Circular Economy and Fly Ash Management

Electric power in India mainly depends on coal-fired power plants. Commonly, Indian coal comprises ash in the range of 30–45%. In order to sustain India’s economic growth, the country total coal demand is forecasted to more than double by 2030. Increasingly huge quantities of fly and bottom ash are produced in the country, thus leading to the necessity to duly plan safe and clean ways to handle, use, and dispose of the combustion by-products. Thermal power plant design nowadays must duly consider apprehensions related to water shortage, environmental guidelines, sustainable management and disposal of ash, along with growing consciousness pertaining to overall cost and power plant efficiency. The current paper discusses the problems associated with fly ash and its handling and mitigation measures. Fly ash generated while burning of coal in thermal power plants can be utilised for several favourable uses like manufacturing of cement, road construction, road embankment and development of ceramics or fertiliser.

In an attempt to probe for alternate techniques in place of chemical pesticides consumed in various crop fields and their retention as residues in agricultural soils and various water resources used in irrigation, soil and water samples were gathered from two locations, Neyveli and Virudhachalam adjacent to Neyveli Lignite Corporation India (NLCIL), Neyveli, Tamil Nadu, India, during off-season. Samples were drawn from the fields cropped with rice, sugarcane, cashew nut, mango, groundnut, gingelly intensively grown in this tract, and water samples were gathered from borewells, irrigation canals, lignite mine water, open wells and natural water and analysed for the residues of pesticides. Results revealed that the soil samples drawn from the cropped fields contained various molecules of different groups of pesticides particularly Quinalphos, Endosulfan, Deltamethrin and Etrimphos, whereas the water samples hardly had pesticide molecules. The findings are interpreted to the role of fly ash as dust insecticide found effective from our laboratory against various pests of crops shows promise and appropriateness in the context of replacing chemical pesticides use in agricultural fields. Various chemical pesticides especially of the dust, granule and wettable powder formulations could be dispensed within the event of the fly ash used as a carrier. As a whole, it is inferred that fly ash use in pest control in different crops in agriculture has immense value in the context of protecting the environment and agricultural produces from the chemical pesticides.

Indian electricity generation is majorly dependent on thermal energy by burning the coal producing large amount of fly ash as by-product. Dumping and disposal of fly ash in ponds and land is a routine practice which raises various environmental concerns. Hence, the Ministry of Environment, Forest and Climate Change (MoEFCC), Govt. of India has made continuous efforts for proper utilization and disposal of fly ash. This by-product’s rich nutrient content has opened doors for its utilization in agriculture rising a tremendous potential in improving crop productivity and soil health. Besides its nutrient efficiency, fly ash treatment showed a significant result in agricultural insect-pest control. However, agricultural use of fly ash is quite limited in comparison to other sectors of India. MoEFCC has revised norms of fly ash usage and also made a mandate for supplying fly ash free of cost to farmers in the radius of three hundred kilometres. Fly ash is also an excellent substitute for reclamation of low-lying areas and helps in restoration and protection of topsoil layer; with an ever-increasing demand for electricity production in India, fly ash production will also increase. Thus, it is high time to explore the untapped potential of fly ash utilization in Indian agriculture for its sustainable management particularly for timber, ornamental, jute and fibre crops and other agriculture and food systems after proper quality testing.

