Monitoring hydrogen sulphide in bottled water products

Hydrogen sulphide should not be detectable in drinking water by either taste or odour. Michael Strahand reports.

Britvic Soft Drinks is a leading supplier of branded still soft drinks and branded carbonates in the UK, producing more than 1.4 billion litres annually and selling them to approximately 200,000 outlets across the country. The company is based in Chelmsford, Essex, and operates seven manufacturing plants across the UK, producing an extensive portfolio of market leading brands including Robinsons, J2O, Tango and Fruit Shoot. Britvic also makes and distributes global brands such as Pepsi and 7UP through an exclusive agreement with PepsiCo.

As well as its manufacturing sites, Britvic's established infrastructure includes a national distribution centre, an IT and central services department, several local distribution centres and an on premise and vending division.

The company produces bottled mineral water under brand names such as Pennine Spring and Drench at its Huddersfield water bottling facility. The site operates two boreholes, one classified as spring water and the other as mineral water. Two high speed water bottling production lines enable uninterrupted 24 hours per day, six days per week operation, allowing the production of an extended selection of 330ml to 2lt bottles and a wide array of packing formats.

Water produced at the Huddersfield site must comply with the quality requirements of The Natural Mineral Water, Spring Water and Bottled Drinking Water (England) Regulations 2007, which specify maximum allowable concentrations for contaminants such as manganese and barium. Legislation also mandates specific mineral content requirements while also requiring retention samples to be tested at regular intervals for micro-biological levels. In order to ensure optimal product quality and compliance with stringent regulations, Britvic has collaborated with Analytical Technology to facilitate accurate monitoring of hydrogen sulphide (H2S).

The Natural Mineral Water, Spring Water and Bottled Drinking Water (England) Regulations 2007 specify that bottled water should not contain any micro-organism, parasite, property, element or substance at a concentration or value which would constitute a potential danger to human health. The legislation states that no company should bottle any water which, at the time of bottling, contains any of the substances listed at a level which exceeds the maximum limit specified. Additionally, where it is found during exploitation that natural mineral water or spring water is polluted, exploitation of the spring from which the water is extracted should stop until the cause of the pollution is eradicated.

H2S is formed when soluble sulphides are hydrolysed in water. The chemical has an offensive rotten eggs odour and taste that are detectable even at very low concentrations. The World Health Organisation (WHO) estimates the taste and odour threshold for H2S in water to be between 0.05 and 0.1 mg/litre. Most of the H2S present in raw waters is derived from natural sources and industrial processes and although there is no data proving oral toxicity of H2S, WHO requires that H2S should not be detectable in drinking water by either taste or odour.

Following a review of Britvic's Hazard Analysis and Critical Control Points (HACCP) plan, it was highlighted that H2S levels in finished bottled products should be closely monitored to ensure best product quality and customer satisfaction. To achieve these goals, Britvic needed a dependable technology that would enable accurate and reproducible measurement of H2S in its water products.

Analytical challenges

H2S levels in water have been traditionally monitored using systems employing selective ion electrodes (SIE) for sensing. While SIE-based analysers provide sufficiently sensitive measurements, the technology has been associated with a number of limitations, the most significant of which being interferences caused by other ions resulting in decreased precision.

As a consequence, the systems require frequent zero and span adjustments to maintain measurement accuracy. In addition, the electrodes can be fouled by proteins or other organic solutes while also being fragile with limited shelf life. As a result, most SIE-based systems are relatively expensive, requiring frequent maintenance.

Britvic sought a system capable of overcoming these analytical challenges and allowing for efficient monitoring of soluble H2S levels in water that comes directly from the two boreholes after processing through air scrubbers/de-gasser towers and after manganese filtration. The company selected the A15/81 dissolved sulphide monitor from Analytical Technology as it is the only system that allows the real time monitoring of soluble H2S in water (Fig. 1). The innovative technology uses a polarographic H2S gas sensor that is isolated from the sample, meaning that the system continues to function regardless of sample quality. This facilitates uninterrupted operation with minimal maintenance and adjustment.

Six monitors were installed, three on each borehole line being fitted in a central location. Sample points were installed in six different sections of the process and connected to the H2S monitors. Following implementation of the new monitors, Britvic experienced a number of benefits with regards to analytical accuracy, turnaround of results and cost efficiencies.

Using the new monitors, Britvic has been able to ensure that its bottled water products remain within regulatory specifications at all times (Fig. 2). The systems employ a gas stripping technique providing extremely high measurement sensitivity and allowing for the analysis of samples down to five parts-per-billion levels. Because the H2S gas sensor is very stable, only monthly zero and span checks are required. Additionally, the monitors can incorporate a separate port to feed distilled water or sulphide standards when needed, without disrupting normal sample inlet flow.

The A15/81 has also been very easy to operate and maintain. Acid usage for pH adjustment in the chemistry module of the instrument is inexpensive and consumption is limited to one gallon every 40 days. The peristaltic pumps used for the sample and acid have a long-life tubing capability (approximately six months), while the pump heads are designed for easy tube changes, taking around 10 minutes to replace both tubes. Furthermore, the sulphide gas sensor simply requires an occasional visual inspection to ensure that no deposits have collected on the sensing membrane.

Britvic has also experienced several key benefits in relation to the company's 'Right First Time', flexible installation and after sales service expectations. Analytical Technology takes a very flexible and professional approach to system implementation and technical support. When requested, support is usually delivered within 24 hours. Additionally, the company has been able to work within Britvic's standards for health and safety and provide risk assessments and method statements to cover all scoped works.


Hydrogen sulphide occurs naturally in drinking water systems or it can be caused by the presence of sulphate-reducing bacteria in a well or water system. It is unlikely that a person would consume a harmful dose of hydrogen sulphide from drinking water, eliminating the need for health-based guidelines. However, WHO has made it clear that hydrogen sulphide should not be detectable in drinking water by either taste or odour. In order to comply with this requirement, Britvic Soft Drinks needed a reliable dissolved sulphide monitor for its Huddersfield water bottling facility. Since implementing the A15/81 dissolved sulphide monitors from Analytical Technology, Britvic has been able to ensure that its bottled products are accurately and continuously monitored for hydrogen sulphide. The company has achieved this goal while also ensuring that costs and maintenance are kept to a minimum and reliable results are generated in real time, guaranteeing optimal product quality.

Dr Michael Strahand is general manager Europe, Analytical Technology, Saddleworth, West Midlands, UK.

Recent Issues