Food Waste Management and Anaerobic Digestion

Food waste is one of the single largest constituent of municipal solid waste stream. In a typical landfill, food waste is one of the largest incoming waste streams and responsible for the generation of high amounts of methane. Diversion of food waste from landfills can provide significant contribution towards climate change mitigation, apart from generating revenues and creating employment 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 utilized as a single substrate in a biogas plant, or can be co-digested with organic wastes like cow manure, poultry litter, sewage, crop residues, abattoir wastes etc or can be disposed in dedicated food waste disposers (FWDs). Rising energy prices and increasing environmental concerns makes it more important to harness clean energy from food wastes.

Anaerobic Digestion of Food Wastes

Anaerobic digestion is the most important method for the treatment of food waste 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 utilization of food 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, the benefits of anaerobic digestion of food waste includes climate change mitigation, economic benefits and landfill diversion opportunities.

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.

Codigestion at Wastewater Treatment Facilities

Anaerobic digestion of sewage sludge is wastewater treatment facilities is a common practice worldwide. Food waste can be codigested with sewage sludge if there is excess capacity in the anaerobic digesters. An excess capacity at a wastewater treatment facility can occur when urban development is overestimated or when large industries leave the area.

By incorporating food waste, wastewater treatment facilities can have significant cost savings due to tipping fee for accepting the food waste and increasing energy production. Wastewater treatment plants are usually located in urban areas which make it cost-effective to transport food waste to the facility. This trend is catching up fast and such plants are already in operation in several Western countries.

The main wastewater treatment plant in East Bay Municipal Utility District (EBMUD), Oakland (California) was the first sewage treatment facility in the USA to convert post-consumer food scraps to energy via anaerobic digestion. EBMUD’s wastewater treatment plant has an excess capacity because canneries that previously resided in the Bay Area relocated resulting in the facility receiving less wastewater than estimated when it was constructed. Waste haulers collect post-consumer food waste from local restaurants and markets and take it to EBMUD where the captured methane is used as a renewable source of energy to power the treatment plant. After the digestion process, the leftover material is be composted and used as a natural fertilizer.

The first food waste anaerobic digestion plant in Britain to be built at a sewage treatment plant is the city of Bristol. The plant, located at a Wessex Water sewage works in Avonmouth, process 40,000 tonnes of food waste a year from homes, supermarkets and business across the southwest and generate enough energy to power around 3,000 homes.

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 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.

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.

Best Ways for Your College to Go Green

college-greenToday a lot of colleges have made an environmental revolution. No more coffee to go, no more plastic bottles to buy on a territory of the campus, the implementation of eco-friendly projects and campaigns – all this now is becoming a sustainable lifestyle for the majority of students.

The effects of climate change are dramatically terrifying. In most colleges, the initiative of the activities to make planet safer comes from administration faculties. However, any little action of every student will help to protect our Earth. Let’s see now how green we may be in a range of college life.

Today you even may look for the university that has its degrees in eco subjects: such as sustainable agriculture, natural resources conservation and indoor gardening and so on.

Energy supply

Whether it is a constructing of building with more efficient environmentally substantial windows and panels that use solar, wind or even water power, during past several years the colleges become a way eco-friendlier. Some programs promote the conservation in any aspect and the composting bins.

Using electronics instead of paper

The world now is digitally focused, and this is good news for a planet. A lot of colleges are equipped with computer classes, electronic libraries, and online testing programs. You may also have with taking notes electronically in order not to waste paper and money on buying notebooks. Instead of buying a book, prefer to borrow it or get only if necessary.

Opening a refectory with a local eco food

Organic food and organic gardening is a modern, healthy part of a sustainable lifestyle. The most colleges now have the individual spaces for organic gardening where any student can work to show their faith-based actions. They can grow plants, vegetables or fruits that are used in the kitchen of the campus for preparing healthy food.

The administration of some universities now got rid of trays – they state it will prevent students from over-eating and wasting food. Instead, a student takes a plate where he can put only as much as he can eat.

Having a place for refilling a water bottle

As you know, only 20% of plastic bottles will be recycled. Tthe question is that where did other 80% proceed to? The management of some colleges take concrete measures to fight this issue: they don’t sell plastic bottles on the territory of campus. As an alternative, they give reusable water bottles and provide with stations of water filling. Isn’t it an amazingly simple and useful to evolve an initiative to become environmentally conscious?

Special campaigns for students

It is important for colleges to have some green project ideas for college students that may evolve students to concrete actions toward the protection of an ecology. It can be something like tree planting, street cleaning or any other environment-themed campaigns.

Organic food is a modern, healthy part of a sustainable lifestyle.

Organic food is a modern, healthy part of a sustainable lifestyle.

The effective way to make the more environmentally sustainable community is creating a communication between students and management. Every student may have his fresh ideas of go green, and it ‘d be good and if the management could encourage them and help to realize.

Transportation

What doesn’t student dream of having his car? But don’t lie to yourself – it is not a secret that the cars are the biggest reason of pollution in the air. Just think about it – do you need a car? Taking a public transport or having a bicycle will not only save a planet but also will save your money.

Many colleges offer carpool boards which allow pairing riders with drivers and a shuttle bus which run on biodiesel that is much safer for the planet than any other fuel.

Good old recycling

Almost every college has recycling bins and trash cans on its territory. The faculty and staff should be responsible for what and where they throw away – it will be a good example for every student.

Creating eco-friendly rules in a campus

  • Turn off everything
  • Using LED light bulbs
  • Reduce, reuse, recycle
  • Water-usage control (only a 5-minute shower)
  • Buy recyclable and eco products
  • Use power bars
  • Wash cups and plates, don’t use disposable paper or plastic utensils
  • Walk, bike and use public transport instead of a car

If you at a moment of decision which higher educational institution to choose – go ahead to pick a “go green” university which has at least some of point mentioned above!

Don’t close your eyes to truth – the climate change, the nuclear waste, etc.

With all these actions, even the little ones, we may protect the environment together and live a sustainable life!

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Wish you a good green luck!