Removal of BOD and nitrogenous pollutants from wastewaters

Claim 1

In the purification of wastewater by an activated sludge system wherein the wastewater is subjected, during continuous flow through successive treating zones, to sequential treatments to effect, in addition to reduction in quantity of BOD content, removal of nitrogenous pollutants, the method which comprises: a. initially mixing influent wastewater containing BOD and nitrogenous material with activated sludge capable of removing BOD, nitrifying and denitrifying, and with free oxygen-containing gas under oxic conditions to provide a mixed liquor; b. passing the mixed liquor from step (a), without intermediate separation of solids therefrom, to further treatment under anoxic conditions in the presence of nitrites and/or nitrates and in the presence of microorganisms effective in degrading nitrites and nitrates present during such treatment of the mixed liquor to innocuous nitrogen gas; c. subjecting mixed liquor discharged from step (b) to further treatment in a subsequent oxidation zone under oxic conditions with oxygen-containing gas; d. directly introducing the mixed liquor from the last treating zone into a settling zone to effect separation of settled solids from supernatant liquid; e. returning a portion of the settled solids as activated sludge to step (a); f. returning a portion of the microorganisms which have undergone oxidative treatment under oxic conditions to step (b); g. while maintaining in at least the first oxic stage of treatment of said mixed liquor a D.O. level of at least 1 ppm and an F s /M a ratio of at least 1.5, wherein F s is equal to 1.5 times the weight of the soluble BOD 5 content of the influent wastewater charged per day to step (a), and M a is the weight of MLVSS in the mixed liquor of step (a) multiplied by an activity coefficient α, wherein α represents the ratio of the oxygen uptake rate of the volatile suspended solids under oxidation to a reference maximum specific oxygen uptake rate MSOUR at the same temperature, Msour being determined by the equation: ##EQU3## said F s /M a ratio being maintained by controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS.

Claim 12

The method of biologically purifying wastewater containing carbonaceous and nitrogenous biodegradable materials which comprises: a. continuously flowing the wastewater without intermediate solids separation through successive treating zones wherein the flowing wastewater is subjected to an initial oxic treating stage and to one or more sequences of biologic treating stages, each of said sequences consisting of an anoxic treating stage followed by an oxic treating stage; b. separating the treated wastewater from the last treating stage to provide a settled sludge fraction and a supernatant liquid effluent; c. mixing in the initial oxic treating stage a recycled portion of said settled sludge fraction capable of removing BOD, nitrifying and denitrifying, with incoming wastewater and with a gaseous stream containing O 2 , to provide in said first treating stage a D.O. level of at least 1 ppm, d. said initial oxic treating stage having one or more individual hydraulically separate oxic treating sections; e. maintaining in the initial oxic section in which the incoming wastewater is first mixed with recycled sludge a ratio of at least 1.5 of soluble carbonaceous food to active biomass, as defined by the expression F s /M a ; wherein F s is equal to 1.5 times the weight of the soluble BOD 5 content of the daily wastewater charged to the first oxic zone and M a is the active portion of the MLVSS in that zone and is equal to α times the weight of MLVSS and α is equal to the ratio of the oxygen uptake rate of the volatile suspended solids in that zone to a reference maximum specific oxygen uptake rate MSOUR at the treatment temperature, MSOUR being determined by the equation ##EQU4## said F s /M a ratio being maintained by controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS; and f. adding to at least the first anoxic treating stage a portion of the mixed liquor returned from a subsequent oxic stage downstream thereof in the sequence.

