| The amount of biological waste sludge increased significantly with the increasing wastewater treatment rate. The cost of treatment and disposal of waste sludge is estimated to be40%～60%of the total costs of wastewater treatment. Therefore, it is of great beneficial to minimize waste sludge production. Recently, sludge reduction by Tubificidae has been proved to be an effective, economical and sustainable technology.In the sludge reduction system with Tubificidae, the content of pollutants would largely affect the growth and development of Tubificidae, thus influencing their performance of sludge reduction. However, to date, little information is available about the effects of pollutant stress on the predation process of Tubificidae and the subsequent release processes of pollutants, as well as the relevant mechanisms. In this thesis, the effect of pollutant stress on sludge reduction by Tubificidae was studied, the performance of pollutant uptake and release by Tubificidae was investigated, and the mechanism was researched. The main results are summarized as follows:1. The effects of chromium (Cr) on the respiration rate of Tubificidae were studied experimentally. The results indicated that the maximum respiration rate of Tubificidae is81.72mg·g-1·h-1·L-1when temperature, pH, and DO is22℃,8.0and3.5-4.5mg·L-1respectively. Low concentration of Cr (VI)(e.g.,0.325mg·L-1) could increase the respiration rate up to158.38mg·g-1·h-1·L-1. On the contrary, high level of Cr (VI)(e.g.,0.650mg·L-1) could inhibit the respiration rate down to43.70mg·g-1·h-1·L-1mg·g-1-h·1·L-1.2. The toxicity of Cr to Tubificidae was tested. The results showed that the safe concentration (SC) for Tubificidae was0.325mg·L-1, and the corresponding superoxide dismutase (SOD) activity was4.49U·mg-1, compared to the SOD activity of2.37U·mg-1in the Cr control test. The SOD activity declined as Cr (Ⅵ) level increased, but it was enhanced until Cr(VI) concentration reached2.56mg L-1. After Cr(VI) concentration was higher than3.40mg L-1, the SOD activity was inhibited with its lowest value at Cr(VI) concentration of37.64mg L-’. At SC level, Cr(Ⅵ) could improve the predation performance of Tubificidae, and achieve a sludge reduction rate of48%, which was4.7%higher than that of control.3. The Cr bioaccumulation by Tubificidae was determined. The results suggested that the Cr concentration in Tubbificidae initially increased and then decreased in a28-day experiment. The maximum Cr content (59.08μg g-1dw) was obtained on day15, and it decreased to31.09μg g-1dw on day28. The fitting results indicated that the two-compartment kinetic model was applicable to simulate the accumulation and elimination of Cr by Tubificidae. The accumulation rate constant K1and the elimination rate constant K2for Cr was10.849and0.196, respectively. The bioconcentration factor was55.35, and the bioaccumulation factor was0.97and0.68on day15and day28, respectively.4. The release of organic pollutants by Tubificidae was investigated. The release rate constant for TOC, TN and TP was3.671,23.683and9.023d-1, respectively, which were determined through dynamic measurements and kinetic fitting. The obtained specific release rate for TOC, TN and TP was0.2114mg·g-1·d-1,0.115mg·g-1·d-1and0.0045mg·g-1·d-1, respectively.5. The operational conditions of full-scale symbiotic system consisting of Tubifix and Microbes were optimized. The results showed that the excessive sludge production rate was reduced from0.21kg·kg-1COD to0.051kg·kg-1COD and sludge settleability was significantly improved in the optimized symbiotic system. The COD removal efficiency increased by8.7%with the reduction of SS concentration in effluent. Tubificidae could cause the increase of NH4+-N concentration in the system, and the problem was resolved by a operation optimization. PO4--P concentration in effluent was kept at0.5mg·L-1with a removal efficiency as high as95%. The model evaluation results showed that the dynamic simulation of the FCASM3and the transmission model for symbiotic system well described the nutrient removal processes in UNITANK. The optimum operating conditions were suggested for the UNITANK process at a WWTP in Zhejiang obtained by modeling analyzation:the oxygen transfer rate50d-1, the solid retention time5d and the influent flow of7500m3/d. |
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