Solar Energy Prospects in Oman

Even the fleetest of glances at a map of worldwide solar energy levels shows Oman to be well placed to exploit the energy-giving rays of the sun. In fact, over the last few years, a gaggle of reports have been published extolling the virtues of exploiting this renewable energy source. However, with increasing and more urbanised populations consuming greater and greater amounts of energy, only now are governments across the Gulf and wider MENA regions seriously looking at harnessing solar power to help fill potential energy deficits.

Mr Jigar Shah, quoted in a recent article, said investors were “desperate to invest in the Middle East solar industry” and were waiting for clear instructions from the governments in the region. He said, “The economics of switching to solar energy are far better here than in South Africa, India, Brazil, China and the US. Now that the costs of developing solar technologies have significantly declined, it is time for the Middle East to turn talk into action.”

That there is huge potential in the solar industry was underlined in no uncertain terms by the announcement last year of a $2 billion project to develop solar energy power resources in Oman. The plans also envisage creating industrial plants for the manufacture of solar panels and aluminium frames, to be used by the power station and also for local consumption and export.

Knowledge and technology transfer were also critical contributors to the success of the project which also aimed to tie-up with major international technology companies and international universities with expertise in renewable energy education, to help train the local population in servicing this burgeoning industry.

David Heimhofer, Chairman of Terra Nex Group and Managing Director of Middle East Best Select Fund, said, “By attracting foreign direct investment in the growing renewable energy sector and using German expertise, Oman will become not just a regional leader in the field, but also benefit from the great intrinsic value within the complete value chain associated with this economic sector. He says“In addition to generating new jobs for the Omani people and boosting exports, this project creates an entire industry that Oman can be proud of.”

The project is expected to deliver more than 2000 jobs for Omanis across a diverse range of industrial sectors and services. In order to increase the skill set of the local population to help service these new jobs, the University of Zurich proposed the setting up of an educational institution in the Sultanate specialising in the field of renewable energy engineering.

Biomass Wastes to Energy for MENA

The high volatility in oil prices in the recent past and the resulting turbulence in energy markets has compelled many MENA countries, especially the non-oil producers, to look for alternate sources of energy, for both economic and environmental reasons. The significance of renewable energy has been increasing rapidly worldwide due to its potential to mitigate climate change, to foster sustainable development in poor communities, and augment energy security and supply.

The Middle East is well-poised for waste-to-energy development, with its rich feedstock base in the form of municipal solid wastes, crop residues and agro-industrial wastes. The high rate of population growth, urbanization and economic expansion in the Middle East is not only accelerating consumption rates but also accelerating the generation of a wide variety of waste. Bahrain, Saudi Arabia, UAE, Qatar and Kuwait rank in the top-ten worldwide in terms of per capita waste generation. The gross urban waste generation quantity from Arab countries is estimated at more than 80 million tons annually. Open dumping is the most prevalent mode of municipal solid waste disposal in most countries.

Waste-to-energy technologies hold the potential to create renewable energy from waste matter, including municipal solid waste, industrial waste, agricultural waste, and industrial byproducts. Besides recovery of substantial energy, these technologies can lead to a substantial reduction in the overall waste quantities requiring final disposal, which can be better managed for safe disposal in a controlled manner. Waste-to-energy systems can contribute substantially to GHG mitigation through both reductions of fossil carbon emissions and long-term storage of carbon in biomass wastes.

Modern waste-to-energy systems options offer significant, cost-effective and perpetual opportunities for greenhouse gas emission reductions. Additional benefits offered are employment creation in rural areas, reduction of a country’s dependency on imported energy carriers (and the related improvement of the balance of trade), better waste control, and potentially benign effects with regard to biodiversity, desertification, recreational value, etc. In summary, waste-to-energy can significantly contribute to sustainable development both in developed and less developed countries. Waste-to-energy is not only a solution to reduce the volume of waste that is and provide a supplemental energy source, but also yields a number of social benefits that cannot easily be quantified.

