WATER & WASTE TREATMENT INNOVATIVE FLOW SOLUTION REDUCES COSTS
Alison Miles from NIVUS, an instrumentation partner in a project at Five Fords WwTW, explains why the choice of flow measurement
technology has helped unlock enormous efficiency
improvements and subsequent savings
E
ngineers working on a project in North Wales have employed innovative techniques to improve wastewater
treatment efficiency at a fraction of the cost of traditional methods, saving an estimated £3.5 million.
Owned and operated by Dŵr Cymru Welsh Water, Five Fords WwTW is a sewage works near Wrexham, serving over 130,000 people. The site operates three ASP (activated sludge process) lanes.
As a Capital Delivery Partner and part of the Welsh Water Alliance, Mott MacDonald Bentley (MMB) was challenged to increase the treatment capacity of the ASP lanes in response to a growing population and increased demand from new anaerobic digestion plants.
The existing layout of the plant delivered wastewater to the ASP lanes at a different flow rate in each lane. This disparity was reflected by dissolved oxygen measurements within the lanes, which indicated that the lanes were not operating efficiently. “One of the lanes, for example, was operating in a super-critical condition, whilst another was sub-critical,” explains MMB’s Jack Jones. “As a consequence, from a process control perspective, the ASP lanes were difficult to manage effectively.” The uneven distribution of flow between the ASP lanes was caused by a number of physical issues in the flow channels that fed them. In addition, a large 800mm relief pipe discharged a mixture of RAS (returned activated sludge) and overspill directly into the main inflow channel, which also affected the flow profile.
The ASP lanes were originally built with
flumes to control flow, but these were replaced with weirs to increase capacity. The requirement for a further increase in capacity
26 MARCH 2025 | PROCESS & CONTROL
therefore meant that a return to flumes would not be practicable, and would not resolve the flow disparity in any case. A flow split chamber with equal weirs was also not considered to be practical, because it would disrupt operation. In addition to resolving the flow disparity in the ASP lanes, it would be necessary to monitor flow in the relief pipe. This also represented a very significant potential cost, because traditional techniques such as electromagnetic flowmeters typically require a full pipe for accurate measurements and involve substantial installation costs and process downtime. A recent trial comparing the NIVUS insertion probe with a traditional ‘magflow meter’ demonstrated a 60% saving in cost and 95% saving in embodied carbon. The magflow option was therefore also disregarded.
The solution “Before making the final decision, a number of internal ‘surgeries’ were conducted involving hydraulic, mechanical and process engineers,” explained Josh Sparks, MMB Contracts
Manager & EICA Regional Practice Lead. The preferred solution involved the deployment of three actuated penstocks that would be lifted into the first three channels. The fourth channel would be isolated, but could be made available if necessary, in the future. Effective control of the penstocks would depend heavily on the reliable measurement of flow in each channel downstream of the penstocks. “This was also a major challenge,” said Sparks. “Most traditional flow measurement methods were ruled out due to the physical constraints of the site, along with the cost of solutions involving significant civil works. As a result, we engaged with NIVUS and determined that their cross-correlation flow meters offered the best solution.” NIVUS was contracted to install flow meters in the relief pipe, in the main inlet channel, and in each of the three ASP inlet lanes. All of these instruments are MCERTS and EX-rated and employ the NIVUS cross-correlation flow measurement method.
Two NIVUS POA wedge sensors were fitted to L-shaped bed-mounted brackets – one on either side of the main inlet channel. These sensors were connected to a (NF750 M9) transmitter, to which the pipe insertion probe (velocity profiler and ultrasonic level) was also connected.
Each of the ASP lanes was fitted with a radar level sensor, working together with POA wedge sensors, which were also mounted on L- shaped bed-mounted brackets. Each of these sensors was connected to a single input transmitter (NF750).
The ultrasonic cross-correlation method developed by NIVUS measures individual velocities continuously at different levels within the flow. This area velocity flow measurement technique provides a 3-dimensional flow profile that is calculated in real-time to provide reproducible and verifiable flow
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