Biologic system pretreatment wastewater comes from several sources. Small communities, strip malls, industrial parks, septic tank haulers, and industrial companies that do not have sanitary sewer available, and therefore have to treat their own wastewater. The wastewater is generated when domestic wastewater and light industrial wastewater are combined and have to be treated together. For example a strip mall on a rural highway that has a motel and a coffee shop or maybe a bakery, or an industrial park with light industrial. The DAF is used to remove some solids, floating material and oils and reduce suspended solids prior to the biologic system to reduce the load. This enables the biologic system to be smaller, produce less sludge and avoid performance issues due to the presence of oils and greases.
Biologic System Pretreatment wastewater is treated by simply processing direct to the DAF or by adding a flocculent. The goal of the DAF here is to to produce a consistent waste stream and reduce the load on the biologic system.
The typical method to treat Biologic System Pretreatment wastewater is as follows:
Stage 1 - Flash Mix:
The wastewater is introduced to the flash mix zone where a polymer flocculent is added. This stage maximizes flocculent dispersion throughout the wastewater.
Stage 2 - Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate the floc into larger particles suitable to be enmeshed with the air bubbles.
Clarifier, Dissolved Air Flotation (DAF):
The flocculated wastewater is introduced into the DAF inlet where the floc particles are comingled with a pressurized dissolved fine bubble recycle stream. The floc particles attach to the bubbles and float to the surface where they are mechanically skimmed into the float scum sludge chamber. The clarified treated water then exits the end of the DAF and flows downstream to sewer or further treatment if necessary. The DAF system bubbles come from a Recycle Air Dissolving system that takes a portion of treated effluent, pressurizes it and introduces air to be dissolved. The dissolved air comes out of solution and forms a fine bubble stream when the pressure is released at the DAF entrance in the presence of floc wastewater.
DAF Sludge Handling:
The resulting DAF waste scum/sludge is removed from the DAF automatically as the scum accumulates and is pumped to the biologic solids tank and handling equipment.
The sludge should be processed with the biologic system sludge and disposed of in accordance with environmental regulations.
Septic tank haulers
Industrial campuses and facilities that must treat their own domestic and light industrial wastewater together.