Evaluation of the co-application of fly ash and sewage sludge on soil biological and biochemical quality.

Disposal of sewage sludge (SS) and fly ash (FA) is a multifaceted problem, which can affect environmental quality. FA has the potential to stabilize SS by reducing metal availability and making the SS suitable for application in the agricultural sector. An experiment was performed to evaluate soil biological quality changes with the combined amendment of SS and FA (fluidized bed combustion ash (FBCA) and lignite fly ash (LFA)). SS was amended with 0, 10, 30, 50 and 100%, (w/w) of FA, and then the FA-SS mixtures were incubated with red soil at 1:1 (v/v). Soil quality parameters such as pH, electrical conductivity, N, soil enzyme activities such as dehydrogenase (DHA), urease (URE), and catalase (CAT), and microbial biomass carbon (MBC) were evaluated at 20, 30, and 60 days of incubation, pH and EC increased with FA-SS dose; however, N decreased. DHA and URE were found to be increased with 10% LFA amendment; thereafter it decreased. However, URE increased up to 30% of FBCA. CAT and MBC increased with both FA amendments, even up to addition of 50% FA. Bioavailable Zn, Cu, and Co contents were decreased by the addition of FA. Principal component analysis showed that pH is the most influential factor. MBC appears to be a sensitive soil indicator for the effects that result from the addition of FA-SS. Phytotoxicity studies with Zea mays showed optimum performance at 30% FA. Addition of 10-30% FBCA or LFA to SS has a positive advantage on soil biological quality.

Management of lignite fly ash for improving soil fertility and crop productivity.

Lignite fly ash (LFA), being alkaline and endowed with excellent pozzolanic properties, a silt loam texture, and plant nutrients, has the potential to improve soil quality and productivity. Long-term field trials with groundnut, maize, and sun hemp were carried out to study the effect of LFA on growth and yield. Before crop I was sown, LFA was applied at various doses with and without press mud (an organic waste from the sugar industry, used as an amendment and source of nutrients). LFA with and without press mud was also applied before crops III and V were cultivated. Chemical fertilizer, along with gypsum, humic acid, and biofertilizer, was applied in all treatments, including the control. With one-time and repeat applications of LFA (with and without press mud), yield increased significantly (7.0-89.0%) in relation to the control crop. The press mud enhanced the yield (3.0-15.0%) with different LFA applications. The highest yield LFA dose was 200 t/ha for one-time and repeat applications, the maximum yield being with crop III (combination treatment). One-time and repeat application of LFA (alone and in combination with press mud) improved soil quality and the nutrient content of the produce. The highest dose of LFA (200 t/ha) with and without press mud showed the best residual effects (eco-friendly increases in the yield of succeeding crops). Some increase in trace- and heavy-metal contents and in the level of gamma-emitters in soil and crop produce, but well within permissible limits, was observed. Thus, LFA can be used on a large scale to boost soil fertility and productivity with no adverse effects on the soil or crops, which may solve the problem of bulk disposal of fly ash in an eco-friendly manner.