The funds required to establish, operate and create rural entrepreneurship can partly come from Swachh Bharat Abhiyan (SBA) (rural) and also from Corporate Social Responsibility (CSR) funds available from the corporate sector in the country. At the later stages of project implementation on rural waste to energy, a competition somewhat similar to clean city can also be initiated with villages implementing these projects in order to keep them clean.

The issue of solid waste management, till now, was not so much of a problem as per capita consumption of materials and hence, per capita generation of solid waste was much lower among rural populace as compared to the urban. Moreover, the rural population was also diffused and most of the solid waste generated was essentially organic in nature (food waste and agri residue), which was either composted or used as fodder. There was very less usage of packaged materials and hence, very little packaging waste generation.

Situation is however fast changing in rural, more so, in rural-urban areas, where use of packaged materials is growing and the waste composition is also becoming complex. This can no longer be handled by simple processing techniques like composting but requires more robust and locally available waste processing options to deal with the solid waste without polluting the environment.

As of now, it is estimated that rural India is generating liquid waste (grey water) of the order of 1,500 to 1,800 crore liters and solid waste (organic/recyclable) 3 to 4 lakh metric tonnes per day respectively. The production of energy from such waste, especially solid waste, will depend upon the specific treatment processes, seasonal variations etc. Important physical parameters are the size of the constituents and the density and moisture content of the waste. The important chemical parameters are the fixed carbon content, calorific value, VS (volatile solid) contents, Carbon to Nitrogen ratio (C:N ratio), toxicity and inert fraction present in waste.

In addition to solid and liquid waste, the rural areas also generate agri-residues and forestry biomass waste, which can be utilized for energy generation. A study carried out by The Energy and Resources Institute (TERI) on availability of biomass for energy generation in selected districts reveals that there is surplus biomass available in rural areas which can be effectively used for energy generation. For example, the survey estimated that there is 54,600 and 70,000 tonnes of annual surplus biomass from agricultural and industrial sources in Pune and Thane districts of Maharashtra.

Technology option for energy generation from waste in rural areas

Different waste processing technology options, which are commercially viable in Indian conditions and can be used at the scale from 50 kg/day to 1.5-2.0 tonnes/day, can be deployed in rural areas include:

1. Anaerobic   (without   air)   digestion   or bio-methanation process and using it for-

a)   Thermal application (e.g. cooking)

b)   Power generation

c)   The residue of the process can be stabilized and used as manure

2. Processing waste into refuse derived fuel (RDF) and using it for-

a)    Thermal application (e.g. cooking mid-day meals in schools)

b)    Power generation by burning RDF

3. Use of waste in gasifiers to convert it into producer gas and use it for power generation

These technology options are describes below.

Anaerobic digestion

Solid and liquid wastes consist of both organic and inorganic constituents, and the degradation of the organic constituents can take place in the presence or absence of oxygen (air). When microbial degradation of organics takes place in the absence of air, the process is known as 'anaerobic digestion' or 'bio-methanation'. This results in the production of biogas, which contains methane, carbon dioxide and traces of other gases.

Anaerobic digestion occurs naturally in swamps, waterlogged soils and rice fields, deep-water bodies and in the digestive systems of animals. Anaerobic processes can take place in a reactor such as digester vessel, covered lagoon or landfill in order to recover the methane gas (as biogas), which can be used for power generation. Waste, which contains particulate organic material (waste sludge, food waste, vegetable waste, etc) must first be solubilized by the action of extra cellular enzymes that are produced by the hydrolytic bacteria. The solubilization of particulate material is relatively slow and takes time. The process can be sometimes hastened by chemical solubilization or leaching.

After solubilization, in next phase, wastes containing soluble organics will require short retention times for achieving high treatment efficiency to produce methane rich biogas using acidogenic and methanogenic bacteria. The typical food waste or vegetable waste having moisture content of 45 per cent or more is an ideal waste to be processed an aerobically as the process requires easily biodegradable waste with high moisture content.

Typical composition of biogas can range from 45 to 65 per cent methane which can be used both for thermal as well as electrical applications. The leftover residue, as stated earlier, can be used as manure.

