Experimental Study On A Novel Composite Flocculant For Surface Water Treatment

Flocculation is one of the important water treatment processes and flocculating agent is the key factors to influence the flocculation effect. Because the traditional flocculating agent is easy to cause the drinking water second pollution and it also leads to the residual aluminum ion concentration of drinking water too high, which is unfavorable to the human body health.In this paper, we prepared a new type of composite flocculant which used the abundant resources, non-toxic natural polymer material chitosan and corn starch as the raw material, and compound with inorganic polymer flocculant Poly chlorinated aluminium iron. We used it in raw water treatment.We investigated the flocculation performance and found that using it in the raw water of Yangtze river the period of wuhan, the floes was large and dense, the flocculating sedimentation time was short.the removal rate of turbidity increased and the water aluminium ion concentration was lower. The research process and results as following:1) Using hydrogen peroxide to prepare chitosan of different deacelation degree and the molecular, making sure the best chitosan b molecular and the deacelation degree to raw water flocculation effect.After analyzing the aluminum ion condition that affect the adsorption raw water, we found that the adsorption process of aluminum ions fit to Freundlich adsorption model.The second step is to make corn starch crosslinking and graft modification, after inspecting its flocculation raw water performance,we found in the raw water the aluminum ion flocculation adsorption efficiency is higher and after processing water aluminium ion content can be dropped to0.055mg/L.The third step is to compound the single component agent with inorganic flocculant polyaluminium chloride iron, through the three factor four levels orthogonal experiment, we determined the best quality ratio for:poly chlorinated aluminium iron (PAFC):chitosan (CTS):modified starch (MS)=25:0.1:1.2) Using the new composite flocculant flocculation to treatment the raw water of wuhan Yangtze river,we inspected the flocculation effect, and the process conditions that will affect the flocculating effect.The results shows that when the dosage is proper.the raw water turbidity removal rate is more than97%. The best process conditions is180rpm fast mixing for2minutes.60rpm slow mixing for8 minutes.and settling for15minutes, the best flocculation effect can make effluent turbidity drop to2NTU, and the aluminium ion concentration fall to0.05mg/L.The flocculation efficiency changed little with different temperature and pH.when the temperature is15℃, the flocculation effect is the best, turbidity removal rate can reach99%, when PH value is between6and7, turbidity removal rate is the highest, it can reach98%,the total removal rate changes not big with different pH value.3) Based on the comparation of several commercialization flocculating agent to raw water flocculation treatment performance, it is known that the homemade new composite flocculant’s processing effect is better than than any other single inorganic polymer floccuiant.By usingthe new composite flocculant, the flocsare large and dense, settling time is short, and turbidity removal can reach98.6%; the concentration of aluminium ion in effluent is only0.0483mg/L. The concentration of aluminium ion in effluent was reduced by66.7%compared with the effluent treated with PAC Comparing the cost of the two kinds of flocculating agent for raw w7ater treatment, the new composite flocculant slightly lower than the traditional flocculant PAC.4)Analysed the mechanism of the new composite flocculant. Each component of the new composite flocculant produced complementary effect and synergistic effect.The electricity and neutralizing action of PAFC,the adsorption and bridging action of CTS improved the removal rate of SS.CTS and MS through the complexation to the aluminum ion, reduced the content of aluminum ions in effluent.Hence the new composite flocculant have an effective flocculation and the characteristics of "low aluminum".