CATION EXCHANGE CAPACITY RULES TREATMENT IN FLOOD AND DRAIN WASTEWATER TREATMENT WETLANDS
BACKGROUND
METHODS
David Austin, M.S., P.E., Certified Ecologist ESA
Flood and drain treatment wetlands are efficient means to treat COD, TSS, and total nitrogen to advanced standards.
1. Apparatus:
Dharma Living Systems
a. Four 12” x 48” fiberglass columns, each with dedicated sump and pump. Columns filled with media. Two columns planted.
Principal treatment mechanisms are:
1) sorption of ammonium cations (NH4
+)
8018 NDCBU, 125 La Posta
in bulk water to media;
b. Flood (45 min) and drain (3 min) cycles controlled by microprocessor.
Taos, New Mexico
NH4+
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
www.dharmalivingsystems.com
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.
NH4+
3. Set-up: Double parallel study with media and plants (Cyperus alternifolius) Vs. no-plants. Plant light provided by 1000 W metal halide lamps.
RESEARCH QUESTION
O2
O2
NO3-
O2
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.
How does the CEC of raw media affect treatment in vertical flow, flood and drain treatment wetlands?
c. Column 3. HDPE
Why does this matter?
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.
Consider theoretical oxygen demand stoichiometry in wetland treatment systems.
a. Note: Mass loading of all columns was the same. Water volumes in LESA and HDPE columns differed due to different porosity.
O2
Dissolved oxygen demand for bulk-water treatment: O2 demand = (COD influent - COD effluent) + 4.6(NO3-)f - 2.86(NO3-)u
b. May-September 2003: 34.2 g/d COD + 3.7 g/d TKN-N
Where:
c. October-December 2003. 17.1 g/d COD + 3.7 g/d TKN-N
COD = chemical oxygen demand, mg/L
2) rapid oxygen saturation of biofilms in the drain phase;
+
3) rapid bacterial nitrification of sorbed NH4 cations;
term eliminated
5. Column preparation:
(NO3)f = nitrate formed, mg/L (nitrification demand)
a Columns seeded with water from mature flood and drain pilot system and nitrifying biosolids.
(NO3)u = nitrate utilized, mg/L (denitrification return)
b. Columns draped in black cloth to prevent sidewall algae formation.
Dissolved oxygen demand in flood and drain wetlands: O2 demand = (COD influent - COD effluent) + 4.6(NO3-)f - 2.86(NO3-)u
-)
4) desorption of nitrate anions (NO3 into bulk water in the next flood cycle;
DRP = Depth of root penetration
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.
Explanation and Consequences:
5) denitrification as nitrate ions serve as terminal election acceptors in bacterial respiration.
a. Dried cheese whey and urea placed in sumps, water manually topped off to preset fill level.
1. Nitrification in drained phase => Negligible nitrification dissolved oxygen demand in bulk water
N2
b. Samples taken from sumps after 24 hours after dosing.
2. Dissolved oxygen demand reduced 20 to 50%, depending on influent COD:TKN
NO3
c. sCOD samples processed in-house by HACH Manganese III method from TSS filtrate.
-
3. Power consumption for total nitrogen removal is approximately 30% of that required in an activated sludge treatment system
d. TSS processed in-house by Standard Methods.
Therefore, for design we must know CEC (NH4+ sorption) in a mature system. Will organic matter CEC make up for low media CEC?
NO3
DRP
Cation exchange capacity (CEC)
-
DRP
c. TKN-N, NO3-N, NO2-N sent to certified contract laboratory for Standard Methods analyses.
If raw media CEC is important, then treatment media design CEC must be specified, otherwise design stoichiometry is defective.
d. Columns sampled over nine month period after maturation.
of media & organic material
HDPE
LESA
Planted columns. Note stunted growth of
shoots & roots in HDPE compared to LESA.
is a fundamental
forcing function
of this ecosystem.
RESULTS:
Frequency distribution of effluent from 24-hours of flood and drain cycles
Total Suspended Solids
300
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.
250
Soluble Chemical Oxygen Demand
Nitrite
70
200
LESA + Plants
HDPE + Plants
HDPE
LESA
60
3. Electrostatically neutral media impair nitrification, especially NO2  NO3.
50
500
LESA + Plants
HDPE + Plants
HDPE
LESA
400
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.
40
150
100
300
50
30
0
200
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.
LESA + Plants
HDPE + Plants
HDPE
LESA
.01
20
.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 Value
100
10
d. Plants in electrostatically neutral media impair second stage nitrification (NO2  NO3) Vs. HDPE alone.
0
0
.01
IMPLICATIONS FOR WETLAND TREATMENT TECHNOLOGY
.1
1
5 10 20 30 50 70 80 90 95
99
99.9 99.99
.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 Value
Percent of Data Less Than or Equal to Indicated Value
LESA columns influent COD concentrations: 600 - 1200 mg/L
HDPE columns influent COD concentrations: 225 - 450 mg/L
Total Nitrogen
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?
Total Kjedahl Nitrogen
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.
Nitrate
LESA + Plants
HDPE + Plants
HDPE
LESA
500
200
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
40
400
100
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.
20
300
0
50
.01
.1
1
5 10 20 30 50 70 80 90 95
99
99.9 99.99
200
Percent of Data Less Than or Equal to Indicated Value
0
100
.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 Value
0
.01
References
80
150
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.
100
60
1. Conduct CEC media comparison for horizontal subsurface flow wetlands. Is media CEC important in constant anaerobic environments?
FISH probe from columns.
Work in progress.
120
LESA + Plants
HDPE + Plants
HDPE
LESA
250
700
SUGGESTED FUTURE RESEARCH
Suggested methods:
140
300
600
2. Investigate microbiological differences in columns / pilots with CEC and non-CEC media. Does CEC structure microbial communities?
LESA + Plants
HDPE + Plants
HDPE
LESA
160
.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 Value
LESA columns influent TKN concentrations: 130 mg/L
HDPE columns influent TKN concentrations: 50 mg/L