Biomass wastes can be efficiently converted into energy and fuels by biochemical and thermal conversion technologies, such as anaerobic digestion, gasification and pyrolysis. Waste-to-energy technologies hold the potential to create renewable energy from waste matter.  The implementation of waste-to-energy technologies as a method for safe disposal of solid and liquid biomass wastes, and as an attractive option to generate heat, power and fuels, can significantly reduce environmental impacts of wastes. In fact, energy recovery from MSW is rapidly gaining worldwide recognition as the fourth ‘R’ in sustainable waste management system – Reuse, Reduce, Recycle and Recover. A transition from conventional waste management system to one based on sustainable practices is necessary to address environmental concerns and to foster sustainable development in the region.

Thermal Conversion of Tannery Wastes

tannery-wastesTanneries generate considerable quantities of sludge, shavings, trimmings, hair, buffing dusts and other general wastes and can consist of up to 70% of hide weight processed. Thermal technologies, gasification in particular, by virtue of chemically reducing conditions, provides a viable alternative thermal treatment for Chrome containing materials, and generates a chrome (III) containing ash. This ash has significant commercial value as it can be reconstituted.

All of the wastes created by the tannery can be gasified following pre-treatment methods such as maceration, drying and subsequent densification or briquetting. A combined drying and gasification process could eliminate solid waste, whilst providing a combustible gas as a tax-exempt renewable energy source, which the tannery can directly reuse. Gasification trials have illustrated that up to 70% of the intrinsic energy value of the wastes currently disposed can be recovered as “synthesis gas” energy.

Gasification technology has the potential to provide significant cost benefits in terms of power generation and waste disposal, and increase sustainability within the leather industry. The gasification process converts any carbon-containing material into a combustible gas comprised primarily of carbon monoxide, hydrogen and methane, which can be used as a fuel to generate electricity and heat.

A wide range of tannery wastes can be macerated, flash dried, densified and gasified to generate a clean syngas for reuse in boilers or other Combined Heat and Power systems. As a result up to 70% of the intrinsic energy value of the waste can be recovered as syngas, with up to 60% of this being surplus to process drying requirements so can be recovered for on-site boiler or thermal energy recovery uses.

A proprietary technology has been in commercial operation at a tanyard on the West Coast of Norway since mid 2001. The process employs gasification-and-plasma-cracking and offer the capability of turning the tannery waste problem to a valorising source that may add values to the plant owner in terms of excessive energy and ferrochrome, a harmless alloy that is widely used by the metallurgical industry. The process leaves no ashes but a non-leaching slag that is useful for civil engineering works, and, hence, no residues for landfill disposal

Energy Potential of Palm Kernel Shells

palm-kernel-shellsThe Palm Oil industry in Southeast Asia and Africa generates large quantity of biomass wastes whose disposal is a challenging task. Palm kernel shells (or PKS) are the shell fractions left after the nut has been removed after crushing in the Palm Oil mill. Kernel shells are a fibrous material and can be easily handled in bulk directly from the product line to the end use. Large and small shell fractions are mixed with dust-like fractions and small fibres. Moisture content in kernel shells is low compared to other biomass residues with different sources suggesting values between 11% and 13%.

Palm kernel shells contain residues of Palm Oil, which accounts for its slightly higher heating value than average lignocellulosic biomass. Compared to other residues from the industry, it is a good quality biomass fuel with uniform size distribution, easy handling, easy crushing, and limited biological activity due to low moisture content. PKS can be readily co-fired with coal in grate fired -and fluidized bed boilers as well as cement kilns in order to diversify the fuel mix.

The primary use of palm kernel shells is as a boiler fuel supplementing the fibre which is used as primary fuel. In recent years kernel shells are sold as alternative fuel around the world. Besides selling shells in bulk, there are companies that produce fuel briquettes from shells which may include partial carbonisation of the material to improve the combustion characteristics. As a raw material for fuel briquettes, palm shells are reported to have the same calorific characteristics as coconut shells. The relatively smaller size makes it easier to carbonise for mass production, and its resulting palm shell charcoal can be pressed into a heat efficient biomass briquette.

