Dissolved air flotation system and methods for biological nutrient removal

A method of treating wastewater comprising:

• directing the wastewater into a contact tank and mixing the wastewater with an activated sludge to form an activated mixed liquor;
• directing the activated mixed liquor into a dissolved air flotation unit and separating the activated mixed liquor to form a floated biosolids and an effluent;
• selectively directing a first portion of the floated biosolids into a fermentation unit and a second portion of the floated biosolids into an anaerobic digester, and fermenting the first portion of the floated biosolids in the fermentation unit to form a fermented solids;
• directing the effluent to a biological treatment unit;
• and
• selectively directing a first portion of the fermented solids into the biological treatment unit and a second portion of the fermented solids into the anaerobic digester, an amount of the first portion of the fermented solids directed into the biological treatment unit being selected responsive to a determination of a required soluble chemical oxygen demand of the biological treatment unit, and biologically treating the effluent with the first portion of the fermented solids in the biological treatment unit to form a biologically treated mixed liquor.

A wastewater treatment system comprising:

• a contact tank having a first inlet fluidly connectable to a source of wastewater to be treated, a first outlet, and a second outlet, the contact tank configured to treat the wastewater with activated sludge to form a first mixed liquor;
• a dissolved air flotation unit having a first inlet fluidly connected to the first outlet of the contact tank, a second inlet fluidly connected to a source of gas, a first floated solids outlet, and an effluent outlet, the dissolved air flotation unit configured to treat the first mixed liquor with the gas to form floated solids and an effluent;
• a fermentation unit having a first inlet fluidly connected to the first floated solids outlet, and a first fermented solids outlet, the fermentation unit configured to treat at least a portion of the floated solids to form fermented solids;
• and
• a biological treatment unit including:
• an anaerobic region having a first inlet fluidly connected to the effluent outlet, and an outlet;
• an aerated anoxic region having a first inlet fluidly connected to the second outlet of the contact tank, a second inlet fluidly connected to the outlet of the anaerobic region, and an outlet;
• an aerobic region having a first inlet fluidly connected to the outlet of the aerated anoxic region, a second inlet fluidly connected to the effluent outlet, and an outlet;
• a first inlet fluidly connected to the effluent outlet;
• a second inlet fluidly connected to the first fermented solids outlet;
• and
• an outlet,
• the biological treatment unit configured to treat the effluent with at least a portion of the fermented solids to form a second mixed liquor.

A method of treating wastewater comprising:

• directing the wastewater into a contact tank and mixing the wastewater with an activated sludge to form an activated mixed liquor;
• directing the activated mixed liquor into a dissolved air flotation unit and separating the activated mixed liquor to form a floated biosolids and an effluent;
• selectively directing a first portion of the floated biosolids into a fermentation unit and a second portion of the floated biosolids into an anaerobic digester, and fermenting the first portion of the floated biosolids in the fermentation unit to form a fermented solids;
• directing the effluent to a biological treatment unit;
• and
• selectively directing a first portion of the fermented solids into the biological treatment unit and a second portion of the fermented solids into the anaerobic digester, and biologically treating the effluent with the first portion of the fermented solids in the biological treatment unit to form a biologically treated mixed liquor, treating the effluent with the first portion of the fermented solids comprising reducing a concentration of dissolved phosphorous in the effluent when forming the biologically treated mixed liquor.