Meeting sanitation and energy needs with Biogas

So is it possible to feed a biogas digester with human waste? Yes it is. The problem however is getting enough of it into the digester. The traditional answer to this has been to build latrine stances which feed, by gravity, directly into the digester

Wantokism

So we’ve been doing some investigation into installing biogas into schools which are using huge amounts of firewood for their cooking needs. These are BIG institutions! We’re talking upwards of 1500 boarding students!

There are a lot of challenges with biogas even at a small scale. Most notably for me the pure amount of unsavoury work it takes to feed the beast! The calculations say that about 60% of fuel needs can be met by Biogas…best case.

These schools happen to have a huge problem with sanitation as well. With no water borne sewage they rely on pit latrines. The maintenance of these systems (either digging new ones, or emptying them) imparts another financial cost of the schools. Not to mention the possible damage to the ground water system! In the area we are working there is no ‘honey sucker’ truck to dispose of human waste…it’s dumped on site, in…

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An Energy Source Few People Know About

One source of energy that has been around for a long time is the methane gas generated by the wastewater treatment process. Twenty years ago some WWTP’s explored the idea of cogeneration to offset their high energy costs. At the time, the cost of converting the methane gas to energy was more expensive than buying it off the grid. Now that has all changed.

Enviro-Care

As the United States moves toward energy independence, it has been exciting to see the many new sources of energy that are available to this country.  On the renewable energy side of the equation, there are hundreds of projects in the wind, solar, hydro, geothermal, tidal, and biofuels sectors.  Many of these are good sources of renewable energy, although currently some are either not practical or readily available.

One source of energy that has been around for a long time is the methane gas generated by the wastewater treatment process.  Twenty years ago some WWTP’s explored the idea of cogeneration to offset their high energy costs.  At the time, the cost of converting the methane gas to energy was more expensive than buying it off the grid.  Now that has all changed.

Private and public wastewater treatment and landfill facilities have jumped on board this cogeneration movement in order to…

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Biomass Feedstock in Middle East and North Africa (MENA)

Map of commonly included MENA (Middle East & N...
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According to a recent study, 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 biomass energy resources which have remained unexplored to a great extent. According to conservative estimates, the potential of biomass energy in the Euro Mediterranean region is about 400TWh per year. Around the region, pollution of the air and water from municipal, industrial and agricultural operations continues to grow.  The technological advancements in the biomass 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 are 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 biomass energy potential is mainly contributed by municipal solid wastes, agricultural residues and 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.

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A Glance at Biomass Resources

Manure, a field in Randers in Denmark
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Biomass energy projects provide major business opportunities, environmental benefits, and rural development.  Feedstocks can be obtained from a wide array of sources without jeopardizing the food and feed supply, forests, and biodiversity in the world.

Agricultural Residues

Crop residues encompasses all agricultural wastes such as bagasse, straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. Large quantities of crop residues are produced annually worldwide, and are vastly underutilised. Rice produces both straw and rice husks at the processing plant which can be conveniently and easily converted into energy. Significant quantities of biomass remain in the fields in the form of cob when maize is harvested which can be converted into energy. Sugar cane harvesting leads to harvest residues in the fields while processing produces fibrous bagasse, both of which are good sources of energy. Harvesting and processing of coconuts produces quantities of shell and fibre that can be utilized.

Current farming practice is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by cattle. These residues could be processed into liquid fuels or thermochemical processed to produce electricity and heat. Agricultural residues are characterized by seasonal availability and have characteristics that differ from other solid fuels such as wood, charcoal, char briquette. The main differences are the high content of volatile matter and lower density and burning time.

Animal Waste

There are a wide range of animal wastes that can be used as sources of biomass energy. The most common sources are animal and poultry manures. In the past this waste was recovered and sold as a fertilizer or simply spread onto agricultural land, but the introduction of tighter environmental controls on odour and water pollution means that some form of waste management is now required, which provides further incentives for waste-to-energy conversion.

The most attractive method of converting these waste materials to useful form is anaerobic digestion which gives biogas that can be used as a fuel for internal combustion engines, to generate electricity from small gas turbines, burnt directly for cooking, or for space and water heating.

Forestry Residues

Forestry residues are generated by operations such as thinning of plantations, clearing for logging roads, extracting stem-wood for pulp and timber, and natural attrition. Harvesting may occur as thinning in young stands, or cutting in older stands for timber or pulp that also yields tops and branches usable for biomass energy. Harvesting operations usually remove only 25 to 50 percent of the volume, leaving the residues available as biomass for energy.

Stands damaged by insects, disease or fire are additional sources of biomass. Forest residues normally have low density and fuel values that keep transport costs high, and so it is economical to reduce the biomass density in the forest itself.

Wood Wastes

Wood processing industries primarily include sawmilling, plywood, wood panel, furniture, building component, flooring, particle board, moulding, jointing and craft industries. Wood wastes generally are concentrated at the processing factories, e.g. plywood mills and sawmills. The amount of waste generated from wood processing industries varies from one type industry to another depending on the form of raw material and finished product.

Generally, the waste from wood industries such as saw millings and plywood, veneer and others are sawdust, off-cuts, trims and shavings. Sawdust arise from cutting, sizing, re-sawing, edging, while trims and shaving are the consequence of trimming and smoothing of wood. In general, processing of 1,000 kg of wood in the furniture industries will lead to waste generation of almost half (45 %), i.e. 450 kg of wood. Similarly, when processing 1,000 kg of wood in sawmill, the waste will amount to more than half (52 %), i.e. 520 kg wood.

