NOVELTY - Transformation of waste biomass to organic acid comprises mixing municipal sludge and granular sludge domesticated through upflow anaerobic sludge blanket (UASB), supplying nitrogen, sealing, fermenting and performing multistage counter-current operation; pouring mixed liquor to centrifugal tubes, centrifuging and obtaining fermentation product; and replenishing fresh feed liquid, respectively mixing added materials in three bottles, continuing fermentation with counter-current operation, and completely performing counter-current operation to accumulate organic acid containing acetic acid.    USE - Method for transformation of waste biomass to organic acid (claimed).    ADVANTAGE - The concentration and productive rate of organic acid respectively reach 10.5+0.5 g/L and 0.020 g/gVS. The concentration and productive rate are respectively increased by 31% and 54% compared with normal anaerobic fermentation of municipal sludge. The degradation rate of zymolyte through multistage counter-current technology can reach 50%, and is increased by 37% compared with normal anaerobic fermentation of municipal sludge.    DETAILED DESCRIPTION - Transformation of waste biomass to organic acid comprises:    (A) performing reverse flow reaction to fermented supernatant fluid and fermented residual zymolyte in multistage reactor, and adding fresh feed liquid to system on flow direction of supernatant fluid so that the sludge zymolyte which is the most difficult to degrade by microorganism, can contact with fresh feed liquid to increase degradation rate of zymolyte;    (B) simultaneously contacting fresh sludge with product having high concentration to reduce inhibiting function, taking anaerobic granular sludge in UASB of some citric acid factory in Wuxi, and adding granular sludge with simulative wastewater having chemical oxygen demand concentration of 20000 mg/L prepared by glucose, into 2 L UASB;    (C) carrying out domestication preprocessing at 35 degrees C, termly monitoring pH variation in reaction bulb during domestication period, and obtaining anaerobic granular sludge having high active acidogenic bacteria as seed sludge when pH of outlet water is maintained at 4.0;    (D) mixing municipal sludge and granular sludge domesticated through UASB at volume ratio of 9:1, supplying nitrogen for 1-5 minutes, sealing at 35 degrees C, fermenting for 8 days using table concentrator with rotating speed at 120 rpm, and performing multistage counter-current operation after concentration of organic acid reached 6-8 g/L;    (E) respectively pouring mixed liquor in three bottles to 500 mL centrifugal tubes, centrifuging for 15 minutes with rotating speed at 8000 rpm, adding fermented residual sludge in first bottle to second bottle, adding fermented residual sludge in second bottle to third bottle, discharging fermented residual sludge in third bottle, adding seed sludge and fermenting sludge to first bottle;    (F) simultaneously adding fermented supernatant fluid in third bottle to second bottle after centrifuging, adding fermented supernatant fluid in second bottle to first bottle, and discharging fermented supernatant fluid in first bottle to obtain fermentation product; and    (G) replenishing fresh feed liquid into third bottle, respectively mixing added materials in three bottles, continuing fermentation with counter-current operation in each 3 days, and completely performing counter-current operation 2-5 times to accumulate organic acid containing acetic acid.    The fresh feed liquid comprises (g/L) dipotassium hydrogen phosphate (3.26x 10-1), potassium dihydrogen phosphate (3.26x 10-1), sodium chloride (6.52x 10-1), magnesium sulfate heptahydrate (1.36x 10-1), calcium chloride dihydrate (8.8x 10-2), hemin chloride (1.42x 10-2), nicotine (1.42x 10-2), p-aminobenzoic acid (1.42x 10-2 ), vitamin B5 (1.42x 10-2), folic acid (7x 10-3), vitamin B6 (7x 10-3), lactoflavin (7x 10-3), vitamin B1 (7x 10-3), EDTA (7x 10-3), vitamin B12 (2.8x 10-3), biotin (2.8x 10-3), ferrous sulfate heptahydrate (2.8x 10-3), manganese chloride (2.8x 10-3), boric acid (4.2x 10-4), cobalt chloride (2.8x 10-4), zinc sulfate heptahydrate (1.4x 10-4), sodium molybdate heptahydrate (4.2x 10-5), nickel chloride (2.8x 10-5) and copper chloride (1.4x 10-5).