WT Interview with Chris Navitsky, P.Eng, Lake George Waterkeeper

WT: I have with me on the phone, Chris Navitsky, who is a professional engineer, and also with Lake George Waterkeeper, thanks for doing this, Chris.

Navitsky: Thank you for the interest!

WT: Can you tell me about the project, what’s up with the woodchips?

Navitsky: This came about from a study we were doing around wastewater treatment plants on the tributaries to Lake George, to monitor them. We are fortunate, Lake George is a beautiful, oligotrophic lake. The nutrient levels in the lake are very low, but we have been seeing subtle changes in the phytoplankton and algal communities. Our hypothesis was that nutrients are seeping into the lake causing algae growth. We are still oligotrophic (relatively low in plant nutrients and containing abundant oxygen) but seeing higher levels of soluble reactive phosphorous and nitrates from a particular community’s wastewater treatment plant, the Town of Bolton. As we finished our year and a half study, we had a couple of recommendations, some operational, working with the town engineer we felt we could eliminate problems with the treatment plant. They do not have a process to treat ammonia, (NH4NO3) or to do the de-nitrification in the plant.

Through our research, we found processes out in the US Midwest that handle high nitrate runoff from the agricultural fields that use fertilizers. They naturally process their water through a woodchip bioreactor, a long trench. The water flow goes through the woodchips, coming out the other end with lower nitrates. Anoxic bacteria live off the carbon in the woodchips, and seeking oxygen, they take the oxygen from the nitrates, (NO3), turning it into nitrogen gas.

We looked at this, the source of our nitrates is the wastewater, but why wouldn’t it work for us? To our knowledge, this is the first application for a municipal wastewater treatment plant. The Town Engineer applied to the New York State Dept of Environmental Conservation to get a demonstration permit/project in 2018, then had a two-and-a-half-year study to evaluate the efficiency of this bioreactor.

We found the woodchip bioreactor process was efficient, we had great results, we also discovered where we can improve the process.

We have to thank the Town of Bolton for being proactive on this, this is a smaller, rural community, the treatment plant being sixty-plus years old. It did not work to retrofit the plant for de-nitrification processing, it would have been too big a price tag or a small community. We went with the sustainable, green technology fit really well. Lake George Waterkeeper catalyzed the project by providing a fifty-thousand-dollar grant, to get the demonstration project to prove this out.

WT: I understand Lake George is attached to Lake Champlain, is that correct?

Navitsky: Yes

WT: Nitrogen and phosphorous are coming into the lake from septic systems or wastewater treatment plants? Who came up with the idea that running high nutrient water through woodchips would reduce the nutrient levels? Can you tell me in simple terms how woodchips take phosphates and nitrates out of the water?

Navitsky: We did not come up with the idea, the lead researcher in the Midwest is Laura Christensen, initially the work was done at Iowa State University in early 2000s. She is the person that came up with this idea, from some research projects to address the nitrogen-filled runoff from agriculture practices, to deal with the huge nutrient loading and the subsequent dead zone in the Gulf of Mexico, at the mouth of the Mississippi River. That was their research project.

We read about this work and decided to try it here. It doesn’t act on phosphorous so much, it is primarily about nitrates. It’s not the woodchips that do the work, it’s the anoxic bacteria. The bacteria live off the carbon in the woodchips, and they obtain their oxygen by breaking down the nitrates (NO3) in the water as it passes through. 

WT: Does this have to work in tandem with a wastewater plant? Or can it work just by passing any nutrient-rich water down the trench bioreactor?

Navitsky: Literally, that is how it works. The research in the Midwest gave us a 5:1 length to width ratio. This longer and narrower trench increases the retention time, the longer flow path gives the volume of water enough time to be processed. They tried different materials for the carbon source, corn husks for the carbon source for the bacteria. Wood chips are the source they rely on, a bit sturdier, not settling as much, a greater porosity.

One of the things we discovered in our study, moving toward some recommendations was about the woodchips themselves.

WT: How long before you have to replace the wood chips?

Navitsky: The Midwest research estimated twelve to fifteen years, they were just getting to the end of their first life cycle for the wood chips. We discovered there was some build-up and settling of biological material, at least in the wastewater conditions, at the inlet part of the bioreactor, and at the outlet. We had to shut it down, remove and replace those woodchips during our study. One of the recommendations we made is to have a “sacrificial” inlet and outlet chamber, to be replaced sooner, on a two to three-year basis, leaving the interior trench woodchips for a longer period.

Unlike the agricultural run-off process, the wastewater treatment plant is running 24/7, running incessantly. Due to the continuous loading, we found that we need a sacrificial inlet and outlet chamber to be changed over more frequently.

WT: When results were announced, there was lots of interest. What are the recommendations coming out of this? Are you testing in other places to scale up?

Navitsky: The main recommendation for wastewater processing is to have the sacrificial inlet and outlet cells, and to increase the size of the woodchips from half-inch to two-inch. They may have degraded quicker than we thought, so we figured it was best to use a larger size chip.

Another recommendation is to have the entire bioreactor wrapped with an impermeable membrane. We initially had a filter fabric on the top that allowed a bit of aerobic exchange, air, and water to get in. We found when we shut down and had forensic excavation, there was a layer of degradation in the top layer where the aerobic exchange was breaking things down.

We are excited about receiving two more grants for the Bolton plant. We are putting in two more bioreactor cells so the entire plant will have the ability to run through the bioreactors. Bolton plant has an average daily flow of about three hundred thousand gallons a day. We weren’t sure the volume that could be processed, it is so dependent on the operator. The demo bioreactor, being 20 by 100 by 4 ft deep could take sixty to one hundred thousand gallons a day, depending on flow, the wastewater characteristics. Water temperature is a huge variable. At this time of year, when the wastewater temperature is 5C, bacteria become dormant, the efficiency drops, you get 20% N removal. In summer when wastewater is 25-28C, bugs are more efficient, we don’t need as long retention time and we get 80-90% N removal.

We are not sure how much average daily water flow this system could support. The bigger municipalities process upwards of two million of gallons a day. We are not sure if there would be enough land area for the number of bioreactor cells that would be required. So, this seems to work best for intermediate or smaller wastewater treatment plants.

WT: What kind of wood chips are you using?

Navitsky: It was mostly hardwood chips. We have to thank the Midwest researchers, they used softwood, pine, conifers, evergreens. We found more carbon content, better results with the hardwoods. As we are in the Adirondacks, ash, maple is what we are using.

WT: When should we call back for the next update?

Navitsky: We are hopefully working with the town, we have a design meeting in a couple of weeks, to help with the recommendations. We want to continue monitoring as well. Our goal is to do a documentary film as the cells are built, to talk about it and make it more available. As of now, all you see is a grass field with a couple of pipes sticking out. We would like continuous monitoring meters and probes, for real-time monitoring. 

Keep in touch, hopefully, we will be constructed this summer up and running and we may have an update for you in the fall.

WT: Thanks so much for doing this.