Method and apparatus for purifying aqueous streams contaminated with organic materials
First Claim
1. Apparatus for separating an aqueous medium contaminated with minor amounts of organic materials into an aqueous fraction relatively concentrated with respect to the organic contaminants and a water fraction relatively free of organic contaminants comprisinga reverse osmosis unit including a high pressure compartment and a low pressure compartment separated by a reverse osmosis membrane,an ultrafiltration unit including a high pressure compartment and a low pressure compartment separated by an ultrafiltration membrane,the high pressure compartment of the reverse osmosis unit being adapted to operate at a substantially higher pressure than the high pressure compartment of the ultrafiltration unit,first conduit means including fluid pressure reducing means for withdrawing a concentrate fraction under a relatively high pressure from the high pressure compartment of the reverse osmosis unit and introducing it into the high pressure compartment of the ultrafiltration unit under a relatively low pressure,second conduit means including fluid pressure increasing means for withdrawing a permeate fraction from the low pressure compartment of the ultrafiltration unit under a relatively low pressure and introducing it into the high pressure compartment of the reverse osmosis unit under a relatively high pressure,the said high pressure compartment of the reverse osmosis unit, the said first conduit means, the said high pressure compartment of the ultrafiltration unit, the said low pressure compartment of the ultrafiltration unit, and the said second conduit means comprising a circuit for substantially continuously recirculating liquid and at least a portion of the contaminated aqueous medium being recirculated therein,a source of aqueous medium contaminated with minor amounts of organic contaminants to be separated into an aqueous fraction which is relatively concentrated with respect to the organic contaminants and a water fraction which is relatively free of the organic contaminants, the said aqueous medium including organic contaminants having molecular weights of less than 10,000 which are soluble therein initially but have a limited solubility range and are precipitated therefrom upon concentration of the contaminated aqueous medium in the high pressure compartment of the reverse osmosis unit,means including third conduit means for withdrawing contaminated aqueous medium from the said source and introducing it at a substantial rate of flow into the said circuit for recirculating liquid,the high pressure compartment of the reverse osmosis unit being adapted to operate at a pressure in excess of the osmotic pressure of the aqueous medium and at a sufficiently elevated pressure to produce a permeate fraction which passes through the reverse osmosis membrane into the said low pressure compartment and a concentrate fraction in the said high pressure compartment which contains the said organic contaminants in sufficiently high concentration to cause precipitation of at least a portion of the organic contaminants therefrom,the high pressure compartment of the ultrafiltration unit being adapted to operate at a pressure less than 200 pounds per square inch and at a sufficiently elevated pressure to produce a permeate fraction which passes through the ultrafiltration membrane into the said low pressure compartmentmeans including fourth conduit means for withdrawing a permeate fraction which is relatively free of organic contaminants from the low pressure compartment of the reverse osmosis unit, andmeans including fifth conduit means for withdrawing a concentrate fraction which is relatively concentrated with respect to the organic contaminants from the high pressure compartment of the ultrafiltration unit.
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Abstract
Aqueous streams contaminated with minor amounts of organic materials are separated into an aqueous fraction which is concentrated with respect to the organic contaminants and a water fraction relatively free of the organic contaminants by a method which includes a unique combination of reverse osmosis (RO) and ultrafiltration (UF). The organic contaminants include substances having molecular weights of less than 10,000 which are soluble in the aqueous stream initially but have limited solubility ranges and are precipitated therefrom upon concentration. The contaminated aqueous stream is circulated from the high pressure compartment of a RO unit to the high pressure compartment of an UF unit, then to the low pressure compartment of the UF unit, and then back to the high pressure compartment of the RO unit. The contaminants are concentrated in the high pressure compartment of the RO unit, and a portion thereof is precipitated or otherwise rendered amenable to removal along with the UF concentrate upon passing the RO concentrate from the high pressure compartment of the RO unit to the high pressure compartment of the UF unit. Soluble organic contaminants remaining in the aqueous stream are removed in the UF permeate and are recycled back to the high pressure compartment of the RO unit for further concentration and precipitation, followed by recycling to the high pressure compartment of the UF unit for removal.