Palm kernel shells have been traditionally used as solid fuels for steam boilers in palm oil mills across Southeast Asia. The steam generated is used to run turbines for electricity production. These two solid fuels alone are able to generate more than enough energy to meet the energy demands of a palm oil mill. Most palm oil mills in the region are self-sufficient in terms of energy by making use of kernel shells and mesocarp fibers in cogeneration. In recent years, the demand for palm kernel shells has increased considerably in Europe, Asia-Pacific, China etc resulting in price close to that of coal. Nowadays, cement industries and power producers are increasingly using palm kernel shells to replace coal. In grate-fired boiler systems, fluidized-bed boiler systems and cement kilns, palm kernel shells are an excellent fuel.

Cofiring of PKS yields added value for power plants and cement kilns, because the fuel significantly reduces carbon emissions – this added value can be expressed in the form of renewable energy certificates, carbon credits, etc. However, there is a great scope for introduction of high-efficiency cogeneration systems in the industry which will result in substantial supply of excess power to the public grid and supply of surplus PKS to other nations. Palm kernel shell is already extensively in demand domestically by local industries for meeting process heating requirements, thus creating supply shortages in the market.

Palm oil mills around the world may seize an opportunity to supply electricity for its surrounding plantation areas using palm kernel shells, empty fruit branches and palm oil mill effluent which have not been fully exploited yet. This new business will be beneficial for all parties, increase the profitability for palm oil industry, reduce greenhouse gas emissions and increase the electrification ratio in surrounding plantation regions.

Biomass Pelletization Process

Biomass pellets are a popular type of biomass fuel, generally made from wood wastes, agricultural biomass, commercial grasses and forestry residues. In addition to savings in transportation and storage, pelletization of biomass facilitates easy and cost effective handling. Dense cubes pellets have the flowability characteristics similar to those of cereal grains. The regular geometry and small size of biomass pellets allow automatic feeding with very fine calibration. High density of pellets also permits compact storage and rational transport over long distance. Pellets are extremely dense and can be produced with a low moisture content that allows them to be burned with very high combustion efficiency.

Biomass pelletization is a standard method for the production of high density, solid energy carriers from biomass. Pellets are manufactured in several types and grades as fuels for electric power plants, homes, and other applications. Pellet-making equipment is available at a variety of sizes and scales, which allows manufacture at domestic as well industrial-scale production. Pellets have a cylindrical shape and are about 6-25 mm in diameter and 3-50 mm in length. There are European standards for biomass pellets and raw material classification (EN 14961-1, EN 14961-2 and EN 14961-6) and international ISO standards under development (ISO/DIS 17225-1, ISO/DIS 17225-2 and ISO/DIS 17225-6).

Process Description

The biomass pelletization process consists of multiple steps including raw material pre-treatment, pelletization and post-treatment. The first step in the pelletization process is the preparation of feedstock which includes selecting a feedstock suitable for this process, its filtration, storage and protection. Raw materials used are sawdust, wood shavings, wood wastes, agricultural residues like straw, switchgrass etc. Filtration is done to remove unwanted materials like stone, metal, etc. The feedstock should be stored in such a manner that it is away from impurities and moisture. In cases where there are different types of feedstock, a blending process is used to achieve consistency.

The moisture content in biomass can be considerably high and are usually up to 50% – 60% which should be reduced to 10 to 15%. Rotary drum dryer is the most common equipment used for this purpose. Superheated steam dryers, flash dryers, spouted bed dryers and belt dryers can also be used. Drying increases the efficiency of biomass and it produces almost no smoke on combustion. It should be noted that the feedstock should not be over dried, as a small amount of moisture helps in binding the biomass particles. The drying process is the most energy intensive process and accounts for about 70% of the total energy used in the pelletization process.

