (for water treatment applications) or as an agricultural soil amendment.

Bioenergy Resources in MENA Countries

The Middle East and North Africa (MENA) region offers almost 45 percent of the world’s total energy potential from all renewable sources that can generate more than three times the world’s total power demand. Apart from solar and wind, MENA also has abundant bioenergy energy resources which have remained unexplored to a great extent.

biomass_resources

Around the MENA region, pollution of the air and water from municipal, industrial and agricultural operations continues to grow.  The technological advancements in the biomass energy and waste-to-energy industry, coupled with the tremendous regional potential, promises to usher in a new era of energy as well as environmental security for the region.

The major biomass producing countries in MENA are Saudi Arabia, Egypt, Yemen, Iraq, Syria and Jordan. Traditionally, biomass energy has been widely used in rural areas for domestic purposes in the MENA region, especially in Egypt, Yemen and Jordan. Since most of the region is arid or semi-arid, the major bioenergy resources are municipal solid wastes, agricultural residues and organic industrial wastes.

Municipal solid wastes represent the best source of biomass in Middle East countries. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita solid waste generation. The gross urban waste generation quantity from Middle East countries is estimated at more than 150 million tons annually.

Food waste is the third-largest component of generated waste by weight which mostly ends up rotting in landfill and releasing greenhouse gases into the atmosphere. The mushrooming of hotels, restaurants, fast-food joints and cafeterias in the region has resulted in the generation of huge quantities of food wastes.

In Middle East countries, huge quantity of sewage sludge is produced on daily basis which presents a serious problem due to its high treatment costs and risk to environment and human health. On an average, the rate of wastewater generation is 80-200 litres per person each day and sewage output is rising by 25 percent every year. According to estimates from the Drainage and Irrigation Department of Dubai Municipality, sewage generation in the Dubai increased from 50,000 m3 per day in 1981 to 400,000 m3 per day in 2006.

The food processing industry in MENA produces a large number of organic residues and by-products that can be used as biomass energy sources. In recent decades, the fast-growing food and beverage processing industry has remarkably increased in importance in major countries of the region. Since the early 1990s, the increased agricultural output stimulated an increase in fruit and vegetable canning as well as juice, beverage, and oil processing in countries like Egypt, Syria, Lebanon and Saudi Arabia.

The MENA countries have strong animal population. The livestock sector, in particular sheep, goats and camels, plays an important role in the national economy of respective countries. Many millions of live ruminants are imported each year from around the world. In addition, the region has witnessed very rapid growth in the poultry sector. The biogas potential of animal manure can be harnessed both at small- and community-scale.

Charcoal Briquette Production in the Middle East: Perspectives

There is a huge demand for charcoal briquettes in the Middle East, especially in Saudi Arabia, Egypt and UAE. However the production of charcoal in the Middle East is in nascent stages despite the availability of biomass resources, especially date palm biomass. The key reason for increasing demand of charcoal briquettes is the large consumption of meat in the region which uses charcoal briquettes as fuel for barbecue, outdoor grills and related activities.

The raw materials for charcoal briquette production are widely available across the Middle East in the form of date palm biomass, crop wastes and woody biomass. With a population of date palm trees of 84 million or 70% of the world’s population, the potential biomass waste from date palm trees is estimated at 730,000 tons / year (approximately 200,000 tons from Saudi Arabia and 300,000 tons from Egypt). Date palm trees produce huge amount of agricultural wastes in the form of dry leaves, stems, pits, seeds etc. A typical date tree can generate as much as 20 kilograms of dry leaves per annum while date pits account for almost 10 percent of date fruits.

The fronds and trunks of date palm trees are potential raw materials for charcoal because of the potential to produce high calorific value and low ash content charcoal. Leaf waste will produce a low calorific value due to high ash content. In addition, woody biomass waste such as cotton stalks that are widely available in Egypt can also be a raw material for making charcoal. The contribution of the agricultural sector in Egypt is quite high at 13.4%.

Charcoal is compacted into briquettes for ease in handling, packaging, transportation and use. Briquettes can be made in different shapes such as oval, hexagonal, cube, cylinder or octagonal. An adhesive (called binder) is needed for the manufacture of the briquette. Two common binders are saw dust and corn starch.

Date palm biomass is an excellent resource for charcoal production in Middle East

Continuous pyrolysis is the best technology for charcoal production. Continuous pyrolysis has the ability to handle large biomass volumes, the process is fast and smoke production is negligible. When using conventional pyrolysis technology  (or batch carbonization), the process is lengthy, processing capacity is small and there are concerns related to harmful smoke emissions.

