Study On The Effect Of Enhanced Coagulation Based On Bottom Sludge On Properties Of Flocs

Bottom sludge enhanced coagulation is a technology that enhances coagulation by adding bottom sludge in coagulation stage.It is generally used because it has the advantages of reducing the dosage and the sludge production,improving the water treatment effect and reducing the operation cost of water plants.But the related theoretical research is relatively backward.Most of them are the study of treatment efficiency and macroscopic aspects and there are few studies on the flocculation characteristics of flocculation process.Due to the diversity and complexity of the treated water,the related research results can not be well unified and guide the production effectively.In this subject,polymeric ferric sulfate and anionic polyacrylamide were respectively used as coagulant and coagulant aids for kaolin water system,and the coagulation process was online monitored by use of IPDA and camera technology.At first the enhancement of conventional coagulation by bottom sludge with different causes was studied,the necessity of the coagulant aid for enhancement effect of bottom sludge was investigated,and then the influence of sludge dosage and hydraulic power conditions on enhancing coagulation of bottom sludge was also studied.Finally,the separate sludge action and the sustainability of bottom sludge enhanced action was investigated.When the electrical neutralization is dominant,adding the precipitated sediment,growth rate of flocs is faster,the size of formed flocs particle is larger,strength factor of flocs increases to 43.58%,recovery factor increases to 58.89%,residual turbidity decreases by 39%,showing obvious enhancement;when aggregation function occupies the leading role gradually,the flocs formed are relatively loose with the smaller size,the recovery ability after breaking is relatively weak,and the bottom sludge has not played a strengthening function.In the incomplete electrical neutralization and aggregation function,the addition of PAM has no obvious improvement on the strengthening effect of bottom sludge;under the condition of near electrical neutralization,appropriate dosage of PAM can improve the growth rate of flocs,and enhance strength and recovery ability of flocs,the fractal dimension of flocs is lower,strengthening effect has been improved.As the amount of sludge increases,the size of flocs increases gradually,but the recovery ability of flocs decreases,and the strengthening effect is unstable.Rapid stirring with short duration(30s)is beneficial to the enhancement action of bottom sludge,while rapid stirring with long duration(90s),the bottom sludge does not show a strengthening effect.When the stirring speed is less than 300r/min,it is helpful for bottom sludge to play a strengthening role,when the stirring speed is too large,the treatment effect is worse because of the breakage of flocs.The addition of bottom sludge at different slow stirring speeds contributes to turbidity removal,and the strengthening effect is most evident at a slow stirring rate of 70r/min.The bottom sludge can adsorb the colloidal particles in the raw water when added separately,which can increase the particle size of the water,and have a certain flocculation function.During many cycles of adding bottom sludge,the growth process of flocs and flocs morphology reaches a stable state,which has a certain strengthening effect on conventional coagulation and has a certain sustainability.