Lack of Organic Carbon as the Condition that Limits Denitrification in the Living Machine Marsh

Introduction We knew the LM marsh wasn’t denitrifying as much as possible. We knew the LM marsh wasn’t denitrifying as much as possible. We were asking why? We were asking why? Two hypotheses: Two hypotheses: Too much dissolved oxygen Too much dissolved oxygen Not enough organic carbon Not enough organic carbon We found that lack of organic carbon is the main condition that prohibits denitrification We found that lack of organic carbon is the main condition that prohibits denitrification

Why is this important? Excessive nitrate can produce eutrophication and microbial growth in the ALJC plumbing would be problematic. Excessive nitrate can produce eutrophication and microbial growth in the ALJC plumbing would be problematic. Ideally, Living Machines should produce water that could be put directly back into the ecosystem. Ideally, Living Machines should produce water that could be put directly back into the ecosystem. Producing info that could be used in future research about these types of systems that would improve their performance. Producing info that could be used in future research about these types of systems that would improve their performance.

Background Wastewater is part of all of our lives and we need to process it somehow Wastewater is part of all of our lives and we need to process it somehow Living Machines are an attractive alternative to traditional wastewater treatment plants because they use natural processes. They are also sufficiently pleasant facilities to locate in a residential area, which allows for the reuse of water. Living Machines are an attractive alternative to traditional wastewater treatment plants because they use natural processes. They are also sufficiently pleasant facilities to locate in a residential area, which allows for the reuse of water. The more compact, reliable and efficient these systems are, the more people will be interested in constructing and using them. The more compact, reliable and efficient these systems are, the more people will be interested in constructing and using them.

Methods Sampling Sampling Took samples from sampling ports in the LM marsh and measured DO and nitrate levels Took samples from sampling ports in the LM marsh and measured DO and nitrate levels Took samples from the marsh influent and effluent sumps Took samples from the marsh influent and effluent sumps Manipulations Manipulations Added sodium acetate to marsh influent water at different concentrations and incubated them in BOD bottles for one to three days. Added sodium acetate to marsh influent water at different concentrations and incubated them in BOD bottles for one to three days. Measured nitrate levels after incubations to determine denitrification rates. Measured nitrate levels after incubations to determine denitrification rates.

Results and Discussion: The marsh already has some denitrification

Carbon works!

Denitrification over Time

But too much carbon interferes

It doesn’t take much…

Conclusion and Future Research Carbon matters and the LM marsh doesn’t have enough. Carbon matters and the LM marsh doesn’t have enough. We have an idea of how much carbon is needed We have an idea of how much carbon is needed We can use that information to add appropriate quantities of carbon directly to the system We can use that information to add appropriate quantities of carbon directly to the system If future research determines how much carbon plants exude that would tell us how many plants the marsh needs. If future research determines how much carbon plants exude that would tell us how many plants the marsh needs.