Disposal, safe management, and gainful utilization of coal-based fly ash are the issues of major concern and challenge in the present century due to alarming increase in the production of ash in India Recent reports indicated that fly ash utilization in agriculture sector has stood at 1.92 mt (million tones) during 2016–17, which constitutes hardly 1.14% alone of the total fly ash utilization. This might be attributed to low product value and presence of heavy metals in fly ash which limits its large-scale applications as agricultural soil amendments. Conversion of fly ash into zeolites (FAZ), a sodium aluminosilicates group of minerals, is an innovative and proven approach but not adequately researched under laboratory conditions to engineer the right quality of zeolite and field conditions to find out the slow nutrient release characteristics and the use efficiency under diverse soil types and agroecological conditions. The improved percent zeolitization of the FAZ will have twin benefits (water and nutrient retention) because of its fine loamy texture and high cation-exchange capacity (CEC). In addition, zeolites can conserve soil organic matter that will help further to improve the efficiency of soil water and nutrient use. This added property will be highly beneficial for tuber crops in particular as they are extensively grown in the country in degraded and marginally fertile soils poor in soil organic carbon (SOC) and as the economic parts are beneath the soil, the physical properties and SOC content are critical for the crop performance. With the funding support of fly ash unit, DST, during 2010–13, low-cost, high-value agricultural grade fly ash zeolites (near-neutral pH, low Na, high CEC, and low heavy metals content) was successfully synthesized and evaluated in sweet potato (Ipomea batatus L.) wherein the tuber yield was found correlated in soils amended with zeolites due to higher nutrient use efficiency with respect to the major nutrients studied, viz. N, P, and K. Research on large-scale field application especially on soil aggregation and compaction properties, soil carbon quality and stability potential aspects of FAZ, adsorption and availability of important soil nutrients NH₄⁺, K⁺, Ca⁺⁺, and Na⁺ must be given utmost priority to further establish the controlled release fertilizer characteristics of FAZ in India.

Results showed that the fly ash as dust could be an active control factor in checking the infestation of crop pests and also safe to different non-target organisms like natural enemies, beneficial insects hovering in and around agro-ecosystems. Application of fly ash @ 40 kg/ha in rice had caused maximum mortality of 73.3% in leaf caterpillar followed by grasshopper (71.0%), horned caterpillar (68.8%). Nine fly ash-based herbal insecticides, viz. neem (Azadiracta indicia A. Juss.), Indian Privet (Vitex negundo Linn.), Eucalyptus (Eucalyptus globulus Labill.), Pongam (Pongamia pinnata Linn.), Turmeric (Curcuma longa Linn.), Chilli (Capsicum annuum Linn.), Sweet flag (Acorus calamus Linn.), Ginger (Zingiber officinale Roscoe) and Adathoda (Adhatoda vasica Linn.) were synthesised using fly ash as a carrier. The eventual fly ash-based herbal pesticides were evaluated against key pests of crops. In vegetables, the fly ash-based herbal pesticides manifested better results against major pests of bhendi and brinjal. Results showed that the combination of treatment fly ash + square stalked vein 10% D acted very effective against mandibulate termite soldier with maximum mortality followed by fly ash + French basil 10% D. The overall mean efficacy of lignite fly ash against housefly, a menace around poultry yard was observed at 83.33% mortality of maggots. These new class of herbal pesticides had also exhibited good control of insect pests, namely Tribolium castaneum Herbst, Callosobruchus chinensis Linn., attacking stored product.

Four fly ash-based insecticides, viz. Fly ash + Endosulfan 4% Dust, Fly ash + Chlorpyriphos 1.5% WDP, Fly ash + Imidacloprid 2.15% Tablet and Fly ash + Fipronil 0.05% Tablet, were synthesized. Fractions of lignite fly ash particles obtained through the ball mill grinder were characterized and fractions which were nearer to nanoparticle (less than 50 μm) were subjected to tests in various experiments. Maximum mean per cent mortality was found in Fly ash + Endosulfan 4% Dust 50% conc. against major pests of rice such as leaf folder, skipper, grasshopper, green horned caterpillar, green leafhopper and brown planthopper followed by Fly ash + Chlorpyriphos 1.5% WDP @ 0.25% which recorded mortality of leaf folder, rice skipper, grasshopper, green horned caterpillar, green leafhopper and brown planthopper. Maximum mortality was found in Fly ash + Endosulfan 4% Dust 50% conc. against major pests of cotton such as spotted bollworm, red cotton bug, aphid, mealy bug and whitefly followed by Fly ash + Chlorpyriphos 1.5% WDP @ 0.25% which recorded higher mortality of spotted bollworm, red cotton bug, aphid, mealy bug and whitefly. In brinjal, Fly ash + Endosulfan 4% Dust 50% conc. controlled major pests such as Epilachna beetle, aphid, mealy bug and lace wing bug followed by Fly ash + Chlorpyriphos 1.5% WDP @ 0.25%. Fly ash + Endosulfan 4% Dust @ 50% conc. gave better control of storage pests such as Tribolium castaneum (Herbst) and Callosobruchus chinensis L. followed by Fly ash + Chlorpyriphos 1.5% WDP @ 0.25%. In the choice test, cockroaches did not accept the test product FA + Imidacloprid, whereas they accepted the product FA + Fipronil to some extent and maximum number of cockroaches got attracted to groundnut candy (>3) in both the experiments and biscuits 2.62 in experiment one and 3.13 in experiment two compared to fipronil (1.5). Overall the preference tests had showed that the out of the two new fly-ash products, FA + Fipronil was found to be potential; however, it might be further enhanced through suitable refinement in the formulation.

