Diffusion Control Of Harmful Gas Evaporation In Temporary Storage Facility Of Drainage System Experimental Research

In recent years,many areas in most cities have been affected by malodorous gases,which has brought about extremely poor physical and mental experiences for people’s daily life and work.Therefore,the control of the generation and diffusion of urban malodorous gas has been a hot research direction in recent years.A large part of the generation of urban malodorous gas comes from the temporary storage facilities of sewage and wastewater in the drainage system.Specific sewage and waste water temporary storage facilities include septic pits,sewage pits in open-air toilets and attached toilets for urban underground rail transit,sewage tanks for pressure-flow drainage pipe lift pump stations,and temporary storage tanks for various purposes.This is because the municipal sewage will stay in the sewage temporary storage facilities for a period of time before flowing into the drainage pipes.The microbial catabolism in the sewage temporary storage facility produces a variety of toxic and harmful odorous gases,such as hydrogen sulfide（H₂S）,methane（CH₄）,and carbon monoxide（CO）.These gases not only bring a foul smell to the environment,but also bring potential safety issues,which may cause poisoning or explosion.The odor solution is limited due to the relatively large number of small temporary storage facilities in the city,and the measures to control the generation and release of H₂S are costly or do not have the treatment conditions.Therefore,this paper proposes a new solution:cover a thin layer on the surface of the sewage,which is called a masking agent,to increase the mass transfer resistance of the dissolved H₂S into the atmosphere.Use the saturated solubility of H₂S in water to make it as soluble as possible,And thus unable to enter the gas phase.The specific research is to determine the appropriate gas masking agent and related application parameters,and to explore the effect of water flow conditions on the application of the masking agent and determine the impact velocity of the masking agent,and to study the effect of the masking agent on endogenous H₂S and exogenous Water quality impact of H₂S temporary storage facilities and differences in microbial community structure.Related research results show:（1）The masking agent based on translucent liquid silica gel（LSR）and polystyrene foam pellets（EPS）and its application parameters were determined.The masking agent can increase the gas-liquid mass transfer resistance,has a good effect on blocking the release of H2S,and can control the harmful effects of the malodorous gas in the temporary storage facility.The mass ratio of LSR and EPS in the masking agent should be 15～40,which can satisfy better stability and fluidity.Under this ratio,the use of masking agent is better.The tile thickness of the masking agent should be between 0.1 and 0.5 cm.（2）The specific influence of the flow characteristics on the masking agent was explored and the impact resistance flow rate was determined.Both horizontal and bottom water inlet methods will affect the use of the masking agent,but under the same water inlet width,water depth and water flow rate,the bottom water inlet will have less impact on the masking agent than the horizontal The effect of influent water on the masking agent.When the inlet water is horizontal,the maximum velocity gradient at the water surface that the masking agent can withstand is 0.07 m/s.When it is bottom inlet,the vertical velocity gradient of the masking agent can withstand 0.02 m/s.（3）The relationship between the effect of the masking agent on the lower sewage water quality and the sewage residence time,the ratio of the inflow and outflow of sewage to the total water body in the pond,and the differences in the number of microorganisms in the pond were explored.When the sewage stays for a long time,the high concentration of hydrogen sulfide in the lower part of the masking agent will gradually increase over time.When the ratio of sewage inflow and outflow to the total water body in the pool is larger,the concentration of dissolved hydrogen sulfide in the pool will be reduced and suppressed.When the ratio of sewage inflow and outflow to the total water body in the pool is small,the concentration of dissolved hydrogen sulfide in the pool will increase.When the area where the microorganisms can be attached is larger,the number of microorganisms will be larger,and the dissolved high-concentration hydrogen sulfide in the lower part of the masking agent will also increase.The larger the water retention time is,the faster the sulfate and dissolved COD content will decrease than the small retention time,while the dissolved H₂S content will be greater than the small retention time.（4）The effect of the masking agent on the temporary storage facilities of endogenous H₂S pollution with sediment and no exogenous H₂S pollution with little or no sediment.The H₂S in the temporary storage facilities with sediments mainly originates from the production of SRB in the sediments.In the temporary storage facilities without sediments or very few sediments,the internal H₂S is mostly H₂S gas entrained from the upstream water flow.For endogenous H₂S,the H₂S concentration in the lower part of the masking agent will increase as the hydraulic retention time of the temporary storage facility increases and the flow of incoming and outgoing water decreases.For exogenous H₂S,the larger the inflow and outflow of the temporary storage facility,the faster the flow velocity,and the lower the H₂S concentration in the masking agent.（5）The anaerobic degree of water samples with masking agent group was higher than that without masking agent group.After adding the masking agent,the water sample in the lower part of the masking agent has better air tightness and higher anaerobic degree,and the anaerobic bacteria have become the dominant bacteria,such as sulfate bacterium and vibrio sulfate.The number of anaerobic bacteria was much higher than that without the masking agent group,which constituted a significant difference.Adding a masking agent group will have a part of the unique bacterial genus than the non-masking agent group.There was no significant difference in the microbial diversity between the masking agent group and the non-masking agent group,but the composition of the anaerobic bacteria group with the masking agent group was higher than that without the masking agent group.