TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The enzyme in the enzyme mixture is glycosidic enzymes, lipases, proteases, oxidases or phytases. The mass ratio of the enzyme mixture: sludge dry solids is 0.1-140 (preferably 1-14) mg/g dry solids. The fermenting bacteria are acidogenic bacteria, acetogenic bacteria or methane producing bacteria, preferably Gluconobacter oxydans, Acetobacter sp., Acetogenium kivui, B. macerans, B. polymyxa, B. coagulans, Lactobacillus buchneri, Clostridium thermoaceticus, Clostridium lentocellum, Clostridium formicoaceticu, Clostridium thermocellum or Pseudomonas sp.. The methane producing bacteria are Methanosarcina barkeri, Methanosarcina mazei, Methanosarcina soehngenii, Methanosarcina acetivorans and/or Methanosaeta sp..    TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The method further comprises adding at least one species of fermenting bacteria to the suspension, hence fermenting the obtained sludge suspension. The pH is adjusted to 6-9 after addition of the chelating reagent by adding an acid or base. The treatment takes place in any anaerobic digester. The produced methane is separated from the sludge suspension. The temperature of the sludge suspension is 4-90 degrees C, preferably 30-60 degrees C. The sludge suspension is subjected to agitation at 0-200 rpm. The sludge is pre-concentrated before the addition of enzymes, chelating reagent and optionally bacteria, by gravitation or enhanced sedimentation to the range of 10-80 g sludge solids per 1 liter sludge suspension.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The chelating reagent is present at 1-75 mM.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The natural polymeric materials are proteins, polysaccharides, polyphenols, lignins, humates, fats, waxes and mineral oils. EXAMPLE - Citric acid (Cit A) or EDTA was added to sludge as powder to a final concentration of 25 mM or 50 mM. Addition of 50 mM EDTA or Cit A decreases the pH to 5.5 and 3.3, respectively. Before enzymes were added the pH of sludge was adjusted to 7 using 1 M sodium hydroxide. Mixtures of enzymes A (mixture of amylase, lipolase, lipase, cellulase, endo-xylanase and dextranase were suspended in polypropylene glycol and fatty alcohol ethoxylate) and B (protease) were added to preconcentrated sludge (total solid (TS) 2%) to the different enzyme concentrations: 68.5 mg (60 mg of A and 8.5 mg of B), 54.8 mg (48 mg of A and 6.8 mg of B), 34.25 mg (30 mg of A and 4.25 mg of B) and 13.7 mg (12 mg of A and 1.7mg of B) of total enzymes per 1 g TS of sludge and reacted for 4 hours. The treatment of the sludge was continuously mixed with propeller stirrer at 200 rpm.