Blower timers significantly reduce packaged treatment energy cost  

A successful two-year trial of interval timers on fans at a wastewater treatment plant resulted in an average energy saving of 50% at a site in Cornwall.

The partnership between WCS Environmental Engineering (WCSEE) and Juliots Well Lodge Retreat has set a precedent for ongoing design and energy saving standards for the wastewater treatment specialist’s HiPAF (High Efficiency Aeration Filter) system.

Energy costs

HiPAFs on site at Juliots Well Lodge Retreat

The HiPAF wastewater treatment system was installed at Juliots Well Lodge Retreat in Camelford, North Cornwall in 2019 to customer specific design specifications and environmental approvals. This included a stringent Environment Agency wastewater permit for biological oxygen demand, suspended solids and ammonia.

The plant is designed to serve 1,230 residents and consistently processes wastewater volumes of up to 181 m3/day. Although HiPAF operations have been very effective year-round, recreation park managers found that rising energy prices were leading to higher-than-expected bills, particularly during peak summer periods and on weekends.

Air blowers are an integral part of the HiPAF system, providing oxygen to the bacteria during the aerobic process. However, without timers installed, blowers typically operate 24/7, which can account for more than 90% of the energy used in a HiPAF.

While energy efficiency has always been a focus of the HiPAF system, WCSEE's engineering team took the opportunity to work closely with Juliots Well to identify ways to further reduce energy use. This included collecting and analyzing data to assess how seasonal variations affect wastewater flow rates into the HiPAF and how dissolved oxygen (DO) levels in the aerobic digester affect the need for blower operation.

By analyzing the data, it was possible to determine how energy consumption and electricity bills could be reduced by using cost-effective timers on the fans.

Probationary period

During the two-year test period, two timers were retrofitted to the HiPAF at Juliots Well, one on each blower, alternating each week to ensure even wear. It is possible to start and stop the blowers up to ten times per hour, so the WCSEE team started with 15-minute on/off intervals as a baseline.

With the fans off, DO levels in the aerobic digestion tank were measured to ensure that the minimum level of 5–6 mg DO per liter of wastewater required for efficient treatment and operation of the HiPAF was met.

By gradually optimizing and extending the timers, it was possible to determine the optimal period of time during which the fans should be switched off without exceeding the DO limits.

At the end of the trial, it was confirmed that Juliots Well can now safely operate the HiPAF blowers at 10 minute on and 20 minute off intervals to meet minimum dissolved oxygen limits. This optimized solution has resulted in significant energy savings while fully complying with the Environment Agency's wastewater permit requirements.

Rick Ackroyd, Managing Director of Juliots Well Lodge Retreat, said:

“With energy costs rising sharply, we were looking for ways to reduce our carbon footprint and energy consumption across the site. WCSEE has been a committed partner in helping us achieve this goal.

“We appreciate their patience and determination in finding an effective solution that will ensure we have a robust and efficient wastewater treatment system with the lowest possible energy consumption, especially during peak periods.”

Setting a precedent

High energy prices and commitments to carbon neutrality mean that energy efficient wastewater treatment is becoming increasingly important for owners and operators of complete systems. To meet increasing expectations, all WCSEE HiPAF wastewater treatment systems now come standard with blower timers pre-set to 15-minute intervals. This ensures the most cost-effective and energy efficient system available and is part of WCSEE's standard control philosophy.

The company's experienced technicians can work closely with customers after installation to further improve the functionality of the HiPAFs, with the timers already delivering efficiency at multiple sites.

Andrew Baird, technical director of WCSEE, said:

“By working closely with Juliots Well Lodge Retreat we were able to offer the client the best total life cycle cost whilst improving the design and operation of the HiPAF wastewater treatment plant.

“With rising energy costs and governments’ net zero ambitions, we look forward to working with our existing and future customers to introduce this energy-saving extension of our highly effective biological treatment technology.”

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