Category Archives: Waste Management

Food Waste Management and Anaerobic Digestion

  By Salman Zafar | May 24, 2013 - 12:59 pm | Anaerobic Digestion, Biogas, Waste Management
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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.

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.

Anaerobic digestion is the most important method for the treatment of organic 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 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.

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 technology is widely available worldwide and successful projects are already in place in many countries which makes it imperative on waste generators and environmental agencies to root for a sustainable food waste management system.

An Introduction to Composting

  By Salman Zafar | April 10, 2013 - 6:43 am | Composting, Waste Management
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The composting process is a complex interaction between organic waste and microorganisms. The microorganisms that carry out this process fall into three groups: bacteria, fungi, and actinomycetes. Actinomycetes are a form of fungi-like bacteria that break down organic matter. The first stage of the biological activity is the consumption of easily available sugars by bacteria, which causes a fast rise in temperature. The second stage involves bacteria and actinomycetes that cause cellulose breakdown. The last stage is concerned with the breakdown of the tougher lignins by fungi.

Central solutions are exemplified by low-cost composting without forced aeration, and technologically more advanced systems with forced aeration and temperature feedback. Central composting plants are capable of handling more than 100,000 tons of biodegradable waste per year, but typically the plant size is about 10,000 to 30,000 tons per year. Biodegradable wastes must be separated prior to composting: Only pure foodwaste, garden waste, wood chips, and to some extent paper are suitable for producing good-quality compost.

Composting Equipment

The composting plants consist of some or all of the following technical units: bag openers, magnetic and/or ballistic separators, screeners (sieves), shredders, mixing and homogenization equipment, turning equipment, irrigation systems, aeration systems, draining systems, bio-filters, scrubbers, control systems, and steering systems. The composting process occurs when biodegradable waste is piled together with a structure allowing for oxygen diffusion and with a dry matter content suiting microbial growth.

Biodegradable wastes must be separated prior to composting: Only pure food waste, garden waste, wood chips, and to some extent paper are suitable for producing good-quality compost.The temperature of the biomass increases due to the microbial activity and the insulation properties of the piled material. The temperature often reaches 65 to 75 degrees C within few days and then declines slowly. This high temperature hastens the elimination of pathogens and weed seeds.

Composting Methodologies

The methodology of composting can be categorized into three major segments—anaerobic composting, aerobic composting, and vermicomposting. In anaerobic composting, the organic matter is decomposed in the absence of air. Organic matter may be collected in pits and covered with a thick layer of soil and left undisturbed six to eight months. The compost so formed may not be completely converted and may include aggregated masses.

Aerobic composting is the process by which organic wastes are converted into compost or manure in presence of air and can be of different types. The most common is the Heap Method, where organic matter needs to be divided into three different types and to be placed in a heap one over the other, covered by a thin layer of soil or dry leaves. This heap needs to be mixed every week, and it takes about three weeks for conversion to take place. The process is same in the Pit Method, but carried out specially constructed pits. Mixing has to be done every 15 days, and there is no fixed time in which the compost may be ready.

Berkley Method uses a labor-intensive technique and has precise requirements of the material to be composted. Easily biodegradable materials, such as grass, vegetable matter, etc., are mixed with animal matter in the ratio of 2:1. Compost is usually ready in 15 days.

Vermicomposting involves use of earthworms as natural and versatile bioreactors for the process of conversion. It is carried out in specially designed pits where earthworm culture also needs to be done. Vermicomposting is a precision-based option and requires overseeing of work by an expert. It is also a more expensive option (O&M costs especially are high).

Composting with Worms

  By Salman Zafar | March 13, 2013 - 3:29 am | Composting, Waste Management
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Vermicomposting is a type of composting in which certain species of earthworms are used to enhance the process of organic waste conversion and produce a better end-product. It is a mesophilic process utilizing microorganisms and earthworms. Earthworms feeds the organic waste materials and passes it through their digestive system and gives out in a granular form (cocoons) which is known as vermicompost. Simply speaking, vermicompost is earthworm excrement, called castings, which can improve biological, chemical, and physical properties of the soil. The chemical secretions in the earthworm’s digestive tract help break down soil and organic matter, so the castings contain more nutrients that are immediately available to plants.

Production of Vermicompost

A wide range of agricultural residues, such as straw, husk, leaves, stalks, weeds etc can be converted into vermicompost. Other potential feedstock for vermicompost production are livestock wastes, poultry litter, dairy wastes, food processing wastes, organic fraction of MSW, bagasse, digestate from biogas plants etc. Earthworms consume organic wastes and reduce the volume by 40–60 percent. Each earthworm weighs about 0.5 to 0.6 gram, eats waste equivalent to its body weight and produces cast equivalent to about 50 percent of the waste it consumes in a day. The moisture content of castings ranges between 32 and 66 percent and the pH is around 7. The level of nutrients in compost depends upon the source of the raw material and the species of earthworm.

