Full-scale Experimental Research On Pelleting Fluidized Bed For Treatment Of Backwashing Wastewater

The waste water produced by waterworks accounts for about 4%-7%of the total production of net water.The recovery and reutilization of production wastewater can effectively alleviate the current water shortage,especially for some water-short areas in Northwest of china.The common process of treating production wastewater is"concentrating-quenching and tempering-dehydration",but this treatment requires many structures and a large area.PFBT is an innovative technology of water treatment,which combines concentration and conditioning,showing great advantages in small area occupation and high hydraulic load.Here we take water production wastewater?sedimentation tank sludge and Filter Backwash Wastewater?as the research object,study on the turbidity removal properties of pelleting fluidized bed for treatment of backwashing wastewater:?1?Through static test,the effect of molecular weight and PAM charge on original water turbidity and settling velocity of flocculation were studied.Ultimately,the backwash water in the A waterworks used the anionic PAM,of which molecular weight is 12 million,and the initial dosage of it was 0.7-1mg/L,under this condition the settling velocity of flocculation can reach 7mm in/s;sludge water in B waterworks used cationic PAM of which molecular weight is 12 million,the initial dosage set as 9-12mg/L,and in this way settling velocity of flocculation is quicker than 7mm/s.?2?the initial rising velocity of the fluidized bed has a significant influence on the formation time of the dense suspension layer.When the initial velocity is 20cm/min,it required160min to form a dense suspension layer;when the initial velocity is 30cm/min,in the limited time of experiment,there was no formation of dense suspension layer;for the sludge used in experiment,the suitable initial rising flow rate was 25cm/min,at which can form a dense suspension layer in about 130min.?3?in the protective test,the operating parameters of fluidized bed in A waterworks is determined by the effluent turbidity,water content of sludge and other indicators:the rising velocity was 30cm/min,the influent flow rate was 35m³/h,the dosage of PAM was1mg/L,the dosage of PAC was 5mg/L,stirring speed was 2r/min,the maximum flow rate of system was 60cm/min.We intermittently discharged mud,and the cycle of which was42h.After the concentration,the water content of sludge ranged in 95-96%.Under theses operating conditions,the turbidity of the effluent can stay stable at about 1NTU for a long time,and the content of Fe and Mn in the effluent can be reduced to 0.12mg/L and0.18mg/L,respectively.The running parameters of fluidized bed in B waterworks are:the rising velocity was 30cm/min,the inlet flow rate of the fluidized bed was 90m3/h,the dosage of PAM was added according to the turbidity of the inlet,the stirring speed was1r/min,and the continuous sludge discharge mode is used.After concentration,the water content of the sludge can reach at 96%.Under this condition,the turbidity of the effluent can keep stable at about 10NTU for quite a long time,which meets the requirements of wastewater treatment.?4?In the experiment,a formula(₀₀₀=?1?1-?×10⁶?for calculating the sludge discharge period of the fluidized bed was derived and verified.By applying this formula,we can predict the sludge discharge period when inlet turbidity and influent flow rate are changed,meanwhile,satisfying the requirement of sludge water content.