Pelletization of Municipal Solid Wastes

MSW is a poor-quality fuel and its pre-processing is necessary to prepare fuel pellets to improve its consistency, storage and handling characteristics, combustion behaviour and calorific value. Technological improvements are taking place in the realms of advanced source separation, resource recovery and production/utilisation of recovered fuel in both existing and new plants for this purpose. There has been an increase in global interest in the preparation of RDF containing a blend of pre-processed MSW with coal suitable for combustion in pulverised coal and fluidised bed boilers.

Pelletization of municipal solid waste involves the processes of segregating, crushing, mixing high and low heat value organic waste material and solidifying it to produce fuel pellets or briquettes, also referred to as Refuse Derived Fuel (RDF). The process is essentially a method that condenses the waste or changes its physical form and enriches its organic content through removal of inorganic materials and moisture. The calorific value of RDF pellets can be around 4000 kcal/ kg depending upon the percentage of organic matter in the waste, additives and binder materials used in the process.

The calorific value of raw MSW is around 1000 kcal/kg while that of fuel pellets is 4000 kcal/kg. On an average, about 15–20 tons of fuel pellets can be produced after treatment of 100 tons of raw garbage. Since pelletization enriches the organic content of the waste through removal of inorganic materials and moisture, it can be very effective method for preparing an enriched fuel feed for other thermo-chemical processes like pyrolysis/ gasification, apart from incineration. Pellets can be used for heating plant boilers and for the generation of electricity. They can also act as a good substitute for coal and wood for domestic and industrial purposes. The important applications of RDF are found in the following spheres:

  • Cement kilns
  • RDF power plants
  • Coal-fired power plants
  • Industrial steam/heat boilers
  • Pellet stoves

The conversion of solid waste into briquettes provides an alternative means for environmentally safe disposal of garbage which is currently disposed off in non-sanitary landfills. In addition, the pelletization technology provides yet another source of renewable energy, similar to that of biomass, wind, solar and geothermal energy. The emission characteristics of RDF are superior compared to that of coal with fewer emissions of pollutants like NOx, SOx, CO and CO2.

RDF production line consists of several unit operations in series in order to separate unwanted components and condition the combustible matter to obtain the required characteristics. The main unit operations are screening, shredding, size reduction, classification, separation either metal, glass or wet organic materials, drying and densification. These unit operations can be arranged in different sequences depending on raw MSW composition and the required RDF quality.

Various qualities of fuel pellets can be produced, depending on the needs of the user or market. A high quality of RDF would possess a higher value for the heating value, and lower values for moisture and ash contents. The quality of RDF is sufficient to warrant its consideration as a preferred type of fuel when solid waste is being considered for co-firing with coal or for firing alone in a boiler designed originally for firing coal.

Biomass Resource Base in MENA Countries

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.

Feedstocks for Anaerobic Digestion Plants

A wide range of feedstock is available for anaerobic digesters. In addition to MSW, large quantity of waste, in both solid and liquid forms, is generated by the industrial sector like breweries, sugar mills, distilleries, food-processing industries, tanneries, and paper and pulp industries. Poultry waste has the highest per ton energy potential of electricity per ton but livestock have the greatest potential for energy generation in the agricultural sector.

Agricultural Feedstock

  • Animal manure
  • Energy crops
  • Algal biomass
  • Crop residues

Community-Based Feedstock

  • Organic fraction of MSW (OFMSW)
  • MSW
  • Sewage sludge
  • Grass clippings/garden waste
  • Food remains
  • Institutional wastes etc.

 Industrial Feedstock

  • Food/beverage processing
  • Dairy
  • Starch industry
  • Sugar industry
  • Pharmaceutical industry
  • Cosmetic industry
  • Biochemical industry
  • Pulp and paper
  • Slaughterhouse/rendering plant etc.

Anaerobic digestion is particularly suited to wet organic material and is commonly used for effluent and sewage treatment. Almost any organic material can be processed with anaerobic digestion. This includes biodegradable waste materials such as waste paper, grass clippings, leftover food, sewage and animal waste. The exception to this is woody wastes that are largely unaffected by digestion as most anaerobic microorganisms are unable to degrade lignin.

Anaerobic digesters can also be fed with specially grown energy crops such as silage for dedicated biogas production. A wide range of crops, especially C-4 plants, demonstrate good biogas potentials. Corn is one of the most popular co-substrate in Germany while Sudan grass is grown as an energy crop for co-digestion in Austria. Crops like maize, sunflower, grass, beets etc., are finding increasing use in agricultural digesters as co-substrates as well as single substrate.

A wide range of organic substances are anaerobically easily degradable without major pretreatment. Among these are leachates, slops, sludges, oils, fats or whey. Some wastes can form inhibiting metabolites (e.g.NH3) during anaerobic digestion which require higher dilutions with substrates like manure or sewage sludge. A number of other waste materials often require pre-treatment steps (e.g. source separated municipal organic waste, food residuals, expired food, market wastes and crop residues).

Bioenergy in Middle East

There is a large potential for renewable resources in the Middle East which have remained more or less unharnessed. 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, the Middle East 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.

The major biomass producing MENA countries are Sudan, Egypt, Algeria, Yemen, Iraq, Syria and Jordan. Traditionally, biomass energy has been widely used in rural areas for domestic purposes in the MENA region. Since most of the region is arid/semi-arid, the biomass energy potential is mainly contributed by municipal solid wastes, agricultural residues and agro-industrial wastes.

