The effect of extract from activated sludge on bacterial population in activated sludge was studied especially focusing on the effect of organic loading and incubation time. A laboratory scale activated sludge reactor was operated, the extract was obtained from the sludge with ethanol as the extractant, and activated sludge was incubated with and without the addition of the extract. The incubation was performed with low (0.5kgCOD/kgMLSS·d) and high (2kgCOD/kgMLSS·d) organic loadings up to 96 hours on a microplate under aerobic condition. Samples were obtained at 24, 48 and 96 hours, and bacterial population in them were analyzed by both polymerase chain reaction (PCR) with restriction fragment length polymorphism (RFLP) and reverse transcription PCR/RFLP. Clear difference in bacterial population was observed within 24 hours of incubation even when low organic loading was applied and increase of biomass amount was thought to be only around 25%.
The application of improperly treated compost is one of the causes of bacterial contamination in the field, crops, food and water. Although there are practical guidelines for treatment of compost published, there could be a misapplication in local situations, such as lack of attention by traditional users, labour ineffectiveness and material unavailability. Considering these setbacks, farmers may unknowingly use improperly treated compost as fertilizer. The objectives of this study were (i) to characterize the die-off represented by kinetic inactivation rate coefficient, κ (h-1) of Enterococcus in clay and sandy loam soils, (ii) to determine the effect of temperature, compost-to-soil ratio and soil type on the inactivation rates of Enterococcus. The soils were amended with compost at a ratio of 1 part compost to 10 parts of soil 1:10, 1:25, 1:50 and 1:100 held at different temperatures (30°C, 40°C and 50°C). The moisture content was set to 25% in all conditions. Enterococcus is enteric bacteria and not always pathogenic but an indicator of pathogenic bacteria. Inactivation of Enterococcus (pathogenic bacteria) in the soil with high temperature under different compost application rates was tried in the laboratory test. As a result, (1) the inactivation rates of Enterococcus in clay soils were 0.015-0.027 h-1 , 0.246-0.322 h-1 , 0.397-0.571 h-1 for 30, 40 and 50°C respectively. Sandy loam soils were 0.056-0.130 h-1 , 0.348-0.447 h-1 and 0.475-0.630 h-1 for 30, 40 and 50°C respectively, (2) inactivation rates of Enterococcus in soils amended with compost from the composting toilet depended on temperature and soil type but not on the compost-to-soil ratios. The experimental conditions in this study are different from the real field situation because temperature and humidity changes over time under field conditions. Therefore, care must be taken when interpreting the results of this study to estimate the die-off rates in real field conditions. Further research is required to simulate the behaviour of pathogenic bacteria in field conditions of a hot semi-arid climate.
Decentralized domestic wastewater treatment systems are generally used in rural areas for preventing pollution of local water environment. Treated waters of decentralized systems potentially contain fecal contaminants and the degree of contamination can vary seasonally. To identify the seasonal characteristics of fecal indicators in the area of decentralized system, seasonal monitoring on the characteristics of fecal indicators (total coliforms, Escherichia coli, and F-specific coliphages) was performed along an open channel receiving johkasou effluents over 3-year period. Fecal indicators were detected higher than environmental quality standard throughout the season, particularly for total coliforms, and the concentrations of Escherichia coli downstream seemed to be higher than upstream in winter. The low water quality was recorded during cold-low flow season and the effluent of johkasou was an important factor reflecting water environment quality. In contrast with most physicochemical parameters, significant seasonal differences of total coliforms and Escherichia coli were not observed both in water and sediment. The principal component analysis results show that four dominant factors related to chemical contaminants, environmental conditions, byproducts, and fecal contaminants were responsible for the water quality data structure and significant seasonal differences were observed for chemical contaminants, environmental conditions, and byproducts, accounting for 59 % of the total variance in the data set. Seasonal maintenance of discharged water quality and controlling downstream network capacities are necessary to reduce the potential impact of johkasou effluents into local water environment.