Enhanced Sludge Reduction Technology Based On Thermophilic Bacteria By Metal Ions

With the development of urban sewage and industrial wastewater treatment, the output of sludge increases greatly. Sludge disposal is a necessary part in wastewater treatment process. The expenses for sludge treatment can account for50%of total plant operation costs. So, the decrease of sludge treatment cost and researchs on the sludge reutilization technologies have attracted much concern. Anaerobic sludge digestion is a process that organic matter in the sludge is decomposed into methane and carbon dioxide by anaerobe in anaerobic conditions. It is the most commonly used sludge biological treatment technology and most economical sludge treatment methods used by large wastewater treatment plant at present. The sludge digestion takes a long time for sludge hydrolysis is slowly. So it needs a large place for digestion tank and high energy consumption for heat preservation. Good pretreatment enables sludge hydrolyze in a short time, hence it could greatly shorten the digestion time.Solubilization by thermophilic enzyme(S-TE) pretreatment is relyed on thermophilic enzyme secreted by thermophilic bacteria. It could accelerate the dissolve of sludge floc and the rupture of microbes’cell membranes and walls by pyrohydrolysis which could decrease the sludge volume and organic matter. In S-TE process, there were two reaction mechanisms:thermal-hydrolyzed reaction and enzyme-catalyzed reaction. Compared with other sludge solubilization technology such as thermal hydrolysis, enzymatic directly, ultrasonic, mechanical and ozone oxidation pretreatment, S-TE pretreatment is safer, easier to operate, more cost-efficient and has lower energy consumption.The thermophilic bacteria seperated from garden soil was used in S-TE tests. Five kinds of metal ions were added to identify their influence on sludge hydrolysis during the processes. The results showed that the five metal ions could facilitate hydrolysis process to some extent within certain concentation range, the highest activity of protease and amylase were observed at5h after hydrolysis. The strongest activation (2.20U/mL) of protease could be obtained at5h with the K+concentration of200μmol/L, which was48.6%higher than the control test. K+was also proved to have strongest affect on amylase hydrolysis. The highest amylase activity could reach3.64U/mL when the concentration of K+was at400μmol/L. The removal of TSS, VSS was enhanced compared with the control test. When400μmol/L Ca2+was added, the removal rate of VSS was68.13%. The concentration of SCOD increased significantly in the initial stage of enzymatic hydrolysis, and then tended to increase slightly in the later stage. The maximum concentration of SCOD reached4590.73mg·L-1at the Mg2+concentration of200μmol·L-1, which was12.6%higher than the control test. The investigation also revealed that the metal ions had not obvious effects on the changes of NH4+-N and soluble phosphate.The research showed that as the impact factor of enzyme activity in the enzyme-catalyzed reaction, metal ions could enhanced the activity of enzyme excreted from thermophilic bacteria to some extent. Therefore, it could accelerate the dissolve of sludge floc and organic matter, and then enhance the effect of sludge reduction.