Utilities Committee Discusses Boxing Day Polymer Incident – 4-5 Months Of Cationic Polymer Emptied Into Anaerobic Digester In One Day

The Utilities Committee met 01/10/2023. Much of the meeting was taken up with discussion of the Polymer Incident of December 26, 2022.

I’ve prepared a complete transcript of the discussion for your downloading pleasure. I find it all very interesting, but because I don’t know anything about how wastewater treatment works or how their various programs work, I’m going to keep this recap brief and skip over all the parts of the discussion I didn’t fully understand, but it’s still available in the transcript whether I understand it or not.

The Appleton Wastewater Treatment Plant has a number of stations where it accepts hauled waste. Hauled waste is waste that is transported to the treatment plant by trucks or some other vehicle as opposed to arriving through the sewer system. It is typically industrial waste of some sort. Because the treatment plant is primarily designed to handle household waste, this industrial waste needs to be pre-treated before it is released into the main part of the treatment plant. The city website has some information on its pretreatment program.

The city accepts a number of difference kinds of hauled waste, dairy waste, leachate from landfills, and food processing waste. The treatment plan has a number of hauled waste stations for different types of waste. Some of the hauled waste enters the treatment facility and some of hauled waste enters the plant’s anaerobic digesters.

On the day after Christmas, the hauled waste program was open even though the rest of the plant was not open for normal business hours. On 12/26/2022 a delivery of a cationic polymer was made to the plant and offloaded into the hauled waste station. That delivery consisted of 4-5 months’ worth of treatment chemicals for a post anaerobic digestion process. The plant uses approximately 35 gallons of cationic polymer a day, but the entire tanker full was emptied into the digester.

Everything in the digester is supposed to be the consistency of tomato juice. However, the cationic polymer is a liquid solid separator, so it ended up causing the liquid to sink to the bottom while a thicker layer formed on top. The treatment plant uses gas in their process, so when this incident happened the gas was able to rise up through the liquid but it wasn’t able to break through the solid mat on top which started to create gas surges.

This situation has possibly never happened before. Ever. There was no literature available to guide them in their response. Not only could they find nothing about this happening on a large scale like they were dealing with, but they could not even find small scale examples to review.

The fire department was called out, and within a couple hours the wastewater treatment plant was able to get regulatory approval to bypass the primary anerobic digester.

Utilities Director Chris Shaw told the committee that they continued to meet their DNR compliance with their WPDES permit which is the permit that pertains to the water that is discharged from the treatment plant into the Fox River.

There is an investigation taking place to figure out how this happened. Alderperson Chad Doran (District 15) asked if that investigation was internal or being conducted by outside people and was told that, at this point, it was an internal investigation.

Alderperson Doran also asked if this was something the city’s insurance would be involved with and was told that the city was looking into that. It sounded like Director Shaw would have been willing to go into more detail about insurance, but another staff member, possibly someone from the City Attorney’s Office, shut down that direction of the conversation.

The effects of this incident on the treatment plan are still, understandably, being assessed. Per Director Shaw, “We’ve had a number of challenges because we’ve induced stresses on equipment that are not part of their design. So, these gas surges, and that sort of thing—they’ve done things to equipment.”

As of the meeting on 01/10/2023, they were confident that one digester was fully functional. That was enough to meet the community’s wastewater treatment needs though perhaps not to continue offering the hauled waste program. Having only one digester did provide the full capacity nor include the redundancy of having two digesters.

They were hoping to return to anaerobic digestion through at least one digester by 01/11/2023.

Direct Shaw said that he would have more to report in a couple weeks. He sounded somewhat positive about how things were going but did not want to give a firm commitment as to when the whole system would be back to normal. “There’s no literature to guide us. We don’t know impact to equipment. We didn’t know impact to biology really. I mean, we had theory, right? And we’re working off of, you know, our credentials kind of thing. You know what I mean? Our engineering folks can’t help us. The state can’t help us. They can—the chemical company couldn’t help us. I mean with confidence. It’s theory/conjecture kind of almost, right? Talking in circles. So, I prefer not to live in that world. I like evidence. I like evidence. Right? So, it’s better to have evidence.”

View full meeting details and video here: https://cityofappleton.legistar.com/MeetingDetail.aspx?ID=1065111&GUID=FD5140FC-27C7-4C1C-B090-D219FAA55BBA