Study On The Environmental And Ecological Impacts Of Constructed Wetlands Treatment Of Oil-field Wastewater

Since 1950s, wetlands have been used for water purification in different parts of the world, as an additional way for traditional sewer systems. Later researches lead to building constructed wetlands, kind of systems easier for optimizing than natural wetlands. Now constructed wetlands for treating wastewater include three types:Surface Flow Constructed Wetlands (SFCW), Subsurface Flow Constructed Wetlands (SSFCW), and Vertical Flow Constructed Wetlands (VFCW).Compared to other types of wastewater, oil-field wastewater is special for its high oil content, high suspended solid content, high salt content, bacteria content. Wastewater in some oil fields also contains surfactant.Using surface flow constructed wetlands to treat oil-field wastewater, compared to traditional biochemical wastewater-treating technologies, calls for lower investment and running cost, gets better treatment effect. Furthermore, it’s better for ecological restoration and constructing ecological landscape. On the other hand, the SFCW needs large constructed areas. Oil fields have vast ground with few settled population, and these areas are unused due to oil extraction. Besides, some oil fields already have natural wetlands around. These are supports for developing constructed wetlands in oil fields.Recent researches focused on treatment process or purification effect, barely mentioned about the environmental and ecological impacts of the constructed wetlands.A constructed wetland in Gudong Oil Field was taken for an example. its oil-field wastewater purification effect and ecological impacts was evaluated. This research provided a reference for building the standards of wetlands maintaining, provided a basis for water circulation using and the goal of zero releasing oil-field wastewater. The natural wetlands near the research spot were sampled as control group.Through field survey, we took water, bottom sediment and reeds samples for analysis. Meanwhile, conducted sample statistics for plant community. Conclusions are as follows.1. The Surface Flow Constructed Wetland ecosystem had less richness recently. Control group had more species than the SFCW, explained by the SFCW’s short constructed time. The introduced reeds had begun to rejuvenation, while other species were absent. In several years, there would be more species in the SFCW.2. The SFCW had better plant diversity than control group. Both Shannon-Weiner index and Simpson index analyses had proved SFCW higher than control group. Though with less species numbers, the community heterogeneity was higher than control group. The SFCW progress’s function of improving community structure in research area was verified.3. Contrastive analysis of reeds revealed that reeds on the SFCW had better growth and physiological indexes than control group. Cover degree, branch diameter, chlorophyll content and other indexes were all observed to be significant higher than control group.4. The SFCW ecosystem had better function than control group around. The biomass of the SFCW was significant higher than control group. The average fresh weight of over ground part of the SFCW was 1.61kg/m2, while the control group was 0.95 kg/mzGenerally, the SFCW in research area had higher ecological quality, more remarkable benefit than natural wetlands as control group, and already had played an important role.