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How it works
Welsh Water goes above and beyond
Welsh Water’s Cog Moors wastewater treatment works processes up to 220 tonnes of wet sludge in a day and produces biosolids via anaerobic digestion that can be used as fertiliser by local farmers. The treatment works features an innovative advanced anerobic digestion facility that employs a thermal hydrolysis process. The process also produces biomethane, which is injected into the gas grid or used in a CHP engine to generate electricity. (For more on the future of biomethane and the gas grid, read Utility Week.)
As part of the BAS, Welsh Water is subject to mandatory offsite laboratory testing of the biosolids it produces, but the utility wanted to go a stage further and introduce more frequent testing to ensure pathogens are at safe levels.
“Requirements state that you only have to test once every three months, but we do in-house testing to keep an eye on things and make sure we are not losing control,” explains Dr Des Devlin, wastewater sludge scientist at Welsh Water. “It’s not just about regulations: we have a moral obligation to ensure biosolids used on land are the best quality they can be.”
Traditional compliance water microbiological testing in an offsite lab can take up to five days for a result, in addition to requiring specialist staff and a clean environment. So the Cog Moors treatment works is now using a Tecta B16 system from IDEXX Laboratories onsite to carry out testing for E. Coli and other undesirables in addition to its usual regulatory duties.
These tests take a maximum of 18 hours to complete.
Devlin says: “In the past, we would typically have had to wait three to four days to get a result back, whereas now we get a result overnight. The test is simpler, so we are able to do it in our relatively crude onsite lab.”
The Tecta system is particularly useful, explains Stephan Calvet, senior field application specialist – EMEA at IDEXX, in situations where people a) don’t have the expertise to conduct a traditional-type test; b) lack the facilities for testing, or c) need a quick turnaround. The B16 is also compact – about the size of a microwave – he adds.
“Regulations state that you only have to test once every three months, but we do in-house testing to keep an eye on things and make sure we are not losing control”
Dr Des Devlin, wastewater sludge scientist, Welsh Water
Why Tecta?
Tecta features automated analysers with either four or 16 incubation chambers to match the number of samples to be tested and user-friendly cartridges that require minimal sample preparation. The system can simultaneously detect total coliforms (a diverse group of bacteria of enteric or environmental origin that indicate general water quality or treatment integrity) and E. coli in 18 hours or less. Highly contaminated samples can return positive results in as little as two hours. This is without the need for input or visual interpretation from a laboratory technician.
The system can also test for faecal coliforms and enterococci (lactic acid bacteria that naturally inhabit the gastrointestinal tract of humans and many animals). Tecta uses an enzyme substrate detection method coupled with a proprietary polymer partition technology to deliver accurate results. Results are emailed automatically, eliminating the need for technicians to be in the lab when results are ready, and enabling prompt action in the event of pathogen levels that are higher than desired.
The Tecta system is also easy to use, even when testing complex biosolids samples. “Maintaining cleanliness and aseptic technique during sample preparation is critical for us. Sample preparation with Tecta is very easy, with fewer opportunities for contamination. This means we have a high degree of confidence that our readings are correct when testing with Tecta,” says Dr Devlin.
Cog Moors now carries out regular biosolids testing every two weeks using the IDEXX Tecta B16. In the unlikely event of a sample with E. coli levels in excess of 1,000 colony-forming units per gram (more than 1,000 live bacteria capable of growing within a gram of a sample), the team can now respond proactively and initiate actions to avoid costly downtime and excess testing. “We can change the process to give us an increased pathogen kill,” explains Devlin.
For Welsh Water, the cost of lost production of biosolids can be up to £10,000 a week each time a biosolid test fails to meet regulatory standards. This is in addition to the cost of remedial testing, which can total £20,000, and the logistical costs of diverting the sludge to another advanced anaerobic digestion facility to be treated to ensure compliance ahead of disposal.
Calvet describes Tecta as “plug and play” technology. “Anywhere you have desk space and a power supply, you can deploy one of these instruments.” For most tests, the process is to fill the cartridge with the sample, dissolve the pre-dosed reagent, pop it inside the instrument, add the test and sample information, and the instrument does the rest. A technician only needs to be present to start the process. The incubation stage is automatic, and the interpretation of the result and reporting is also done automatically. This means it is possible to obtain results over the weekend if necessary.
Calvet explains: “With Tecta, if you get rush samples in at the last minute, or something’s gone wrong on site and you want to double-check it, you can pop the sample in, go home for the weekend, and know you’ll get your results by email and can relay them to whoever might be on site for remedial work. So you’re unlocking a tonne of flexibility.
“You can train your operators – anyone who’s on site – to do this. It takes about 20 minutes to train someone.”
