Study On The Application Of Cascade Flocculation In Treatment Of Paper Making Wastewater

In this paper, step coagulation (coagulation and sludge return method) process for optimizing the treating of papermaking wastewater,Furthermore,The biological quantitative reduction on aerobic excess sludge in papermaking wastewater are Preliminarily Studied.The PO43—P and NH4+—N,which come from the process of biological quantitative in aerobic excess, can balanced the acid of N/P in the anaerobic, which can reduce the costs of disposal.In this research, the coagulation sedimentation is firstly used to treat the paper making mixed wastewater., Study of factors affecting pre-flocculation stage.Then single factor and orthogonal test method are used to research how every factor effect the results of the experiments and to get relationship curves of the factor and the results of the experiments (the removal efficiency of COD) to determine the best values of the factors. Lastly the wastewater is treated by step coagulation again. By the way, the biologicalquantitative reduction on aerobic excess sludge is tested by simulation the anaerobic reactor in paper mill.Through the experiments,the paper making wastewater treatment process is identified.And the optimum operating conditions are also determined.The identified treatment process is four-step process,including Preparation of Flocculant PAC, pre-coagulation treatment, A/O processing phase and later step coagulation. The optimum operating conditions for the Preparation of Flocculant PAC is that Hydrochloric acid concentration is15%, the reaction temperature was controlled at103-105℃, reaction time is6.7h, basicity is controlled at75-78%.The optimum operating conditions for the pre-coagulation treatment is that the reacting temperature is at the normal atmosphere temperature and pH, the dosage of PAC is2ml/L, and then15s for mixing. The optimum operating conditions for the biochemical treatment is that the anaerobic reaction time is24h on temperature36-38℃, meanwhile the stirring speed is60-70r/min.in the process.Then aerobic reaction time is24h on temperature is36-38℃, keep the dissolved oxygen at2-2.5mg/L. The optimum operating conditions for the step coagulation.is that the reacting temperature is at the normal atmosphere temperature, the dosage of PAC is3.0ml/L and PAM2.0ml/L, pH is pH is7.0-7.53and then the Sludge return flow is40-60%.The small-size experiment prove that coagulation—A/O—step coagulation (coagulation and sludge return method) process is an economic and efficient process of paper making wastewater treatment. In the optimum operating conditions, treating the wastewater with this method received a significant effect:the COD is debased from1800-2800mg/L to100mg/L, the removal efficiency reaching96%;the chroma is debased from380-400times to25times, and the other main water quality parameters have respectively achieved national papermaking wastewater discharge standards. In this paper,when the experiment achieve stability, the theoretical of sludge gas production is about5.0m3/m3mud, and the emission of components is about3.2mg/L, at the same time, he emission of is about7.0mg/L, which is the four-fold to the control components. The PO43-—P and NH4+—N came from aerobic excess sludge can replace30%urea, phosphoric acid which are dosed in the process of the sewage treatment, which has a long-term economic benefits to the factory.