Volume 13 – No.6 – 2004 REPRINT pp. 545 - 549
TREATMENT OF POLLUTED CREEK WATER BY MULTIFUNCTIONAL CONSTRUCTED WETLAND IN CHINA’S SUBTROPICAL REGION Jie Chang - Chunlei Yue - Ying Ge - Yinmei Zhu
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© by PSP Volume 13 – No 6. 2004
Fresenius Environmental Bulletin
TREATMENT OF POLLUTED CREEK WATER BY MULTIFUNCTIONAL CONSTRUCTED WETLAND IN CHINA’S SUBTROPICAL REGION Jie Chang 1, Chunlei Yue 2, Ying Ge 1 and Yinmei Zhu 2
2
1 College of Life Science, Zhejiang University, 310012, Hangzhou, China College of Environment and Resources, Zhejiang University 310029, Hangzhou, China
SUMMARY West Lake is one of the most famous lakes for sightseeing in China. It has been polluted by discharges such as domestic wastewater and agricultural runoff along the upland regions. A medium-scale pilot (MSP) of vertical/ reverse-vertical flow-constructed wetland was established to treat the polluted creek water draining into this lake and to collect data for the construction and operation of a fullscale system in the future. The influent and effluent concentrations of pollutants were monitored for one year and the average removal rates of chemical oxygen demand, biochemical oxygen demand, total nitrogen, ammonia nitrogen and nitrate nitrogen were found to be 40.86%, 47.7%, 48.7%, 93% and -33.05%. Although removal rate of nitrate nitrogen was negative, its concentration in the influent remained at a low level. From the monitoring results it was seen that this constructed wetland could be appropriate for improving the quality of the polluted creek water. In addition, the constructed wetland planted with Lolium perenne and Coix lacryma-jobi reached a high biomass production bringing great economic benefits.
Constructed wetland (CW) provides a number of mechanisms, such as sedimentation, plant uptake, denitrification, volatilization, chemical adsorption and precipitation, for removing pollutants from the water in its passage through the wetland [1]. These methodologies have the advantages of reliability, cost effectiveness, versatility over conventional engineering means and capability of treating more than one type of pollutants simultaneously. The growing recognition of their attributes has spurred the construction of wetlands for wastewater treatment and CWs have been used successfully for improving the quality of river water [2, 3], storm water [4], oilfield drainage [5], and municipal sewage [6]. But, until now much less is known about using CWs to treat polluted creek water. In this research, a medium-scale pilot of vertical/reverse-vertical flow-constructed wetland was used to treat the polluted creek water draining into West Lake and to collect data needed to evaluate the possible use of a largescaled wetland to improve water quality of this lake. Considering that plants growing in CWs can bring economic benefits, their biomass production was also assessed.
KEY WORDS: Constructed wetland; pollutant removal; water resource reservation; Lolium perenne; Coix lacryma-jobi.
MATERIALS AND METHODS Research site
INTRODUCTION West Lake is a shallow (mean depth 1.5 m), freshwater lake located in Western Hangzhou, China and famous for its scenic beauty, but polluted by discharges such as domestic wastewater and agricultural runoff along the upland regions and, therefore, in the recent years a high nutrient loading has caused heavy eutrophication. There are four main creeks draining their polluted water into this lake and it is of great importance to reduce their external pollutant loading to improve the quality of lake water.
A medium-scale pilot (MSP) CW with vertical/reverse-vertical flow was established near Longhongjian Creek in the western part of West Lake (30 º16’N; 120 º12’E) to purify the creek’s discharge consisting of domestic wastewater, aquiculture effluents and agricultural run-off. The MSP plant was twin-shaped, consisting of two chambers, each having 9×9 m2 surface area. Both chambers shared a drainage layer, which was filled with gravel to a depth of 15 cm and covered with a commonly used geotextile. Each was filled with homogenous sand to a thickness of 55 and 45 cm, respectively, for the vertical
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© by PSP Volume 13 – No 6. 2004
Fresenius Environmental Bulletin
and reverse-vertical flow chambers. Two terrestrial species, Lolium perenne and Coix lacryma-jobi, were planted in the vertical and reverse-vertical flow chambers, respectively. L. perenne is an important forage grass species, and C. lacryma-jobi can be used as papermaking material. The MSP plant was intermittently fed with a hydraulic loading rate of 1000 mm/day.
Water and Wastewater” [7]. When the plants in this wetland entered into senescence, their above-ground biomass was harvested, dried at 80 ºC for at least 48 h and then weighed. RESULTS AND DISCUSSION COD and BOD removal
Sampling and measurements
COD concentration (mg/L) )
7
70
6
60
5
50
4
40
3
30
2
20
1
10
0
Removal rate (%)
COD in the influent varied from 39 to 52 mg/L (Fig. 1) and COD removal rate ranged between 26 and 61%, with a median removal value of 40.86%. BOD concentrations in influent and effluent were averaged as 4.00 and 2.18 mg/L, respectively, resulting in a median removal rate of 47.67% (Fig. 1). The removal rate of BOD varied with the change of the seasons, being higher in summer than in winter (p
