With the ever increasing population and urbanization, the country is facing a huge challenge in waste management. The volume of waste is projected to increase from 62 million tonnes at present to about 165 million tonnes by 2030. Dumping of garbage at the current rate without any treatment would require about 1240 hectares of landfill area per year and with projected generation of 165 million tons of waste by 2030. Setting up of landfills for 20 years with 10 m height will require 66,000 hectares of land. This necessitates the importance of scientific solid waste management in today’s context.
Waste-to-energy is an option for sustainable solid waste management and it is the need of the hour to realise its potential as one of the most significant future renewable energy sources, which is economically viable and environmentally sustainable. Studies suggest that the MSW generated in India mostly consists of a large fraction of organic wastes (40-60%). Unscientific waste disposal practice in landfill site produce greenhouse gas (GHG) emissions and other air pollutants. Methane emitted from landfills is one of the most important contributors to GHGs.
Scientific and most popular techniques for disposal of wet waste include composting and bio-methanation plants. As per information available for 2013-14, compiled by CPCB, municipal authorities have so far only set up 553 compost & vermicompost plants, 56 bio-methanation plants, 22 RDF plants and 13 Waste to Energy (W to E) plants in the country. Many of these plants have experienced failure due to several issues related to the segregation of waste, low calorific values of the waste and challenges in the operation and maintenance of the plants (CPCB 2013-14).
The CSIR-CMERI, Durgapur has developed an integrated Municipal Solid Waste disposal system (i-MSWDS) for disposal of solid waste in a scientific way in-line with Solid Waste Management Rules (SWM) 2016 prescribed by Union Ministry of Environment, Forests and Climate Change (MoEF&CC), Govt. of India.
The integrated municipal solid waste disposal system starts with the mechanized segregation of solid waste. The mechanized segregation system segregates solid waste into metallic waste (metal body, metal container etc.), biodegradable waste (foods, vegetables, fruits, grass etc.), non-biodegradable (plastics, packaging material, pouches, bottles etc.) & inert wastes (glass, stones etc.).
The bio-degradable component of the waste can be decomposed in an anaerobic environment popularly known as bio gasification. In this process biogas is liberated through conversion of organic matter. The biogas has a typical volumetric composition of 55 – 60% methane and 35 – 40% CO2 with traces of moisture and other impurities such as hydrogen sulphide and it can be used as fuel for cooking purpose. The gas can also be utilized in gas engine for generation of electricity.
The residual slurry is a good organic manure and utilized as fertilizer. The organic waste is also converted to compost in a natural process known as vermi-composting by introducing earthworms. The vermi-compost is utilized in organic farming.
Biomass waste such as dry leaves, dead branches, dry grass etc. are disposed of by first shredding it to a suitable size followed by mixing with the slurry of the biogas digester. This mixture is feedstock for briquette, which is utilized as fuel for cooking. These briquettes are also being utilized in gasifier for production of syngas which is a mixture of mainly carbon monoxide and hydrogen. The syngas has calorific value equivalent to that of biogas and hence can be utilized in gas engine for generation of electricity. The ash produced from burning of briquette is mixed with cement and water in an appropriate proportion for production of bricks which is used for construction work.
The polymer waste consisting of plastics, sanitary waste etc. is being disposed through two main processes i.e. pyrolysis and plasma gasification. In the pyrolysis process, the polymer waste is heated to a temperature of 400 – 600°C in an anaerobic environment in presence of suitable catalyst. The volatile matter from the polymer waste comes out as a result of heating which on condensation gives pyrolysis oil. Different heating mechanisms such as solid fuel based, liquid fuel based and gaseous fuel based in standalone mode or in combined mode have been developed for carrying out the process.
The pyrolysis oil is termed as Petro Alternate Fuel (PAF). The crude pyrolysis oil after purification can be used in industrial boilers, generators etc. for heating / power generation purposes. The non-condensed syngas from the pyrolysis process is fed to the gas engine for generation of electricity. The solid residue known as char is mixed with the biogas slurry for production of briquette. These briquettes are being utilized for heating the reactor of the pyrolysis process thereby making the process self-sustainable in terms of fuel.
The polymer waste or sanitary items are also disposed of utilizing high temperature plasma. The plasma gasification process converts the waste into syngas which can be utilized for generation of electricity. The residual ash is mixed with cement for preparation of bricks.
The construction and demolition (C&D) waste is crushed in a jaw crusher and then segregated in different sizes in the trommel. The fines are mixed with cement and water in appropriate proportion. The prepared mixture is then filled in the mould cavity of brick press. Then it is being pressed using hydraulic press to give it a proper shape and compaction. The bricks are cured to achieve desired strength. Finally, the prepared bricks are tested for engineering properties. The ready bricks are being used as construction materials. The oversized crushed materials are used as aggregate in PCC road making.
The Socio-Economic Impact of the iMSWDS
CSIR-CMERI has already installed a MSW Management Pilot Plant in CMERI Colony where day-to-day waste generated at CMERI Colony is being processed aiming towards a “Zero Waste CSIR-CMERI Colony". No waste is discarded from the Colony in last two years. The CSIR-CMERI MSW Management Technology is Completely Energy Sustainable. The Cyclic Model of Waste Processing facilitates this energy sufficiency of the MSW Technology.
CSIR-CMERI steadily envisions a ‘Zero-Landfill’ and a ‘Zero-Waste City’, by possibly espousing a business model for the MSMEs whereby individuals can deliver their household wastes to the garbage collectors who are incentivized for delivering the wastes to the MSW facilities. This will give the necessary enthusiasm for the citizens of a city to participate in waste management efforts.
CSIR-CMERI organises a 3-day Workshop on handling of municipal solid waste and legacy waste. Programs such as these are intended to raise the awareness levels of young minds on waste management and skill them with appropriate know-how on advanced and indigenously developed MSW Technologies.
The MSW management technology is also a perfect testimony of a decentralised model of technology implementation. It can help involve participation of the local community in the operations and maintenance of the technology, thereby empowering the community with necessary skills for employment opportunities. A decentralised model of waste processing also helps reducing expenditure on transportation thereby saving valuable resources on fossil fuels, which is both import-dependent and pollution causing. indirectly it will also have consequences on reducing medical expenses and protect mankind against toxic gases and wastes.
CSIR-CMERI has already installed and commissioned biogas plant of different capacity at different location in West Bengal. In addition, CSIR-CMERI, Durgapur is engaged in providing waste management solutions CRPF Group Centre, Amrawati and PHE Department, Govt. of Manipur.