81 Citations
47 Claims
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1. Apparatus for separating an aqueous medium contaminated with minor amounts of organic materials into an aqueous fraction relatively concentrated with respect to the organic contaminants and a water fraction relatively free of organic contaminants comprising
a reverse osmosis unit including a high pressure compartment and a low pressure compartment separated by a reverse osmosis membrane, an ultrafiltration unit including a high pressure compartment and a low pressure compartment separated by an ultrafiltration membrane, the high pressure compartment of the reverse osmosis unit being adapted to operate at a substantially higher pressure than the high pressure compartment of the ultrafiltration unit, first conduit means including fluid pressure reducing means for withdrawing a concentrate fraction under a relatively high pressure from the high pressure compartment of the reverse osmosis unit and introducing it into the high pressure compartment of the ultrafiltration unit under a relatively low pressure, second conduit means including fluid pressure increasing means for withdrawing a permeate fraction from the low pressure compartment of the ultrafiltration unit under a relatively low pressure and introducing it into the high pressure compartment of the reverse osmosis unit under a relatively high pressure, the said high pressure compartment of the reverse osmosis unit, the said first conduit means, the said high pressure compartment of the ultrafiltration unit, the said low pressure compartment of the ultrafiltration unit, and the said second conduit means comprising a circuit for substantially continuously recirculating liquid and at least a portion of the contaminated aqueous medium being recirculated therein, a source of aqueous medium contaminated with minor amounts of organic contaminants to be separated into an aqueous fraction which is relatively concentrated with respect to the organic contaminants and a water fraction which is relatively free of the organic contaminants, the said aqueous medium including organic contaminants having molecular weights of less than 10,000 which are soluble therein initially but have a limited solubility range and are precipitated therefrom upon concentration of the contaminated aqueous medium in the high pressure compartment of the reverse osmosis unit, means including third conduit means for withdrawing contaminated aqueous medium from the said source and introducing it at a substantial rate of flow into the said circuit for recirculating liquid, the high pressure compartment of the reverse osmosis unit being adapted to operate at a pressure in excess of the osmotic pressure of the aqueous medium and at a sufficiently elevated pressure to produce a permeate fraction which passes through the reverse osmosis membrane into the said low pressure compartment and a concentrate fraction in the said high pressure compartment which contains the said organic contaminants in sufficiently high concentration to cause precipitation of at least a portion of the organic contaminants therefrom, the high pressure compartment of the ultrafiltration unit being adapted to operate at a pressure less than 200 pounds per square inch and at a sufficiently elevated pressure to produce a permeate fraction which passes through the ultrafiltration membrane into the said low pressure compartment means including fourth conduit means for withdrawing a permeate fraction which is relatively free of organic contaminants from the low pressure compartment of the reverse osmosis unit, and means including fifth conduit means for withdrawing a concentrate fraction which is relatively concentrated with respect to the organic contaminants from the high pressure compartment of the ultrafiltration unit.
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18. A method of separating an aqueous medium contaminated with minor amounts of organic materials into an aqueous fraction relatively concentrated with respect to the organic contaminants and a water fraction relatively free of organic contaminants comprising
introducing aqueous medium contaminated with organic materials into a reverse osmosis unit including a first high pressure compartment and a first low pressure compartment separated by a reverse osmosis membrane, the contaminated aqueous medium containing soluble organic contaminants and being introduced into the said first high pressure compartment and maintained therein under a pressure in excess of the osmotic pressure of the contaminated aqueous medium and under a sufficiently elevated pressure whereby reverse osmosis permeate is produced which passes through the reverse osmosis membrane into the said first low pressure compartment and reverse osmosis concentrate is produced which is retained in the said first high pressure compartment by the reverse osmosis membrane, the reverse osmosis permeate being a water fraction which is relatively free of the organic contaminants and the reverse osmosis concentrate being an aqueous fraction which is sufficiently concentrated with respect to the organic contaminants to cause precipitation of at least a portion of the initially soluble organic contaminants therefrom, withdrawing the reverse osmosis permeate from the said first low pressure compartment, withdrawing the reverse osmosis concentrate from the said first high pressure compartment, introducing the reverse osmosis concentrate into an ultrafiltration unit including a second high pressure compartment and a second low pressure compartment separated by an ultrafiltration membrane, the reverse osmosis concentrate containing precipitated organic contaminants which are retained by the reverse osmosis membrane and being introduced into the said second high pressure compartment and maintained under a pressure which is substantially lower than the pressure existing in the said first high pressure compartment, the said pressure being less than 200 pounds per square inch but sufficiently elevated whereby ultrafiltration permeate is produced which passes through the ultrafilitration membrane into the said second low pressure compartment and ultrafiltration concentrate is produced which is retained in the said second high pressure compartment by the ultrafiltration membrane, the ultrafiltration permeate being an aqueous medium contaminated with soluble organic materials which are not retained by the ultrafiltration membrane and the ultrafiltration concentrate being an aqueous fraction relatively concentrated with respect to the organic contaminants, withdrawing the ultrafiltration concentrate from the said second high pressure compartment, withdrawing ultrafiltration permeate from the said second low pressure compartment, introducing the withdrawn ultrafiltration permeate into the said first high pressure compartment and producing therefrom reverse osmosis concentrate containing precipitated organic contaminants which are retained by the ultrafiltration membrane and additional reverse osmosis permeate, at least a portion of the contaminated aqueous medium being substantially continuously recirculated in a circuit for recirculating liquid which includes the high pressure conpartment of the reverse osmosis unit, the high pressure compartment of the ultrafiltration unit and the low pressure compartment of the ultrafiltration unit, and introducing into the said circuit for circulating liquid fresh contaminated aqueous medium to be separated into an aqueous fraction relatively concentrated with respect to the organic contaminants and a water fraction relatively free of the organic contaminants, the said fresh contaminated aqueous medium being introduced at a substantial rate of flow and including at least one contaminating organic material having a molecular weight of less than 10,000 which is soluble therein initially but has a solubility range such that at least a portion thereof is precipitated from the reverse osmosis concentrate whereby the said precipitated contaminating organic material is retained by the ultrafiltration membrane in the said second high pressure compartment and is withdrawn in the ultrafiltration concentrate.
Specification