background flood and drain treatment wetlands are efficient means to treat cod, tss, and total...

BACKGROUND

Flood and drain treatment wetlands are efficient means to treat COD, TSS, and total nitrogen to advanced standards.

Principal treatment mechanisms are:

1) sorption of ammonium cations (NH4+) in bulk water to media;

2) rapid oxygen saturation of biofilms in the drain phase;

3) rapid bacterial nitrification of sorbed NH4+ cations;

4) desorption of nitrate anions (NO3-) into bulk water in the next flood cycle;

5) denitrification as nitrate ions serve as terminal election acceptors in bacterial respiration.

David Austin, M.S., P.E., Certified Ecologist ESA

Dharma Living Systems

8018 NDCBU, 125 La Posta

Taos, New Mexico

www.dharmalivingsystems.com

0

50

100

150

200

250

300

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99

LESA + PlantsHDPE + PlantsHDPELESA

Percent of Data Less Than or Equal to Indicated Value

0

20

40

60

80

100

120

140

160

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99


Percent of Data Less Than or Equal to Indicated ValuePercent of Data Less Than or Equal to Indicated Value

0

100

200

300

400

500

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99



NH4+

NO3-

NH4+

O2O2

O2O2

NO3-

NO3-

N2

Cation exchange capacity (CEC)

of media & organic material

is a fundamental

forcing function

of this ecosystem.

RESEARCH QUESTION

How does the CEC of raw media affect treatment in vertical flow, flood and drain treatment wetlands?

Why does this matter?

Consider theoretical oxygen demand stoichiometry in wetland treatment systems.

Dissolved oxygen demand for bulk-water treatment: O2 demand = (COD influent - COD effluent) + 4.6(NO3-)f - 2.86(NO3

-)u

Where:

COD = chemical oxygen demand, mg/L term eliminated

(NO3)f = nitrate formed, mg/L (nitrification demand)

(NO3)u = nitrate utilized, mg/L (denitrification return)

Dissolved oxygen demand in flood and drain wetlands: O2 demand = (COD influent - COD effluent) + 4.6(NO3-)f - 2.86(NO3

-)u

Explanation and Consequences:

1. Nitrification in drained phase => Negligible nitrification dissolved oxygen demand in bulk water

2. Dissolved oxygen demand reduced 20 to 50%, depending on influent COD:TKN

3. Power consumption for total nitrogen removal is approximately 30% of that required in an activated sludge treatment system

Therefore, for design we must know CEC (NH4+ sorption) in a mature system. Will organic matter CEC make up for low media CEC?

If raw media CEC is important, then treatment media design CEC must be specified, otherwise design stoichiometry is defective.

METHODS1. Apparatus:

a. Four 12” x 48” fiberglass columns, each with dedicated sump and pump. Columns filled with media. Two columns planted.

b. Flood (45 min) and drain (3 min) cycles controlled by microprocessor.

2. Media: 67 liters of media in each column.

a. Electrostatically neutral HDPE (9 mm Rauschert® Bioflow 9), porosity = 0.9, CEC effectively 0 meq / 100 g

b. Lightweight expanded shale aggregate (LESA), 3 mm x 6 mm, porosity = 0.4, meets ASTM C-330-04, CEC approximately 4 meq / 100 g

c. Oxygen transfer rate in flood and drain cycles with clean water determined to be slightly higher in HDPE than LESA.

3. Set-up: Double parallel study with media and plants (Cyperus alternifolius) Vs. no-plants. Plant light provided by 1000 W metal halide lamps.

a. Column 1. LESA + Plants Note: Surface area of clean LESA calculated to be 855 – 1400 m2/m3. b. Column 2. HDPE + Plants Note: Surface area of clean HDPE Media calculated to be 855 m2/m3.

c. Column 3. HDPE

d. Column 4. LESA

4. Wastewater: Dried cheese whey + urea pearls + well water. Water volume in columns flooded to top of media column with wastewater.

a. Note: Mass loading of all columns was the same. Water volumes in LESA and HDPE columns differed due to different porosity.

b. May-September 2003: 34.2 g/d COD + 3.7 g/d TKN-N

c. October-December 2003. 17.1 g/d COD + 3.7 g/d TKN-N

5. Column preparation:

a Columns seeded with water from mature flood and drain pilot system and nitrifying biosolids.

b. Columns draped in black cloth to prevent sidewall algae formation.

c. Columns dosed and allowed to mature for three months prior to sampling.

