Study On Sludge Thickening And Digestion Reactor (STDR) With Internal Circulation

Traditionally, the sewage sludge was thickened and digested separately in two tanks, one called gravitational thickening tank and other called digestor. But new concept was introduced in this paper, that sludge could be thickened and digested in one reactor, called Sludge Thickening and Digestion Reactor (STDR) with internal circulation. STDR was designed based on current sludge thickening and digestation equipments, and also used modern anaerobic reactor for reference. A pilot experiment was carried on to study the STDR.The design method and principle was explained in detail in the paper. The primary design idea of STDR was too broaden the function of conventional gravitational thicker, and make it into a new kind of sludge treatment equipment in which sewage sludge can be condensed and digested at the same time.The inoculants of anaerobic bacteria were put into the STDR at one time to startup the reactor. During the start-up, some indexes were primarily inspected, such as pH, VFA, Total Alkalinity (TA), Bicarbonate Alkalinity (BA), sludge thickness of each part, gas production, sludge wash-out of the upper effluent, the change of VS/TS. All of the indexes showed that the digesting status in the STDR was very good.In the final time of the start-up, the feeding sludge load was stabilized for 16 days in the designed amount (70L/d, HRT=3.1d). The first 8 days the amount of discharged sludge from the STDR's bottom was 1.5L, and the other 8 days is 3L. The test results showed that in these two cases the discharged sludge concentrations were up to 110g/L (89.04% in containing water rate) and 80g/L (91.27% in containing water rate), the VSS loads were up to 10.9 KgVSS/m3·d and 5.4 KgVSS/m3·d, the VSS reduce levels were 80.7% and 71.1%. If the expected discharged sludge concentration was 80~100g/L, the STDR could produce 20 times decrease of the sludge volume, and the thickening and digestation effects of the STDR were separately better than conventional gravitational thickening tank and anaerobic digestor.In additional, the quantity of required energy of STDR was estimated in this paper. The results showed that energy used for internal circulation by the STDR was less than energy used for mixion by conventional anaerobic digestor, and quantity of heat required was also less than conventional digestor.