Fly ash, one of the numerous substances that causes air, water and soil pollution, has been discovered as a pesticide against various pest forms that hamper agriculture and an active carrier in chemical pesticides (dust, wettable powder, granules and capsules) and herbal insecticides (dust) formulations. Insecticidal action of the fly ash dust was detected for the first time in the country on various kinds of insect pests inflicting crops like rice, vegetables, oilseeds, pulses, greens, fruit trees, besides pests of grains in storage yards too. Mode of action of fly ash dust on insect forms was characterised based on its physical and internal damage both on the insect bodies and crop plants. Interestingly, fly ash on application to rice soils had promoted resistance to the plant to thwart pests attack. Nano-fly ash of two fractions of size ranging down 50 µm was detected to be highly potential in killing the pests. Four chemical insecticides, viz. BHC 10% Dust, BHC 50% WDP, Malathion 25% WDP and Carbofuran 3% WDG, were synthesized with the two selected lignite fly ash fractions. All of them faired best in killing various pest’s species in rice compared to the respective chemical insecticides. It is felt that use of fly ash as a carrier in the synthesis of chemical and herbal pesticides may replace with long run the conventional carriers like Calcite, Magnesite for eventual decline in the cost, and hence, will be a breakthrough in the pesticide industry. As an attempt to exploit particle, morphology and mineralogical contents of fly ash of two sizes ranging from among 10 to 50 μm were selected for their increased pesticidal action. SEM studies carried to have a close-up view of the individual particle of the lignite fly ash and coal fly ashes revealed that they were mostly of nanoparticle types. Secondly, morphometric features of the lignite fly ash nanoparticles were of spherical shape containing mostly of silica as silicon di oxide (SiO₂) and showed two forms, namely amorphous which is rounded and smooth and crystalline which is sharp and pointed. These differently sized particles of fly ash are best suited to adhere to the body skin of the insects having dense cover of structures like fine hairs, scales, spine-like processes, nodules, pustules, ventricles. Further, such fly ash particles when delivered in the field through dusters cling firmly to the plants and the bodies of insects and per cent deposition was high. Mineral contents of the fly ash revealed the presence of Silica, Alumina, Calcium, Ferric Oxide and traces of Zn, Pb, Zr, Sr, S, Th, Cu, Mn, etc. Among these, silica has been observed to strengthen the pesticide property of fly ash followed by Al, Ca, Fe and sulphur. From the above, it is inferred that such nano-fly ash particle technology has great scope in pest control in agriculture and allied arenas of farm folks through promoting organic agriculture tactics.

The present study deals with the behaviour of fly ash concrete at elevated temperatures. Concrete specimens of cubes of 100 mm, cylinders of 100 mm diameter and 300 mm height and prisms of 100 × 100 × 500 mm are cast by replacing the cement with fly ash in a range of 30–50% by mass of cement. The specimens are cured for 7 and 28 days, then dried and are exposed to elevated temperatures ranging from 100 to 500 °C for a period of 1 and 3 h, to investigate the effect of temperature on compressive strength, split tensile strength and flexural strength. It is observed that the residual compressive strength, split tensile strength and flexural strength of fly ash concrete initially increased with increase in temperature, later decreased with further increase in temperature.

