Bench‐scale experiments were conducted to investigate the effectiveness of an extraction and washing technique for the cleanup of contaminated soil using surfactants. The organics studied as model contaminants were 1,2,4‐trichlorobenzene (TCB), aniline, phenol, and 2,4‐dichlorophenol (DCP). A sandy loam was used as a model field soil. The results demonstrated the effectiveness of the extraction and washing process for decontamination of the sandy loam soil. As much as 99% of the organic contaminants studied were removed by the process depending upon the compound and the number of washes and rinses. The hydrophilic compounds—aniline, DCP, and phenol—were removed effectively from the soil by washing with deionized water alone. Surfactant washing had no advantage over water washing for these compounds. For the removal of TCB, a combination of washing with surfactant and rinsing with water was required. Alum coagulation was effective in separating clay and colloidal particles from the wash liquid but a relatively high alum dose was required and was observed to enhance adsorption of the contaminants on the clay particles. A small residual contaminant concentration remained in the soil.

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Experiments were conducted with pilot small-scale biogas digesters designed for the family level in developing countries. Four 3.5 m3 ferrocement digesters equipped with manually operated mixers were fed a mixture of nightsoil, water hyacinth (Eichhornia crassipes) and rice straw and operated semi-continuously at hydraulic retention times (HRT) of 30, 50 and 70 days, corresponding to organic loadings of 1.2, 0.75 and 0.53 kg m-3 day-1 of total volatile solids (TVS), respectively. Although more biogas was produced at a HRT of 30 days with respect to the unit weight of TVS, the rates of biogas and methane production within these loading rates were similar and approximately 0.283 and 0.186 m3 (kg TVS)-1 day -1, respectively. A major operational problem was excessive scum accumulation in the digester due to the low specific gravity of the plant matter substrates. A parallel batch experiment using 20-1 aspirator glass bottles yielded biogas production rates of 0.400 and 0.406 m3 (kg TVS)-1 at the end of 30 and 50 days, respectively. Manually operated biogas plants using heterogenous substrates in which plant matter is a major component may have little potential for poor farmers in developing countries.

This study evaluated shredded rubber tires mixed with raw primary sludge to determine the optimum particle size and mix ratio for efficient composting. Of the three sizes and mix ratios tested, the 1.27-2.54 cm size and the rubber chip to sludge mix ratio of 2 : 1 were found to be optimum. Anaerobically digested and secondary biological sludges were then composted with the optimum size rubber chips. Due to their high moisture content and low C/N ratio, all three sludges required a moisture absorbing amendment and supplemental carbon. Sawdust was tested and found to be a suitable amendment. Heavy metal levels increased due to the concentrating effect as organic matter was decomposed. Rubber chips contributed zinc and iron to the finished compost. Although elevated after five cycles, the increases in zinc and iron were not high enough to limit the use of shredded rubber in composting sewage sludge.

This paper reports the characterization and humidity sensing studies of CuO–ZnO nanocomposites prepared by solid‐state reaction method. The electrical resistance of nanocomposites continuously decreased when relative humidity (RH) was increased from 10% to 95% RH. Nanocomposites with 1 wt% of CuO in ZnO showed the best results with a sensitivity of 29.95 MΩ/%RH. This sample also showed low hysteresis and high reproducibility. This sample had an average particle and crystallite size of 200 nm and 70 nm, respectively. Measurement of crystallite size by both the methods, that is, Scherer's formula and Williamson and Hall method matched with an error of ±4%.