Schematic of Pelletization of Woody Biomass

Before feeding biomass to pellet mills, the biomass should be reduced to small particles of the order of not more than 3mm.  If the pellet size is too large or too small, it affects the quality of pellet and in turn increases the energy consumption. Therefore the particles should have proper size and should be consistent. Size reduction is done by grinding using a hammer mill equipped with a screen of size 3.2 to 6.4 mm. If the feedstock is quite large, it goes through a chipper before grinding.

The next and the most important step is pelletization where biomass is compressed against a heated metal plate (known as die) using a roller. The die consists of holes of fixed diameter through which the biomass passes under high pressure. Due to the high pressure, frictional forces increase, leading to a considerable rise in temperature. High temperature causes the lignin and resins present in biomass to soften which acts as a binding agent between the biomass fibers. This way the biomass particles fuse to form pellets.

The rate of production and electrical energy used in the pelletization of biomass  are strongly correlated to the raw material type and processing conditions such as moisture content and feed size. The The average energy required to pelletize biomass is roughly between 16 kWh/t and 49kWh/t. During pelletization, a large fraction of the process energy is used to make the biomass flow into the inlets of the press channels.

Binders or lubricants may be added in some cases to produce higher quality pellets. Binders increase the pellet density and durability. Wood contains natural resins which act as a binder. Similarly, sawdust contains lignin which holds the pellet together. However, agricultural residues do not contain much resins or lignin, and so a stabilizing agent needs to be added in this case. Distillers dry grains or potato starch is some commonly used binders. The use of natural additives depends on biomass composition and the mass proportion between cellulose, hemicelluloses, lignin and inorganics.

Due to the friction generated in the die, excess heat is developed. Thus, the pellets are very soft and hot (about 70 to 90oC). It needs to be cooled and dried before its storage or packaging. The pellets may then be passed through a vibrating screen to remove fine materials. This ensures that the fuel source is clean and dust free.

The pellets are packed into bags using an overhead hopper and a conveyor belt. Pellets are stored in elevated storage bins or ground level silos. The packaging should be such that the pellets are protected from moisture and pollutants. Commercial pellet mills and other pelletizing equipment are widely available across the globe.

4 Tips For Keeping Your Home Energy Prices Low

Heating can be very expensive nowadays and keeping the heat contained within your home can be a challenge. You will see that energy prices manage to hike year after year and it is important to keep the heat contained in a home where there is particularly cold weather outside to assist with your overall energy costs.

Ensure efficient heating system

Modern houses normally have a good heating system and there is a lot of regulation around this to ensure that when people are buying new homes, the efficiency has been taken into consideration from the manufacturers. There are websites like myjobquote.co.uk that you can use in order to arrange local boiler engineers to come out and review your current heating systems to ensure they are effective.  They would also offer services such as a boiler power flush if it is required – again supporting the effectiveness of your appliance.

If your boiler or radiators are not working greatly then a boiler service cost quote may be required in order to make sure they get repaired and are working as well as possible. If any of your heating equipment is faulty and not working correctly then you will overcompensate in terms of the heating you put on in the home which would then significantly increase your costs.

Take action on drafts

If there are any potential drafts and air seeping out of the home, then it will affect the warmth of your home and ultimately your energy bill.  Be sure to take action when you recognise any of these problems.

Some common draft points will be doors and windows and are usually pretty noticeable if there is a problem. Nowadays most homes have double glazed windows and secured doors where this shouldn’t be an issue. If your house has a chimney, then this is another potential area for cold air to get in. If not in use you may wish to consider sealing this off in totality.

Set timers for heating

Putting the heating on and off all the time could also be affecting your bills. Consider getting a timer where you can control the heating at intervals that suit you. Clearly, this wouldn’t be suitable all the time and if you are in the home and there is additional heat required then you can “boost” to allow more heat to come out for longer.

Setting the timers will assist with being disciplined on a routine and you can know pretty accurately what it is that you will be spending every month.

Energy monitors

Energy monitors are becoming really popular nowadays with the users able to then see immediately how much energy they are consuming.  Most energy providers now give this service where you can get one of these appliances installed (generally for free or a very little cost).

