Using Compact Combined Constructed Wetland as Post Treatment for Biogas Wastewater Somanat Somprasert The Joint Graduate School of Energy and Environment King Mongkut s University of Technology Thonburi Assoc. Prof. Dr. Suwasa Kantawanichkul Department of Environmental EngineeringChiang Mai University
Biogas System in Pig Farm
Pig Farm Problems Pig manure Wastewater Noxious Odors Mosquito and other insects
Benefit of the Biogas system Advantage Wastewater treatment Biogas Energy Fertilizer from sludge Disadvantage! Can not remove Nitrogen and Phosphorus COD still higher than the pig farm wastewater standard of Thailand ( <400 mg COD L -1 )
Combined Constructed Wetland Constructed wetland Engineered systems designed and constructed to utilize the natural processes Combined constructed wetland Horizontal flow bed Vertical flow bed Design for nutrient removal
Horizontal Flow Bed Vertical Flow Bed
Compact Combined Constructed Wetland Vertical flow vegetated bed laid over horizontal flow sand bed Small area required
Methodology
Reactor Four concrete tanks, 0.5x1.0 1.0x1.0 m 3 Each tank was separated into two parts by a plastic PVC sheet Umbrella sedge 0.25 m interval 16 plants per square meter
Cyperus flabelliformis Rottb. Vertical flow Sampling point Sampling points Gravel Sand Stand pipe Wastewater storage tank with mixer Effluent storage bucket Horizontal flow Sand Effluent storage bucket Effluent to municipal sewer Sampling point 0.125m 0.75m 0.125m
Recirculation ratio 1:1 Intermittent feeding ( 4 hrs on 4 hrs off) Hydraulic Loading Rates, HLRs 4, 6, 8, 10, 12, 16 and 20 cm d -1 Hydraulic retention times Vertical flow bed 1 to 25 hours Horizontal flow bed 11-86 hours
H-V H Effluent V Effluent
Wastewater Pig farm wastewater : effluent from anaerobic channel digester followed by UASB COD : 870 to 1,070 mg L -1 TN : 450 to 560 mg L -1 Nitrogen loading rate* 102 to 456 kgn ha -1 d -1 COD loading rate* 214 to 856 kgcod ha -1 d -1 * based on raw wastewater concentration
HLR 4 cm d - 1 and 16 cm d -1 November to March (winter) HLR 8 cm d - 1 and 12 cm d -1 April to June (summer) HLR 6 cm d - 1 and 10 cm d -1 April to August (summer and rainy season) Temperature : 21 to 32 C
At the beginning of the experiment
Removal Efficiency Nitrogen removal COD removal
Nitrogen removal Nitrogen removal rates was 323 kgn ha -1 d - 1 High nitrogen removal rate compare to the experiments in Taiwan (14-30 kg ha -1 d -1 ) Nitrogen removal efficiency were in the range of 52-83% Decrease when HLR increase
Nitrogen removal TN Removal efficiency (%) 100 90 80 70 60 50 40 30 20 10 0 4 6 8 10 12 16 20 HLR, cm/d All Horizontal flow bed Vertical flow bed
Nitrogen removal TKN Removal efficiency (%) 100 90 80 70 60 50 40 30 20 10 0 4 6 8 10 12 16 20 HLR, cm /d All Horizontal flow bed Vertical flow bed
Nitrogen removal Horizontal flow bed o Remove nitrogen in form of oxidized nitrogen o o NO 2,3 -N Denitrification o Denitrifier bacteria o 2.3 x 10 3 to 5.7 x 10 4 MPN
Nitrogen removal Vertical flow bed o Remove nitrogen in form of NH 3 -N N and organic N o Nitrification o Nitrifier bacteria 1.2 x 10 4 to 5.6 x 10 5 MPN o Plant uptake
Nitrogen removal Most of nitrogen was loss by volatilization, Accumulated in microbial cell and adsorb in sand and/or by Anammox process Nitrogen uptake by plant was in the range of 1-14% 1 14% highest at HLR 4 cm d -1
COD removal COD:BOD 5 COD removal rates 179 to 735 kgcod ha -1 d -1 COD removal efficiencies 79 to 97%
COD removal Removal efficiency, % 100 90 80 70 60 50 40 30 20 10 0 4 6 8 10 12 16 20 HLR, cm/d All Horizontal flow bed Vertical flow bed
COD removal Similar COD removal efficiency in all hydraulic loading rates HLR 6 cm d -1 shows the highest COD removal efficiency Achieve the national effluent standard of COD for medium scale pig farm
COD removal Horizontal flow bed Denitrification occurred Large amount of denitrifier bacteria 2.7 10 4 MPN Most COD was used in denitrification reaction Filtration Half of the influent COD was in the suspended form At HLR 8 cm d -1 Removal efficiency dropped FCOD closely to total COD
COD removal Vertical flow bed Input COD was already utilized in the denitrification process Left only COD in the difficult to degrade form Low COD removal efficiency in vertical flow bed
Dry season Plants
Wet season Plants
Plants Above ground : approximately 100 200 cm (after 3 months) Below ground approximately 15-50 cm (after 3 months)
Plants
Conclusion High removal efficiency for COD and nitrogen The COD and nitrogen effluent achieve the national standard except in the high flow rate For COD < 400 mg L -1 For TKN < 200 mg L -1 Suitable to use as secondary treatment for
Acknowledgement Thailand Research Fund (RGJ. Program) The Joint Graduate School of Energy and Environment, King Mongkut s University of Technology Thonburi (JGSEE) Department of Environmental Engineering, Chiang Mai University CP Chomthong farm