AW’s disposal is a large environmental concern and the methods used range from simpler to complex for AW application. Interest in the potential diversion of AW for useful purposes is growing with several different methods. These include the application of AW to soils to support the soil’s physical properties, increase soil organic matter, and improve soil bulk density and water holding capacity (Khaleel et al., 1981).


Different approaches to use AW for useful purposes include compost formation for soil application, the direct burial of CR to the soil, biochar production, biosorbent production for heavy metals removal, and biofuel production, etc. In ancient times, AW was not a problem nowadays. Fanners used to bury these wastes on the fields by using plows or allow them to naturally decompose to supply nutrients to the soil. Another approach was the CR burning on the field not associated with the smog problem. Like cotton stalks as fuelwood, AW is also practiced for an economical source of fiielwood and the good reason of less deforestation for fuelwood. Incineration was also done for the last option for the wastes, which cannot be used for any profitable or useful purpose (Girotto et al., 2015).


Composts from AW supply different nutrients to plants and soil (Figure 2.3). It provides organic matter to soil improving the soil capability to hold more water, bulk density, detoxify the soil from different toxic metals by adsorbing them on organic matter and ultimately improving plant growth (Zhang et al., 2017). It is proved that compost is the combination of different plant nutrients (Karak et al., 2015), but influence of composts on different toxic metals binding and crop productivity enhancement. The composts of different AW are effective in alleviating heavy metals toxicity and enhance crop production (Chen et al., 2017). There are also the procedures and techniques to make composts more effective by additional bacterial inoculum or earthworm's addition (vermin-composting) (Huang et al., 2017).


FIGURE 2.3 Composting.


As there are a lot of risks associated with the use of fossil fuels, the researchers are looking for readily available fuel sources. AW is a good raw material for this. Like anaerobic digestion (AD) of cow dung with new feedstock such as CR yields into biogas which can fulfill the energy requirement of a small house to a whole community. It can replace biomass-cooking fuels and also reduce indoor air pollution. After biogas production from cow dung and CR, a by-product called digestate is also produced, which acts as a fertilizer or soil conditioner and provides the nutrients to soil. The supply of digestate to soil reduces the fanners’ dependency on nitrogen phosphorus and potassium- containing synthetic fertilizers only by 0.1, 1.6%, and 31%. By using CR in combination with cow dung, their burning into the fields is avoided, which contributes to air pollution in India and climate change globally (Sfez et ah, 2017). CR plays an important role in the household of the rural communities, not having the proper facilities of fuel and energy sources for cooking and heating then houses. Uses of AW for household energy and heating are about 77.5% of the total rural households in India and 55.3% in Pakistan. Due to the consistent and cheap supply of the fuel sources as AW, only 2% in India and 5-7% households in Pakistan have shifted from AW fuel to other energy sources in a decade (Ravindra et ah, 2019a, b).


It was the easiest way to bum CR on the spot by setting fire. It has some advantages, as if it does not require any labor to collect and transport it to other place for its proper disposal. It was also thought that setting file to the CR supplies ash to the soil is a good source of organic matter in agr icultural soils. However, later on, it was observed that CR burning in the fields does not supply organic matter to the soils but decomposes the existing organic matter by increasing the soil temperature and burning the soil organic matter, hi addition to the soil organic matter loss, the smoke raised from the CR burning resulted in smog condition as evident in subcontinent, especially in India and Pakistan (Ni et al., 2015). This practice is also common in China, and the emissions from the CR burning were calculated in the last 2 decades in 17 districts. It was found that 2707.34 Tg of CO, was emitted CR burning (Sun et al., 2016).

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