Technical Research On Efficient DWTP Residues Treatment And Project Demonstration

Conventional drinking water treatment plant(DWTP) residues treatment process which comprised of thickening,conditioning,and dewatering was always suffered by problems such as inordinate land occupation,large quantities of structures,complexity of construction,and so on.As a further development technology based on conventional clarifier,pellet flocculation blanket process(PFB) had been widely used in kinds of high turbidity suspensions solid/liquid separation successfully.Compared with conventional clarifier process,when applying in DWTP residues treatment,PFB possessed advantages such as high treatment efficiency,better performance of sludge thickening,smaller area of land occupation,convenient management,and so on.In this paper,the application of PFB was investigated in ferric sludge conditioning process in Yangliuqing water plant.Optimal selection of pre-treatment mixing reactor of PFB,optimization of operating conditions and operating condition analysis of demonstration projects were studied.Experimental results showed that:The experimental results of the optimal selection of PFB pre-mixing technology showed that,when applying static mixer or tubular coagulator as pre-coagulaiton process,the treatment effect was better than other choices.When tubular coagulator was used as pre-coagulator,effluent turbidity could be less than 5 NTU,with an average velocity of deposition of particles of 15.34 mm/s,a maximal upflow rate of 68.4 cm/min,and the corresponding results of static mixer was:average effluent turbidity of 6.77NTU,terminal settling velocity of 13.13 mm/s,and maximal upflow rate of 63.6 cm/min.Considering cost of construction and convenient of fixing,static mixer was selected as pre-coagulator on both pilot-scale and full scale experiments in this investigation.It was necessary to dose polymer(PAM in this study) and make appropriate mechanical agitating for PFB process used in DWTP residues treatment.Under experimental condition of 1.2 mg/L PAM dosage,6 rpm agitating strength,and 31.85 cm/min upflow rate,pilot experimental effluent turbidity and sludge moisture content could be less than 10NTU and below 96%respectively with inlet SS of 216.5-563.5 mg/L.Moreover,under the pilot scale experiment,the variation of up-flow rate and agitating strength appeared no obvious effect on thicken sludge concentration.The full scale experimental results indicated that,by applying PFB process,under experimental condition of PAM dosage of 1.22 mg/L,agitating rotation velocity of 6 rpm,effluent turbidity,sludge moisture content and maximal upflow rate could be less than 10NTU,below 96%and 66.4 cm/min respectively with inlet SS ranged between 108 mg/L and 195 mg/L.When PAM dosage was 1.4 mg/L,the system run much higher than optimal dosage,outlet AM residues was lower than 0.02×10-3 mg/L, much lower than 0.5×10-3 mg/L's upper limit required in National Standards for Drinking Water Quality(GB5749-2006),with the AM clearance higher than 99.5%. Stable monitoring results showed that,treatment effects in spring and winter were a little better than that in autumn and summer with effluent turbidity between 8 NTU and 15 NTU,and sludge moisture content below 96%.