Apart from charcoal, continuous pyrolysis also gives bio oil, wood vinegar and syngas. Syngas can be converted into electricity by using a gas engine or converted into a wide variety of biofuels through different processes. Bio oil can be used as boiler fuel and marine fuel. Wood vinegar can be used as biopesticide and liquid organic fertilizer. Low water content in date palm waste fronds and trunks make it very suitable for thermochemical conversion technologies, especially pyrolysis and gasification.

 

Charcoal can also be used for the production of activated charcoal/carbon. Activated carbon is used by a lot of industries for purification processes. In addition, a number of industries that are using petcoke as fuel can switch to charcoal due to its better combustion properties and eco-friendly nature.

For more information on how to set up charcoal production plant based on date palm biomass or other crop residues in the Middle East, please email salman@bioenergyconsult.com or eko.sb.setyawan@gmail.com

5 Interesting Facts About Waste-to-Energy Projects

Waste-to-energy (also known as energy-from-waste) is a complicated technology in the realm of renewable energy. There are a lot of hidden truths and myths about this technology that people need to be aware of. Renewable energy technologies, like solar and wind, have much more simple processes and gain most of the attention from media outlets.

On the converse, renewable energy sources that are highly complex like nuclear energy have a bunch of media attention as well.

So, why don’t we discuss a bit more about this relatively unknown technology and asset class? Here I’ll discuss a number of the most important facts about waste-to-energy (abbreviated as WTE).

Interesting Facts About Waste-to-Energy

Let’s get into our facts about waste-to-energy that you need to know.

1. Waste-to-Energy Can Provide Baseload Power

The most familiar renewable energy resources such as wind and solar can only provide power if the sun is shining or the wind is blowing. WTE projects can actually provide baseload power that is used to serve consumers and the grid no matter the time of day or if the sun is shining or not.

Baseload power is essentially when intermittent resources like solar and wind become more prevalent.

2. Not All WTE Projects are Clean and Green

While waste-to-energy projects would seem to be green and clean because they turn trash into power or gas. However, some projects require long hauling of trash to bring to the actual incineration facility. This actually ends up require much more emissions from the trash haulers than alternatives.

One solution to this would be to help promote the use of electric vehicles and electric vehicle technology to be installed in trucking, like waste hauling.

3. WTE Projects Can Reduce Use of Landfills

Landfills have increased at an exponential pace the in last 100 years. Waste-to-energy projects are an awesome alternative to landfills as the trash is used to provide electricity or fuel.

WTE projects reduce waste volumes by approximately 90%, which results in fewer landfills that are needed to process ash. This ends up protecting our natural resources and land in a dramatic fashion.

5. WTE Projects have Multiple Revenue Streams

Waste-to-energy projects are extremely complicated and expensive to build. Most of the investor economic interest is driven by financial incentives, renewable identification numbers, tax credits, etc. to help these projects get financed.

Beyond these other financial incentives, some of the waste-to-energy projects produce a byproduct, named biochar, which has multiple applications and fetches good prices. The biochar can usually end up providing the most value in the revenue stream or investability of the project itself.

In addition to other economic streams, waste-to-energy projects usually require high tipping fees. A tipping fee is what the trash hauler has to pay in order to dump the trash at the facility. With WTE projects, the tipping fee can end up being 50-60% of the overall revenue stack.

5. WTE Facilities are Net Greenhouse Gas Reducers

Methane has more than 20 times the potency of carbon dioxide and is ranked as a very dangerous contributor to climate change and warming of our planet. WTE facilities avoid the productions of methane and end up producing up to 10 times more the electricity than landfill gas projects. If you didn’t know, landfills can actually end up producing electricity by capture the methane gas and compressing it into a consumable natural gas for power.

Sysav–WTE-plant-Sweden

Sweden is one of the best proponents of waste-to-energy in the world

WTE projects will usually have much more capacity than any landfill gas projects.

Conclusions

You can’t use waste-to-energy projects at your home similar to solar or even wind to get free electricity. However, knowing about projects in your area and the relevant suppliers will help you understand whether or not the technology is a perfect fit for your community. If you see a project coming online in your surrounding area, you should know how to ask the right questions.

At the end of the day, WTE projects are green and clean. They just need to have the right systems in place to make them more efficient and less risky to appeal new investor appetite. What fact was your favorite about waste-to-energy?

