Yoshinobu Ishibashi

Quantitative bioregeneration of granular activated carbon loaded with phenol and 2,4-dichlorophenol

Lignite based granular activated carbon of 20×30 mesh size was used to investigate the extent of bioregeneration of phenol and 2,4-DCP in a batch system. The adsorption isotherm fits very well with the Freundlich isotherm and it is apparent that 2,4-DCP is more adsorbable than phenol. The degree of reversible adsorption for phenol and 2,4-DCP were 32.9 and 10.6 %, respectively. The low percentages of their reversibility meant that the adsorption phenomena of both phenol and 2,4-DCP were not fully physicosorption. The microorganisms can regenerate 31.4 % (21.2 mg g−1) of GAC loaded with phenol and 14.3 % (24.8 mg g−1) of GAC loaded with 2,4-DCP over a period of 7–10 days. The bioregeneration of phenols closely followed the first order kinetics with the rate constant of 0.046 day−1 at initial phenol concentration of 100 mg l−1 and biomass concentration of 20 mg l−1 MLVSS. The rate constant was 0.021 day−1 at initial 2,4-DCP concentration of 200 mg l−1 and 200 mg l−1 MLVSS. In addition, the increasing in initial concentration of biomass in the solution shortened the time required to reach the asymptotic limit on the bioregeneration but rendered little impact on the bioregeneration percentage.

A modeling approach to bioregeneration of granular activated carbon loaded with phenol and 2,4-dichlorophenol

A predictive isotherm model was developed to evaluate the extent of bioregeneration of granular activated carbon loaded with phenol and 2,4-dichlorophenol (2,4-DCP). Two basic substrates (116 mg/L of phenol and 100 g/L 2,4-DCP) as single solute were prepared. The mixture of them was provided to bisolute system for assessing the competitive adsorption. The effect of by-products, which were generated during biodegradation of substrate and measured as COD, on bioregeneration in the bisolute was investigated. Freundlich adsorption parameters (Kads and 1/n) of 2,4-DCP were obviously higher than those of phenol in both single and bisolute. By-products in the bulk solution brought an adverse effect on adsorption capacity of GAC in all cases. By taking into account the by-product effect on adsorption, the Freundlich isotherms were used to formulate a predictive model of bioregeneration. Simulated results showed good consistency of observed results. Practical relevant of the proposed model for assessing of bioregeneration in the wastewater treatment was discussed by applying model to the BAC-SBR in the steady-state operation.

Groundwater Flow and Arsenic Contamination Analyses in Southern Bangladesh

Arsenic contamination had been found all over Bangladesh in 1993, however, the groundwater flow and the mechanism of arsenic contamination have not been made clear yet. Because the arsenic contamination spreads through the groundwater, it is important to understand the groundwater flow. We performed the field measurement from December 23rd to 25th, 2003 and from May 19th to 21st, 2004. Then we performed the numerical analyses of groundwater flow and arsenic transportation using MODFLOW to grasp the field groundwater condition. As a result of the field measurement, the underground condition of our study area is reductive. Besides, using MODFLOW, we could reproduce the groundwater flow properly and estimate a flux of groundwater drawn from wells, and then, predict the future contamination.

Geochemical Evidence of Arsenic Transport in Shallow Ground Water, Bangladesh

High Arsenic (As) in the shallow groundwater (GW) of the Southern Western Bangladesh has been recognized as the natural catastrophe since 1990s. This paper aims to unveil the likely geochemical phenomena that may dominate in both release and transport of As in that shallow alluvial aquifer. Observed linear relationships between As and Iron (Fe) contents both in sediment (R2 = 0.42) and in GW (R2 = 0.46) reflect their probable co-existence and co-precipitation characteristics. Speciation analysis with geochemical code PHREEQC shows that some Fe minerals have already been reached at the super saturation state, indicating further the subsequent co-precipitation of the accompanying As. Linear Equilibrium partition coefficient Kd (As) was noticed to vary inversely with dissolved Fe in a relatively high pH, reflecting the leaching potentiality of As from sediment to groundwater, due to the loss of promising sorption sites. HCO3 was reportedly found as the efficient leaching (24.5 µg/l) agent in releasing adsorbed As from the aquifer sediment.

Cryptosporidium and cyclospora -associated Diarrhea in Kathmandu, Nepal

Publisher Summary The purpose of this chapter is to discuss Cryptosporidium and cyclospora-associated diarrhea in Kathmandu, Nepal. This chapter describes a study that determines the bacteriological indicator of drinking water contamination, taken together with the isolation or the detection of enteropathogens in diarrheal fecal samples collected in all four seasons in Kathmandu Valley, Nepal. A total of 737 diarrheal fecal samples collected from children attending Out Patient Hospital in Kathmandu were included in this study. The various methods employed to carry out the study were bacterial culture, electron microscopy, cell culture methods, direct saline and iodine wet mounts, sucrose floatation technique, and fluorescent antibody technique. The results showed the presence of eight species of bacteria, three genera of viruses, and five species of protozoan parasites. The study presented in this chapter highlights the magnitude and pattern of enteropathogens in all four seasons, together with the status of fecal contamination of drinking water in Nepal. Therefore, an inclusive program needs to be launched to battle diarrhea-related morbidity, mortality, and its socio-economic impact in Nepal, and the results of such a program should be monitored by periodical survey.