NOVELTY - NOVELTY -The method comprises pre-treating a sludge using a low intensity ultrasonic wave, and soaking a crop straw in water of a pre-processing pool. The sludge is a sewage and waste discharge of a plant biological treatment system. A sludge floc is ultrasonically cracked using a probe ultrasonic processor, where the sludge floc has total chemical oxygen demand (TCOD) of 1000-3000 mg/l. The low intensity ultrasonic cracking residual sludge has a concentration of 2-3 wt.% and a cracking time of 3-8 minutes. The sludge is cracked using an ultrasonic processor and 4-8 type of probe.    USE - The method is useful for mixing and fermenting the sludge and straw, which is useful for improving middle temperature of anaerobic digestion (claimed) in a sewage treatment plant.    ADVANTAGE - The method effectively reduces ultrasonic preprocessing energy consumption and anaerobic digestion time, and improves hydrolysis acid generating rate and anaerobic digestion performance. The method is capable of economically fermenting the mixed sludge and straw with improved efficiency in an environment-friendly manner.    DETAILED DESCRIPTION - The method comprises pre-treating a sludge using a low intensity ultrasonic wave, and soaking a crop straw in water of a pre-processing pool. The sludge is a sewage and waste discharge of a plant biological treatment system. A sludge floc is ultrasonically cracked using a probe ultrasonic processor, where the sludge floc has total chemical oxygen demand (TCOD) of 1000-3000 mg/l. The low intensity ultrasonic cracking residual sludge has a concentration of 2-3 wt.% and a cracking time of 3-8 minutes. The sludge is cracked using an ultrasonic processor and 4-8 type of probe at an ultrasonic frequency of 20-40 kHz. The probe has a diameter of 20-30 mm. The ultrasonic processor has a density of 0.5-0.8 kW/m3. The crop straw is crushed and sieved using a mechanical crusher. The sieved straw is stored in a ventilation dry place for making powder of 20-50 meshes. The straw is soaked in water with a mass ratio of 10:20 for 20-40 hours in a pre-treatment tank. The crop straw has a TCOD of 2000-5000 mg/l. A cellulose in a liquid phase material is obviously increased. The pre-treating crop straw mixture of organic rubbish and the sludge are mixed with a mass ratio of 1:1.4-1:2.5 at a certain temperature for a hydraulic retention time of 240-260 hours. An INDEPENDENT CLAIM is included for an application of a mixed fermentation method for improving middle temperature of anaerobic digestion.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of a method for fermenting a mixed low intensity ultrasonic cracking sludge and crop straw.