Non-bulking activated sludge process

Claim 1

IN THE OPERATION OF AN ACTIVATED SLUDGE SYSTEM HAVING AT LEAST TWO SUCCESSIVE AERATION STAGES, THE METHOD OF INHIBITING PROLIFERATION OF FILAMENTOUS BIOMASS WHICH COMPRISES: AERATING IN AN INITIAL STAGE A MIXED LIQUOR COMPRISING BODCONTAINING AQUEOUS WASTE IN ADMIXTURE WITH ACTIVATED SLUDGE WHILE CONTROLLING AT LEAST ONE VARIABLE SELECTED FROM THE GROUP CONSISTING OF INITIAL STAGE INFLUENT RESIDENCE TIME, ACTIVATED SLUDGE RECYCLE RATE, AND INITIAL STAGE MLVSS CONCENTRATION SUCH THAT THE RATIO OF SOLUBLE FOOD TO ACTIVE BIOMASS AS DETERMINED BY THE EXPRESSION F2/MZ IS AT LEAST 4 AND THERE IS MAINTAINED IN THE MIXED LIQUOR DURING SAID INITIAL STAGE A DISSOLVED OXYGEN CONTENT NUMERICALLY EQUAL IN PARTS PER MILLION TO AT LEAST 2 OR ONE-TENTH THE NUMERICAL VALUE OF THE RATIO F2/MA, WHICHEVER IS THE GREATER, WHEREIN FS IS EQUAL TO 1.5 TIMES THE WEIGHT OF SOLUBLE BOD5 CHARGED PER DAY TO THE MIXED LIQUOR AND MA IS EQUAL TO THE QUANTITY OF MLVSS IN THE MIXED LIQUOR IN SAID STAGE MULTIPLIED BY AN ACTIVITY COEFFICIENT DETERMINED BY THE RATIO OF THE MAXIMUM SPECIFIC OXYGEN UPTAKE RATE OF THE VOLATILE SUSPENDED SOLIDS (VSS) UNDER AERATION TO THE PREDETERMINED REFERENCE MAXIMUM SPECIFIC OXYGEN UPTAKE RATE MSOUR FOR THE SAME TEMPERATURE, MSOUR BEING DETERMINED BY THE EQUATION: 1N MSOUOR = 33.92 - 8640/T(*K).

Claim 4

The method of treating BOD-containing aqueous waste which comprises aerating a mixed liquor comprising such waste in admixture with activated sludge in an initial liquid treating stage while controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS concentration to maintain a high ratio of food to biomass and a dissolved oxygen content in the mixed liquor of such initial stage numerically equal in parts per million to at least 2 or one-tenth the numerical value of the ratio Fs/Ma, whichever is the greater, thereby promoting selective production and growth of dense, rapid-settling microorganisms and thereafter transferring the so-aerated mixed liquor to at least one additional stage of aeration to substantially complete the oxidation and assimilation of remaining BOD values; said high ratio of food to biomass in said initial stage being at least equal to a value expressed by the ratio Fs/Ma wherein Fs is equal to 1.5 times the weight of soluble BOD5 charged per day to said initial aeration stage and Ma is equal to the weight of MLVSS in said stage times the coefficient Alpha , Alpha being the ratio of the oxygen uptake rate of the MLVSS present in said mixed liquor divided by the reference maximum specific oxygen uptake rate MSOUR at the treating temperature, MSOUR being determined by the equation: 1n MSOUR 33.92 - 8640/T(*K).

Claim 5

The method of treating BOD-containing aqueous waste which comprises aerating a mixed liquor comprising such waste in admixture with activated sludge in an initial liquid treating stage while controlling at least one variable selected from the group consisting of initial stage influent residence time, activated sludge recycle rate, and initial stage MLVSS concentration to maintain a high ratio of food to biomass and a dissolved oxygen content in the mixed liquor of such initial stage numerically equal in parts per million to at least 2 or one-tenth the numerical value of the ratio Fs/Ma, whichever is the greater, thereby promoting selective production and growth of dense, rapid-settling microorganisms and thereafter transferring the so-aerated mixed liquor to at least one additional stage of aeration to substantially complete the oxidation and assimilation of remaining BOD values; said high ratio of food to biomass in said initial stage being at least equal to a value expressed by the ratio Fs/Ma wherein Fs is equal to 1.5 times the weight of soluble BOD5 charged per day to said initial aeration stage and Ma is equal to the weight of MLVSS in said stage times the coefficient Alpha , Alpha being the ratio of the oxygen uptake rate of the MLVSS present in said mixed liquor divided by the reference maximum specific oxygen uptake rate MSOUR at the treating temperature, MSOUR being determined by the equation: 1n MSOUR 33.92 - 8640/T(*K).