The government is also doing a lot more to try and encourage every household to have one of these to help with the energy cost hike challenges.

Sustainable Environment in Singapore: An Attraction for Businesses and Investors

In addition to a robust economy, Singapore’s sustainable environment is another leading factor that has attracted numerous investors. Most cities in the world have failed to address environmental issues brought about by urbanization. Towns or urban areas cover over 2% of the Earth’s surface; they are responsible for about 80% of the greenhouse gases emitted while using up almost 75%  of nature’s resources.

However, a host of countries in Southeast Asia are leading the way to change this contrary notion about cities and urban regions. Research conducted by several world-leading environmental bodies and institutions determined that Singapore is indeed one of the most environmentally sustainable nations.

Singapore’s first prime minister kickstarted the dream of making Singapore a green city. His main agenda was to make Singapore stand out from the rest of the Asian countries and also attract investors from all over the world. The first step undertaken to achieve this dream was the eradication of the houseboats and overcrowded slums along the banks of Singapore River.

Incorporation services Singapore are offering entrepreneurs moving to Singapore a platform to incorporate their businesses in Singapore. This allows them to run their firms within the stipulated terms while also receive the government’s backing.

On the world’s Environmental Performance Ranking, Yale University and the U.N place Singapore at seventeenth globally and first position in Asia. Contrary to popular belief, Singapore’s efforts and strict green technology guidelines, which were set and backed up by the government, helped in making it an eco-friendly city.  

So how exactly does Singapore afford to provide suitable surroundings perfect for its citizens and also attract investors and entrepreneurs from overseas?

Government Support

As discussed before, adoption of green technology is one of the leading things that has made Singapore an eco-friendly city. Singapore has been able to morph into a modernized city-state without having a negative impact on nature.

The Singapore government’s Cleantech division, which is a subsidiary of the board tasked with economic growth, has offered continued support to companies in the clean technology business. This has led to the business sector growing tremendously in areas such as renewable energy, water conservation, green buildings, etc.

Growing ICT Center

Companies such as Hewlett Packard (HP) and International Business Machines Corporation have partnered with the Ministry of Environment and Water Resources. The main idea behind these partnerships is to ensure that Singapore’s ICT industry thrives. HP, for example, has been tasked with designing and manufacturing energy efficient systems that will cut power costs while still providing a working platform for businesses.

There is no shortage of green spaces in Singapore

Low Energy Costs and Environmental Remedies

Accommodating over 7000 companies from different nations across the globe is no mean feat. As such, Singapore’s government and other agencies know that a green environment is not the only requirement to attract more investors.

Through an alliance known as the Singapore Sustainability Alliance, an umbrella consisting of government groups, non-governmental organizations, and teaching institutions, Singapore has been able to come up with policies that create a sustainable environment. Other than this, the alliance has overseen the adoption of systems that include proper water use, renewable energy, energy efficiency, waste management, etc. which have significantly improved business growth.  

Towards Sustainable Biomass Energy

biomass-balesBiomass is one of the oldest and simplest ways of getting heat and energy, and it’s starting to make a comeback due to its status as renewable resource. Some, however, aren’t so sure that using more of it would be good for our environment. So, how sustainable is biomass energy really?

What is Biomass?

Biomass is organic material from plants and animals. It naturally contains energy because plants absorb it from the sun through photosynthesis. When you burn biomass, it releases that energy. It’s also sometimes converted into a liquid or gas form before it is burned.

Biomass includes a wide variety of materials but includes:

  • Wood and wood processing waste
  • Agricultural crops
  • Garbage made up of food, yard and wood waste
  • Animal manure and human sewage

About five percent of the United States’ energy comes from biomass. Biomass fuel products such as ethanol make up about 48 percent of that five percent while wood makes up about 41 percent and municipal waste accounts for around 11 percent.

The Benefits of Biomass

Biomass is a renewable resource because the plants that store the energy released when it is burned can be regrown continuously. In theory, if you planted the same amount of vegetation that you burned, it would be carbon neutral because the plants would absorb all of the carbon released. Doing this is, however, much easier said than done.