Do you know much about waste-to-energy projects? Let us know in the comments below. We’d love to hear from you.

WTE Prospects in the Middle East

A combination of high fuel prices and a search for alternative technologies, combined with massive waste generation has led to countries in the Middle East region to consider Waste to Energy (or WtE) as a sustainable waste management strategy and cost-effective fuel source for the future. We look at the current state of the WtE market in the Middle East.

wastetoenergy-plant-qatar

It is estimated that each person in the United Arab Emirates produces 2 kg of municipal solid waste per day – that puts the total waste production figure somewhere in the region of 150 million tonnes every year. Given that the population currently stands at over 9.4 million (2013) and is projected to see an annual average growth figure of 2.3% over the next six years, over three times the global average, it’s clear that this is a lot of waste to be disposed of.

In addition, the GCC nations in general rank in the bottom 10% of the sustainable nations in the world and are also amongst the top per capita carbon-releasers.

When we also consider that UAE are actively pursuing alternative energy technologies to supplement rapidly-decreasing and increasingly-costly traditional fossil fuels, mitigate the harmful effects of landfill, and reduce an ever-increasing carbon footprint, it becomes apparent that high on their list of proposed solutions is Waste to Energy (WtE). It could be an ideal solution to the problem.

What is WtE

Waste-to-Energy works on the simple principle of taking waste and turning it into a form of energy. This can be electricity, heat or transport fuels, and can be achieved in a variety of ways – the most common of which is incineration. MSW is taken to a WtE plant, incinerated at high temperatures and the resultant heat is used to boil water which creates steam to turn turbines, in the same way that burning gas or coal produces power. Gasification and anaerobic digestion are two further WtE methods which are also used.

However, WtE has several advantages over burning fossil fuels. Primarily amongst them are the potential to minimise landfill sites which have caused serious concern for many years. They are not only unsightly, but can also be contaminated, biologically or chemically. Toxic waste can leach into the ground beneath them and enter the water table.

Landfill sites also continuously emit carbon dioxide and methane, both harmful greenhouse gases – in addition methane is potentially explosive. Sending MSW to landfill also discourages recycling and necessitates more demand for raw materials. Finally, landfill sites are unpleasant places which attract vermin and flies and give off offensive odours.

Waste to Energy Around the World

WtE has been used successfully in many countries around the world for a long time now. Europe is the most enthusiastic proponent of WtE, with around 450 facilities; the Asia-Pacific region has just over 300; the USA has almost 100. In the rest of the world there are less than 30 facilities but this number is growing. Globally, it is estimated that the WtE industry is growing at approximately US $2 billion per annum and will be valued at around US $80 billion by the year 2022.

WTE_Plant_Belgium

Waste-to-Energy is now widely accepted as a part of sustainable waste management strategy.

The USA ranks third in the world for the percentage of waste which is incinerated for energy production. Around 16% of the rubbish that America produces every day is burned in its WtE plants. Advocates claims the advantages are clear:

  • reducing the amount of greenhouse gas emitted into the environment (estimates say that burning one ton of waste in a WtE plant saves between one half and one ton of greenhouse gases compared to landfill emissions, or the burning of conventional fuels),
  • freeing up land which would normally be used for landfill (and, therefore, extending the life of existing landfill sites),
  • encouraging recycling (some facilities have managed to reduce the amount of waste they process by up to 90% and the recycling of ferrous and non-ferrous metals provides an additional income source), and,
  • most importantly, producing a revenue stream from the sale of the electricity generated.

In one small county alone, Lancaster, Pennsylvania, with a population of just over half-a-million people, more than 4.4 billion kWh of electricity has been produced through WtE in the last 20 years. This has generated over USD $256 million through its sale to local residents.

Waste-to-Energy in the Middle East

Given WtE’s potential to not only reduce greenhouse gas emissions and pollution on a local scale, but also to produce much-needed electricity in the region, what is the current state of affairs in the Middle East. There are several WtE initiatives already underway in the Middle East.

Qatar was the first GCC country to implement a waste-to-energy programme and currently generates over 30MW of electricity from its Domestic Solid Waste Management Center (DSWMC) located at Messeid (Doha). Saudi Arabia and the UAE have both stated that they have WtE production capacity targets of 100MW. Bahrain, Kuwait and Oman are also seriously considering waste-to-energy as a means to tackle the worsening waste management problem.

