Lack of Organic Carbon as the Lack of Organic Carbon as the Condition that Limits Condition that Limits

Denitrification in the Living Denitrification in the Living Machine MarshMachine Marsh

IntroductionIntroduction

We knew the LM marsh wasn’t denitrifying as We knew the LM marsh wasn’t denitrifying as much as possible.much as possible.

We were asking why?We were asking why? Two hypotheses:Two hypotheses:

Too much dissolved oxygenToo much dissolved oxygen Not enough organic carbonNot enough organic carbon We found that lack of organic carbon is the main We found that lack of organic carbon is the main

condition that prohibits denitrificationcondition that prohibits denitrification

Why is this important?Why is this important?

Excessive nitrate can produce eutrophication Excessive nitrate can produce eutrophication and microbial growth in the ALJC plumbing and microbial growth in the ALJC plumbing would be problematic.would be problematic.

Ideally, Living Machines should produce Ideally, Living Machines should produce water that could be put directly back into the water that could be put directly back into the ecosystem.ecosystem.

Producing info that could be used in future Producing info that could be used in future research about these types of systems that research about these types of systems that would improve their performance.would improve their performance.

BackgroundBackground

Wastewater is part of all of our lives and we Wastewater is part of all of our lives and we need to process it somehowneed to process it somehow

Living Machines are an attractive alternative Living Machines are an attractive alternative to traditional wastewater treatment plants to traditional wastewater treatment plants because they use natural processes. They because they use natural processes. They are also sufficiently pleasant facilities to locate are also sufficiently pleasant facilities to locate in a residential area, which allows for the in a residential area, which allows for the reuse of water.reuse of water.

The more compact, reliable and efficient these The more compact, reliable and efficient these systems are, the more people will be systems are, the more people will be interested in constructing and using them.interested in constructing and using them.

MethodsMethods

SamplingSampling Took samples from sampling ports in the LM Took samples from sampling ports in the LM

marsh and measured DO and nitrate levelsmarsh and measured DO and nitrate levels Took samples from the marsh influent and effluent Took samples from the marsh influent and effluent

sumpssumps ManipulationsManipulations

Added sodium acetate to marsh influent water at Added sodium acetate to marsh influent water at different concentrations and incubated them in different concentrations and incubated them in BOD bottles for one to three days.BOD bottles for one to three days.

Measured nitrate levels after incubations to Measured nitrate levels after incubations to determine denitrification rates.determine denitrification rates.

Results and Discussion:Results and Discussion:The marsh already has some denitrificationThe marsh already has some denitrification

Nitrate and Dissolved Oxygen Levels in the Living Machine Gravel Marsh 11/10/03

y = -0.1759x + 4.6782

R2 = 0.6876

0

1

2

3

4

5

6

7

8

InfluentC10 SC10 MC10 LC9 SC9 MC9 LC6 SC6 MC6 LC5 SC5 MC5 LC1 SC1 MC1 LEffluentLocation

DO (mg/l)

NO3 (mg/l)

Linear (NO3 (mg/l))

Carbon works!Carbon works!

Nitrate after 48 hrs

0

1

2

3

4

5

6

No Carbon added Carbon added

NO

3 (mg/l)

Denitrification over TimeDenitrification over Time

Nitrate Levels in Sparged Test Bottles Over Time

0

1

2

3

4

5

6

0 24 48 72Time (hrs)

NO3 (mg/l)

2.88 g/l

2.3 g/l

1.79 g/l

1.15 g/l

0.58 g/l

0.29 g/l

0

0

But too much carbon interferesBut too much carbon interferes

Carbon vs NO3 at 48hrs

y = -0.1326x + 2.3219R2 = 0.0053

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5

Carbon added (g/l)

NO

3 (mg/l)

It doesn’t take much…It doesn’t take much…

Carbon vs NO3 at 48 hrs - run #2

y = -8.0737x + 3.2739

R2 = 0.3865

-2

-1

0

1

2

3

4

5

6

7

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Carbon added (g/l)

NO

3 (mg/l)

Conclusion and Future ResearchConclusion and Future Research

Carbon matters and the LM marsh Carbon matters and the LM marsh doesn’t have enough.doesn’t have enough.

We have an idea of how much carbon is We have an idea of how much carbon is neededneeded We can use that information to add We can use that information to add

appropriate quantities of carbon directly to appropriate quantities of carbon directly to the systemthe system

If future research determines how much If future research determines how much carbon plants exude that would tell us how carbon plants exude that would tell us how many plants the marsh needs.many plants the marsh needs.