| Service area is one of the important facilities in the highway. In recent years. The number of highway service area is continuously rising by time. The service area is far away from the municipal sewage system, the need for wastewater treated by onsite system is urgent. Service area sewage contains high concentration of ammonia nitrogen and total phosphorus (TP), concentration often changes with time, weather etc. According to the service area sewage pollution and characteristics of all kinds of sewage treatment system. A new type of tidal flow constructed wetland was chosen to treat the sewage.The tidal flow operation mode could improve reaeration ability and oxygen content of the wetland. Favorable oxygen environment is helpful to degrade organic matter. A reed bed and a calamus bed were employed separately tin the two tidal flow constructed wetlands. The optimal operation mode was determined by comparation study. Under the optimum operating conditions, sewage purification ability, heavy metal removal capacity and methods to improve purification effect of tidal flow constructed wetland were studied to provide a scientific basis for sewage treatment facilities in service area. Through experimental research, the flowing conclusions can be reached:At different reaction time and idle time, the pH、 dissolved oxygen(DO) of influent and effluent varied a lot. And the removal of TP、 ammonia nitrigen、 total nitrogen, chemical oxygen demand(CODcr)、 suspended solid(SS) in reed bed calamus bed constructed wetland was different. When the reaction time was set to 6-24h and idle time was set to 6h or 24h, tidal flow constructed wetland reached the best efficient. Reaction time of 6h and idle time of 6h were used as the appropriate operation condition.Too low or too high concentration of ammonia nitrogen of influent to disturb pollutants removal. When the concentration range of TP varied between 0.96 mg·L-1 and 5.71 mg·L-1,56.00% of TP were removed by reed bed constructed wetland and 51.67% by calamus bed constructed wetland. When the concentration of ammonia nitrogen varied between 11.00 mg·L-1 and 65.45 mg·L-1,46.03% of ammonia nitrogen was removed by reed bed constructed wetland and 48.44% by calamus bed constructed wetland. The tidal flow reed bed constructed wetland exhibited the higher removal on TP than that of calamus bed tidal flow constructed wetland. And calamus bed tidal flow constructed wetland could remove more ammonia nitrogen than reed bed wetland. The variation of influent concentration can affect removal efficient of CODcr to a certain extent, but both wetland systems reached more than 80% of removal rate.The removal rate of SS and TP in runoff waste water both reached about 90% and 50% in two wetland systems. The removal rate of ammonia nitrogen was about 40%-50% and the removal rate of CODcr maintaining in the range of 80%-90%, but nitrate nitrogen and nitrite nitrogen were slightly accumulated in wetland system. When the average concentration of total Zn in influent was 1.098 mg·L-1,52.74% of dissolved Zn and 62.65% of total Zn were removed by reed bed wetland, and 47.60% of dissolved Zn and 59.15% of total Zn were removed by calamus bed wetland. The wetland showed a better elimination capacity on the total Zn than dissolved Zn. The tidal flow reed bed constructed wetland exhibited the higher removal on pollutant and Zn than that of calamus bed tidal flow constructed wetland.Two stage flow constructed wetlands reached higher (P<0.01) removal rate of various pollutants than the reed bed or calamus bed wetland works alone. The concentration of ammonia nitrogen in effluent reached the reuse standard of city sewage (GB/T18920-2002).The concentration of CODcr reached the quality standard of miscellaneous domestic water (CJ/T48-1999).The concentration of pollutants in all levels of wetland series decreased in a stair-step. And treatment ability of the second stage wetland bed was weaker than the first stage. The reed bed-calamus bed series exhibited the higher removal on TP, ammonia nitrogen and total nitrogen than the calamus bed-reed bed series.Reed rhizosphere urease activity was higher than calamus. It explained the fact that reed bed wetland had better elimination capacity on nitrogen than calamus bed wetland. Heavy metal Zn had certain inhibitory effect on reed rhizosphere urease activity; but little influence on calamus. Phosphatase activity can be greatly influenced by heavy metal Zn, and Zn showed certain stimulative effect on reed and inhibitory effect in calamus. |
PDF Full Text Request