Another potential is that it serves as a use for waste materials that have are already been created. It adds value to what otherwise would be purely waste.

Additionally, many forms of biomass are also relatively low-tech energy sources, so they may be useful, or even required for older buildings that need an electrical renovation.

Drawbacks of Biomass

A major drawback of using biomass fuel is that it is not an efficient process. In fact, burning it can release even more carbon dioxide than burning the same amount of a fossil fuel.

While you can replenish the organic matter you burn, doing so requires complex crop or forest management and the use of a large amount of land.  Also, some biomass, such as wood, takes a long time to grow back. This amounts to a delay in carbon absorption. Additionally, the harvesting of biomass will likely involve some sort of emissions.

 Is it Sustainable?

So, is biomass energy sustainable? Measuring the environmental impacts of biomass fuel use has proven to be complex due to the high number of variables, which has led to a lot of disagreement about this question.

Some assert that biomass use cannot be carbon neutral, because even if you burned and planted the same amount of organic matter, harvesting it would still result in some emissions. This could perhaps be avoided if you used renewable energy to harvest it. A continuous supply of biomass would likely require it to be transported long distances, worsening the challenge of going carbon neutral.

With careful planning, responsible land management and environmentally friendly harvesting and distribution, biomass could be close to, if not entirely, carbon neutral and sustainable. Given our reliance on fossil fuels, high energy consumption levels and the limited availability of land and other resources, this would be an immense challenge to undertake and require a complete overhaul of our energy use.

How to Improve the Biomass Industry

Biomass could emerge as a major solution to our energy and sustainability issues, but it isn’t likely to be a comprehensive solution. There are some things we can do, though, to make biomass use more sustainable when we do use it.

  • Source locally: Using biomass that comes from the local area reduces the impact of distributing it.
  • Clean distribution: If you do transport biofuel long distances, using an electric or hybrid vehicles powered largely by clean energy would be the most eco-friendly way to do it. This also applies to transporting it short distances.

Measuring the environmental impacts of biomass fuel use is complex due to high number of variables

  • Clean harvesting: Using environmentally friendly, non-emitting means of harvesting can greatly reduce the impact of using biomass. This might also involve electric vehicles.
  • Manage land sustainably: For biomass to be healthy for the ecosystem, you must manage land used to grow it with responsible farming practices.
  • Focus on waste: Waste is likely the most environmentally friendly form of biomass because it uses materials that would otherwise simply decompose and doesn’t require you to grow any new resources for your fuel or energy needs.

Is biomass energy sustainable? It has the potential to be, but doing so would be quite complex and require quite a bit of resources. Any easier way to address the problem is to look at small areas of land and portions of energy use first. First, make that sustainable and then we may be able to expand that model on to a broader scale.

Insights into MSW-to-Energy

You know the saying: One person’s trash is another’s treasure. When it comes to recovering energy from municipal solid waste — commonly called garbage or trash— that treasure can be especially useful. Instead of taking up space in a landfill, we can process our trash to produce energy to power our homes, businesses and public buildings.

In 2015, the United States got about 14 billion kilowatt-hours of electricity from burning municipal solid waste, or MSW. Seventy-one waste-to-energy plants and four additional power plants burned around 29 million tons of MSW in the U.S. that year. However, just 13 percent of the country’s waste becomes energy. Around 35 percent is recycled or composted, and the rest ends up in landfills.

Recovering Energy Through Incineration

The predominant technology for MSW-to-energy plants is incineration, which involves burning the trash at high temperatures. Similarly to how some facilities use coal or natural gas as fuel sources, power plants can also burn MSW as fuel to heat water, which creates steam, turns a turbine and produces electricity.

Several methods and technologies can play a role in burning trash to create electricity. The most common type of incineration plant is what’s called a mass-burn facility. These units burn the trash in one large chamber. The facility might sort the MSW before sending it to the combustion chamber to remove non-combustible materials and recyclables.

