anaerobic treatment

May 5, 2021

wastewater discharge limits


A large renewable energy company had ambitious plans when it bought a decommissioned plant in Missouri: to mass-produce corn oil-based biodiesel with an eye to ramp up fast. But after investing millions to purchase and retrofit the facility, the company got a surprise. The municipal wastewater treatment plant underestimated the discharge limits; now, the operator could only run at 10 to 15% capacity to send its high-strength wastewater to the City.

There was an urgency to move forward to begin to get a return on a major investment, but as important was to have a viable, long-term solution. Vetting, building, and mobilizing what turned out to be a complex, sustainable system takes time.

The project entails a lot of research and understanding of what’s in the wastewater, production processes to reduce contaminants, and technologies and vendors to support the project from start to finish. SCS Engineers came in to assist.

Nathan Hamm, program lead for wastewater and liquids management practice, said:
It was clear that we would have to find an immediate, short-term solution while looking for a long-term answer to the wastewater problem. We quickly identified and helped our client connect with another treatment plant for the interim where it could transport wastewater. This enabled the ramp-up while we searched for an economically viable strategy to take them into the future and give them the option for growth even beyond their current expansion plans should they choose.

The initial goal was to find a way to partner with the City to enhance their treatment system so the client could stay local.

SCS worked with the City’s wastewater treatment consultant on a two-part answer: restoring an anaerobic digester owned by the City located at its wastewater treatment plant to increase capacity; building a dedicated wastewater force main/pipeline from the operation to the municipal treatment plant.  It was an economical plan that would perform the intended function. But the City would only commit to this arrangement for five years.

“We needed more security and certainty so our client’s investment would return value over the long run. We began evaluating various systems for on-site wastewater treatment, looking at both anaerobic and aerobic options to treat the contaminated water,” Hamm says.

There are plenty of challenges to take on, such as high BOD strength, high sulfates, high temperatures, and in this case, limited spare plant space for a robust wastewater treatment system.

Following a wastewater characterization study to analyze what the plant was generating and identify process changes to reduce wastewater generation and contaminant concentrations, SCS whittled the alternatives down to anaerobic treatments. Compared to aerobic options, they are less energy-intensive and generate less sludge. As a bonus, they create methane to power the client’s boiler.

Ultimately, the selection was an anaerobic membrane bioreactor (AnMBR) system, which leverages bacteria to break down organics in untreated water and filters out solids. The operator now treats 100% of the wastewater on-site and discharges directly to the municipal treatment plant well below permit limits.

“What’s most important to our client is that with this investment they have complete control and for the long term. They own and run the system, are well-positioned to comply with discharge limits, even if they were to get tighter. And they are ready to increase production,” Hamm says.

Progressing from identifying a fitting technology to launching the whole system is a multi-leg journey. Early on, SCS vetted installations in several states from New York to Georgia and took the client to the top performers.

Hamm states,
We vet first to ensure the system’s integrity and that it will serve our client’s needs. But it is important that once we do our due diligence, they see the system in operation and talk to operators about what they like and did not like. 

Next, we helped evaluate proposals and assessed capital and operating costs to determine if they are reasonable and comprehensive to avoid costs later. There is a lot to digest, and we want to make sure our client has every bit of information to support their decision.


The SCS team negotiated a design-build contract then oversaw the construction process.

“We served as the liaison between the plant and contractor, which is important to safeguard that our client gets what they need and what they paid to get. Taking on this role helps us stay on top of scheduling moving faster while maintaining efficiency and safety,” Hamm says.

The foundation work was a project in and of itself. The structure needed to support numerous tanks and treatment vessels, including a 2-million gallon digester tank.

The design-builder originally hired another contractor for the foundation, but SCS could do the job for about half the cost.

“We brought in our geotechnical engineers and a vendor we knew working in the area to perform a thorough assessment and pile load test.  Following the load testing, we were confident we could build a structure to support the system, limit the differential settlement to acceptable levels, and perform well,” Hamm says.


The new wastewater treatment system is up and running smoothly.

“We are on weekly calls even four months in to review performance tests confirming the system is operating effectively. And we have determined it is,” says Hamm.

“Our client is running at full capacity. They no longer haul wastewater offsite. They eliminated their hefty monthly wastewater treatment surcharges because they are discharging clean water. And they will likely pay off their investment in less than three years,” Hamm says.


Related Information

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Posted by Diane Samuels at 6:00 am