Effluent treatment is one of the chief concerns of pulp and paper mills. Pulp mills need to efficiently produce pulp as well as treat the effluent at a reasonable cost. Typical BOD5 (biochemical oxygen demand) concentrations from pulp mills range from 100 to 5,000 ppm BOD5. In addition, this wastewater is toxic to fish, low in dissolved oxygen levels, and usually hot. Prior to discharge, wastewater needs to be neutralized, oxygenated and cooled to properly control the organics in the wastewater.
Jet aeration systems use a combination of pumps and blowers to provide efficient oxygen transfer and mixing. Jet aeration systems efficiently treat pulp and paper mill wastewater while requiring little maintenance. For these reasons, jet aerators are often considered the best method of treating wastewater for pulp and paper mills.
A pneumatic backflush system can virtually eliminate all in-basin maintenance and manual cleaning, thereby maintaining high oxygen transfer rates and efficiencies.
By simply shutting off the pump, opening the backflush valve and continuing to supply air to the system, the unit’s aerodynamic design converts the submerged aeration system into a pneumatic air lift pump.
In the backflush mode, air flow blows backward through the system, displacing the liquid in the liquid distribution line and pumping the surrounding liquid in the reverse direction through the jets and liquid lines. This cleans the jet nozzles and the submerged aeration system of fouling material and debris. Most plants backflush their aeration tank once each month to maintain maximum efficiency.
AOX (adsorbable organic halogens) are formed by a chemical reaction from the pulp bleaching processes which use chlorine or chlorine dioxide as bleaching agents. Jet aeration systems produce acceptable AOX levels in the effluent. Efficient mixing results in low AOX effluent.