Biomass selection and control for continuous flow granular/flocculent activated sludge processes

A separator within a clarifier in a system for biological treatment of wastewater including organic sewage, comprising:

• a clarifier tank with an inflow pipe receiving activated sludge from upstream liquid process zones of the system,
• the separator including an energy dissipating inlet connected to the inflow pipe and receiving sludge having both floc and granular biomass,
• the energy dissipating inlet having a bottom plate and internal baffles configured to direct sludge in generally even distribution radially outwardly into liquid volume of the clarifier, such that sludge solids settle by gravity to a tank floor sloped downwardly toward the center of the clarifier, with granular sludge settling faster than floc sludge and the floc sludge settling slower and more outwardly,
• the separator further including the clarifier having a granular sludge exit through the tank floor, near the center of the clarifier, and a floc sludge exit through the tank floor spaced outwardly from the granular sludge exit, and
• the separator further including an annular sludge dividing deflector plate extending up from the tank floor and positioned radially inwardly from the floc sludge exit, so that floc sludge, which tends to settle more slowly and travel farther outwardly in the clarifier than granular sludge, tends to settle on the tank floor outwardly of the dividing deflector plate while the denser granular sludge tends to settle inwardly of the dividing deflector plate,
• whereby sludge exiting the granular sludge exit has a higher concentration of granular sludge than sludge exiting at the floc sludge exit of the clarifier.

A wastewater treatment system for biological treatment of wastewater including organic sewage, the system including a liquid process configuration for removal of at least nitrogen and for concentrating biomass, in a continuous flow process, comprising:

• a plurality of process zones, including a first process zone receiving influent wastewater in continuous flow and mixing the influent wastewater with biomass to produce a mixed liquor,
• a biomass separator downstream of the process zones, to produce a mixed liquor,
• the mixed liquor in the process zones including a first type of sludge and a second, faster settling sludge that settles faster than the first type of sludge,
• a biomass separator downstream of the process zones, receiving mixed liquor with the first and second types of sludge, the separator having separation means for separating out the second type of sludge from the mixed liquor, so that the separator produces a first effluent with predominantly the first type of sludge and a second effluent enriched in the second type of sludge, and
• a stream of clarified liquid to join the mixed liquor entering the separator when needed for dilution of the flow into the separator to enhance separation.

A wastewater treatment process with a series of biological process zones, with continuous flow of wastewater through the series of zones, a first of the biological process zones being an anaerobic zone for encouraging selective growth of granular biomass, comprising:

• providing at least two successive stages in the anaerobic zone, including a first stage and a second stage,
• into a continuous flow of influent wastewater, introducing a first portion of a recycled activated sludge (RAS) stream from a downstream process zone of the series of biological process zones to produce a continuous combined raw influent/RAS flow into the first stage,
• the first stage being of limited volume, and dwell time in the first stage being no greater than 30 minutes, so as to provide for intimate contact between the incoming wastewater, rich in food, and the RAS, rich in biological activity, such that granular biomass present in the RAS is exposed to the food of the incoming wastewater for consumption and storage leading to growth of granules in further non-anaerobic zones,
• operating a mixer in the first stage to mix the RAS and incoming wastewater to provide a mixed liquor,
• moving the mixed liquor in continuous flow to the second stage,
• introducing to a bottom region of the second stage a second, remaining portion of the RAS to mix with the mixed liquor in the second stage,
• in the second stage, operating a mixer intermittently such that mixing of the incoming RAS and sludge from the first stage occurs for a time, then the mixer is shut off for a selected period of time whereby heavier granular biomass tends to settle deeper than floc biomass in the second stage, so that said remaining portion of RAS entering the second stage comes into intimate contact with the settled granular biomass and particulate BOD, and
• the proportions of incoming wastewater and RAS in the first stage being such as to create a food to mass ratio (F/M) of at least 5.