NOVELTY - Extracting DNA from activated sludge, by centrifuging sewage sample, removing supernatant, adding tris(hydroxymethyl)aminomethane-base-EDTA-sodium chloride-polyvinylpyrrolidone (TENP) buffer, centrifuging, adding phosphate buffer saline to precipitate, centrifuging, processing pretreated sludge sample, performing cell lysis, adding sodium dodecyl sulfate, proteinase K and RNAase, tris saturated phenol, centrifuging, adding phenol, chloroform, and isoamyl alcohol (25:24:1) to supernatant, centrifuging, adding isopropanol and centrifuging to obtain precipitate.    USE - The method is useful for extracting DNA from activated sludge in anaerobic reactor.    ADVANTAGE - The method enables easy extraction of DNA from the activated sludge and provides high yield of highly pure DNA.    DETAILED DESCRIPTION - Method for extracting DNA from activated sludge in anaerobic reactor, involves (a) subjecting sewage sample (30 ml) to centrifugation at 9000 revolutions per minute (rpm) and 4 degrees C for 5 minutes, and removing supernatant liquid to collect precipitate, (b) adding tris(hydroxymethyl)aminomethane (tris)-base-EDTA-sodium chloride (NaCl)-polyvinylpyrrolidone (PVP) (TENP) buffer in an amount five times the volume of the precipitate, and three sterile glass beads, vortexing for 5 minutes, centrifuging at 9000 rpm and 4 degrees C for 5 minutes, and removing supernatant liquid to collect precipitate, (c) repeating the step (b) until supernatant becomes clear, (d) adding phosphate buffered saline (PBS) buffer in an amount five times the volume of the precipitate, vortexing and centrifuging at 9000 rpm and 4 degrees C for 5 minutes, and removing supernatant liquid to collect precipitate, (e) repeating the step (d) twice, (f) adding PBS buffer in an amount five times the volume of the precipitate, (g) processing pretreated sludge sample (1 g) by adding extraction buffer (200 mu l), adding two glass beads, and vortexing for 5 minutes such that the sample is suspended fully to obtain suspension, (h) freezing the suspension in refrigerator at below -25 degrees C for 30 minutes, heating frozen suspension in water bath at 65-70 degrees C for 30 minutes, and shaking every 10 minutes to lyse the cells completely, (i) repeating the step (h) thrice, (j) adding lysozyme (4 mu l) (50 mg/ml) to the suspension, allowing the suspension to stand at room temperature for 5 minutes, and heating the suspension at 94 degrees C in water bath for 1 minute, (k) adding sodium dodecyl sulfate (SDS) buffer (400 mu l), proteinase K (1 mu l) (20 mg/ml), and RNAase (1.5 mu l) (20 mg/ml) to the suspension, mixing and placing the suspension in water bath at 37 degrees C for 1 hour, (l) adding and mixing tris saturated phenol in an amount equal to that of the suspension at room temperature, performing centrifugation at 12000 rpm for 5 minutes, and transferring supernatant to another centrifuge tube, (m) adding liquid mixture comprising phenol, chloroform, and isoamyl alcohol in a volume ratio of 25:24:1 to the supernatant in an amount equal to the amount of the supernatant, mixing at room temperature, performing centrifugation at 12000 rpm for 5 minutes, and transferring supernatant to another centrifuge tube, (n) adding isopropanol in an amount 0.6 times the volume of the supernatant, mixing and placing solution at room temperature for 2 hours, performing centrifugation at 12000 rpm (room temperature) for 10 minutes, and discarding supernatant, and (o) washing precipitate using 70% ethanol thrice, drying precipitate at room temperature, and dissolving the precipitate in sterile distilled water to obtain DNA.