Patent ID: 8900456

Claim:
A method of treating plant wastewater discharged from any one of a chemical, petroleum, and petrochemical plant and containing an organic compound comprising: a pre-treatment step of feeding the plant wastewater to an anoxic tank, adding compounds containing a nitrogen component and a phosphorus component to the plant wastewater, performing an anaerobic biological treatment on the plant wastewater, and discharging the thus treated plant wastewater as pre-treated water; a primary treatment step of introducing the pre-treated water into an anaerobic biological treatment tank, performing an anaerobic biological treatment on the pre-treated water, thereby decomposing the organic compound into organic compounds of smaller molecular size and a mixture gas containing methane and carbon dioxide, and discharging the thus treated water as primary treated water; a secondary treatment step of introducing the primary treated water into an aerobic biological treatment tank, performing an aerobic biological treatment on the primary treated water, and discharging the thus treated water through solid-liquid separation means as secondary treated water; and a tertiary treatment step of introducing at least a part of the secondary treated water into a reverse osmosis membrane separation unit, and separating the part of the secondary treated water into RO permeated water and RO concentrated brine, wherein at least a part of the RO concentrated brine is recycled to the anoxic tank.