Industrial Wastes

The food industry produces a large number of residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry with everything from meat production to confectionery producing waste that can be utilised as an energy source.

Solid wastes include peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fibre from sugar and starch extraction, filter sludges and coffee grounds. These wastes are usually disposed of in landfill dumps.

Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations as well as wine making.

These waste waters contain sugars, starches and other dissolved and solid organic matter. The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist.

Pulp and paper industry is considered to be one of the highly polluting industries and consumes large amount of energy and water in various unit operations. The wastewater discharged by this industry is highly heterogeneous as it contains compounds from wood or other raw materials, processed chemicals as well as compound formed during processing.  Black liquor can be judiciously utilized for production of biogas using anaerobic UASB technology.

Municipal Solid Wastes and Sewage

Millions of tonnes of household waste are collected each year with the vast majority disposed of in open fields. The biomass resource in MSW comprises the putrescibles, paper and plastic and averages 80% of the total MSW collected. Municipal solid waste can be converted into energy by direct combustion, or by natural anaerobic digestion in the engineered landfill. At the landfill sites the gas produced by the natural decomposition of MSW (approximately 50% methane and 50% carbon dioxide) is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. The organic fraction of MSW can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.

Sewage is a source of biomass energy that is very similar to the other animal wastes. Energy can be extracted from sewage using anaerobic digestion to produce biogas. The sewage sludge that remains can be incinerated or undergo pyrolysis to produce more biogas.

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Role of Waste-to-Energy in Waste Management

Waste-to-energy provides the fourth “R” in a comprehensive solid waste management program: reduction, reuse, recycling, and energy recovery. The benefits of full-scale implementation of energy recovery as a final step in waste management are evident:

  • conservation of natural resources and fossil fuels
  • drastic landfill reduction
  • lower greenhouse emissions

The need for an integrated solid waste management strategy in a city, state, or country becomes more evident as that region’s economy grows and the standard of living improves. With increases in consumption, the amount of waste generated also increases. This creates stresses on the land used for disposal, can lead to environmental pollution, and can be detrimental to public health if the waste is not disposed properly.

Use of Ultrasound in Anaerobic Digestion – Industrial Examples

Ultrasound activated sludge disintegration could positively affect sludge anaerobic digestion. Due to sludge disintegration, organic compounds are transferred from the sludge solids into the aqueous phase resulting in an enhanced biodegradability. Therefore disintegration of sewage sludge is a promising method to enhance anaerobic digestion rates and lead to reduce the volume of sludge digesters.

The addition of disintegrated surplus activated sludge and/or foam to the process of sludge anaerobic digestion can lead to markedly better effects of sludge handling at wastewater treatment plants. In the case of disintegrated activated sludge and/or foam addition to the process of anaerobic digestion it is possible to achieve an even twice a higher production of biogas. Here are few examples:

STP Bad Bramstedt, Germany (85,000 PE or 4.49 MGD) First fundamental study on pilot scale by Technical University of Hamburg-Harburg, 3 years, 1997 – 1999 • reduction in digestion time from 20 to 4 days without losses in degradation efficiency • increase in biogas production by a factor of 4 (renewable energy!) • reduction of digested sludge mass of 25%

STP Ahrensburg, Germany (50,000 PE or 2.64 MGD) Preliminary test on pilot-scale by Technical University of Hamburg-Harburg, 6 months, 1999 • increase in VS destruction of 20% • increase in biogas production of 20%

STP Bamberg, Germany (230,000 PE or 12.15 MGD) 1) Preliminary full-scale test, 4 months, 2002 2) Full-scale installation since June 2004 • increase in VS destruction of 30% • increase in biogas production of 30% • avoided the construction of a new anaerobic digester (3,000 m?? vol.)

STP Freising, Germany (130,000 PE or 6.87 MGD) Fundamental full-scale study by University of Armed Forces, Munich, 4 months, 2003 • increase in biogas production of 15% • improved sludge dewatering of 10%

STP Meldorf, Germany (20,000 PE or 1.06 MGD) ( BNR Oxidation Ditch plant ) 1) Preliminary full-scale test, 3 months, 2004 2) Full-scale installation since December 2004 • increase in VS destruction of 25% • increase in biogas production of 25% • no foam or filamentous organisms present in the anaerobic sludge digester

STP Ergolz 2, Switzerland (65,000 PE or 3.43 MGD) Full-scale test, 3 months, 2004 • increase in VS destruction of 15% • increase in biogas production of 25%

STP Beverungen, Germany (50,000 PE or 2.64 MGD) Full-scale test, 3 months, 2004/2005 • increase in VS destruction of 25% • increase in biogas production of 25%

STP Au, Illertissen/Ulm, Germany (70,000 PE or 3.70 MGD) Full-scale test, 3 months, 2004/2005 • increase in VS destruction of 15% • increase in biogas production of 25%

STP Zeist, Netherlands (75,000 PE or 3.96 MGD) Full-scale installation since May 2005 • increase in VS destruction of 25% • increase in biogas production of 25%

STP Kleinsteinbach, Germany (40,000 PE or 2.11 MGD) Full-scale installation since July 2006 • increase in VS destruction of 25% • increase in biogas production of 25%