Study On The Effects Of Sludge Reflux Under Different Conditions On Flocculation Strengthening

Sludge reflux enhancing flocculation refers to that the sludge formed in the coagulation and flocculation stage is added back to the raw water system again to enhance flocculation effect,with the advantages of reducing the dosage of coagulant and sludge yield,stable operation and far better flocculation effect than traditional conventional flocculation.But the present research about sludge reflux Enhancing flocculation mostly limited to macro research,micro flocculation theory research is not mature,lack of coagulation floc morphological characteristics in the process of the micro research.to some extent,it restricts the further development of the micro flocculation mechanism,and can't timely guidance and be applied to production practice.In this study,polymeric ferric sulfate and anionic polyacrylamide were selected as coagulants and coagulants aids for kaolin raw water system.Then,intelligent photometric dispersion analyzer(IPDA)was used to monitor the flocculation process online and record the final flocculation efficiency.The experiment mainly studied the effect of the basic elements of flocculation(coagulant,coagulant aids and hydraulic conditions)to strengthen the sludge reflux enhancing flocculation;explored the different sampling conditions of sludge to strenthen the effects of sludge,including change the amount of sludge and the storage time of sludge,etc;finally investigated the influence of different pretreatment to sludge on sludge reflux enhancing flocculation,including sludge ultrasonic activation,thermal activation and acid activation.When the amount of coagulant is near or near electrical neutralization,the size of flocculation particles formed by adding sludge increases obviously,the strength of flocculation increases,the crushing resistance increases,and the remaining turbidity decreases by 37.0%.When the coagulant is added in excess,the sweeping effects is dominant,resulting in smaller size of the flocs and poor recovery of the broken flocs.When it'selectrical neutralization,adding PAM with 0.1 mg/L can significantly improve the turbidity removal ability,and adding bottom sludge can also increase the size and strength of flocs.In the condition of sweeping effects and incomplete electrical neutralization,adding PAM has little relation with sludge reflux enhancing flocculation.In addition,the shorter the stirring time,the better the flocculation.Under the condition of slow stirring strength at 70 r/min,the best flocculation effect is achieved by sludge reflux.The larger the adding amount of sludge,the larger the size of floc and the stronger the strength of flocs.The flocculation size was the largest at 3 times of sludge addition,but the turbidity removal effect was not the best,indicating that the influence of sludge addition was unstable.The longer the sludge is stored,the slower the growth rate of the floc,the smaller the size of the floc,and the lower the turbidity removal ability of the solution system.When the sludge activated by pretreated acid,the bottom sludge can further strengthen flocculation under appropriate pH,resulting in more stable flocculation size and better turbidity removal ability.On the contrary,when the pH is too high or too low,the bottom sludge can not play the role of strengthening flocculation.After thermal activation treatment of sludge,the temperature of sludge is over 50?,the floc size is small,floc growth rate is slow,and recovery ability is poor;when the temperature of sludge is below 20?,floc particle size is bigger,but the turbidity removal ability is worse;when the temperature of sludge is between 20?and 40?,the sludge can strenthen flocculation more stable,floc growth rate is faster,the floc size is larger,and recoverability after crushing is stronger.By 10min and 40kHz ultrasonic pretreatment,the bottom sludge can further strengthen the effects of bottom sludge,to ensure the optimal particle size of the flocs,and the flocs can rapidly accumulate and settle to achieve the effect of removing turbidity,which is a relatively better activation point for ultrasonic pretreatment.