By Prof. Dr. P. K. Jena

The Urban Solid Waste (USW) management has assumed greater importance in recent years for cities of India, in view of their location in sensitive areas and hazardous effect on environment and public health. The USW handling involves effective collection, transportation, processing and safe disposal of the inert materials. The general methods to be adopted for USW management should take into account the concept of “3Rs” – Reduce, Reuse and Recycle.

First, necessary steps have to be taken to collect all types of solid wastes in the urban areas in different locality and transport the materials to a centralized place where the organic matters, recyclable materials like plastic, glass and metallic scraps and the inert materials like building and road deberries can be separated out into mainly three fractions. After separating out the wastes into three fractions, the recyclable materials should be sold to the respective industries, the organic fractions has to be processed for composting and fuel generation through anaerobic digestion and the rest fraction like building and road deberries should be used for land filling. The hazardous wastes like medical wastes should be incinerated in a scientific manner before it is disposed in the land.

The organic solid wastes can be processed in three different ways namely, incineration, aerobic digestion and anaerobic digestion.

a) Incineration Process

The incineration process for treating the organic solid wastes aims at generating heat energy. This is a method extensively used for disposing hazardous waste materials like biological and medical wastes. In some countries, the incineration of organic or hazardous materials is carried out in a suitable reactor to generate heat which is utilized for producing electricity. But, it has been observed that, the best incinerator process can only recover a fraction of the total calorific value of the organic wastes. Further, incineration releases toxic gases and also ash which can pollute the air in the locality and water bodies.

Management of USW through incineration has also received very little attention in India. This may be due to low organic material (40 – 60%), high moisture content (40 – 60%), and low calorific value content (800 – 1100 kcal/kg) in the solid waste. The first large scale USW incineration plant was constructed at Timarpur, New Delhi, in 1987 with a capacity of 300 t/day at a cost of Rs. 250 million.

But, the plant became out of operation after six months due to poor performance. The incineration of solid waste for gasification to produce fuel gas has also been practiced in India but mostly using agro residues, saw mill dust and forest wastes. The first gasification unit has been installed at Nohar, Hanungarh, Rajasthan, by Narvreet Energy Research and Information (NERI) for burning of agro wastes, sawmill dust, and forest wastes. The waste feeding rate is about 50 – 150 kg/h with efficiency of about 70 – 80%. Another similar unit has been installed at Gaul Pahari campus, New Delhi by Tata Energy Research Institute (TERI). However, this technology can be applied to urban solid waste also after proper drying and shredding.

b) Aerobic Composting 

The aerobic composting means, the composting of solid wastes in presence of air. The composting can be carried out in a smaller scale or centralized place on larger scale at a suitable place preferably in the outskirts of the urban area. It is reported that, during the 4th five – year plan (1969 – 1974) of India, bulk grants and loans were used to be given to the state governments for setting up composting plants particularly in cities with population more than 30 lakhs. Many large scale composting plants with capacity ranging from 150 – 300 tonnes per day have been set up in cities like Bangalore, Baroda, Mumbai, Calcutta, Delhi, Jaipur and Kanpur during 1975 – 1980 in the central scheme of urban waste disposal. Surprisingly in India, the development of composting plants due to various reasons has not been encouraging. It is reported that, at present only about 9% of USW is treated through simple composting.

The organic wastes can be also subjected to vermi composting, where both the earthworm and aerobic micro organisms play the composting role. At first, microbial decomposition of the organic matter takes place through extra cellular enzymatic activity which is called primary decomposition. Then, the earthworm feed on this decomposed matter, ultimately producing fine odorless granular product. This product is very suitable as biofertilizer in agriculture. Vermi composting has been used in some of the cities like Hyderabad, Bangalore, Mumbai and Faridabad.

c) Anaerobic Composting

In anaerobic process, the composting is done in absence of oxygen in a closed system.  The thermophilic digestion which is done by anaerobic micro organisms is a faster process to produce methane and the residue as a suitable compost. In this process, the energy recovery through biogas generation is quite fast. This biogas contains about 55 – 60% methane. It has been estimated that, by doing anaerobic digestion in proper way, 1 ton of organic wastes can produce nearly 2 to 4 times as much methane in three weeks compared to the same amount of landfill can produce in 6 to 7 years. The methane which is produced can be used for cooking and also for producing electricity. A 50 ton/day anaerobic digestion plant can produce 40,000 m3 of biogas with a methane content of 55 – 65% and this can generate about 1.2 MW of power.

In India, by various organizations, a number of developmental work have taken place for producing methane gas by this process. Every family in small scale can have anaerobic biogas reactor to produce methane gas at least to meet their fuel requirement for cooking and lighting the house at night along with producing compost of high quality. It is reported that, the biomethanation of organic wastes are being planned in some cities of India along with high grade compost. One ton of dry organic waste can produce 400 kg of compost and 800 cum. of biogas. .

d) Urban Solid Waste Management of Bhubaneswar – Cuttack twin city.

The above mentioned anaerobic USW management practice should be done for Bhubaneswar – Cuttack twin city in Odisha as these two fast growing cities are being polluted immensely. This anaerobic process for treating organic solid wastes of the twin city should be an ecological one. However, efforts should be made as mentioned earlier to separate out other solid waste like metal scraps, plastics, glass etc. which will be sold for recycling and the other inert solid wastes like building and road deberries along with hazardous waste after proper incineration for land filling.

It has been reported that, Bhubaneswar and Cuttack Municipal Corporations on May 20th 2014 signed jointly an agreement with a Mumbai based company to set up a solid waste treatment plant within 2 years at a cost of Rs. 200 crores. It is reported that, the plant plans to produce compost and 11.5 MW of electricity as      byproduct. It is stated that, the plant will initially treat about 350 tonnes of solid wastes generated from Bhubaneswar city and 150 tonnes from Cuttack city every day. If it is the    anaerobic digestion process, then it should be environmentally friendly and the electricity to be produced should be based on the combustion of methane gas produced during the process of anaerobic digestion. It will also produce large amounts of compost. It is understood that, the state government in 2010 has identified about 62 acres of land at Bhuasuni on the city outskirts for the plant.

The citizens of Bhubaneswar and Cuttack are eagerly awaiting for the implementation of the plant by 2016. The authorities should start their programme without further delay. If it is implemented successfully, it whould be possible to set up such units for other urban areas in the state. However, till such plants are set up, the municipal corporation of different urban areas in the state should urgently adopt aerobic composting and vermi composting of the urban wastes at suitable sites in order to produce value added compost from these harmful organic wastes. If this practice is delayed further, the urban population would suffer greatly by various diseases originating from these wastes.

It may be mentioned here that, in most of the urban areas of India the situation is very similar to that of the Bhubaneswar – Cuttack twin city. Therefore, the respective authorities in those areas should plan and execute processing of their urban organic wastes by ecologically sound anaerobic digestion process. This will go a long way in keeping our urban areas clean – a major action towards          “Swachha Bharat”.

The author is Ex-Director General, Council of Scientific & Industrial Research.