TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Process: The P stage of pre-treatment is adopting precipitation or air-float process to remove most part of oil, part of suspended substance (SS) and COD in wastewater, and to ensure fine treatment effect in the latter anaerobic process. The primary anaerobic first A stage process is mixing the water from P segment with water from the latter aerobic process that can fully using basicity in the aerobic water to neutralize acidic palm oil wastewater, and reducing concentration of suspended substance in anaerobic feed water, where the ratio of primary water to the aerobic water is 1:1-1:3, the pH value of mixed liquid is controlled at 5.0-6.5, and the concentration of COD is controlled at 8000-30000 mg/L; lifting the mixed liquid to the primary anaerobic reactor by pump, controlling the primary anaerobic at hydrolysis-acidification stage by load and pH regulation; where the primary hydrolysis anaerobic reactor adopts similar upflow anaerobic sludge blanket (UASB) structure, and it also equipped with defoaming device that adopts water nozzle to remove the foam and floating slag on the top layer of reactor, throwing engineering bacteria B120 to eliminate effect of oil in wastewater on the acidate bacteria, where the original strain of the engineering bacteria is provided by America BIO-SYSTEMS company having web site of http://www.biobugs.com.. In S stage, the primary anaerobic water enters the latter precipitation or air-float process after precipitation or air-float process in back end to remove suspended substance in wastewater to ensure stable operation of secondary methanogenic anaerobic reactor. In secondary anaerobic second A stage, wastewater in the secondary anaerobic reactor finishes mainly methanogenic process and greatly reduces COD in the wastewater, generating a large amount of methane, where the methane generated by the system can be directly used as fuel or for generating electricity after collected and pre-treated; throwing engineering bacteria B120 in anaerobic reactor to eliminate effect of oil, sulfide and ammonia in wastewater on the methanogen, and to improve anaerobic treatment effect; the original strain of the engineering bacteria is provided by America BIO-SYSTEMS company having website of http://www.biobugs.com; and the anaerobic reactor can adopt UASB, anaerobic upflow sludge blanket filter (UBF), advanced burner reactor (ABR), or expanded granular sludge bed (EGSB) form. In O stage, aerobic process adopts existing aerated lagoon, sequencing batch reactor (SBR), biological contact oxidation, or biological aerated filter.