An enormous amount of fly ash is generated in thermal power plants in India, which affects the environment and living organism. By means of fly ash in concrete in place of cement reduces the consumption of natural resources, diminishes the environmental pollution and also economical as replacing the cement which is costlier by the fly ash. The recent investigations by many researchers have revealed that the use of cementitious materials such as fly ash and GGBS in concrete is trustworthy and also economical. This present experimental research is to study the using non-conventional building material like fly ash for the development of new material and technologies. The present study involves replacing of cement with fly ash in the range of 30, 40 and 50% by mass of cement for M-30 grade concrete mix with 0.48 water cementitious material ratio. Concrete cubes, cylinders and prisms are cast, tested and compared in terms of strength at different ages of curing. The experimental results have revealed that the compressive strength has increased marginally for specimens with replacement of cement by 30% fly ash at age of 7, 28, 56 and 91 days.

Naturally occurring silica source materials, including fly ash, when developed as suitable silica source formulations, can be utilised as green technologies for fortifying the target crop cultivars with induced resistance to biotic and abiotic stresses. Silica sources/products availed from natural or biological sources may have added advantage in organic-certified crop production systems. The potential for utility of applied silica for induced resistance to biotic stresses appears more promising in monocot crops like rice and sugarcane, since they are silica-hungry. There is adequate evidence of silica content in target tissues being associated with genetic variation for host plant resistance to pests in rice and sugarcane. Since farmers tend to select and adopt crop varieties mostly for agronomic attributes like higher yield and crop duration, there is scope for fortifying them with such applied silica by minimising the losses caused by biotic stresses like pests and diseases among such agronomic ally promising and locally popular crop varieties. The major mechanisms by which resistance to biotic stresses like insect pests and diseases could be induced by applied silica include anatomical changes like enhanced silica deposition in the target tissues in epidermal layer as improved structural barrier for their entry and/or biochemical changes due to modifications in metabolic functions including the jasmine acid pathway. Adequate knowledge base is available on the scope for such applied silica products in also countering abiotic stresses such as drought and lodging tendency. There is good scope for locally optimising the application regime of such silica products so to maximise the cost-effectiveness. The results of recent collaborative R&D in sugarcane against borer pests in India are illustrated as case study. The scope for public–private R&D partnership targeting the formulation and market availability of such silica source products as potential components of evergreen revolution in India is indicated. Multidisciplinary and inter-institutional R&D collaboration is reckoned as the promising strategy.

Rice (Oryza sativa L.) is the most irreplaceable staple food for over three billion people of Asia. In Tamil Nadu, it is being grown throughout the year at different seasons under low land submerged conditions. As a result of continuous cropping, removal of silicon from soil leads to its deficiency. The rice crop shows the largest uptake of silicon playing a major role in mitigating the biotic and abiotic stresses. The fly ash is the storage of silicon in significant amount irrespective of different sources of fly ash, viz. fly ash from sugar factory, thermal power station and modern rice mill. The availability of fly ash is plenty, which poses a problem to the environment. Hence, the present study was carried out to explore the possibility of utilizing the fly ash as a source of silicon for mitigating the biotic and abiotic stress in rice. In view of the above, field experiments were conducted in low silicon soils to examine the effect of fly ash @ 25 t ha⁻¹ with silicate solubilizing bacteria @ 2 kg ha⁻¹ and farm yard manure @ 12.5 t ha⁻¹, with graded level of soil test-based potassium on growth and yield, incidence of pests, silicon uptake and changes in biochemical constituents, viz. total phenol, OD phenol, reducing, non-reducing sugars and proline in different plant parts such as leaf blade, leaf sheath cum stem and in ear head at different growth stages of the rice cultivar BPT 5204 under induced drought and flood conditions. The experiments were conducted at Agricultural Engineering College and Research Institute Farm, Kumulur, Trichy District, during 2012 in split plot design with two replications. The results revealed that application of fly ash with silicate solubilizing bacteria + farm yard manure with 100% soil test-based potassium increased the rice grain yield by 22 and 10.3%, under induced drought and flood stress conditions, respectively, over control. The biochemical constituents played an important role in reducing the pest incidence in induced drought and flood stress. However, the effect was more pronounced under induced drought over flood stress condition. Hence, the application of fly ash with silicate solubilizing bacteria + farm yard manure with 100% soil test-based potassium helps to improve the growth and yield of rice. It also helps in mitigating the biotic stresses in rice by the influence of Si under induced abiotic stress, viz. drought and flood. Other biochemical constituents were also favorably correlated with the reduced incidence of pests and increased yield of both grain and straw.