Research On The Mode Of Runoff Quality-dependent Diverter Based On Photoelectric Technology

Nowadays,runoff pollution has became the main pollutant source of urban river system and the primary mission of storm water management.The traditional rainwater diverter mode based on the theory of "first flush\" is unable to differentiate the contaminated water arnd clean water because of its irrelevance with the rainwater quality.For this purpose,a new rainwater diverter mode based on the photoelectric sensing technology was proposed.We established a relationship between the water quality and its transmissivity with its threshold value determined.The two rainwater diverter modes were applied into the real rainfalls and their effects on runoff pollution abatement were assessed by calculating the intercepted rainwater volumes and pollution loads respectively.A rainwater diverter was designed and developed.It was put into test operations of simulated rainwater,after which the running stability and actual effect on pollution abatement were analyzed.The main conclusions are as follows.(1)There are pollution to some extent in the rainwater from three kinds of underlying surfaces in Yangzhou.Particles smaller than 150 ?m have a large proportion in all the rainwater.The phosphoric pollutant exists mainly in the form of particle,the nitrogenous pollutant mainly in the form of dissolution and organic pollutant exists in both forms.(2)The 650 nm semiconductor laser was chosen to set into the photoelectric detector in the diverter.The Pearson correlation coefficients between the SS,CODcr,TP and TN concentrations and its attenuation rates of transmission light were 0.867,0.872,0.828 and-0.655.The R2 of regression analysis on the above indicators were 0.738,0.734,0.729 and 0.427,with the Kendall consistency coefficient of 0.793.These results indicated a good consistency between the rainwater quality and its transmissivity.The attenuation rate of transmission light of 0.3(30%)was chosen to be the threshold value to distinguish between the contaminated water and clean water,the critical concentrations are as follows:SS=25.mg·L-1,CODcr=10.00mg·L-1 and TP=0.25mg·L-1.(3)The rainwater quality reveals different variation trends in each rainfall due to the complex effect form many factors.In the unimodal rainfall which has a late rain peak,the initial rainwater quality is relatively good and the pollutant concentrations would first rise then go down after a while,which indicates a late flush.If there is a early rain peak in the rainfall,the pollutant concentrations in the initial rainwater would be extremely high and decrease rapidly in the next 20 min,which indicates a typical first flush.In the rainy season,the underlying surface would be relatively clean and the rainwater quality is good from beginning to end.(4)A 0.2236 hm2 actual area was used as a survey region and 7 rainfalls were monitored from the view of water quantity and quality.We used 5 mm rainfall as the traditional rainwater diverter volume and 0.3 attenuation rate of transmission light as the photoelectric rainwater diverter threshold value.The two modes were applied to the actual rainfalls.According to the analysis,we found that the traditional mode would intercept the clean water and discharge the contaminated water while the photoelectric mode could managed to simply intercept the contaminated water on the basis of the transmissivity.The intercepted water volume in photoelectric mode was up to 3.75 times of that in the traditional mode and 0 m3 at a minimum.The SS concentrations in its intercepted rainwater was 2.32,2.87 and 2.54 times of those in the traditional mode.The pollutant concentrations in its discharged rainwater remained at a low level.To sum up,the traditional mode has a poor adaptability to the change of rainwater quantity and quality.It is inappropriate even for the first flush case,not to mention the continuous rainfall and the multimodal rain.In contrast,the photoelectric mode is adaptable to all kinds of rainfall.(5)The rainwater diverter based on the photoelectric sensing technology was designed.A prototype with DN200 inlet and discharging tubes was made and test operations of simulated rain were experimented.The results showed that the Pearson correlation coefficients between the SS,CODcr and TP concentrations and its attenuation rates were 0.936,0.916 and 0.928.The attenuation rates of each door leaf's switchover s ranged from 0.289?0.310(0.290±0.006),which is close to the threshold valve 0.3,The average concentrations of SS,CODcr and TP of each door leaf's switchovers were 24.84mg·L-1 39.89mg·L-1 and 0.249mg·L-1 with their standard deviations of 0.66mg·L-1,1.82mg·L-1 and 0.01 mg·L-1 and variable coefficients of 2.65%,4.66%and 4.55%.The relative errors between these average concentrations and those critical concentrations set early were 0.64%,0.28%and 0.40%.The above shows that the door leaf has a good responsiveness to the pollutant concentrations and there is good consistency between the rainwater quality and its transmissivity.The rainwater diverter based on the photoelectric sensing technology could distinguish between the contaminated rainwater and clean rainwater precisely.