There are nearly 3600 types of earthworms which are divided into burrowing and non-burrowing types. Red earthworm species, like Eisenia foetida, and are most efficient in compost making. The non-burrowing earthworms eat 10 percent soil and 90 percent organic waste materials; these convert the organic waste into vermicompost faster than the burrowing earthworms. They can tolerate temperatures ranging from 0 to 40°C but the regeneration capacity is more at 25 to 30°C and 40–45 percent moisture level in the pile. The burrowing types of earthworms come onto the soil surface only at night. These make holes in the soil up to a depth of 3.5 m and produce 5.6 kg casts by ingesting 90 percent soil and 10 percent organic waste.

The types of vermicomposting depend upon the amount of producton and composting structures. Small-scale vermicomposting is done to meet personal requirements and farmers/gardeners can harvest 5-10 tons of vermicompost annually. On the other hand, large-scale vermicomposting is done at commercial scale by recycling large quantities of organic waste in modern facilities with the production of more than hundreds of tons annually.

Benefits of Vermicompost

The worm castings contain higher percentage of both macro and micronutrients than the garden compost. Apart from other nutrients, a fine worm cast is rich in NPK which are in readily available form and are released within a month of application. Vermicompost enhances plant growth, suppresses disease in plants, increases porosity and microbial activity in soil, and improves water retention and aeration. Vermicompost also benefits the environment by reducing the need for chemical fertilizers and decreasing the amount of waste going to landfills. Vermicompost production is trending up worldwide and it is finding increasing use especially in Western countries, Asia-Pacific and Southeast Asia.

A relatively new product from vermicomposting is vermicompost tea which is a liquid produced by extracting organic matter, microorganisms, and nutrients from vermicompost. Unlike vermicompost and compost, this tea may be applied directly to plant foliage, reportedly to enhance disease suppression. Vermicompost tea also may be applied to the soil as a supplement between compost applications to increase biological activity.

Vermicompost may be sold in bulk or bagged with a variety of compost and soil blends. Markets include home improvement centers, nurseries, landscape contractors, greenhouses, garden supply stores, grocery chains, flower shops, discount houses, and the general public.

Food Waste Management

  By Salman Zafar | February 21, 2013 - 12:41 am | Biogas, Waste Management
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The waste management hierarchy suggests that reduce, reuse and recycling should always be given preference in a typical waste management system. However, these options cannot be applied uniformly for all kinds of wastes. For examples, organic waste is quite difficult to deal with using the conventional 3R strategy.

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.

There are numerous places which are the sources of large amounts of food waste and hence a proper food-waste management strategy needs to be devised for them to make sure that either they are disposed off in a safe manner or utilized efficiently. These places include hotels, restaurants, malls, residential societies, college/school/office canteens, religious mass cooking places, airline caterers, food and meat processing industries and vegetable markets which generate organic waste of considerable quantum on a daily basis.

The anaerobic digestion technology is highly apt in dealing with the chronic problem of organic waste management in urban societies. Although the technology is commercially viable in the longer run, the high initial capital cost is a major hurdle towards its proliferation.

The onus is on the governments to create awareness and promote such technologies in a sustainable manner. At the same time, entrepreneurs, non-governmental organizations and environmental agencies should also take inspiration from successful food waste-to-energy projects in Western countries and try to set up such facilities in cities and towns.

Food Waste Management in USA

  By Salman Zafar | February 10, 2013 - 11:37 pm | Anaerobic Digestion, Waste Management, Waste-to-energy
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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 13 percent of the total municipal solid waste generated in the country is contributed by food scraps. According to USEPA, about 34 million tons of food waste was thrown away into landfills or incinerators in 2010. As far as United Kingdom is concerned, households throw away around 8 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.

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 in USA to strive for a sustainable food waste management system.

Different Strategies in Composting

  By Salman Zafar | February 6, 2013 - 11:11 pm | Composting, Waste Management
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The methodology of composting can be categorized into three major segments—anaerobic composting, aerobic composting, and vermicomposting. In anaerobic composting, the organic matter is decomposed in the absence of air. Organic matter may be collected in pits and covered with a thick layer of soil and left undisturbed six to eight months. The compost so formed may not be completely converted and may include aggregated masses.

Aerobic composting is the process by which organic wastes are converted into compost or manure in presence of air and can be of different types. The most common is the Heap Method, where organic matter needs to be divided into three different types and to be placed in a heap one over the other, covered by a thin layer of soil or dry leaves. This heap needs to be mixed every week, and it takes about three weeks for conversion to take place. The process is same in the Pit Method, but carried out specially constructed pits. Mixing has to be done every 15 days, and there is no fixed time in which the compost may be ready. Berkley Method uses a labor-intensive technique and has precise requirements of the material to be composted. Easily biodegradable materials, such as grass, vegetable matter, etc., are mixed with animal matter in the ratio of 2:1. Compost is usually ready in 15 days. When transferring compost, be sure to use the safest, tear-resistant compostable plastic bags available in the market.

Vermicomposting involves use of earthworms as natural and versatile bioreactors for the process of conversion. It is carried out in specially designed pits where earthworm culture also needs to be done. Vermicomposting is a precision-based option and requires overseeing of work by an expert. It is also a more expensive option (O&M costs especially are high). However, unlike the above two options, it is a completely odorless process making it a preferred solution in residential areas. It also has an extremely high rate of conversion, so quality of the end product is very high with rich macro and micronutrients. The end product also has the advantage that it can be dried and stored safely for a longer period of time.