Adapted from an article by Dave Quelch, ABLE Instruments & Controls Ltd.
H2S stinks – and not just for those stuck smelling it. Complaints about hydrogen sulfide odors can cause citations, penalties or worse for the facilities involved. One way to avoid those complaints is to monitor H2S levels so that you can work proactively to keep them below the odor threshold.
Monitoring H2S Levels
A low level analyzer or monitoring system is essential to monitoring H2S levels before they become nuisance odors. Most permits in the US require a fence-line upper limit of 30 ppb (parts per billion) H2S. Although that level is below what are considered the most noticeable levels of hydrogen sulfide (3 to 5 ppm or 3000-5000 ppb), many people are sensitive enough that they can smell as little as 10 ppb (.01 ppm). Instruments with high lower detection limits won’t be able to help you there.
Thames Water recently upgraded and expanded their network of low-level H2S monitors at Mogden Sewage Treatment Works in the UK. This was done as part of a major site enhancement that would expand capacity and help the facility meet tighter regulations.
Mogden Sewage Treatment Works
Mogden Sewage Treatment Works was built between 1931 and 1935 and is the second largest in the UK. It serves approximately 2.1 million people and covers an area of 55 hectares (.21 square miles), though some of the wastewater has travelled over 20 miles by the time it reaches Mogden. Over half of the power used by the plant is renewable energy that has been generated on site as part of the sewage treatment process.
Last year, as part of a more than 180 million dollar enhancement to the site, Thames Water asked ABLE Instruments, Jerome’s distributor in the UK, to assist with an upgrade to Mogden’s boundary monitoring network. The entire project was designed to extend sewage capacity at Mogden by 50%. Because the increase in capacity would undoubtedly mean an increase in H2S, Thames Water decided that an upgrade was in order.
The upgraded H2S boundary monitoring system would help ensure that the newly enhanced sewage treatment works was able to handle the increased amount of sewage without causing an increase in nuisance odors in the surrounding area. With a number of Jerome analyzers already in place around the facility, it was simply a matter of expanding the network. Thames Water purchased 15 more Jerome gold film hydrogen sulfide analyzers, bringing their total to nearly 30, and began installing them throughout the works.
Jerome® H2S Analyzers
Jerome gold film hydrogen sulfide analyzers are rugged, reliable, easy to use and can detect as little as 3 ppb (parts per billion) of H2S in air. The technology has been proven in the field and in the lab for more than 35 years and is in active use by many regulatory agencies and landfill, water treatment and waste management facilities across the world.
When planning your odor monitoring solution, one of the first decisions you’ll make is whether to use fixed point instruments, hand-held instruments, or both. Thames Water’s Mogden facility decided to use a combination. The Jerome 651, shown above, is our fixed point monitoring solution. It is designed to provide long-term, continuous monitoring even in rough weather conditions. It can be stationed on a pole, fence or even a wall and multiple units can be linked to form a perimeter monitoring system. The 651 has a detection range of 3 ppb to 50 ppm and has programmable high limit alarms that can send out alert emails if your H2S levels ever rise above a set level.
The attached weather station provides information on wind speed and direction so you can more accurately identify where an odor is coming from. Plus, the Jerome 631 analyzer within the box can be detached and used on its own to sweep an area and further pinpoint the source of a hydrogen sulfide hotspot.
The Jerome J605 is our most advanced portable H2S analyzer. It features a lower detection limit of 3 ppb with a resolution of 20 ppt (parts per trillion), giving it improved accuracy in the single figure ppb region which is, of course, very useful for nuisance odor monitoring since the odor threshold for some people is as little as 10 ppb. The J605 is lightweight and has an ergonomically designed handle for increased portability. It can also store up to 20,000 data points, has a battery life of 18 hours, and has automated sampling and field regeneration functions, making it ideal for short term, long term and even unattended H2S monitoring.
Success at Mogden
To accommodate the new equipment installations that would expand operations at Mogden Sewage Treatment Works, Thames Water reshaped the western embankment as well as enhanced the landscape to the west of the site. This served to decrease sewage overflow during heavy rain and also helped Thames Water to meet tighter quality standards for the effluent they discharge. Combined with the expanded network of Jerome H2S monitors, the changes are helping to reduce odor at and around the site.
With the success of the Jerome instruments at Mogden Sewage Treatment Works, Thames Water has recently purchased 6 additional analyzers, which will be used to help reshape odor boundaries at their Acton site, which is undergoing a similar expansion.