Investigation And Analysis Of Odorous Pollution In Urban Rainwater Outlet And Preliminary Study On Odorizing Mechanism

The rainwater outlet widely distributes in the city each place,is the indispensable subsidiary structure in the rainwater pipe network system.Because of the structure characteristics and the inconvenience of operation and maintenance of the rainwater outlet,the malodorous gas emission is widespread,which poses a potential threat to the urban environmental quality and residents physical and mental health.However,there is no systematic research on the current situation of odorous pollution and its mechanism.In this paper,the rainwater outlet in Xi’an city is taken as the research object.Based on the field investigation on the odor intensity,content type,temporary water quality and odorous gas component characteristics of the rainwater outlets in the study area,the regional distribution characteristics and pollution sources of the odorous of the rainwater outlets were investigated;Based on the long-term monitoring of odor intensity and the analysis of runoff water quality,the temporal and spatial variation regularity and influencing factors of the daily and seasonal variation of odorous were determined;By setting up a laboratory-scale simulated fetid rainwater outlet reactor,the variation rule of odorous system and the mechanism of fetor formation under different external conditions were studied,and a preliminary scheme of control was proposed.the main conclusions of the study are as follows:（1）The odorous pollution of the rainwater outlet in the catering districts is more serious than that in other functional areas.The incidence of odorous pollution is more than 90%,and the number of restaurants in the neighborhood is the most correlated index of environmental pollution source.The first two types of the contents of the odorous rainwater outlets in the catering and the commercial districts account for the highest proportion are temporary water,food waste,as well as sediment deposition and conventional household garbage,its proportion in the total contents was 86.8%and 65.6%respectively.（2）There was a significant positive correlation between the degree of temporary water quality pollution and the intensity of odor.And the index with the highest correlation is DO,sulfate,COD.VSCs account for more than 90%of the contribution of odor pollution and are the most important odorous gases to control.（3）The daily and seasonal variation of the odor intensity of the rainwater outlet is obvious,the daytime odorous pollution is more serious than that of the night,and the summer odorous pollution is more serious than that of other seasons.The daily average odor intensity in the rainwater outlets of the catering and commercial districts is 14%higher than that at night.The main reason is that the volatilization and diffusion of the odor are enhanced by the increase of the daytime temperature and sunshine;Due to the influence of high temperature in summer,the intensity of odor in the rainwater outlet is significantly higher than that in other seasons.（4）Short-term rainfall will lead to increase the intensity of odor at the rainwater outlet,while long-term rainfall will weaken the intensity of odorous pollution.After a single precipitation event（15 mm level）,the average increase of the rainwater outlet in catering area and commercial area was 34.02%and 134.8%,and the maximum fluctuation of malodor occurred at day0-1 and hour1-7 after precipitation,the causes include short-term retention of rainwater and supplemental sulfate reduction carried by road runoff.However,long-time high-intensity precipitation will weaken the intensity of odor directly because of low temperature and dilution and scouring.（5）Lower temporary water storage led to more active odorous system at the rainwater outlet.The odor intensity in the simulated reactor was 54.14%higher than that in the control group.The high organic load of COD in the temporary storage water and the large amount of organic nitrogen caused by degradation are the direct causes of the odorous pollution in the rainwater outlet.The reduction of sulfate in temporary water to H₂S is an important way for the formation of odorous pollution and VSCs.The low p H and low DO are the stable signs of the odorous system in the rainwater outlet.（6）Both artificial stormwater runoff and organic natural refuse contribute to the enhancement of odorous pollution.The results showed that the concentration of H₂S and DMDS in odorous gases increased after precipitation.The sulfate carried by rainwater and the DO change of odorous system during precipitation contribute to this result.Due to the promotion of lignin and cellulose on the formation of volatile sulfides,the concentration of VSC increased significantly,and DMDS increased the most.