(GIST OF SCIENCE REPORTER) Integrated Municipal Solid Waste Disposal System

[November-2021]

Integrated Municipal Solid Waste Disposal System

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. Studies suggest that the MSW generated in India mostly consists of a large fraction of organic wastes (40-60%). Unscientific waste disposal practices in landfill sites produce Greenhouse Gas (GHG) emissions and other air pollutants. Methane emitted from landfills is one of the most important contributors to GHGs.

Key highlights:

Scientific and most popular techniques for the 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 (CSIR-Central Mechanical Engineering Research Institute), 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 the 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.) and 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 the 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 purposes. The gas can also be utilised in gas engine for the generation of electricity.
Biomass waste such as dry leaves, dead branches, dry grass, etc. is 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 utilised as fuel for cooking. These briquettes are also being utilised in gasifier for the production of syngas which is a mixture of mainly carbon monoxide and hydrogen. The syngas has a calorific value equivalent to that of biogas and hence can be utilised 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 the production of bricks which are 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 a 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 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 the generation of electricity. The solid residue known as char is mixed with the biogas slurry for the production of briquette. These briquettes are being utilised 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 utilising high-temperature plasma. The plasma gasification process converts the waste into syngas which can be utilised for the generation of electricity. The residual ash is mixed with cement for the 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 the 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.