Experimental Study On The Treatment Of Low Temperature And Low Turbidity Water With Enhanced Coagulation

Mopanshan water treatment plant was newly-built and has become the only drinkingwater supplier for Harbin in2010. Mopanshan reservoir is the main source for Mopanshanwater treatment plant. However, the dense forests around the water source, household garbageand sanitary sewage, fertilizers, and pesticides all affect the water quality in the reservoir. Inaddition, the reservoir is located in Heilongjiang Mopanshan mountains,where the watertemperature is below10℃for5-6months and the turbidity is lower than3NTU throughoutthe year. The formation of a typical low temperature and low turbidity water increases thedifficulty of water treatment.With the raw water of low temperature and low turbidity in Harbin Mopanshan Reservoiras the study object, this paper consists of two parts. First, based on the paper " ExperimentalStudy on Enhanced Coagulation to Mopanshan Reservoir Water"（Zhen Zhang, HarbinEngineering University,2011）, the enhanced coagulation is further studied; Second,Experimental studies are carried out on the control of residual aluminium in the polymericaluminum chloride（PAC） coagulation，the formation mechanism and influence factors ofresidual aluminum in the polymeric aluminum chlorid coagulation is investigated, andmethods of controlling residual aluminum are proposed. Meanwhile, chitosan is studiedthroughout the text as a newly emerging coagulant,, including the effect of chitosancoagulation and residual aluminum control.The experimental results indicate that, for low temperature and low turbidity water，potassium permanganate can enhance coagulation to a limited extent. Activated carbonpowder can enhance the effect of coagulation in the removal of organic matter, and the rate oforganic matter removal rises with the increasement of dosage Chitosan can enhancecoagulation and is an effective flocculant with the optimum dosage as0.2mg/L. Thecombination of potassium permanganate and activated carbon powder can enhancecoagulation in the removal of organic matter, and the removal rate of COD_Mn and UV₂₅₄ canbe increased by12%-18%. Potassium permanganate in combination with chitosan can rise theremoval rate of organic matter by10%while reduce the dosage of PAC.Under the same dosage, the amount of residual aluminum is high when coagulating with PAC with high Ala content, and when using PAC with high content of Alband Alcthe amountof residual aluminum is low. The direct cause of the formation of residual aluminum is thedifferent efficiency of aluminum, which is because that different hydrolytic-polymericaluminum species in PAC has different coagulation effect. The amount of residual aluminumincreases with increasing water temperature, but the impact is relatively small, and theoptimal pH is around7. The dosage of chitosan with0.2mg/L can effectively reduce theamount of residual aluminum with the removal rate around38%.This study focuses on the enhanced coagulation process and the residual aluminum. Theconvientional method is further improved in the removal of the organic matter and aneffective method of controlling the residual aluminum when coagulating with PAC is putforward, all for the guarantee of the safety of drinking water.