Refuse Derived Fuel (RDF)

Refuse Derived Fuel (RDF) commonly refers to solid waste that has been mechanically processed to produce a storable, transportable, and more homogeneous fuel for combustion. The typical processes involved in producing waste to RDF pellets include following steps:

·      Drying to reduce moisture content

·      Size reduction

·      Screening

·      Pneumatic separation for the removal of non-combustible materials

·      Mixing with additives

·      Pelletisation

The waste is pre-processed to remove incombustible materials, thus increasing the calorific value of the fuel. The incombustible materials are removed using various mechanical methods for example, ferrous metals are removed using magnetic separators; glass, grit, and sand is removed through screening. Some systems utilize air classifiers, trommel screens or rotary drums to further refine the waste. To reduce the cost of producing RDF, one can also look at producing waste fluff instead of Pelletisation which adds to the cost, but pellets can be stored for longer time and can be transported easily. Good candidate wastes for producing RDF include agri residues, hard woody waste, waste plastics, paper, rags, leather and such organic waste which are not easily biodegradable and have low inherent moisture content (typically in the range of 10%).

RDF can be co-fired with fossil fuels in existing industrial (e.g. boilers in sugar mills or paper and pulp industry which are often located in rural areas) or utility boiler, or it can be used as the sole or primary fuel in specially designed "dedicated" boiler for producing either heat or power or both. Co-firing of RDF has the obvious advantage of capital cost savings since a new boiler is not required. However, RDF as the primary fuel burning in a dedicated boiler has become more common, since the dedicated boiler can be designed to accommodate some of the characteristics of RDF that can otherwise cause operating problems in existing boilers designed for conventional fuels.

The processed RDF can also be used as fuel in cooking mid-day meals for the schools. Biomass based briquettes or pellets are already being used as fuel in such scheme in suitably designed stoves. Use of this fuel comes out to be cheaper than using LPG and thus reduces the cost of cooking. The gross calorific value of RDF with binder is in the range of 4000-4500 Kcal/Kg and without binder 3000-3700 Kcal/Kg.

If power generation through use of RDF is considered as an option in rural settings, it is suggested to use "hub and spoke" model wherein RDF processing is in semi-mechanized manner in decentralized locations, preferably close to the source of waste. This would not only ensure that the cost of processing is less but also transportation cost of waste is minimized and power generated in this manner can be easily transported and stored.

Use of Gasifiers

Conventional incineration uses air for combustion and oxidation reactions whereas gasification operates in a partial oxidation mode (gasification). The consequence of this is that flue gas streams from incinerators are at a high volume, requiring major investment for gas cleaning equipment, whereas pyrolysis and gasification produce more concentrated syngas (synthesis gas) which can be cleaned in significantly lower volume (and lower cost) equipment. Typical output of gasification process can be:

·      Produce syngas that is cooled and cleaned prior to the direct generation of electricity with gas engines.

·      Produce a transportable fuel, either as a solid char that is subsequently combusted to generate energy conventionally, or clean methanol/ hydrogen for use as fuel, or bio-oil that can be used as a low-grade fuel.

Typical wastes which can be gasified are again similar to one which are subject to RDF processing, viz. agri residues, hard woody waste, waste plastics, paper, rags, leather and such organic waste which are not easily biodegradable and low inherent moisture content (typically in the range of 10%). Use of biomass based gasifiers also has found application in mid-day meal preparation for thermal application. Coal based gasifiers were extensively being used by Ceramic clusters in Gujarat and industry found it to be cheaper than using LPG. The issue to be addressed in using gasifiers however is to develop environmental standards and protocols for the sector and scaling out of the technology diffusion.

Recommendations

Based on above summary of technological options, it can be said that:

·      Producing RDF from source segregated waste and use in already existing boiler or dedicated boiler holds promise and the technologies are commercially available,

·      Bio-methanation must be considered a high priority for waste-to energy projects in rural areas due to the combination of cost, technology, effectiveness and environmental benefits.

·      Gasification has a distinct promise, and although there are limitations to its uptake, these can be solved as the technology matures.

Swachh Bharat Abhiyan

To make these projects effective, their long term operation and maintenance needs to be ensured. The rural youth can be trained to manage these projects and can thus get livelihood out of keeping the rural areas clean and managing waste scientifically and also generating energy in the process of managing waste. This will also be in accordance with Swachh Bharat Abhiyan (SBA) launched by the Prime Minister, which attempts to ensure that India becomes clean and affordable and sanitation services are provided and used by all

The funds required to establish, operate and create rural entrepreneurship can partly come from SBA (rural) and also from Corporate Social Responsibility (CSR) funds available from the corporate sector in the country. At the later stages of project implementation on rural waste to energy, a competition somewhat similar to clean city can also be initiated with villages implementing these projects in order to keep them clean. A suitable recognition at the village Panchayat level will keep them motivated in the long term and help sustaining these initiatives.