| China has entered the peak period of highway construction. Highways are generally laid among multi cities, with long mileage, thus management facilities are needed at regular intervals, including toll stations, maintenance work area, tunnels control centers and service areas etc. Because the amount of sewage of these facilities is not huge, the sewage usually is treated by septic tank before discharge, thus water quality generally does not meet the compliance. So post-treatment of the discharge will be the focus of this paper. In this paper, feasibility of artificial marsh for discharge treatment will be analyzed.Upon artificial marsh for discharge treatment the following experiment were conducted: Temperature changes on wetland purification effect; hydraulic retention time on the purification effect; comparison of the effect of different plants on the nitrogen removal; the relationship between microbe growth and the removal of pollutants; relationship of the amount of microbe and efficiency of pollutant removal;N, P concentration change through the soil layer; the N, P element accumulation in the artificial marsh. The derived results and conclusions are as follows:1.temperature had a noticeable impact on total nitrogen removal, when the temperature was between 20～28℃, removal rate had no significant change, CODcr removal rate was about 70%; Effluent total nitrogen was better in summer than in winter; removal of the phosphorus was due largely to substrate adsorption, temperature affected the removal of Phosphate accumulating bacteria, so temperature affected phosphorus removal.2. Analysis of removal rate of a variety of pollutants under different hydraulic retention time demonstrated that increased residence time led to increased removal rate, but the best HRT CODcr was 5d, when the residence time exceeding the best time, CODcr removal rate started to decline. Best HRT of Ammonia was 6d; removal rate would drop when extended to 7d, because the residence time was too long, the system was in severe hypoxia, which inhibited the nitrification effect, resulting in decreased removal efficiency. Best HRT of Phosphorus was 7d.3. The vertical flow constructed wetland system on pollutant removal rate higher than the level flow constructed wetland system.4.On the results of different plants, reeds had better nitrogen removal efficiency than cattail. 5.Analysis of microbe concentration on the reed wetland system revealed that the 10～20cm layer contained the most and this level was the main reaction layer in wetland system, the amount of micro-organisms proved the removal rate advantage of reed wetlands over other types of wetland system.6.Sample points from 1 to 4 revealed decreasing N, P concentration in the water, which indicated that N, P may enter the soil or plants, may also be decomposed by micro-organisms. Compared non-plant system to plant system the P removal rate did not decrease so significantly as N did, which led to the conclusion that plants and microbes contributed little to the removal of phosphorus, that in wetlands P removal was mainly due to substrate adsorption.7. The N, P concentration in reeds, cattails wetlands and non-planting wetland reached 95.2～193.7 mg/l and 7.6～10.73mg/l in soil substrate respectively, and increased depth of soil profile had decreased nutrient concentration. Reeds and cattails wetlands differed on concentration of different nutrients, possibly due to different intake amount of different nutrients. in the vicinity of plant roots N, P concentration were the highest compared to other places, this may caused by the nutrients from plant litter, which led to decreasing nutrient concentration with increasing soil depth.
|
PDF Full Text Request