Optimising E. coli disinfection in the Hunter

The presence of virulent strains of E. coli can cause significant distress to people. One team is working to catch them in drinking water samples, so they can be eliminated early.

Dr. Vikaskumar Shah, Ashley Sneddon, and Luke Bianchi are advancing their research to enhance the detection of E. coli in drinking water samples throughout the Hunter region. Each is a dedicated member of the Hunter Water community.

“We have a great passion for the water industry, serving customers and protecting public health,” Shah said. “These were the key factors in bringing everyone to the water industry. It is a most fulfilling career that combines public service with essential work, creating a great environment for professional growth and continuous learning. An excellent work culture driven by values of trust, wellbeing, inclusion, learning, and leading has given us a strong sense of pride in being part of Hunter Water.”

**Why study E. coli?**

Most strains of E. coli do not cause disease, as they live naturally in the gut. However, virulent strains can cause gastroenteritis, urinary tract infections, neonatal meningitis, haemorrhagic colitis and Crohn’s disease. Common signs and symptoms include severe abdominal cramps, diarrhea, vomiting and sometimes fever.

It is one of the biggest challenges associated with improving water quality. Shah pointed out that managing and eliminating E. coli from drinking water systems involves many issues.

“The biggest challenges associated with managing microbiological quality of drinking water include protecting drinking water catchments and source waters from human and domesticated animal faeces, treatment of water during wet weather events and supply of water with consistently good chlorine residual to large populations using ageing infrastructure,” he said.

Hunter Water has worked hard to overcome these challenges and provide safe drinking water to hundreds of thousands of residents.

“Hunter Water is committed to providing customers with high quality, reliable and safe drinking water and protecting public health,” Shah said. “As required by our Operating Licence, we maintain a Drinking Water Quality Management System (DWQMS) that is consistent with twelve elements of the Australian Drinking Water Guidelines (ADWG). Quality is ensured by specifying health-based and aesthetic criteria and using a multiple barrier approach from catchment to tap water quality. This involves a risk-based approach in which potential threats to water quality are identified and managed to minimise any risks to drinking water quality.”

Standards for E. coli

Australia enforces stringent regulations concerning E. coli levels in drinking water. Per the ADWG, no E. coli should be present in any 100mL sample. Hunter Water oversees the water supply systems to comply with ADWG standards and reliably fulfils microbiological regulatory requirements, with at least 98 per cent of routine sample tests showing no E. coli detection.

“Hunter Water’s two largest water treatment plants (WTP), Grahamstown and Dungog WTPs, use conventional and direct filtration treatment processes to treat water sourced from Grahamstown Dam and Chichester Dam respectively,” Shah said. “Anna Bay, Nelson Bay, and Lemon Tree Passage WTPs treat groundwater sourced from Tomago and Tomaree Sandbeds, and Gresford WTP uses microfiltration to treat water sourced from Allyn River and the Paterson River.”

Furthermore, all six WTPs use chlorine to provide a disinfection barrier. Treated water supplied from WTPs is transported through a closed distribution system and stored in several network reservoirs. Chlorine is boosted throughout the distribution system to ensure a continuous, safe drinking water supply.

A multi-disciplinary approach

Hunter Water’s successful multi-barrier approach relies on several collaborating teams to ensure a safe water supply. The catchment operations team is responsible for protecting drinking water catchments and groundwater aquifers, managing the operation of dams and weirs, and ensuring compliance with water management licenses to provide the highest quality raw water to treatment plants. The water treatment operations team manages the treatment and disinfection of raw water across six treatment plants, ensuring that the treated water meets ADWG standards and overseeing the Laboratory Services and Treatment Operations contracts.

The water network operations team distributes safe, reliable water to customers through a closed distribution system, where drinking water is transported, stored and routinely monitored, sampled and analysed. This team also manages the operation of the drinking water network, including reservoirs, water pumping stations, pipes and disinfection systems. The maintenance and asset solutions teams provide ongoing support for maintenance and upgrades. The information controls and energy team supports system monitoring and control, operational information and energy needs. The strategy team focuses on long-term strategies, while the planning and engineering team conducts investigations and prepares business cases to improve water quality for customers. The wastewater and environment teams ensure compliance with wastewater treatment standards and environmental water quality, while the customer service team continuously supports its customers.

Disinfection optimisation strategy

In the mid-2010s, following several detects of E. coli in drinking water samples, Hunter Water reviewed historical monitoring results, showing some areas of its water network with low chlorine residual levels. Hunter Water conducted various investigations to address this issue and developed a disinfection optimisation strategy (DOS). The first phase of the DOS commenced in December 2014, which included optimisation of the operation and performance of network and treatment plant assets and processes to improve chlorine residual in the network. Concept design for the second phase commenced in 2018. Detailed design began in 2022, and delivery works are underway to improve the performance of network chlorinators.

“These works include upgrading four existing chlorinators, installing five new chlorinators, and installing mixers and analysers at three reservoirs,” Shah said. “The long-term goal for DOS implementation is to continue improving microbiological water quality, consistently provide good chlorine residual throughout the network and manage the operations safely and efficiently.”

Since the implementation of DOS in 2014, E. coli detections have been infrequent, at low levels and generally in the presence of good chlorine residual (≥0.2 milligrams per litre). This may indicate the transient nature of detections, which could be due to the dislodging of biofilms and the presence of environmental E. coli or E. coli with chlorine-resistant genes. E. coli is generally not observed in follow-up drinking water samples collected during investigations.

One area that requires further investigation is faecal source tracking (FST) methods, which could help identify the contributing sources of E. coli detections and implement management practices to improve the quality of water supplied to customers.

“Hunter Water has utilised E. coli fingerprinting and phylogrouping testing services from the Australian Water Quality Centre (AQWC) for FST purposes,” Shah said. “Available literature suggests FST as an emerging science, so Hunter Water is looking to enhance its understanding of FST methods and interpretation of results.”

Applying theoretical techniques to the network

In December 2022, Hunter Water developed a checklist for investigating E. coli detections to ensure that there are no errors in sampling, laboratory analysis and reporting of these results. This beneficial initiative, the first of its kind in the Australian water industry, showcases Hunter Water’s values of leading and learning.

“The checklist has been incorporated under Hunter Water’s existing Laboratory Services Contract with Australian Laboratory Services (ALS),” Shah said. “This contract commenced in July 2022 following a competitive open tender process.”

Hunter Water intends to continue collecting FST data as required and look for opportunities to enhance our understanding of environmental E. coli, E. coli with chlorine resistance genes, FST methods, and the interpretation of the results.

“We will continue to regularly audit and inspect assets and procedures, review verification monitoring data, invest in new technology and equipment as necessary, and work with trusted partners to supply safe water to customers,” Shah said.

Awards and the future

In an Australian Water Association (AWA) competition with posters from significant urban water utilities and major engineering consultancies, the win means a lot for Shah and the team at Hunter Water.

“This award is a great recognition of Hunter Water’s values – leading and learning, the depth of science and research expertise across Hunter Water, and Hunter Water’s commitment towards continuous improvement of water quality for our customers,” Shah said. “This award further showcases a great example of collaborative teamwork and integration of strategy, planning and research projects into Hunter Water’s operations.”

With an eye to the future, Shah pointed out that at Hunter Water, water is life.

“Our customers and community are at the heart of all we do. Hunter Water is a trusted, innovative organisation with a values-driven culture working towards securing a sustainable, resilient, and prosperous future. Hunter Water is committed to maintaining high quality, valued and affordable water services for all.”