| Summary: | 碩士 === 長榮大學 === 職業安全與衛生學系碩士班 === 94 === A research of waste treatment efficiency promotion in a water treatment plant during high turbidity influent.
Our analysis of batch wastewater treatment revealed that the turbidity of backwash wastewater and SS went down below 50 NTU, 13 minutes after backwashing. And the result of the sedimentation test for backwash wastewater showed that SS removal percentage reach as high as 80 % for only 15 minute operating time when we added PAC into the backwashing water. The operating time for the test without addition of PAC to reach the same effect is around 30-40 minutes. The difference in operating time shows that the PAC addition can improve the settling velocity.
Furthermore, the sludge concentration test and precipitation test revealed that 1000 mg sludge bulk could be concentrated into 700 ml, after the cationic polymer was put into the sedimentation tank when the set time was at 1,440. That bulk was further reduced into about 500 ml after jar test. It was observed that the dose of 15 mg/l had the best effect, reducing the sludge into 510ml at 280 minute. It is observed that if we apply cationic polymer at some points before dosing treatment, we can highly improve the concentrating effect on sludge, reduce the size of the sludge.
During high- turbidity influent, the filter run time can be shortened from regularly 60-80 hours to 36 hours or even fewer. The backwash wastewater volume increases with the backwashing frequency. For this, it is expedient to lower the SS density of supernatant. For example, the backwash wastewater in the early stage can be disposed in the wastewater tank and the backwash wastewater in the late stage can either be discharged directly or recycled on the purpose of decreasing the effluent rate. Another example is use PAC addition, by doing which the settling velocity of SS in wastewater is enhanced and the density of the discharged and recycled water decreases.
Taking the economy into consideration, water treatment plant can use 4 times the turbidity rate of annual average or 95% cumulative probability of annual turbidity as design basis. Together with appropriate design criteria, the design for waste water disposal can count up the minimal size as waste treatment unit. During high turbidity influent, we can put coagulant into wastewater tank. The data of this research pointed out that it is economic to design a sedimentation tank on basis of 95 % cumulative probability of annual turbidity on 650NTU and improve waste-treating capability by dosing cationic polymer to the sedimentation tank.
We analyzed the solids in the river by the waste treatment plant during the torrential rain. We found that turbidity of raw water is 2,110 mg/L and that of the effluent water is 2,111 mg/L. This finding showed that the effluent water from the waste treatment plant had little effect on density of SS in raw water. This finding showed that the waste in bypassing water, discharged from the waste treatment facility, had little effect on density of SS in raw water.
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