Mansfield Sewage Treatment Works

diffuclear graph

diffuCLEAR performance change graph

Diffuser Remediation Makes Savings for Severn Trent

Air Technology’s diffuCLEAR validated acid cleaning treatment has revitalised the performance of the Activated Sludge Plant (ASP) aeration lanes at Severn Trent’s Mansfield Sewage Treatment Works, improving the efficiency of the process and reducing the energy required to achieve DO targets. The work was carried out economically and with no interruption to the process, and was backed up with full measurement and validation of the improvements achieved.

Mansfield STW in Nottinghamshire is a medium sized works serving a population equivalent of 105,000, with an average inlet flow of 22,700m3/day. Secondary treatment is carried out in a four lane, two pass ASP. During blower testing, Air Technology engineers identified that some of the diffuser grids were starved of air because of scale and biofilm buildup, resulting in high blower pressures and poor oxygen transfer.  As a result they were asked to apply diffuCLEAR to improve air flow.

diffuCLEAR combines highly effective acid-cleaning treatment with the added benefit of validation and certification of the results. Special insertion flowmeters are introduced into the pressurised pipeline, flow rates measured and recorded along with blower pressures before the diffuCLEAR treatment commences. diffuCLEAR technicians fit valves to the pipeline that allow the chemicals to be introduced in a closely controlled, atomised mist that travels through the pipe and goes to work on the biofilm and scaling that obstruct airflow through the diffusers.  All this is achieved with no disruption to aeration.

The diffuCLEAR treatment restores the diffusers to near new performance  reducing the pressure required from the blowers to achieve efficient air movement, and also helps re-establish more efficient fine bubble diffusion maximise ASP performance.

diffuCLEAR cleaning took place on the Mansfield site over two visits. The flowmeter results were assessed immediately after diffuCLEAR treatment, and again two weeks later.

 The results were striking. In the post-treatment assessment on one of the zones, with pressure at 625mBar, there was an immediate increase in flow rate of 75%. Two weeks later, the improvement was even greater, with flows that had originally been seen at 625mBar now being achieved at below 550mBar, resulting in a direct saving of around 45,600kWh. Further improvements in performance were likely over subsequent weeks as the diffusers continue to clear.

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