Research On Sludge Treatment With Advanced Oxidation Technology Based On Sulfate Radicals

Anaerobic digestion plays an important role in the excess sludge treatment for it is a kind of very effective sludge stabilizing treatment process, and has the advantages of recycling stabilization and harmlessness. It is hard for anaerobic microbe to use organic matter because most of the sludge is microbial cells organic matter which protect by microorganism cell wall, it limited the sludge anaerobic digestion, caused the sludge anaerobic digestion process of sludge retention time long (20～30d) and digester volume big, etc.The researchers use all sorts of cell disruption technology to promote the decomposition of sludge, chemical oxidation method is valuable for sludge pretreatment. At present, about sulfate free radicals (SO4-·) advanced oxidation technology research mostly concentrates on the degradation of organic pollutants in the soil or water, there have been very few reports on the sludge treatment. Dewi et al. use peroxymonosulphate pretreatment sludge to enhance the biogas production in the anaerobic digestion. Appels et al. study show that peroxymonosulphate pretreatment can significantly improve sludge anaerobic digestion performance. The use of acid free radicals in sludge handing is novel.The disintegration of excess sludge with sulfate free radical which produced by heat-activated potassium persulfate was studied in this paper. Compared with heating alone, experiment investigated the changes of the sludge’s nature before and after the treatment. The results indicated that the sludge dissolution ratio displayed a linear decreasing with the increase of reaction time. Elevated temperature can improve the efficiency of heat-activated potassium persulfate and the sludge disintegration rate. In the following operation condition, reaction temperature of90℃, heating time of90min and the potassium persulfate (K2S2O8) dosage of0.5g per gram SS, the sludge dissolution ratio was16.9%.In this operation, more microbial extracellular polymeric substances (EPS) were decomposed, and more intracellular material was released to the liquid phase. The concentration of soluble fraction of the chemical oxygen demand (SCOD) increased to719mg/L, which is435mg/L by single heating treatment; the concentration of total nitrogen (TN), total phosphorus (TP) increase46%and 60%respectively than single heating processing. Part of organic nitrogen was mineralized by oxidants to ammonia nitrogen (NH4+-N), whose concentration increased from15mg/L to27.8mg/L.The influence of sulfate free radical pretreatment on mesophilic anaerobic digestion was also studied in this work. The results show that pretreatment can effectively improve sludge anaerobic digestion performance. After pretreatment, average gas production is38mL/d which increased46%compared to the original sludge in the process of sludge anaerobic digestion; total gas production increased45%compared to no pretreatment; the removal rate of volatile suspended solids (VSS), total chemical oxygen demand (TCOD) is higher14.9%and11.5%respectively than untreated sludge. After pretreatment, the concentration of volatile fatty acids (VFA) increased from210mg/L to730mg/L in the sludge solution, at the same time alkalinity is also increased, so as to ensure the anaerobic digestion system in normal operation.