These mass-burn systems use excess air to facilitate mixing, and ensure air gets to all the waste. Many of these units also burn the fuel on a sloped, moving grate to mix the waste even further. These steps are vital because solid waste is inconsistent, and its content varies. Some facilities also shred the MSW before moving it to the combustion chamber.

Gasification Plants

Another method for converting trash into electricity is gasification. This type of waste-to-energy plant doesn’t burn MSW directly, but instead uses it as feedstock for reactions that produce a fuel gas known as synthesis gas, or syngas. This gas typically contains carbon monoxide, carbon dioxide, methane, hydrogen and water vapor.

Approaches to gasification vary, but typically include high temperatures, high-pressure environments, very little oxygen and shredding MSW before the process begins. Common gasification methods include:

  • Pyrolysis, which involves little to no oxygen, partial pressure and temperatures between approximately 600 and 800 degrees Celsius.
  • Air-fed systems, which use air instead of pure oxygen and temperatures between 800 and 1,800 degrees Celsius.
  • Plasma or plasma arc gasification, which uses plasma torches to increase temperatures to 2,000 to 2,800 degrees Celsius.

Syngas can be burned to create electricity, but it can also be a component in the production of transportation fuels, fertilizers and chemicals. Proponents of gasification report that it is a more efficient waste-to-energy method than incineration, and can produce around 1,000 kilowatt-hours of electricity from one ton of MSW. Incineration, on average, produces 550 kilowatt-hours.

Challenges of MSW-to-Energy

Turning trash into energy seems like an ideal solution. We have a lot of trash to deal with, and we need to produce energy. MSW-to-energy plants solve both of those problems. However, a relatively small amount of waste becomes energy, especially in the U.S.

Typical layout of MSW-to-Energy Plant

This lack may be due largely to the upfront costs of building a waste-to-energy plant. It is much cheaper in the short term to send trash straight to a landfill. Some people believe these energy production processes are just too complicated and expensive. Gasification, especially, has a reputation for being too complex.

Environmental concerns also play a role, since burning waste can release greenhouse gases. Although modern technologies can make burning waste a cleaner process, its proponents still complain it is too dirty.

Despite these challenges, as trash piles up and we continue to look for new sources of energy, waste-to-energy plants may begin to play a more integral role in our energy production and waste management processes. If we handle it responsibly and efficiently, it could become a very viable solution to several of the issues our society faces.

Renewable Energy from Food Residuals

Food residuals are an untapped renewable energy source that mostly ends up rotting in landfills, thereby releasing greenhouse gases into the atmosphere. Food residuals are difficult to treat or recycle since it contains high levels of sodium salt and moisture, and is mixed with other waste during collection. Major generators of food wastes include hotels, restaurants, supermarkets, residential blocks, cafeterias, airline caterers, food processing industries, etc.

In United States, food scraps is the third largest waste stream after paper and yard waste. Around 12.7 percent of the total municipal solid waste (MSW) generated in the year 2008 was food scraps that amounted to about 32 million tons. According to EPA, about 31 million tons of food waste was thrown away into landfills or incinerators in 2008. As far as United Kingdom is concerned, households throw away 8.3 million tons of food each year. These statistics are an indication of tremendous amount of food waste generated all over the world.

The proportion of food residuals in municipal waste stream is gradually increasing and hence a proper food waste management strategy needs to be devised to ensure its eco-friendly and sustainable disposal. Currently, only about 3 percent of food waste is recycled throughout U.S., mainly through composting. Composting provides an alternative to landfill disposal of food waste, however it requires large areas of land, produces volatile organic compounds and consumes energy. Consequently, there is an urgent need to explore better recycling alternatives.

Anaerobic digestion has been successfully used in several European and Asian countries to stabilize food wastes, and to provide beneficial end-products. Sweden, Austria, Denmark, Germany and England have led the way in developing new advanced biogas technologies and setting up new projects for conversion of food waste into energy.

