Feb 7 - Email Response from Pete Gabor Concerning DO Probe Prioritization

Original Email, from Clayton Bennett:

Pete,

I wanted to check with you concerning the short-term and long-term vision and timeline for our D.O. probes in the aeration basin in terms of automation for driving ideal blower speed.

Our technician Carlton Mull has spec'd 14 new probes to replace problematic probes, which would cost $30k to $40k. This month, we have other more urgent costs.

Notes: 2025 02-February 07 - D.O. Probe Prioritization vs ABF Equipment

G. Clayton Bennett
Ph: (901) 636-0306

Email Response, from Pete Gabor:

Clayton,

This topic warrants a discussion in person when I am on-site next week (Tuesday 2025 02February 11). There are several things to consider that isn’t communicated well in an email. If you have the availability, I suggest we carve out a couple minutes Tuesday-Thursday to provide some more context and talk through what I’ve written below.

Why DO and aeration is important:

Blowers for aeration is typically the largest contributor of energy costs at a treatment facility; it varies per plant, and I haven’t looked at yours, but it’s usually 50-70% of total plant energy consumption. If you can control the aeration process more efficiently it will reduce costs, provide higher effluent quality, and help with the formation of H2S. You’ll also be able to avoid conditions where the DO is low which causes bulking sludge and filament bacteria growth

To answer your question: DO probes are only one piece to automate the process. It will require functioning DO probes, functioning actuators to control the air flow, and air flow meters. I believe some of the actuators and flow meters will need to be repaired in addition to replacing the DO probes.

I would like to spend some time next week looking over the aeration system to see roughly what it would cost to get to the point where it can be automated and some estimates on savings. This will give you an estimated return on investment to determine if it’s worth doing.

Should you invest in replacing 14 probes:

There’s no right or wrong answer. A DO probe for each basin (28 total; 14 north, 14 south) would be ideal as we would know the DO level throughout, however aside from the initial investment; there is an ongoing maintenance cost for each probe that should be factored in.

If you don’t want to incur the cost of adding a DO probe in every basin, there are a couple different control strategies that don’t require a DO probe in every basin:

  1. Zone-based DO monitoring

  2. Divide the north and south sides into control zones

  3. Install 1-2 DO probes per group of 2-3 basins (total 8-14 probes instead of 28)

  4. Control the average DO per zone by adjusting the air flow.

  5. Locate the DO probes in strategic locations:

  6. Install DO probes at the first aeration zone (influent end) to track DO at start.

  7. Install at Mid-point to ensure adequate mixing and aeration distribution

  8. Install DO probes at final aeration zone (effluent end) to verify proper oxygen levels before exiting.

  9. Add a portable DO probe that communicates back to the Ovation system. Monitor the DO level. Move the portable DO probe around to different basins to locate where the DO fluctuates the most. In those areas, add permanent DO probes and incorporate into the control. We may be able to pull historical data to avoid adding a portable probe.

This would require 4-8 DO probes per side (total 8-16), a temporary portable probe setup, and additional DO probes where it fluctuates.

I’d like to spend some time looking into your plant’s process specifically to see what makes the most sense.

DO Probe selection:

I suspect the DO probes already have this functionality, but if they don’t, I highly recommend using an automated cleaning system for the DO probes. It periodically shoots air or water at the sensor to make sure nothing forms on it that prevents it from reading accurately. The DO probes will last longer, remain accurate longer, and need less field maintenance. It costs more to implement it, but a worthwhile investment in the long run.

Lastly, If you’d like to hop on a call before next week to discuss, please let me know.

Thanks,

Pete

Peter Gabor

Project Technical Leader