Evaluation of the microbial risk reduction due to selective closure of the raw water intake before drinking water treatment

Abstract

Short-term peaks in pathogen concentrations may increase the risks for waterborne diseases considerably. In this study the occurrence of indicator organisms and pathogens in the river Gö ta ä lv at the raw water intake to Gö teborg was evaluated and related to risk for drinking water consumption. About half of the 24 pathogen samples, taken during event and non-event conditions, were positive for at least one of the following: Cryptosporidium, Giardia, norovirus, enterovirus, Campylobacter and E. coli O157. Positive pathogen detects were often associated with heavy rainfalls and viruses with a sewage emergency discharge. The annualised probability of infection from this type of event was calculated from pathogen concentrations in a QMRA model. Given that the water intake is not closed, the risk given present water treatment seems to be acceptable for Giardia; however, it is at a borderline for Cryptosporidium and insufficient for noro-and enteroviruses. Present results emphasise the need for an appropriate intake regulation with respect to high pathogen loads, as the risk increases with time of exposure to pathogen contaminants. Rather than a threshold level on E. coli, reports on upstream microbial discharges are valuable for quick pathogen indications.

Precipitation Effects on Microbial Pollution in a River: Lag Structures and Seasonal Effect Modification

“…Kistemann et al [2] studied three surface water reservoirs in Germany, comparing mean levels before and after runoffs, and detected elevated parasites and indicator bacteria concentrations with increasing water levels. Åström et al [3] also studied Göta Älv with data from 2004 and found correlations between accumulated rainfall and elevated concentrations of E. coli, and also other pathogen indicators such as intestinal enterococci. Studies have also shown associations between precipitation and outbreaks of gastrointestinal illnesses (GI), indicating that rainfall has an important role in pathogen contamination in water supplies [4]–[7].…”

“…Several studies have shown relationships with prior weather events, especially wet weather, and raw water quality parameters [1]–[3]. Heavy rainfall has also been linked to the majority of observed drinking water-related outbreaks of gastrointestinal diseases in developed nations worldwide [4]–[7].…”

“…The river Göta Älv runs through this region, serving as a freshwater supply for 0.7 million people. The river is at risk of pathogen contamination from multiple sources, including runoff from agricultural land and point sources such as sewer system discharges [3]. More frequent events of heavy rainfall may increase the risk of contamination, increasing the challenges of providing safe water drinking water [9], [10].…”

A quantitative exposure model simulating human norovirus transmission during preparation of deli sandwiches

“…(Sant'Ana et al, 2014;Franz et al, 2010), Listeria monocytogenes (Mataragas et al, 2010;Carrasco et al, 2010) and Escherichia coli 0157 (Strachan et al, 2006). Regarding HuNoV, a number of QMRA models have been developed to evaluate the risk of HuNoV in drinking water (Aström et al, 2007) and recreation water Soller et al, 2010). In foods however, the number of HuNoV QMRA studies is limited and mainly concentrated on initial contamination of fresh produce (Kotwal, 2013;Mara and Sleigh, 2009;Hamilton et al, 2006).…”

Association between Precipitation Upstream of a Drinking Water Utility and Nurse Advice Calls Relating to Acute Gastrointestinal Illnesses

“…The river Göta Älv is a municipal surface water source for the City of Gothenburg and is exposed to upstream run-offs from agricultural areas and occasionally by overflowing combined sewer systems [14]. We previously analyzed the relationship between daily upstream precipitation, water turbidity, and indicator bacteria at the river water intake to the drinking water utility at Alelyckan, and found clear positive associations peaking two days after rainfall (Tornevi et al unpublished data).…”