Claim 13

The method of biologically purifying wastewater containing carbonaceous and nitrogenous biodegradable materials which comprises: a. continuously flowing the wastewater without intermediate solids separation through successive treating zones wherein the flowing wastewater is subjected to an initial oxic treating stage and to one or more sequences of biologic treating stages, each of said sequences consisting of an anoxic treating stage followed by an oxic treating stage; b. separating the treated wastewater from the last treating stage to provide a settled sludge fraction and a supernatant liquid effluent; c. mixing in the initial oxic treating stage a recycled portion of said settled sludge fraction capable of removing BOD, nitrifying and denitrifying, with incoming wastewater and with a gaseous stream containing O 2 , to provide in said first treating stage a D.O. level of at least 1 ppm, d. said initial oxic treating stage having one or more individual hydraulically separate oxic treating sections; e. maintaining in the initial oxic section in which the incoming wastewater is first mixed with recycled sludge a ratio of at least 1.5 of soluble carbonaceous food to active biomass, as defined by the expression F s /M a ; wherein F s is equal to 1.5 times the weight of the soluble BOD 5 content of the daily wastewater charged to the first oxic zone and M a is the active portion of the MLVSS in that zone and is equal to α times the weight of MLVSS and α is equal to the ratio of the oxygen uptake rate of the volatile suspended solids in that zone to a reference maximum specific oxygen uptake rate MSOUR at the treatment temperature, MSOUR being determined by the equation ##EQU4## said F s /M a ratio being maintained by controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS; and f. adding to at least the first anoxic treating stage a portion of the mixed liquor returned from a subsequent oxic stage downstream thereof in the sequence.

Claim 23

The method of biologically purifying wastewater containing carbonaceous and nitrogenous biodegradable materials which comprises: a. continuously flowing the wastewater without intermediate solids separation through successive treating zones wherein the flowing wastewater is subjected to an initial oxic treatment and to one or more sequences of biologic treating stages, each of said sequences consisting of an anoxic treating stage followed by an oxic treating stage; b. separating the treated wastewater from the last treating stage to provide a settled sludge fraction and a supernatant liquid effluent; c. mixing in the initial oxic treating stage a recycled portion of said settled sludge fraction capable of removing BOD, nitrifying and denitrifying, with incoming wastewater and with a gaseous stream containing O 2 , to provide in said first treating stage a D.O. level of at least 1 ppm, d. said initial oxic treating steps having one or more individual hydraulically separate oxic treating sections; e. maintaining in the initial oxic section in which the incoming wastewater is first mixed with recycled sludge a ratio of at least 1.5 of soluble carbonaceous food to active biomass as defined by the expression F s /M a ; wherein F s is equal to 1.5 times the weight of the soluble BOD 5 content of the daily wastewater charged to the first oxic zone and M a is the active portion of the MLVSS in that zone and is equal to α times the weight of MLVSS and α is equal to the ratio of the oxygen uptake rate of the volatile suspended solids in that zone to a reference maximum specific oxygen uptake rate MSOUR at the treatment temperature, MSOUR being determined by the equation ##EQU5## said F s /M a ratio being maintained by controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS; and f. adding to at least the first of said anoxic stages a portion of the recycled sludge fraction from the aforesaid separating step.

Claim 24

The method of biologically purifying wastewater containing carbonaceous and nitrogenous biodegradable materials which comprises: a. continuously flowing the wastewater without intermediate solids separation through successive treating zones wherein the flowing wastewater is subjected to an initial oxic treatment and to one or more sequences of biologic treating stages, each of said sequences consisting of an anoxic treating stage followed by an oxic treating stage; b. separating the treated wastewater from the last treating stage to provide a settled sludge fraction and a supernatant liquid effluent; c. mixing in the initial oxic treating stage a recycled portion of said settled sludge fraction capable of removing BOD, nitrifying and denitrifying, with incoming wastewater and with a gaseous stream containing O 2 , to provide in said first treating stage a D.O. level of at least 1 ppm, d. said initial oxic treating steps having one or more individual hydraulically separate oxic treating sections; e. maintaining in the initial oxic section in which the incoming wastewater is first mixed with recycled sludge a ratio of at least 1.5 of soluble carbonaceous food to active biomass as defined by the expression F s /M a ; wherein F s is equal to 1.5 times the weight of the soluble BOD 5 content of the daily wastewater charged to the first oxic zone and M a is the active portion of the MLVSS in that zone and is equal to α times the weight of MLVSS and α is equal to the ratio of the oxygen uptake rate of the volatile suspended solids in that zone to a reference maximum specific oxygen uptake rate MSOUR at the treatment temperature, MSOUR being determined by the equation ##EQU5## said F s /M a ratio being maintained by controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS; and f. adding to at least the first of said anoxic stages a portion of the recycled sludge fraction from the aforesaid separating step.