Contamination of soil and groundwater by pesticide leaching has become a serious threat to subsurface environment. Hazards of the leaching potential of various pesticides were studied in a shallow unconfined aquifer located in Northwest Bangladesh. Pesticide leaching potential was quantified using a one-dimensional advective-dispersive transport equation for a non-conservative chemical that follows first order decay and linear adsorption in soils. Leaching potential index (LPI) was calculated for sixty-nine sites in the study area to evaluate the relative vulnerability to pesticide leaching and to prioritize sites for soil sampling. The numerical ranks of computed LPI were grouped by quantiles into very high, high, moderate, low and very low categories and based on these rankings, the most vulnerable site was selected. Six soil samples were collected from this site at different depths (0.0, 1.5, 3.0, 4.5, 6.0, and 7.5m). The soil-water from the collected samples was extracted following the standard procedure and tested using GC and HPLC for pesticide residues. Results showed no trace of known pesticide residues in the soil-water but few unknown peaks were detected indicating the use of some unknown chemicals in the study area.
The quantitative and qualitative evolution of dissolved organic matter was followed at different stages of water treatment and in tap water to assess dissolved organic carbon (DOC) removal. Both DOC and 3- dimensional excitation emission matrix (EEM) fluorescence spectroscopy were used to evaluate the efficiency of the process. On the average, 53% of DOC was removed during the treatment process at the treatment plant. After water released in the distribution system, an increase of 27% DOC was observed in tap water, suggesting a production of organic carbon within the network. The EEM permitted to distinguish three main fluorophores, tryptophan-like (T) and humic-like (A and C) in raw water as well as in treated water. In tap water, an increase of fluorescence intensity (FI) was also observed, 31%, 34% and 59% on the average for fluorophores A, C and T, respectively. The tryptophan-like fluorophore is related to microbial activities and suggests an important development of microbial community within the distribution system due to the inefficiency of organic matter removal during the water treatment process.
Liners play an important role in minimizing migration of contaminants in landfill engineering. Adsorption studies were carried out in order to assess the suitability of local materials with additives as liners .The red soil along with admixtures has been found to retain heavy metals and alkali metals effectively. For different dilution ratios, it was found that adsorption efficiency decreases with increasing dilution ratio. Empirical adsorption models like Langmuir and Freundlich were applied for the experimental data and both were found to vary linearly. Monolayer sorption capacity was obtained using Langmuir isotherm, which was used to arrive at adsorption rankings for different mixtures. The correlation coefficient varied from 0.9058 to 0.9884 for Langmuir and from 0.9096 to 1 for Freundlich, which suggests that both isotherm models fit very well. Constant pH batch adsorption studies were carried out at pH 4, 6, 8, 10, and 12. It was found that adsorption is pH dependent and maximum adsorption takes place at a pH range of 6 to 8 for all elements, except for hexavalent chromium. Confirmatory tests were done by taking scanning electron microscopy (SEM) images and electron dispersive spectroscopy (EDS) for thorough understanding of soil mineral structure.
After several decades of water and sanitation sector development in developing countries, ambient water pollution is still one of the major environmental problems. Safe and convenient sanitation, toilet use, public health issues, hygiene behavior and ambient water quality improvement are purposes and benefits of sanitation. The sanitation indicator of Millennium Development Goals (MDGs) showed that the proportion of population with access to improved sanitation in Thailand was 99 % in 2004, however, ambient water quality deterioration is still a major environmental problem. Therefore, pollutant discharge and affordability should be discussed in a quantitative manner. In this paper, municipal wastewater pollutant discharge contribution to ambient water pollutant loads was given attention. The pollutant load per capita flowing into water body (PLCwb) were estimated as 7.2 g-BOD person-1day-1, 9.2 g-TN person-1day-1 and 1.2 g-TP person-1day-1, in Pak Kret Municipality, a peri-urban area of Bangkok, Thailand. PLCwb can evaluate both anthropogenic pollutant removal effects of wastewater treatment systems and natural purification effects in ambient water. Scenario-based analysis showed water quality improvement in the Chao Phraya River to be 0.12-0.26 mg-BOD l-1, 0.19-0.33 mg-TN l-1 and 0.03-0.05 mg-TP l-1 compared to the current annual average water quality of 1.94 mg-BOD l-1, 1.19 mg-TN l-1, and 0.22 mg-TP l-1. Pollutant discharges per capita (PDCs) estimation results and cost-benefit comparison results showed the effectiveness of PDCs to evaluate various municipal wastewater treatment systems.