Wastewater pollution from stormwater overflows or Combined Sewer Overflows (CSOs) has been a hot topic in 2021, with Southern Water fined a record £90million for water discharges sewers not authorized in July, and other water companies under scrutiny for polluting waterways with environmental factors. activists and the general public.
The Environment Agency is currently surveying over 2,000 sewage treatment plants to check whether they are operating in accordance with their environmental permits. In response to public pressure, the UK Environment Bill finalized post-Brexit includes a legal obligation for water companies to achieve progressive reduction of negative CSO impacts, and an obligation to monitor water quality. river water upstream and downstream of each CSO. This is in addition to the strategic priorities of Ofwat and the water companies it regulates to significantly reduce CSO wastewater discharges at the next price review (PR24), among other objectives to boost performance from 2024 to 2029. Another related issue is the flooding of properties by the sewer system, particularly in basements below ground level. So how can water companies reduce wastewater pollution from sewer systems? Using Yorkshire Water as an example, what are some of the contributing factors? What measures are already in place to combat wastewater pollution? What additional technologies do water companies need to combat leaks? And what innovations are on the horizon to tackle this problem?
Taking Yorkshire Water as an example, the scale of the challenge becomes apparent. The area served by Yorkshire Water has approximately five million customers at 2.6 million properties, 1,087 km of rivers and 1 billion liters of wastewater treated daily. Assets to be operated and maintained include 12 long sea falls, 640 sewage treatment sites, 56,000 km of sewers, 2,700 pumping stations, 2,241 licensed storm overflows and over 2 million manholes. Properties with cellars below ground level, typically Victorian terraces, are more prone to internal flooding. “The majority of flooding incidents are from the lateral sewers serving Victorian terraces,” says Thomas Ogden, technical innovation specialist at Yorkshire Water, “there are very few manholes on the lateral sewers, so there is a need to have monitors to go into ravines or piles of dirt – we have 2,000 monitors at property level Mr Ogden says flooding of external properties is more of an issue in the housing stock from of the 1960s and 1970s, because in this case there are generally no cellars, more manholes, a smaller sewer network with a narrow pipe diameter (150 mm) and very little flow. provides a wish list of technologies that Yorkshire Water would find useful in dealing with property flooding (Table 1).
In terms of sewage pollution of rivers, the majority of pollution incidents originate from the sewer network, for example risers, pumping stations and treatment works. Much of Yorkshire Water’s sewer system is within 50m of a watercourse, for example motorway gullies, motorway drains and underground watercourses are often close to watercourse. There are currently 3,500 level monitors in the sewer network, or approximately 1 per 15 km of sewer network, located to monitor CSOs and pollution hotspots in particular. There are 20 designated bathing waters (including one indoor bathing water). Water companies are now monitoring discharges into waterways, to comply with the Environment Act 2021. “It is no longer enough to know if discharges are happening,” says Mr Ogden, “we want to know the volume of the spill and its composition, to understand the impact on the water quality of the river during heavy rains”. Mr Ogden says analyzes are needed to link data sets of water levels, flows and quality and provide a better understanding of the bigger picture. You can only manage what you can measure, and various technologies could help improve understanding (Table 2).
In addition to the wish lists in Tables 1 and 2, Ogden suggests other technology solutions that could help, including full line monitoring, energy harvesting, ease of installation, monitoring and analysis. low-cost throughputs to enable corrective action at the right time. Full pipe monitoring would help identify blockages earlier than just spot monitoring at a manhole which will only detect blockages when sewage is coming up the pipe (image 1). Energy harvesting would help extend the life of assets, allow for increased frequency of readings and frequency dial. Mr. Ogden says that ideally monitors should be quick and easy to set up; configuration must be possible via a web-based platform, with all installation data available online; and site information must be collected to enable a correct first response (photos, access, traffic management details). Flow monitoring should be inexpensive and ideally permanent online flow monitoring rather than the costly flow surveys that are currently undertaken. Importantly, analyzes are needed to combine all data with precipitation forecasts, including long-term weather forecasts to predict when a developing blockage will cause a problem and when to intervene. The analysis could also help quantify environmental damage.
Various innovative technologies are available or under development to monitor water pollution, from a low-cost device that can monitor basic parameters to an AI-based sewer network control system. fully fledged. A brief overview of a selection is provided in Table 3. Some of them help fill the technology gaps identified above.
With the current drive to reduce wastewater discharges, water companies will seek technological solutions to help them go beyond regulatory requirements and meet customer expectations.