Fly-ash products from biomass co-combustion for VOC control

Experiments were conducted in a continuous flow reactor at room temperature to evaluate the elimination of low-concentration toluene in the gas phase to verify if fly-ash products from biomass combustion in an ozonation system could be used in the removal of volatile organic compounds. The fly-ash products from pure biomass combustion (Ash₁₀₀) demonstrated the highest ozonation activities upon the removal of low-concentration toluene (1.5 ppmv), followed by the fly-ash products from co-combustion (Ash₃₀) and the coal combustion (Ash₀). Kinetic experiments showed that the activation energy of the toluene elimination process was substantially reduced with the use of ozone and the reaction intermediates, such as formic acids, aldehydes, etc. Results also showed that the intermediates were reduced with increasing humidity level. The combined use of fly-ash products and zeolite 13X enhanced the removal of toluene to above 90% and suppressed the release of residual ozone and intermediates by holding them in the adsorbed phase.     

Inoculation of Rhizobium (VR-1 and VA-1) induces an increasing growth and metal accumulation potential in Vigna radiata and Vigna angularis L. growing under fly-ash

Fly-ash-tolerant Rhizobium strains were isolated from plants grown in fly-ash-contaminated soil, axenically under laboratory conditions. Saplings of both plants were raised in N₂-free Jenson medium and inoculated with 2.6 × 10⁸ cell ml⁻¹ and 5.2 × 10⁸ cell ml⁻¹ of culture after 10 d of growth. Plants were transferred into 100% fly-ash under natural condition. Rhizobium-inoculated plants grown on 100% fly-ash showed marked increase in relation to root-shoot length, biomass yield, photosynthetic pigment, protein content and nodulation frequency compared to uninoculated plant grown in control (100% fly-ash). Inoculation of fly-ash-tolerant Rhizobium increased the accumulation of Fe, Zn, Cu Cd and Cr in different tissues vis-à-vis enhanced translocation of metals to the aboveground part of plant. Although inoculation of fly-ash-tolerant Rhizobium strains (VR-1 and VA-1) enhanced the translocation of more Fe to shoot parts, nevertheless, the amount of Rhizobium inoculants supplied to the plant was found to be very important since it has a positive role in increasing plant growth through increased N₂ supply via nitrogenase activity. Results suggest that an integrated approach employing biotechnological means and inoculation of plants with host-specific fly-ash-tolerant Rhizobium strain may prove a stimulus to a fly-ash management programme.     

Growth and metal accumulation potential of Vigna radiata L. grown under fly-ash amendments

The study was undertaken with the aim of testing the feasibility of growing Vigna radiata on fly-ash dykes or on fly-ash contaminated soil. Experiments were conducted in earthen pots (12″) having various amendments of fly-ash with garden soil, press mud and farm yard manure and harvested after 60 days of growth. Various growth variables were analyzed, viz., root-shoot length, biomass yield, number of branches, photosynthetic area and pigments, protein content, in vivo nitrate reductase activity and nodulation frequency. The metal accumulation potential (Fe, Zn, Cu, Cr, Cd) in roots and shoot tissues of plants was determined in various fly-ash amendments and seeds were also examined for their metal content so that they can be utilized for growing in fly-ash-contaminated areas. Our results show that the plants grown in 100% fly-ash accumulated significant amounts of metals due to which general vigor and development of plant are affected. V. radiata grown on ameliorated fly-ash showed tolerant characteristics. Plants accumulated metal in the order Fe > Cu > Zn > Cr > Cd. However, their concentration was more in shoot than root tissue except in the case of Fe, which was found to have accumulated more in root tissues. Press mud (25%) amended with fly-ash was found to be the best ameliorant to support plant growth. It may be concluded from the present study that V. radiata was an ideal crop for growing in fly-ash-contaminated areas for the revegetation of fly-ash landfills.     

Impacts of fly-ash on soil and plant responses

Coal combustion produces carbon dioxides, SOx, NOx and a variety of byproducts, including fly-ash, flue gas and scrubber sludge. Fly-ash consists of minute glass-like particles and its deposition on leaves inhibits the normal transpiration and photosynthesis of plants. Fly-ash also affects the physicochemical characteristics of soil because it is generally very basic, rich in various essential and non-essential elements, but poor in both nitrogen and available phosphorus. The massive fly-ash materials have been a potential resource for the agricultural activities as well as the other industrial purposes. Practical value of fly-ash in agriculture as an 'effective and safe' fertiliser or soil amendment can be established after repeated field experiments. Here remains to be disclosed the biological processes and interactions due to 'lack and excess' of the fly-ash exposures along with abiotic and biotic factors. These may involve the symbiotic fixation of nitrogen and the biological extraction of metals following immobilisation of toxic heavy metal ions, as well as other neutralisation and equilibration processes during weathering. Nitrogen-fixing plants with an apparent heavy metal-tolerance can be helpful as the early colonisers of fly-ash dumps and nearby areas. Electronic Publication     

Selenium concentrations in crops grown on low-selenium soils as affected by fly-ash amendment

Summary Studies were conducted under greenhouse and field conditions to evaluate the feasibility of using fly-ash amendments to produce selenium-adequate crops (0.10 to 0.30 ppm Se) on low-Se soils without adversely affecting either the crops or the soils. Two soils, a fine-loamy Alfisol belonging to the Honeoye series and a coarse-loamy Inceptisol belonging to the Mardin series were used to make 3 soil treatments thus: Honeoye, limed Mardin and unlimed Mardin. Fly-ash was mixed with the soils at rates of 0, 2500, 5000, 5000, 10000, 25000 and 50000 ppm. In the greenhouse studies the test crops were corn (Zea mays L.), alfalfa (Medicago sativa), birdsfoot trefoil (Loitus corniculatus) and dry beans (Phaseolus vulgaris L.). There were no yield differences due to fly-ash additions. The rates of 25,000 and 50,000 ppm fly-ash produced the desired Se levels in the utilizable parts of the crops. In the field studies, conducted on another fine-loamy Alfisol belonging to the Lima series and using fly-ash at the rates of 0, 11.2, 22.4 and 112.0 metric tons/ha, it was observed that the yields of corn and dry beans grown were also not influenced by the treatments. Increased levels of Se in corn grains (0.10 ppm) and stover (0.08 ppm) and dry bean seeds (0.14 ppm) were observed at the application rate of 112 metric tons per ha.The results indicate that fly-ash has a potential for producing forages and feed crops containing adequate amounts of Se to protect livestock from Se-responsive diseases.