Fasil Ejigu Eregno

Quantitative microbial risk assessment combined with hydrodynamic modelling to estimate the public health risk associated with bathing after rainfall events

This study investigated the public health risk from exposure to infectious microorganisms at Sandvika recreational beaches, Norway and dose-response relationships by combining hydrodynamic modelling with Quantitative Microbial Risk Assessment (QMRA). Meteorological and hydrological data were collected to produce a calibrated hydrodynamic model using Escherichia coli as an indicator of faecal contamination. Based on average concentrations of reference pathogens (norovirus, Campylobacter, Salmonella, Giardia and Cryptosporidium) relative to E. coli in Norwegian sewage from previous studies, the hydrodynamic model was used for simulating the concentrations of pathogens at the local beaches during and after a heavy rainfall event, using three different decay rates. The simulated concentrations were used as input for QMRA and the public health risk was estimated as probability of infection from a single exposure of bathers during the three consecutive days after the rainfall event. The level of risk on the first day after the rainfall event was acceptable for the bacterial and parasitic reference pathogens, but high for the viral reference pathogen at all beaches, and severe at Kalvøya-small and Kalvøya-big beaches, supporting the advice of avoiding swimming in the day(s) after heavy rainfall. The study demonstrates the potential of combining discharge-based hydrodynamic modelling with QMRA in the context of bathing water as a tool to evaluate public health risk and support beach management decisions.

On-line monitoring of Escherichia coli in raw water at Oset drinking water treatment plant, Oslo (Norway).

The fully automated Colifast ALARMTM has been used for two years for daily monitoring of the presence/absence of Escherichia coli in 100 mL raw water at Oset drinking water treatment plant in Oslo, Norway. The raw water is extracted from 35 m depth from the Lake Maridalsvannet. E. coli was detected in 18% of the daily samples. In general, most samples positive for E. coli were observed during the autumn turnover periods, but even in some samples taken during warm and dry days in July, with stable temperature stratification in the lake, E. coli was detected. The daily samples gave useful additional information compared with the weekly routine samples about the hygienic raw water quality and the hygienic barrier efficiency of the lake under different weather conditions and seasons. The winter 2013/2014 was much warmer than the winter 2012/2013. The monitoring supported the hypothesis that warmer winters with shorter periods with ice cover on lakes, which may be a consequence of climate changes, may reduce the hygienic barrier efficiency in deep lakes used as drinking water sources.

Evaluating the Trend and Extreme Values of Faecal Indicator Organisms in a Raw Water Source: A Potential Approach for Watershed Management and Optimizing Water Treatment Practice

This study demonstrates the use of microbial load time series, through trend and extreme event analysis, to evaluate the effectiveness of watershed management strategies and to understand the probabilistic behaviour of extreme events. Heterotrophic plate count (HPC), Clostridium perfringens, intestinal enterococci, Escherichia coli, and coliform bacteria, were monitored from 1999 to 2012 at Nedre Romerike Vannverk (NRV) drinking water treatment plant, which takes its source water from Glomma River, Norway. Mann-Kendall test, Seasonal Mann-Kendall test, and Sen’s Slope Estimator were used for trend analysis over years and also seasonal trends were examined through linear regression. Mann-Kendall test results show a decreasing trend for all indicator microorganisms except Escherichia coli. Seasonal trend analysis results also indicate that Clostridium perfringens during autumn and intestinal enterococci during spring have a significantly decreasing trend. An increasing trend was observed for all pathogens during the summer season. Trend analysis results offer insights and crucial perspective for policy makers and planners to evaluate the existing watershed management strategies. Moreover, extreme microbial load events in the raw water was analysed using the POT method to estimate return levels of extreme indicator microbial load corresponding to selected return periods. It is of importance to calculate the return period of extreme microbial load events for the purpose of designing optimal pathogen barriers and performing risk analysis.

Performance of biochar and filtralite as polishing step for on-site greywater treatment plant

Purpose – The purpose of this paper is to investigate the performance of biochar and fine filtralite as a polishing filter material in further removing organic matter, phosphorous, nitrogen, turbidity and indicator microorganisms from effluents of a compact greywater treatment plant (GWTP). Design/methodology/approach – A filtration experiment was carried out using columns filled with biochar and fine filtralite as filter material and unfilled column as a control. The effluent from the GWTP was pumped using a peristaltic pump at a rate of 280 l/m2-d and was fed in upward flow into the columns. The quality parameters of the raw greywater, effluents from the GWTP and the polishing columns were studied for six months of operation period. Findings – The results indicate that the process of polishing considerably improved the effluent quality of the system. Biochar performed best in removing organic matter, total N, turbidity and odor. Filtralite was superior in removing P. The contribution of the polishing st...