6. Dosing and sampling: Dosing of columns every other day May -15AUG 2003, daily 15AUG-DEC 2003.

a. Dried cheese whey and urea placed in sumps, water manually topped off to preset fill level.

b. Samples taken from sumps after 24 hours after dosing.

c. sCOD samples processed in-house by HACH Manganese III method from TSS filtrate.

d. TSS processed in-house by Standard Methods.

c. TKN-N, NO3-N, NO2-N sent to certified contract laboratory for Standard Methods analyses.

d. Columns sampled over nine month period after maturation.

HDPE LESA

Planted columns. Note stunted growth of shoots & roots in HDPE compared to LESA.

0

100

200

300

400

500

600

700

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99



0

10

20

30

40

50

60

70

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99



RESULTS: Frequency distribution of effluent from 24-hours of flood and drain cycles

CONCLUSIONS

1. CEC media (LESA) overwhelmingly outperformed electrostatically neutral media (HDPE).

2. Failure to specify media CEC would be a fundamental design error for flood and drain wetlands.

3. Electrostatically neutral media impair nitrification, especially NO2 NO3.

4. Poor NO2 NO3 nitrification in HDPE columns suggests a microbiological basis to performance differences.

5. Role of plants in treatment is dictated by CEC:

a. Plants in CEC media (LESA) improve COD & TSS treatment Vs. LESA alone.

b. Plants in CEC media have little effect on nitrification and may adversely affect denitrification Vs. LESA alone.

c. Plants in electrostatically neutral media (HDPE) actively harm treatment Vs. HDPE alone.

d. Plants in electrostatically neutral media impair second stage nitrification (NO2 NO3) Vs. HDPE alone.

IMPLICATIONS FOR WETLAND TREATMENT TECHNOLOGY

1. Cation exchange in subsurface flow wetlands for any hydraulic regime may play a significant role in treatment and should be investigated.

2. The answer to conflicting studies on the role of plants in media-based wetland treatment may be, “You are all correct in your conclusions!”

Why? Data from this study definitively support all following statements: “Plants substantially aid treatment.” “Plants do nothing for treatment.” “Plants substantially harm treatment.” 3. Plant Vs. no-plant performance comparisons for media based wetland treatment systems are invalid unless fundamental forcing functions such as media CEC (and others e.g. H2S toxicity) are accounted for.

SUGGESTED FUTURE RESEARCH

1. Conduct CEC media comparison for horizontal subsurface flow wetlands. Is media CEC important in constant anaerobic environments?

2. Investigate microbiological differences in columns / pilots with CEC and non-CEC media. Does CEC structure microbial communities?

Suggested methods:

a. Comparative full cycle rRNA followed by quantitative FISH analysis of prokaryote communities to determine structural differences.

b. Comparative prokaryote : eukaryote ratios (FISH) to see if TSS performance difference results from differing grazer communities.

c. Comparative FISH survey of nitrifier communities (chemoautolithotrophs, Anammox, and heterotrophic nitrifiers).

d. N - species & N14/N15 exhaust gas analysis to trace physiological fingerprints of nitrifier communities

References

Austin, D. Lohan, E. Verson, E. 2003. Nitrification and Denitrification in a Tidal Vertical Flow Wetland Pilot. Proceedings Water Environment Federation Technical Conference, Los Angeles 2003.

Behrens, L. 1999. US Patent 5,863,433.

Sun, G. Gray, K.R. Biddlestone, A.J. Cooper, D.J. 1999. Treatment of Agricultural Wastewater in a Combined Tidal Flow-Downflow Reed Bed System. Wat. Sci. Tech. 40(3). Pp 139-146. 1999.

Tanner, C., D’Eugenio, J. McBride, G., Sukias, J., Thompson, K. 1999. Effect of water level fluctuation on nitrogen removal from constructed wetland mesocosms. Ecological Engineering 12 (1999) 67-92.

Soluble Chemical Oxygen Demand

Total Nitrogen

Total Kjedahl Nitrogen

Nitrate

Nitrite

0

50

100

150

200

250

300

.01 .1 1 5 10 20 30 50 70 80 90 95 99 99.9 99.99



Total Suspended Solids

LESA columns influent COD concentrations: 600 - 1200 mg/LHDPE columns influent COD concentrations: 225 - 450 mg/L

LESA columns influent TKN concentrations: 130 mg/LHDPE columns influent TKN concentrations: 50 mg/L

DRP = Depth of root penetration

DRP

DRP

CATION EXCHANGE CAPACITY RULES TREATMENT IN FLOOD AND DRAIN WASTEWATER TREATMENT WETLANDS

FISH probe from columns. Work in progress.

background flood and drain treatment wetlands are efficient means to treat cod, tss, and total...

Documents