Municipal solid wastes represent the best source of biomass in MENA countries. The high rate of population growth, urbanization and economic expansion in MENA region is not only accelerating consumption rates but also accelerating the generation of municipal waste. 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.

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 Middle East 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 Middle East. 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. There are many technologically-advanced dairy products, bakery and oil processing plants in the region.

Agriculture plays an important role in the economies of most of the countries in the Middle East.  The contribution of the agricultural sector to the overall economy varies significantly among countries in the region, ranging, for example, from about 3.2 percent in Saudi Arabia to 13.4 percent in Egypt. Large quantities of crop residues are produced annually in the region, and are vastly underutilised. 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 in rural areas. Energy crops, such as Jatropha, can be successfully grown in arid regions for biodiesel production. Infact, Jatropha is already grown at limited scale in some Middle East countries and tremendous potential exists for its commercial exploitation.

The Middle Eastern countries have strong animal population. The livestock sector, in particular sheep, goats and camels, plays an important role in the national economy of the Middle East countries. Many millions of live ruminants are imported into the Middle Eastern countries 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.

Solid Wastes in Middle East

 

The high rate of population growth, urbanization and economic expansion in the Middle East is not only accelerating consumption rates but also increasing the generation rate of all  sorts of waste. 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.

Saudi Arabia produced 13 million tons of garbage in 2009. With an approximate population of about 28 million, the kingdom produces approximately 1.3 kilograms of waste per person every day.  According to a recent study conducted by Abu Dhabi Center for Waste Management, the amount of waste in UAE totaled 4.892 million tons, with a daily average of 6935 tons in the city of Abu Dhabi, 4118 tons in Al Ain and 2349 tons in the western region. Countries like Kuwait, Bahrain and Qatar have astonishingly high per capita waste generation rate, primarily because of high standard of living and lack of awareness about sustainable waste management practices.

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.

Municipal solid wastes represent the best source of biomass in Middle East countries. Municipal solid waste is comprised of organic fraction, paper, glass, plastics, metals, wood etc. Municipal solid waste can be converted into energy by conventional technologies (such as incineration, mass-burn and landfill gas capture) or by modern conversion systems (such as anaerobic digestion, gasification and pyrolysis). At the landfill sites, the gas produced by the natural decomposition of MSW is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. In addition, the organic fraction of MSW can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.

Anaerobic digestion is the most preferred option to extract energy from sewage, which leads to production of biogas and organic fertilizer. The sewage sludge that remains can be incinerated or gasified/pyrolyzed to produce more energy. In addition, sewage-to-energy processes also facilitate water recycling. Municipal solid waste can also be efficiently converted into energy and fuels by advanced thermal technologies, such as gasification and pyrolysis. Infact, energy recovery from MSW is rapidly gaining worldwide recognition as the 4th R in sustainable waste management system – Reuse, Reduce, Recycle and Recover.

Trends in Food Waste Management

Food waste is an untapped energy source that mostly ends up rotting in landfills, thereby releasing greenhouse gases into the atmosphere. Food waste is 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 waste 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 waste 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. The two most common methods for food waste recycling are:

  • Composting: A treatment that breaks down biodegradable waste by naturally occurring micro-organisms with oxygen, in an enclosed vessel or tunnel;
  • Anaerobic digestion (AD): A treatment that breaks down biodegradable waste in the absence of oxygen, producing a renewable energy (biogas) that can be used to generate electricity and heat.

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.

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, abattoir wastes, etc.

Conclusions

Food waste is one of the single largest constituent 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 wastes. Anaerobic digestion technology is widely available worldwide and successful projects are already in place in several European as well as Asian countries which makes it imperative on waste generators and environmental agencies to root for a sustainable food waste management system.

Biomass Energy in Vietnam

Vietnam is one of the few countries having a low level of energy consumption in the developing world with an estimated amount of 210 kg of oil equivalent per capita/year. Over half of the Vietnamese population does not have access to electricity. The development of power sources is limited mainly to large central power plants using hydropower and traditional fossil fuels. Vietnam is facing the difficult challenge of maintaining this growth in a sustainable manner, with no or minimal adverse impacts on society and the environment.

Therefore, there exists considerable potential role for promotion of sustainable energy sources like hydroelectricity, biomass and solar power. This includes both grid connection of the larger renewable energy systems, and a considerable market for renewable systems for the many communities and houses that are likely to remain off-grid.

Biomass energy potential is estimated at 1,430 MW by 2002, and could supply 9,020 GWh of electricity annually. The possible major biomass sources likely to be exploited in the near future for power production are paddy straw, rice husk and bagasse. Their estimated potential is 730 MW, and could provide 4500 GWh of electricity yearly. Rice husk and bagasse are the biomass resources with the greatest economic potential, estimated at 50 MW and 150 MW respectively (ENERTEAM, 2003). Biomass fuels sources that can also be developed include forest wood, rubber wood, logging residues, saw mill residues, sugar cane residues, bagasse, coffee husk and coconut residues. Currently biomass is generally treated as a non-commercial energy source, and collected and used locally.

The biogas potential in the country is large due to livestock population of more than 30 million, mostly pigs, cattle, and water buffalo. Although most livestock dung already is used in feeding fish and fertilizing fields and gardens, there is potential for higher-value utilization through biogas production. It is estimated that more than 25,000 household biogas digesters with 1 to 50 m3, have been installed in rural areas. The Dutch-funded Biogas Program operated by SNV Vietnam constructed some 18,000 biogas facilities in 12 provinces between 2003 and 2005, with a second phase (2007-2010) target of 150,000 biogas tanks in both rural and semi-urban settings.