Application of wastewater land treatment technique to the construction of ecological engineering in sand land

In this paper a studies on the feasibility of harmlessness and resource of wastewater, which was discharged from a thermal power plant, by using slow rate filtration of land treatment technique for the fast recovery of vegetation in the Kubuqi sand land were carried out. The selected arbor, shrub and herbage in the land treatment system were poplar (Populus alba Var. Pyramidalis bunge), seabuckthorn (Hippophae rhamnoides) and sweet clover (Melilotus suaveolens) respectively. Three levels of wastewater hydraulic loading were designed in the field pilot experiment. They were high plot with 3000 mm/a irrigation (H), medium plot with 1500mm/a irrigation (M) and low plot (L) with small volume of irrigation only used in the period of transplant seedlings. The performance indicate that the purification function of power plant wastewater by pre-treatment through combination of precipitation pool with storage ponds is effective and therefore the effluent after pretreatment can be used to irrigation vegetation. The experiment results show that the volume of tree crown for poplar in H plot and M plot was up to 1.07 and 2.21 times comparing with L plot respectively. The annual yield (dry weight) of sweet clover in H plot and M plot was up to 2.33 and 3.0 times comparing with L plot respectively. The height of seabuckthorn in H zone and M plot was up to 1.08 and 1.32 times comparing with L plot respectively. There is direct proportion between growth status of vegetation and hydraulic loading of irrigation. The contents of heavy metals for sweet clover (Cd 0.021 mg/kg、Pb0.001 mg/kg、Cr 0.01mg/kg、As 0.043mg/kg) are much lower than the food standards of grain and vegetables, therefore the sweet clover for raising livestock is safe. Wastewater in this area is valuable source. Its reasonable utilization can contribute important benefits in economy and ecology in the ecological construction and developing effective agriculture and animal husbandry.