Granulation Process Of Denitrifying Granular Sludge

These days, wastewater treatment engineers are facing more and more challenge with the development of industry. The aggravation of water eutrophication and increase of high concentration nitrogen wastewater have made people take more interest in nitrogen-removal technology than ever. High-efficiency, energy-saving and equipment-miniaturization are developing tendency for current wastewater biological treatment. In view of principal part ofbio-treatment technology------activated sludge, sludge granulation is an important method torealize this goal. Anaerobic granular sludge has widely been studied and applied. However, thus far culture condition, formation mechanism and characteristics of denitrifying granule slu(?)e have rarely been reported.With aerobic activated sludge inoculated in up-flow sludge blanket (USB), good denitrifying granule sludge was cultured. When glucose was used as carbon source and hydraulic flow rate was 3.3 m·h^-1, MLSS and MLVSS in sludge blanket were 27.5 g·h^-1 and 23.1 g·h^-1, respectively. Maximum sludge removal rate measured in the test was 0.98 gN·gVSS^-1·d^-1 (30℃ ) . When methanol was used as carbon source, denitrifying rate was higher and maximum sludge removal rate measured was 3.73 gN·gVSS^-1·d^-1 (30℃) .This study showed that sludge granulation resulted from evolvement of biome. Formation of carrier and appearance of sandlize sludge were important process for formation of granule sludge. Characteristics of carrier had great effect on formation of tight granule sludge, while formation of mature granule sludge resulted from multiplication of denitrifying bacteria on the surface of sandy sludge, which was similar to crystal growth. This approved and added to Crystal Nucleus Hypothesis theory on formation of granule sludge by Lettinga.During experimental process, it was found that inoculum quality, culturing load, etc. had influenced granulation process in varying degree. It seemed that the low ratio of VSS/SS was favourable to form well granules. And also, sludge load was well remain in low level and denitrification rate should be hold at about 98%.