Microbe management: MBBR upgrade at Bolton-upon-Dearne WwTW
Galliford Try is installing a tertiary treatment system that is set to result in significant savings for Yorkshire Water
• Meet EA ammonia consent of 3mg/l at 95 percentile and 1.5mg/l at 50 percentile by 1 April 2020
• Install new elevated inlet works to meet capacity requirements
• Like-for-like pump replacement in low-level inlet pumping station
By Robin Hackett
Faced with an Environment Agency consent to reduce ammonia at its Bolton-upon-Dearne Wastewater Treatment Works in Rotherham, Yorkshire Water has opted to install a moving bed biofilm reactor (MBBR) system that it expects to deliver quality results at a lower cost than activated sludge processes (ASPs).
“ASPs have generally been the go-to technology for us,” Yorkshire Water project manager Sam Akeroyd says. “Both work well but, on a cost basis, this is much more efficient. I can imagine a lot of water companies will be moving towards it.”
This is Yorkshire Water’s biggest MBBR installation to date and follows on from the recent £4 million upgrade undertaken by AGT (AECOM Galliford Try) at the nearby Tankersley works, which serves around 2,000 customers.
The Bolton-upon-Dearne scheme, led by Galliford Try, involves similar work but on a much more substantial scale, coming at a cost of £12.3 million and serving approximately 25,000 residents.
The project got underway in May 2017 and will improve the quality of the water released back into the River Dearne, with the works’ current ammonia output of around 13mg/l risking toxic impacts on fish and macro-invertebrates. When the Environment Agency consent comes into force on 1 April 2020, that must fall to 3mg/l at 95 percentile – meaning 95 per cent of samples come in below that level – and 1.5mg/l at 50 percentile.
“Once you’ve got them running, the MBBR does exactly what it needs to do,” Simon Jones, Galliford Try project manager, says. “At Tankersley, we’ve got a 0.65mg/l target at 50 percentile but it’s generally running about 0.1mg/L, so it’s almost completely ammonia-free.
“You can get the same effect if you build ASP lanes and everything else, but then you’re talking a massive amount of capital. It’s a technology that works, that is more economical and does exactly what you require it to do as long as it’s maintained. And it’s a low-maintenance piece of kit.”
The MBBR concept was invented in the late 1980s by Prof. Hallvard Ødegaard, who said he was aiming to “adopt the best from both the activated sludge process and the biofilter processes without including the worst”.
While it was developed with nitrogen removal in mind, further uses – including combating ammonia – have expanded the possibilities for its applications.
“With the Environment Agency going through cycles for what they want to improve and the issues ammonia causes to the natural environment, it’s quite a hot topic now,” Jones says.
In essence, the MBBR – which is supplied by Veolia – is a tertiary treatment system that involves growing a biofilm of bacteria and other microorganisms on perforated plastic discs inside tanks.
Aeration grids inside the tanks provide air bubbles that cause the discs to rotate and feed the bacteria.
“The discs have a live surface area, and the idea is that we get bugs that grow on there and they eat the ammonia,” Jones says. “The more aeration we give, the more feed we give to them, enriched with ammonia, the more active it becomes.”
Bolton-upon-Dearne will operate using two pairs of 14m-by-14m concrete tanks in a lead-lag system. After undergoing primary and secondary treatment, the flow will enter the first of one of the pairs of tanks to draw out some of the ammonia before entering a second to reduce levels further.
It exits into a collection chamber featuring 10-micron drum filters, which will remove any microorganisms that have died.
“Bugs will always be on aeration, always be moving around and banging into each other, so that creates its own level of waste,” Jones explains.
While MBBRs are lauded for their relative ease of use, the installation presents some challenges. For one, the initial seeding process is expected to take anywhere between eight and 16 weeks but can be unpredictable.
“That’s not an exact science,” Akeroyd says. “It depends on the ambient temperature and the size of the MBBR – which is significant here – but we’ve got Veolia, who designed and manufactured it, and Galliford Try have their own process engineers who are the best at what they do, so there’s a lot of expertise.”
The three blowers used to aerate the MBBR will also result in a significant increase in power requirements at a site that can only be accessed via a single lane.
“We’ve needed a power upgrade up to 450kVA,” Akeroyd adds. “The transformer that serves the site serves all the housing estate around here, and there’s a lot of new developments going on as well.
“Working with a third-party power company is always a challenge. We’re at their mercy. Because there’s only a single access to site, they’ll have to dig up that road to put in the HV [high-voltage] cables.
“At that point, we’ll pretty much be on a site shutdown because for health and safety reasons we can have no site ingress.”
The new inlet was built offsite
The Bolton-upon-Dearne works has seen several upgrades over the last 100 years, most recently in the 1990s, and many aspects of the site have remained in satisfactory shape, but the inlet works can no longer cope with demand and must be replaced as part of the current project.
“It’s about 50 years old,” Akeroyd says. “The main issue we had with the old inlet, and what posed the biggest problem for the site going forward, was that the receiving chamber wasn’t big enough for the volume coming in and the screening process wasn’t working – rags were constantly bypassing the screens and following through into the secondary treatment area.”
That issue will be resolved when the new inlet works, supplied by SPIRAC, becomes operational. The stainless steel inlet was designed and built offsite before being put together onsite in modules in a process Akeroyd likens to constructing a Meccano set.
The process was made easier by Galliford Try Technical Services, which created a federated 3D model that incorporates the details from all the various stakeholders involved in the project.
“SPIRAC brought in their modular design and put it together on site, and using these models can tell us where there could be clashes and prevent that,” Akeroyd says. “That could be days or even weeks saved on schedule. It’s been really good.”
Galliford Try Technical Services is a new division for the contractor.
“We do a lot of design in-house with our PMEICA [process, mechanical, electrical, instrumentation, control and automation] team,” Matt Terry, GT Technical Services’ senior CAD designer and BIM co-ordinator, says.
“That’s something Galliford Try hadn’t done in the past but this is a division that’s going to be used by all sectors of Galliford, including aviation and telecoms. It’s something we’ll build up over time.”
Terry has come up against some significant challenges in modelling Bolton-upon-Dearne.
“One of the more difficult aspects of this scheme was trying to get the information from particular vendors,” Terry says. “Things like the inlet works and MBBR are quite straightforward, but the hardest part is trying to get all the historical data from the 1960s and 1970s, which is all done in 2D, and a lot of upgrades had been done but hadn’t been recorded.”
That creates problems on site, and the team were forced to raise the inlet works to allow reinforcements to be added underneath after historical drawings misrepresented the depth of the underlying pipework from the CSO to the storm tanks.
“It was almost creating a bow in the middle where the pipework runs, so we had to reinforce a lot more after realising the drawings were completely wrong,” Akeroyd says.
While such complications can mean delays, the project is expected to be completed by the spring and, once it is fully operational, the range of benefits will be significant.
“Because of all the advance work we’ve done on the primary and secondary treatment, the flow will pass through to the tertiary treatment stage a lot better, and the MBBR can then do exactly what it’s required to do: feed on the ammonia,” Jones says.
“That improves the quality of the water in the river, and that can only be better for Yorkshire Water when it goes into the clean-water supplies. It’s great for nature.”
This article originally appeared in the October issue of WET News
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