Establishing Of Constructed Wetland And Its Treatment Effect On Polluted Irrigation Water From Yellow River

The Yellow river (YR), one of the largest freshwater ecosystems, is the most important water supply in northern China. However, owing to industrial and agricultural development, water pollution becomes increasingly serious, especially in the Baiyin region (BYR). Irrigation with polluted YR water has been common in BYR because, located in a semi-arid region, water supply is extremely limited. This has contributed significantly to the contaminations such as heavy metal (HM) contamination in the soil. The potential risk of consuming crops growing in contaminated soils to human health widely exists in many places due to anthropogenic pollutant emissions. It also changes the construction of the soil and distroys the agricultural ecosystem.The constructed wetland and the sampling plots (A and B) for this study are located in Silong town of BYR. According to the current situation of the research and application during which the CW is used in the disposition of sewage, this study established the surface flow constructed wetland, and select Typha angustifolia as wetland plant, and soil as substrate. The hydrolic retention time (HRT) is 3 days, the hydraulic loading is 0.17 m3/(m2/d). Plot A was irrigated with untreated YR water and plot B with CW treated YR water. The differences between the two kinds of water, the contaminants in the soil and the fertility of soil in the two farms and the physiological condition and accumulation of heavy metals of the crops in the two farms were analyzed respectively. We evaluated the risk of the local people who eat the crops. The results showed:1. After treat the YR water with CW, dissolved oxygen content was significantly increased, total phosphorus, total nitrogen, chemical oxygen demand, biochemical oxygen demand, volatile phenol and four HMs (Copper, Cu; Zinc, Zn; Lead, Pb; Cadmium, Cd) concentrations were significantly decreased. These results showed that CW could effectively reduce the concentrations in the contaminated YR water.2. The concentrations of four HMs in the soil from farm B were significantly decreased compared to farm A in June and July, also the fertility of soil was decreased.3. The soil has been polluted by Cd and Pb in farm A, however, after being irrigated with CW treated water, the HMs pollution and the potential ecological risk in soil has been significantly reduced (P<0.05), which showed that CW could effectively reduce the HMs pollution on agricultural soils.4. The wheat planted in the farm A had a higher bioaccumulation than that in farm B, and the Pb exceeded the safe concentration, while all the concentrations of four HMs in farm B were inside the safe concentration. CW could reduce the HMs content and oxidative damage, and increase the resistance of wheat significantly (P<0.05).5. The Hazard quotient (HQ) of Pb for children and adult males were above 1 in plot A, while HQ of each metal for different groups of people were all below 1 in plot B. Indicating that the consumption of wheat grain from plot A has a potential health risk to children and adult males, while consumption of wheat grain from plot B irrigated with CW pre-treated water is relatively safe.In conclusion, irrigation with contaminated water from the YR led to accumulation of contaminations such as HMs in farmland soil and wheat grain, which can be a potential health risk to the residents. The CW planted with cattail can effectively reduce such risk through reducing the level of contaminations in irrigation water. Therefore, CW can be used as a system to pre-treat irrigation water in upper YR and protect the residents from the potential HMs toxicity.