Excess Sludge Treatment By Supercritical Water Oxidation

Sludge into the environment withnot handled properly on not only the survival of humanity would cause serious harm to the environment, but also a waste of resources and energy. How to yield large, complex components sludge, through scientific treatment, to reduction, stabilization, detoxification and resources, which has become the world's environmental sector in China and one of the topics of widespread concern.On this basis, the excess sludge from industrial wastewater treatment plant was studied in order to improve the efficiency of excess sludge treatment by supercritical water oxidation as the research object, Removal ratio of chemical oxygen demand (COD_cr), total nitrogen, and ammonia were investigated in different reaction conditions. Variations of total phosphorus in sludge and orthophosphate concentrations of liquid were analyzed, and studied the reaction of the interaction between factors, and then studied on kinetics and the change rule of migration of heavy metal of supercritical water oxidation of excess sludge.The results show that carbon materials were preferentially oxidized, removal ratio of COD_cr of excess sludge treatment by supercritical water oxidation was efficiency ideal and removal rate of total nitrogen was low than COD_cr, ammonia nitrogen removal effect is poorer, total nitrogen mainly free ammonia and ammonium phosphate form existence, sludge with phosphate form elements mainly exists in sludge residue.Optimization of temperature, pressure, retention time and oxidant dosage was studied in order to improve the efficiency of excess sludge treatment by supercritical water oxidation. Box- Behnken experiment design was applied with the removal ratio of COD_cr, total nitrogen and orthophosphate concentrations of liquid, as response value. It was shown that reaction pressure >temperature> retention time>oxidant dosage. Interaction was discovered among pressure, temperature and retention time.The optimal reaction condition was temperature of 434°C, pressure of 29 MPa, retention time of 278 s and oxidant dosage rate of 216%, under which a maximum CODCr removal rate ranging from 97.72% to 98.32% was achieved.The results show that the values of activation energy and frequency factor of the kinetics of supercritical water oxidation of excess sludge treatment were 89.3 KJ/ mol and 2.84, respectively. The equation of removal rate of COD_cr by supercritical water oxidation can be said:This paper detected 6 kinds of heavy metal ions, the results show that he concentration of heavy metal ion of water were low after excess sludge treatment by supercritical water oxidation, and reflect the water total chromium and total cadmium exceeds bid, the copper and zinc of excess sludge always exceed total ratio, still needing further treatment. In sub-critical and supercritical condition of heavy metals in the sludge scraps complex compounds are form existence, and gradually increase, crystallization phenomenon part two conditions similar.Crystallized subcritical conditions existed in the sludge scraps SiO₂, ZnAl₂Se₄, Cu₅FeS₄, AlP, GaP, CaF₂, C₁₀H₁₂Cr₂N₂O₇ heavy metal compound, in supercritical conditions for PbZnSiO₄, LiBr, (NH₄)CO₂(OH), Fe₃(PO₄)₂,Pb₂O₃, CaCuO₂, heavy metal ions can effectively stable from excess sludge treatment by supercritical water oxidation.The results show that volume of excess sludge treatment by supercritical water oxidation reduced 93% 95%, have good reduction effect. After processing solid product is reddish brown, found its element mainly for O, Si, Al, Fe, P, S and Ca, quality percentage 26.58%, 7.55%, 14.28%, 6.84%, 3.44%, 3.35% and 4.89% , respectively.