Natural Clay Minerals as Potential Arsenic Sorbents from Contaminated Groundwater: Equilibrium and Kinetic Studies

Arsenic (As) contaminated groundwater is a worldwide concern due to its chronic effects on human health. The objectives of the study were to evaluate natural inexpensive raw laterite (RL) and kaolinite (RK) for their potential use as As sorbents and to understand the As sorption on laterite and kaolinite by employing sorption and kinetic models. Raw laterite and RK were tested for EC, pH, XRF and CEC as basic parameters. Batch sorption and kinetic experiments data were fitted in the sorption (Langmuir and Freundlich) model and kinetic (pseudo-first and pseudo-second order) reaction equations, respectively. Morphological and structural changes were observed in RL and RK samples before and after As saturation by employing FTIR and SEM. The major constituent in RL was Fe and Al oxides while in RK major oxides were silica and Al. The Freundlich sorption model well explained the experimental data, indicating a greater sorption capacity of RL on a hetero-layered surface compared to RK. The kinetic reaction equations showed that equilibrium was achieved after a contact time of 240 min and the adsorption was chemisorption in nature. The RL and RK were found to be effective sorbents for As removal, however, RL showed maximum As adsorption and thus superior in comparison with RK. Structural and morphological characterization reveals the role of Fe and Al oxides in the case of RL, and Al oxides in the case of RK, in the adsorption of As. Hence this study concludes that these naturally occurring inexpensive resources can be used as sorbent agents for As-contaminated drinking water treatment

Isolation and Characterization of Phosphate Solubilizing Microbes from Rock Phosphate Mines and Their Potential Effect for Sustainable Agriculture

Continuous application of phosphate (P) mineral to soil renders apatite addition during each crop growing season which is of great concern from a sustainable agriculture viewpoint. Use of efficient phosphate solubilizing microbes (PSB) is one of the most effective ways to solubilize this apatite mineral in the soil. The current study targeted hydroxyapatite mines to explore, isolate and characterize efficient P solubilizers to solubilize apatite in the soil. Efficiency of isolated microbes to solubilize rock phosphate (hydroxyapatite) and tri-calcium phosphate (TCP) as well as indole-3-acetic acid (IAA) and 1-aminocyclopropane-1-carboxylate deaminase (ACC) activity were tested. Identification and phylogenetic analysis of bacterial and fungal isolates were carried out by 16S rRNA and internal transcribed spacer (ITS) rDNA sequence analyses, respectively. The isolated bacterial strains were identified as Staphylococcus sp., Bacillus firmus, Bacillus safensis, and Bacillus licheniformis whereas fungal isolates were identified as Penicillium sp. and Penicillium oxalicum. Results showed that the impact of identified strains in combination with three phosphate fertilizers sources (compost, rock phosphate and diammonium phosphate (DAP)) was conspicuous on maize crop grown in pot. Both bacterial and fungal strains increased the P uptake by plants as well as recorded with higher available P in post-harvested soil. Penicillium sp. in combination with compost resulted in maximum P-uptake by plants and post-harvest soil P contents, compared to other combinations of P sources and bio-inoculants. Screening and application of efficient P solubilizers can be a better option to utilize the indigenous phosphate reserves of soil as well as organic amendments for sustainable agriculture

Organic Amendments and Elemental Sulfur Stimulate Microbial Biomass and Sulfur Oxidation in Alkaline Subtropical Soils

Sulfur deficiency arising due to intensive cultivation, use of sulfur free fertilizers and reduction in atmospheric sulfur depositions has become a major issue limiting crop production in many parts of the world. Elemental sulfur could be a good source of available S, but its slow oxidation is a problem for its efficient use as a sulfur fertilizer. Main objective of the study was to assess the effect of organic amendments (OA) and elemental sulfur (ES) on microbial activities, sulfur oxidation and availability in soil. A laboratory incubation experiment was carried out for a 56 days period using two sulfur deficient alkaline soils. Organic amendments (OA), i.e., farmyard manure (FYM), poultry litter (PL) and sugarcane filter cake (SF), were applied (1% w/w) with or without elemental sulfur (ES) at 50 mg kg−1. Application of ES alone or in combination with OA significantly increasedCO2-C evolution, microbial biomass, and enzyme activities in the soils, except dehydrogenase activity (DHA) which was not affected by ES application. Combined application of OA and ES had a more pronounced effect on microbial parameters compared to ES or OA applied alone. Ratios of dehydrogenase activity-to-microbial biomass C and arylsulfatase activity-to-microbial biomass C were high in ES+FYM and ES+SF treatments, respectively. Elemental sulfur got sufficiently oxidized resulting in significant improvement in plant available S. Relatively more ES was distributed into C-bonded-S than ester bonded-S. Increase in sulfur availability in ES+OA amended soils was the combined function of sulfur oxidation and mineralization processes through improved microbial activity

Immobilization of Cd, Pb and Zn through Organic Amendments in Wastewater Irrigated Soils

Due to the scarcity of water, raw sewage effluents are often used to irrigate arable suburban soils in developing countries, which causes soil contamination with toxic metals. Soil microorganisms involved in biochemical transformations are sensitive to heavy metals contamination. The study was designed to investigate the effect of organic amendments on the microbial activity of cadmium (Cd), lead (Pb) and zinc (Zn) fractions and their bioavailability in soils contaminated with wastewater irrigation. Three metal contaminated soils under wastewater irrigation were collected, ground, sieved and added to incubation jars. Two organic amendments: wheat straw and chickpea straw, were applied (1% w/w) to the soil before incubation for 84 days at 25 °C. The CO2-C evolution after 1, 2, 3, 5, 7, 10 and 14 days was measured and thereafter was also measured weekly. Soil samples collected at 0, 14, 28, 42, 56, 70 and 84 days after incubation were analyzed for microbial biomass carbon (MBC). Sequential extraction for metal fractionation of samples was carried out collected at 0, 28, 56 and 84 days. Three soils differed significantly in evolved MBC and ∑CO2-C. Chickpea straw addition significantly increased soil MBC as compared to the wheat straw. Organic amendments significantly increased ∑CO2-C evolution from the soils, which was higher from chickpea straw. The addition of crop residues did not affect total Pb, Cd and Zn contents in soils. The concentration of exchangeable, carbonate bound and residual fractions of Pb, Cd and Zn decreased (6–27%), while the organic matter bound fraction increased (4–75%) with straw addition. Overall, the organic amendments improved microbial activity and reduce the bioavailability of toxic metals in wastewater irrigated soils. Furthermore, organic amendments not only reduce economic losses as they are cheap to produce but also minimize human health risks from heavy metals by hindering their entry into the food chain