Anaerobic Digestion of Food Waste

Anaerobic digestion is the most important method for the treatment of organic waste, such as food residuals, because of its techno-economic viability and environmental sustainability. The use of anaerobic digestion technology generates biogas and preserves the nutrients which are recycled back to the agricultural land in the form of slurry or solid fertilizer.

The relevance of biogas technology lies in the fact that it makes the best possible use of various organic wastes as a renewable source of clean energy. A biogas plant is a decentralized energy system, which can lead to self-sufficiency in heat and power needs, and at the same time reduces environmental pollution. Thus, anaerobic digestion of food waste can lead to climate change mitigation, economic benefits and landfill diversion opportunities.

Of the different types of organic wastes available, food waste holds the highest potential in terms of economic exploitation as it contains high amount of carbon and can be efficiently converted into biogas and organic fertilizer. Food waste can either be used as a single substrate in a biogas plant, or can be co-digested with organic wastes like cow manure, poultry litter, sewage, crop residues, slaughterhouse wastes, etc.

A Typical Energy Conversion Plant

The feedstock for the food waste-to-energy plant includes leftover food, vegetable refuse, stale cooked and uncooked food, meat, teabags, napkins, extracted tea powder, milk products, etc. Raw waste is shredded to reduce to its particle size to less than 12 mm. The primary aim of shredding is to produce a uniform feed and reduce plant “down-time” due to pipe blockages by large food particles. It also improves mechanical action and digestibility and enables easy removal of any plastic bags or cling-film from waste.

Fresh waste and re-circulated digestate (or digested food waste) are mixed in a mixing tank. The digestate is added to adjust the solids content of the incoming waste stream from 20 to 25 percent (in the incoming waste) to the desired solids content of the waste stream entering the digestion system (10 to 12 percent total solids). The homogenized waste stream is pumped into the feeding tank, from which the anaerobic digestion system is continuously fed. Feeding tank also acts as a pre-digester and subjected to heat at 55º to 60º C to eliminate pathogens and to facilitate the growth of thermophilic microbes for faster degradation of waste.

From the predigestor tank, the slurry enters the main digester where it undergoes anaerobic degradation by a consortium of Archaebacteria belonging to Methanococcus group. The anaerobic digester is a CSTR reactor having average retention time of 15 to 20 days. The digester is operated in the mesophilic temperature range (33º to 38°C), with heating carried out within the digester. Food waste is highly biodegradable and has much higher volatile solids destruction rate (86 to 90 percent) than biosolids or livestock manure. As per conservative estimates, each ton of food waste produces 150 to 200 m3 of biogas, depending on reactor design, process conditions, waste composition, etc.

Biogas contains significant amount of hydrogen sulfide (H2S) gas that needs to be stripped off due to its corrosive nature. The removal of H2S takes place in a biological desulphurization unit in which a limited quantity of air is added to biogas in the presence of specialized aerobic bacteria that oxidizes H2S into elemental sulfur. The biogas produced as a result of anaerobic digestion of waste is sent to a gas holder for temporary storage. Biogas is eventually used in a combined heat and power (CHP) unit for its conversion into thermal and electrical energy in a co­generation power station of suitable capacity. The exhaust gases from the CHP unit are used for meeting process heat requirements.

The digested substrate leaving the reactor is rich in nutrients like nitrogen, potassium and phosphorus which are beneficial for plants as well as soil. The digested slurry is dewatered in a series of screw presses to remove the moisture from slurry. Solar drying and additives are used to enhance the market value and handling characteristics of the fertilizer.

Diverting Food from Landfills

Food residuals are one of the single largest constituents of municipal solid waste stream. Diversion of food waste from landfills can provide significant contribution towards climate change mitigation, apart from generating revenues and creating employment opportunities. Rising energy prices and increasing environmental pollution makes it more important to harness renewable energy from food scraps.

Anaerobic digestion technology is widely available worldwide and successful projects are already in place in several European as well as Asian countries that makes it imperative on waste generators and environmental agencies to root for a sustainable food waste management system.