Adsorption kinetics of hexavalent chromium on to natural red-earth: a laboratory simulated study.

Heavy metal contamination of water is a significant threat to organisms and to public health. Among them, chromium is one of the important heavy metals in the environment that originates mainly from anthropogenic activities. Natural red earth (NRE), a ferrous-coated natural sand, is one of the materials that could be used to remove heavy metals from contaminated water. Laboratory-scale simulated experiments were carried out to identify the retention behavior of Cr(VI) on NRE. The effects of solution pH, initial Cr(VI) concentration, the amount of NRE used and the contact time were examined. Almost 63% Cr(VI) was adsorbed within 20 minutes. When particle size ranged from 125 to 180 µm, the Cr adsorption data followed the Langmuir isotherm model, providing a higher R2 value of 0.9523, suggesting monolayer coverage on the homogeneous surface with a uniform distribution of energetic adsorption sites. The monolayer coverage of Cr on NRE is estimated as 11.35 mg/g. The data showed that NRE can be used to remove Cr(VI) from aqueous solutions effectively, and this method is found to be simple, effective, economical and environmentally friendly.

Development of sewage sludge-based synthetic aggregates for containerized ornamentals.

Potential utilization of synthetic aggregates (SAs) developed from sewage sludge (SS) as a component of containerized media for French marigold (Tagetes patula) cultivation as a peat substitution was investigated in this study. The six different containerized media utilized were: peat only, SA 20%: peat 80%, SA 40%: peat 60%, SA 60%: peat 40%, SA 80%: peat 20% and SA only. The physical and chemical characteristics of all media were determined. SA-based media showed higher pH, electrical conductivity (EC), bulk density, particle density and nutrient contents (N, P, Ca and Mg) compared to peat media. The highest plant length, number of flowers per plant, shoot fresh weight, shoot dry weight, root length, root fresh weight and root dry weight obtained from the medium having SA 40%: peat 60% increased by 13.69%, 23.53%, 41.46%, 58.95%, 2.43%, 39.09% and 21.68%, respectively, compared to the peat control. The addition of 60% and 100% of SAs to the growth media gave the lowest growth and yield parameters compared to the peat control due to their high EC and pH. Plant tissues obtained from media with added SAs showed increased N, P, Ca and Mg contents compared to plant tissues obtained from peat media. Media with added SAs did not significantly increase concentrations of Cu, Cd, Cr and Pb in plant tissues but the Zn concentration was significantly increased. SA addition to media did not pose any phytotoxicity risks in French marigold plants. SAs can be suggested as viable potting media components to substitute for the widely used and more expensive peat utilized in horticulture.

A review on alum sludge reuse with special reference to agricultural applications and future challenges.

Alum salts are commonly used in the water industry to promote coagulation in the production of clean drinking water, which results in the generation and accumulation of 'waste' by-product 'alum sludge' in large volumes. Effective and efficient management of alum sludge in an economically and environmentally sustainable manner remains a significant social and environmental concern with ever increasing demand for potable water as a result of rapidly escalating world population and urban expansion. Various intensive practices have been employed to reuse the alum sludge in an attempt to figure out how to fill the gap between successful drinking water treatment process and environmentally friendly alum sludge management for over the years. This paper primarily aimed at comprehensive review of the existing literature on alum sludge characteristics, its environmental concerns and their potential utilization, especially in agricultural and horticultural sectors leading to update our recent state of knowledge and formulate a compendium of present and past developments. Different types of alum sludge utilizations in various fields were recognized and examined. The strengths, weaknesses, opportunities and potential risks of alum sludge reuse options with particular reference to agriculture were highlighted and knowledge gaps were identified. Research priorities and future challenges that will support in the development of effective alumsludgemanagement practices in agriculture with multi-prong strategies were discussed.

Sewage sludge sugarcane trash based compost and synthetic aggregates as peat substitutes in containerized media for crop production.

Effect of partial substitution of peat in growth media by sewage sludge sugarcane trash based compost (SSC) and synthetic aggregates (SA) on the physical and chemical characteristics of the growth media and on the growth and nutrition of lettuce (Lactuca sativa L.) grown in the substituted media was investigated under this study. SSC was produced from sugarcane trash and sewage sludge. Unconventional SA were produced by low productive acidic red soil with paper waste and starch waste. The treatments assayed were: SSC (40%)+Peat (60%), SA (40%)+Peat (60%), SSC (60%)+SA (40%), SSC (40%)+SA (20%)+Peat (40%) and SSC (40%)+SA (40%)+Peat (20%). Peat only was used as the control. The physical and chemical properties of all growing media were analyzed. SSC-SA based substrates showed adequate physical and chemical properties compared to peat for their use as growing media in horticulture. In relation to the plant growth in peat control, plants grown in the SSC-SA based substrates reached better growth and nutrition. The concentration of trace elements in plant tissues was far lower than the ranges considered phytotoxic for plants. Utilization of SSC and SA can be considered as an alternative media component to substitute the widely using expensive peat in horticulture.