Study On The Influence Of Sediment In Stormwater Inlet On Odor Gas Generation In A Northern City

Urban stormwater outfall is an indispensable accessory structure in the road drainage system.Due to its structural characteristics and inconvenient operation and maintenance,there is a common phenomenon of malodor pollution,which poses a potential threat to urban environmental quality and residents’ health.At present,there is a lack of systematic research on the production mechanism,variation rule,influencing factors and control measures of odorous gas in stormwater outfall.In this paper,the regional distribution characteristics,pollution sources and influencing factors of the stormwater odors in a northern city were identified by measuring the odors intensity and the thickness of each component of the contents in the selected area.The regional stormwater inlet was divided into five categories(Class Ⅰ--urban secondary trunk road,Class Ⅱ--urban branch road,class Ⅲ--living service area,class Ⅳ--residential area,class Ⅴ--administrative office area),and the odor intensity,odor gas components and bottom sediment characteristics of stormwater inlet were monitored for a long time,and the variation rule of odor intensity of stormwater inlet and the influence of bottom sediment on the formation of odor were investigated.A small analog reaction device for malodorous rainwater nozzle was built,and the malodorous gas was initially controlled by using two methods of adding reagent and setting up sewage intercepting hanging basket.The main conclusions of this study are as follows:(1)The stench intensity of stormwater mouth was positively correlated with the thickness of contents and sediment,and the stench performance of stormwater mouth was significantly different among different functional areas.The intensity of rain halitosis increased with the increase of content thickness.The contents contained food waste,sediment and litter,and the regional rain water halitosis intensity had the strongest correlation with sediment thickness.The research area includes three functional areas: road,residential area and campus.Among them,62.2%,70.2% and21.7% of the stormwater intakes in each functional area had higher odor intensity in July than in December,and under the same sediment depth,more serious odor pollution would occur in the stormwater intakes.At the same time,the content collection results showed that the halitosis value of rainwater increased with the increase of contents and sediment content in the collection device.(2)The odor intensity of a typical stormwater inlet under long-term monitoring is classified as class Ⅲ > Class Ⅰ > Class Ⅱ > Class Ⅳ > Class Ⅴ.The odor components are complex,and the odor intensity is positively correlated with COD,sulfate and total nitrogen contents in the bottom sediment.Among them,the average odor values of class Ⅰ to Ⅴ rainwater inlet were 81.26,74.39,167.92,45.49 and 45.22,respectively.A total of 31 odor components,including volatile sulfur compounds,alkanes and oxygen-containing organic compounds,were determined,and the contribution of volatile sulfur compounds to odor was the highest.The mean Pearson correlation coefficients between odor intensity and dissolved COD,sulfate and total nitrogen contents were 0.829,0.860 and 0.836,respectively.(3)After rainfall,the odor intensity,COD content,sulfate content and total nitrogen content of five types of typical storm water inlet all increased first and then decreased.The halitosis value of class I to Ⅴ increased by 34.4%,38.3%,20.6%,25%and 30.2%,respectively,and decreased to the original level after 9,10,7,6 and 7 days,respectively.The contents of COD,sulfate and total nitrogen reached the highest value on the first day after rainfall,and then decreased to the original level at different rates respectively.(4)Microbial viability ratio and community composition play an important role in the production of malodorous gases in rainwater vents.There was a positive correlation between the intensity of halitosis and the proportion of live bacteria in 5types of typical rainwater,and the correlation coefficient was between 0.7 and 0.8.The composition of microbial population can indirectly and directly affect the generation of odorous gas.During the cell metabolism of Firmicutes and Bacteroidota,cellulose can be synthesized to improve the anti-scour of sediment.Meanwhile,Bacteroidota and Proteobacteria can promote the secretion of EPS to improve the anti-scour of sediment.Desulfobulbus is causing an increase in sulfur in the environment with an increase in organic pollutants.The sediment at the bottom of the stormwater mouth produces foul-smelling gas under the action of microorganisms.Under anaerobic conditions,the sulfates in the sediments at the bottom of the rain outfall are reduced to hydrogen sulfide by sulfate-reducing bacteria.Organic pollutants such as proteins are degraded to produce volatile sulfur compounds.Other organic compounds are degraded to produce organic acids,alcohols,halogenated hydrocarbons,ammonia and other odor gases.(5)The malodorous gas can be controlled effectively by adding trichloroisocyanuric acid disinfection tablets and setting up fouling hanging baskets.The experiment showed that the slow release effect of trichloroisocyanuric acid disinfection tablets in the sediment was better than that of the upper hanging slow release effect.The odor value of the former increased by 29.4% and that of the latter34.4% after they were mixed into the rainwater.The field test showed that the overall odor intensity of rainwater mouth with sewage interception hanging basket was lower,and the halitosis value of rainwater mouth without sewage interception hanging basket was 16.38 and 9.68 higher than that of rainwater mouth without sewage interception hanging basket on campus.