Reuse of Industrial Wastewater Effluent in the Petrochemical Industry
335
3.3 Chemical Flocculation and OAF
Laboratory and pilot plant studies have been carried out, developing design and
operational parameters for this process. The flotation unit is covered in order to
avoid VOC emission, therefore nitrogen is used instead of air. The flotation
system consists of three parallel units with a capacity of 200 m 3 hr- 1 each. The
flocculant in use is a cationic polyelectrolite in a dose of 7 to 10 mg rl. Later
studies performed by Galil and Wolf (2000) on this wastewater indicated that the
chemical flocculation - DAF could efficiently remove the emulsified phase, which
could be aggregated and separated up to the surface. However, it was found that
the process could also remove substantial amounts of dissolved organic matter,
due to the hydrophobic characteristics of some of the substances, which could
bind to the solid surfaces.
3.4 Biological Treatment
A comparative study has been carried out including activated sludge, rotating
biological contactor (RBC), and aerated lagoons. These bioprocesses represent
two different concepts: activated sludge and RBC are considered as intensive
processes, developing high concentrations of active biomass and high cell
residence time (CRT), while aerated ponds are considered as a partial bioprocess,
involving low biomass and low CRT values (no biosolids recycling). The aerated
ponds alternative was adopted because of the possibility of lowering the
investment cost. It was clear that in this case, additional treatment would be
necessary. This alternative was based on sharing the bioprocess tasks between: (1)
the aerated ponds, performing carbonaceous substrate removal (2 days detention
time); (2) chemical clarification for efficient removal of suspended bio-solids and
colloids synthesized by the aerated ponds; (3) completion of the bioprocess within
the recirculated cooling system by using its biooxidation capacity. The experience
accumulated over the past 10 years shows that this combination has achieved good
and reliable biotreatment. However, in the future, the aerated ponds will be
upgraded to an intensive biological process, which will perform carbonaceous
substrate removal and nitrification.
3.5 Chemical Clarification
A lime contact flocculation-clarification unit, designed for a flow of 600 m 3 hf l is
operated for efficient separation of biosolids, as well as for softening the effluent
which goes to the water-cooling system. A second identical unit works on the
treatment of water from inside the cooling system (side-stream treatment). Part of
the side stream-treated effluent goes back to the cooling system, while the
remaining effluent is disposed to the neighboring river (Fig. 1). Both lime contact
flocculation-clarification units are operated at pH values of 10.7 for enabling
removals of calcium carbonate and magnesium hydroxide.
335
3.3 Chemical Flocculation and OAF
Laboratory and pilot plant studies have been carried out, developing design and
operational parameters for this process. The flotation unit is covered in order to
avoid VOC emission, therefore nitrogen is used instead of air. The flotation
system consists of three parallel units with a capacity of 200 m 3 hr- 1 each. The
flocculant in use is a cationic polyelectrolite in a dose of 7 to 10 mg rl. Later
studies performed by Galil and Wolf (2000) on this wastewater indicated that the
chemical flocculation - DAF could efficiently remove the emulsified phase, which
could be aggregated and separated up to the surface. However, it was found that
the process could also remove substantial amounts of dissolved organic matter,
due to the hydrophobic characteristics of some of the substances, which could
bind to the solid surfaces.
3.4 Biological Treatment
A comparative study has been carried out including activated sludge, rotating
biological contactor (RBC), and aerated lagoons. These bioprocesses represent
two different concepts: activated sludge and RBC are considered as intensive
processes, developing high concentrations of active biomass and high cell
residence time (CRT), while aerated ponds are considered as a partial bioprocess,
involving low biomass and low CRT values (no biosolids recycling). The aerated
ponds alternative was adopted because of the possibility of lowering the
investment cost. It was clear that in this case, additional treatment would be
necessary. This alternative was based on sharing the bioprocess tasks between: (1)
the aerated ponds, performing carbonaceous substrate removal (2 days detention
time); (2) chemical clarification for efficient removal of suspended bio-solids and
colloids synthesized by the aerated ponds; (3) completion of the bioprocess within
the recirculated cooling system by using its biooxidation capacity. The experience
accumulated over the past 10 years shows that this combination has achieved good
and reliable biotreatment. However, in the future, the aerated ponds will be
upgraded to an intensive biological process, which will perform carbonaceous
substrate removal and nitrification.
3.5 Chemical Clarification
A lime contact flocculation-clarification unit, designed for a flow of 600 m 3 hf l is
operated for efficient separation of biosolids, as well as for softening the effluent
which goes to the water-cooling system. A second identical unit works on the
treatment of water from inside the cooling system (side-stream treatment). Part of
the side stream-treated effluent goes back to the cooling system, while the
remaining effluent is disposed to the neighboring river (Fig. 1). Both lime contact
flocculation-clarification units are operated at pH values of 10.7 for enabling
removals of calcium carbonate and magnesium hydroxide.