Separation Process
Water clarification systems utilize micro-scale air bubbles to capture suspended solids and separate them from industrial process water through buoyancy. Dissolved air flotation introduces pressurized water saturated with dissolved air into an atmospheric clarification basin containing paper mill white water or de-inking effluent. Pressure drop across specialized discharge nozzles releases air as fine bubbles ranging between ten and one hundred micrometres in diameter.
These rising micro-bubbles attach to suspended cellulose fines, mineral fillers, ink particles and adhesive stickies, floating the agglomerated solids into a dense surface sludge blanket. A mechanical skimmer continuously sweeps the floated scum into a collection trough while clarified water exits through submerged underflow baffles.
Mill Water Loop
Water clarification via dissolved air flotation governs freshwater consumption and fibre recovery efficiency across recycled containerboard and tissue manufacturing mills. Reclaimed process water must maintain suspended solids concentrations below fifty parts per million to prevent nozzle clogging in high-pressure shower systems across the forming section. Chemical conditioning preceding the flotation tank destabilizes colloidal charges through coagulant dosing before long-chain polymers bind destabilized flocs together.
Optimizing bubble size distribution determines the rising velocity of the solids aggregate, balancing clarifier hydraulic retention times against raw pulp feed rates. Clean underflow water recirculates directly back into pulping and dilution circuits, reducing thermal energy loss by maintaining elevated water temperatures across the mill system. Thickened skimmer solids enter sludge dewatering units, yielding a dry cake suitable for land application, thermal incineration or composite board production.
Process Limitation
Clarification by dissolved air flotation loses operational efficacy when processing wastewater containing excessive levels of dissolved organic substances or non-foaming surfactant chemistries. Surfactants lower surface tension excessively, preventing micro-bubbles from forming stable physical bonds with hydrophobic contaminants. High effluent temperatures above sixty degrees Celsius suppress air solubility within the saturation vessel, reducing bubble volume and slowing float rates.
Severe hydraulic surges also overwhelm retention basins, carrying unseparated solids under the discharge baffles and contaminating clean white water collection tanks.