Abu Dhabi’s government is currently spending around US $850 million to build a 100 MW plant which is expected to be operational by 2017 and which will supply around 20,000 households with electricity. In Sharjah, the world’s largest household waste gasification plant, costing in excess of US $480 million, is due to be open in 2015.

However, not all the GCC members are as enthusiastic about WtE. Dubai’s government has recently scrapped plans for a US $2 billion project which would have made use of the 7,800 tonnes of domestic waste which is produced in Dubai every single day.

We asked Salman Zafar, Founder of Doha-based EcoMENA, a popular sustainability advocacy, why given the sheer scale of the waste in the Gulf region, the production of this form of energy is still in its infancy. “The main deterrent in the implementation of WtE projects in the Middle East is the current availability of cheap sources of energy already available, especially in the GCC,” he commented.

Salman Zafar further says, “WtE projects demand a good deal of investment, heavy government subsidies, tipping fees, power purchase agreements etc, which are hard to obtain for such projects in the region.” “The absence of a sustainable waste management strategy in Middle East nations is also a vital factor behind the very slow pace of growth of the WtE sector in the region. Regional governments, municipalities and local SWM companies find it easier and cost-effective to dump untreated municipal waste in landfills,” he added.

So, how can WtE contribute towards the region’s growing power demand in the future?

“Modern WtE technologies, such as RDF-based incineration, gasification, pyrolysis, anaerobic digestion etc, all have the ability to transform power demand as well as the waste management scenario in the region,” he continued. “A typical 250 – 300 tons per day WtE plant can produce around 3 – 4 MW of electricity and a network of such plants in cities across the region can make a real difference in the energy sector as well as augmenting energy reserves in the Middle East. In fact, WtE plants also produce a tremendous about of heat energy which can be utilised in process industries, further maximising their usefulness,” Salman Zafar concluded.

New technologies naturally take time to become established as their efficiency versus cost ratios are analysed. However, it is becoming increasingly clearer that waste-to-energy is a viable and efficient method for solid waste management and generation of alternative energy in the Middle East.

Biogas from Slaughterhouse Wastes

Slaughterhouse waste (or abattoir waste) disposal has been a major environmental challenge in all parts of the world. The chemical properties of slaughterhouse wastes are similar to that of municipal sewage, however the former is highly concentrated wastewater with 45% soluble and 55% suspended organic composition. Blood has a very high COD of around 375,000 mg/L and is one of the major dissolved pollutants in slaughterhouse wastewater.

slaughterhouse-waste

In most of the developing countries, there is no organized strategy for disposal of solid as well as liquid wastes generated in abattoirs. The solid slaughterhouse waste is collected and dumped in landfills or open areas while the liquid waste is sent to municipal sewerage system or water bodies, thus endangering public health as well as terrestrial and aquatic life. Wastewater from slaughterhouses is known to cause an increase in the BOD, COD, total solids, pH, temperature and turbidity, and may even cause deoxygenation of water bodies.

Anaerobic Digestion of Slaughterhouse Wastes

There are several methods for beneficial use of slaughterhouse wastes including biogas generation, fertilizer production and utilization as animal feed. Anaerobic digestion is one of the best options for slaughterhouse waste management which will lead to production of energy-rich biogas, reduction in GHGs emissions and effective pollution control in abattoirs.

Anaerobic digestion can achieve a high degree of COD and BOD removal from slaughterhouse effluent at a significantly lower cost than comparable aerobic systems. The biogas potential of slaughterhouse waste is higher than animal manure, and reported to be in the range of 120-160 m3 biogas per ton of wastes. However the C:N ratio of slaughterhouse waste is quite low (4:1) which demands its co-digestion with high C:N substrates like animal manure, food waste, crop residues, poultry litter etc.

Slaughterhouse effluent has high COD, high BOD, and high moisture content which make it well-suited to anaerobic digestion process. Slaughterhouse wastewater also contains high concentrations of suspended organic solids including pieces of fat, grease, hair, feathers, manure, grit, and undigested feed which will contribute the slowly biodegradable of organic matter. Amongst anaerobic treatment processes, the up-flow anaerobic sludge blanket (UASB) process is widely used in developing countries for biogas production from abattoir wastes.

Slaughterhouse waste is a protein-rich substrate and may result in sulfide formation during anaerobic degradation. The increased concentration of sulfides in the digester can lead to higher concentrations of hydrogen sulfide in the biogas which may inhibit methanogens. In addition to sulfides, ammonia is also formed during the anaerobic digestion process which may increase the pH in the digester (>8.0) which can be growth limiting for some VFA-consuming methanogens.