Study On Enhanced Coagulation Characteristics And Seasonal Adaptability

Coagulation is an important means of water treatment,and has far-reaching effects on downstream processes such as sedimentation,filtration,disinfection,membrane treatment and biological treatment.The pre-coagulation separation biological treatment combination process is a process of intensifying coagulation pretreatment of sewage,reducing refractory organic matter,total phosphorus,organic nitrogen,adjusting water quality,and adapting it to subsequent biological treatment.The process greatly reduces the facility volume,reduces the construction cost,and improves the reaction efficiency,flexibility and adaptability,and is a promising water treatment process.However,the temperature has a great influence on the coagulation process.The efficiency is generally higher at normal temperature(15~30?),but the low temperature has negative impact on the process.Effects of low temperature on enhanced coagulation were studied.A new composite coagulant called Homemade coagulant was synthesized.Effects of enhanced coagulation on removals of dissolved organic matter,dissolved organic nitrogen and so on under room temperature or low temperature(2-5 ?)were detected,and their influences on following biological treatments were investigated by using membrane fractionation distribution,HPSEC,three-dimensional fluorescence spectrum(3DEEM)and differential ultraviolent absorbance.Results show that,under room temperature,removals of particulate COD,particulate nitrogen,colloidal COD and colloidal nitrogen were highly correlated with turbidity removal of coagulation using aluminum chloride(Al Cl3),poly aluminum chloride(PACl)and Homemade coagulant as coagulant separately,while the relation was not clear between dissolved parameters and turbidity removal.Removal of fluorescence value of dissolved organic matter after coagulation was much higher than that of dissolved COD.Dissolved organic nitrogen(DON)is the main part removed by preset coagulation besides particulate nitrogen(PN)and colloidal nitrogen(CN).Low temperature affected enhanced coagulation in many aspects.It inhibited turbidity and COD removals of above 3 coagulants with the order being Al Cl3>PACl>Homemade coagulant.It exhibited differential influences on removals of particulate,colloidal and dissolved COD and nitrogen,and it showed greater adverse effects on particulate and colloidal COD and nitrogen.Fluorescence value of dissolved organic matter in low temperature water showed a significant increase and its removal by coagulation was high,comparing with those in room temperature water.Low temperature coagulation exerted greater impacts on ultraviolet differential absorbance than room temperature.Under low temperature,slight increases of total nitrogen(TN)removal,DN and DON removals were achieved by using Homemade coagulant as coagulant,and removals of PN and CN were maintained,comparing with room temperature.As an example,when Homemade coagulant dosage was above 30mg/L,DON removal achieved 28.5%-41.7% in low temperature,while the removal was only 17%-31.4% in room temperature.A large part of COD and some TN were removed by coagulation as pretreatment,which means a great part of aeration pond duration would be saved and removal efficiency of TN would be stabilized.Thus in winter,decrease of biological treatment efficiency could be alleviated to some extent by using enhanced coagulation with adaptable coagulant such as Homemade coagulant as pretreatment,which would relieve stress of denitrogen and stabilize treatment efficiency.