| 摘要 |
Disclosed is a continuous process for purifying contaminated waste water. First the water passes through an equalization zone including at least two separate compartments, in one of which the pH of the water is adjusted to a range of from about 6.5 to 9.5. The water flows through the separate compartments such that the concentration of contaminants in the water exiting the equalization zone will approach about constant concentration which changes only gradually even though influent contaminant concentration changes rapidly. Water in at least one compartment of the equalization zone is aerated so that the dissolved oxygen in the water is at least three parts of dissolved oxygen per million parts of water. Solids are skimmed from the surface of the water in the zone, and coagulant is added to the effluent water from the equalization zone so that colloidal particles in the water flocculate. The water from this equalization zone is then filtered to remove flocculated particles. The effluent from the filter will preferably have less than about ten parts of suspended solids per million parts of water and/or less than about ten parts of oil and grease per million parts of water. This effluent is aerated, preferably by aspiration, and is treated in a four stage biological treating zone. In the first stage, the water contacts an activated sludge which decontaminates the water by biodegrading contaminants. In the second stage, water from the first stage is clarified to separate suspended sludge particles from decontaminated water. The bulk of the separated sludge particles is recycled to the first stage, and the bulk of the clarified, decontaminated water is withdrawn. In the third stage, that portion of the separated sludge particles not recycled is concentrated by removing additional residual water. In the fourth stage, the concentrated sludge particles are digested. In accordance with an important feature of our invention, the water-sludge mix as it flows between the first and second stages is aerated by aspirating air into the water-sludge mix and then subjecting this mix to a high hydrostatic pressure. Preferably the sludge flowing between the second, third and fourth stages is also aerated. The water separated from the second stage is filtered to remove any minute suspended sludge particles which may be present. The preferred filter medium is sand or combinations of sand and coal, and may be followed by treatment with activated carbon. Interstage aeration is conducted at pressures above atmospheric. This ensures substantial transfer of oxygen to the water. Also, activated sludge from the third and fourth stages may be recycled to the activated sludge-water mixture that exited the first stage. The average age of the sludge in the system is greater than ten days. The dissolved oxygen concentration in the water flowing into the second stage clarifier is at least about five parts of dissolved oxygen per million parts of watEr.
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