| Using reclaimed water irrigation can extend its application scopes, and is one of measures of urban waster water resource recovery. From adopting hydroponics indoor, soil column simulated, location in field and other methods, the effect of reclaimed water irrigation on ecosystem of greenbelt plants—soil—soil microorganism in Shenzhen and groundwater quality were studied; and the same time, the public health risk of harmful chemical substance and pathogenic microorganism number in reclaimed water quality were evaluated from using the Four-step Evaluation Method proposed by USA National Academy of Sciences (NAS), in order to provide scientific basis for reclaimed water irrigation greenbelt in Shenzhen, conclusions obtained as following:It was feasible to irrigate greenbelt by reclaimed water, and it was harmless for greenbelt ecosystem and public health risk. The reasonable reclaimed water irrigation enhanced growth of plants, increased soil nutritional components, caused non-pollution to groundwater quality, and potential risk of harmful chemical substance and pathogenic microorganism number in reclaimed water quality to public health were within risk threshold value, it was safe and could be widely extension and application.(1) The effect of reclaimed water irrigation on greenbelt plants had positive and negative aspects. Short-term reclaimed water irrigation enhanced greenbelt plants growth; Long-term single reclaimed water irrigation alleviated plant roots growth, decreased root vigour and restricted plant growth; the effect of reclaimed water and clear water irrigation to resistance physiological indexes had fluctuation change, had no obvious difference. To analyze leaf of plant irrigated by reclaimed water also showed that nutritional component in leaf increased obvious; toxicity ion and heavy metal content had a increasing trend, but the total content was relative minimal, and had non-pollution for greenbelt plant irrigated by reclaimed water.(2) Once reclaimed water irrigated greenbelt soil, its pH value decreased, organic matter contents increased, soil porosity enlarged, bulk density and field moisture capacity reduced; the distribution of nutritional components toxicity ion content and heavy metal accumulation were different among soil layers, and had significant difference;Being uptaked and utilized by plant root, there were more distributed on 20-40cm soil layer. salt ions in reclaimed water were accumulated in soil, it's harmless for plant growth under short-term irrigation or reclaimed water and clear water irrigation by turns; But it could cause soil salinization once irrigated greenbelt in long-term and single reclaimed water, so as to damage plant growth by its stress.(3) Reclaimed water irrigation could also cause soil microorganism multiply and growth. quantity of soil bacteria, fungi and actinomycetes have obvious seasonal variation pattern, comparing with clear water irrigation, the number had a increasing trend, and related with different plant species; among them, soil bacteria predominate in the population, the number was most on 20-40cm soil layer, less on other layers and had no significant difference.(4) There was certain effect on groundwater quality using reclaimed water irrigation, it had non-pollution to groundwater quality. Being irrigated soil column by reclaimed water, the quality indexes values of penetration liquid were obviously increased, and had significant difference between clear water irrigation (CK), but the indexes were all withinⅣclass water of Quality Standard for Ground Water(GB/T 1484-93).(5) From citing the method of constructing regression Logistic equation based on the relationship between the relative electric conductivity (REC) in the leaf and concentration (value), then the median-lethal concentration(LT50)was determined, so as to determine the upper threshold value, which was tested it equated the results and could be citied on study adversity conditions of plant endured; from it could gain the 5 optimal quality indicators of reclaimed water were Chloride<531.48mg·L-1, Residual Chlorine<2.59mg·L-1, Total Salt<1605.5mg·L-1, Suspensions<141.63mg·L-1, pH value between 5.29 and 10.28 respectively.(6) Using the Method of Four Step risk Assessment proposed by NAS, the harmful chemical substance and pathogenic microorganism number in reclaimed water to public health risk was evaluated and results showed that the health risk P of the chemical carcinogens, the chemical non-carcinogens were 10-6/a, 10-7/a number level respectively, which were less than the risk upper threshold value 10-5/a, 10-6/a number level respectively established by international authority institute; the health risk P of the pathogenic microorganism were 10-6 number level, which were less than the risk upper threshold value were 10-4 number level. Accordingly, reclaimed water used in greenbelt irrigation was safe and feasible, and would be harmless for public health.
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