With the fast development of national economy and the enhancing of people's living standard in China,the irrigation water for farmland is continual occupied by industrial and urban water consumption,causing water shortage for agriculture severity day by day; Meanwhile, with aggravation of the amounts of industrial and domestic sewage,causing the water quality of each large water area throughout the country polluted,agriculture has been badly challenged by water short due to water quality. Therefore,we have to use large amount of sewage to irrigate farmland in agriculrure,and it can be forecast that the areas of sewage irrigation are increasing no reducing for a long time.Although sewage irrigation can offer water and nutrient resources,in China,because of the low handling capacity for sewage the large disposal cost of sewage and the weak awareness of environmental protection for people,which irrigated farmland with large amount of no handling or lacking necessary pre-processing sewage,the water quality exceeds standards seriously.Blind sewage irrigation has caused the accumulation of poisonous and harmful substance in some regional soils and water sources,and environment has also been polluted in varying degrees,so that it has threated people health seriously in some region.Based on plentiful literature reviews, the author reviews the current situation of sewage irrigation and its risk analysis,and points to remaining problems in current risk analysis of sewage irrigation;carrying risk identification on sewage irrigation causing diverse risks by using AHP,then in accordance with the weight of risks,selecting and ranking them, ascertaining that the research objects are soil-crop, surface water, people health and ground water; pointing out evaluation indicators of soil-crop, surface water, people health and ground water ,which show the degree of sewage irrigation pollution,and then presenting the calculation method for degree of sewage irrigation total risk by generalling evaluation indicators of diverse risks;researching on the probability distribution of sewage irrigation risks,with non-parameters inspection,and getting the distribution function and characteristics of sewage irrigation risks.Based on the theory research,this paper makes risk analysis of sewage irrigation in some sewage irrigation area, region of Nan Jing city,using the practical data of the place. Based on above works,the paper researches further on degree of acceptable risk for contamination in irrigation area, the age of safety for sewage irrigation and utilizes the predicting of water quality based on fuzzy Markov chain model with weights to forecast the surface comprehensive water quality.Finally, this paper puts forward five countermeasures and suggestions about the problems of that sewage irrigation may cause some environmental risks. |