Following are the sequences and process for the chemical treatment of the effluent where all the doses mentioned are from a typical case. ( For a specific project a Jar Test is recommended to determine exact doses.)
Add Bentonite @ 50-100 gram per m3/ or up to the point when floating oil has disappeared after through mixing.
Add Alum solution/Poly-Aluminum Chloride (PAC) slowly till coagulated particles show pin flocks.
Test a small batch in a beaker to determine the exact dose.
Experiments showed from 350 to 400 ppm Alum dosing effecting reduction in COD by 45-55 % , in BOD by 45-55 % , in TSS by 45-55 % and in Colour Removal by 70-75 % in case of Parboiled Rice Mill Effluent.
Experiments showed from 350 to 400 ppm PAC dosing effecting reduction in COD by 80-85 % , in BOD by 75-80 % , in TSS by 70-80 % and in Colour Removal by 85-92 % in case of Parboiled Rice Mill Effluent.
Add Chitosan from 0.5 to 1 ppm (1mg. /Liter) if oil is present in the raw effluent and or Polyelectrolyte (such as the one supplied by SNF, Ashland-Hercules or equivalent) @ 10-50 ppm, till the pin flocks have turned into larger flocks and are clearly visible.
If need be, small batch test should be conducted to determine the dose.
At this point as the flocks will have clearly formed which means the coagulation is complete.
So it is time for flocculation to begin.
Check the pH. If it is in the acidic side add pre-diluted lime/caustic solution till the pH reaches 6.5-7 while stirring well.
Till this point if you are using a mechanical stirrer use it at 120-150 rpm for 10-15 min.
Add pre-diluted anionic PAM (Polyacrylamide) in pre-diluted solution @ 2-10 ppm (2 gm to 10 mg of PAM powder/Liter) up to the point when all the flocks have come together and formed larger and quickly settling flock.
In case of ready made PAM solution is used, the dose will be accordingly to the situation and strength of the preparation.
During this flocculation phase use the stirrer at 10-20 rpm for 10-15 min.
Stop all agitation and let the flocks settle down. This phase will require between 40-60 minutes.
After the larger flocks settle down at the bottom, drain them out through the bottom port.
Start filtration of the remaining supernatant or take it to secondary biological treatment prior to filtration as may be the design according to requirement.
Schematic Diagram of Advanced Effluent Treatment Plant for Parboiling or Puffed Rice Mill and other similar food processing industries.
Effluent is collected in an underground collection tank which doubles up as an aerobic bioreactor where Activated Sludge Process (ASP) or Granulated Aerobic Sludge Process (GASP) is followed depending on design.
In case of parboiling rice mil & some other industries, released effluent from the processing area have temperature as high as 55 degree C.
To recover the energy heat exchangers can be installed.
It will also reduce problem of thermal loading in the collection pond causing damages to microbial population.
In case of industries with critical TDS components of pollutants, specialty treatment by resins are looked upon as possibility.
If there is a need, secondary microbial and or algal treatment is considered as option in addition to this design before filtration.
Secondary and intermediate holding tank to transfer supernatant after chemical treatment before filtration enhances the capacity of the ETP.
Designs for Civil construction and fabrication of supports and mounds are provided for the clients upon such request.
Upon request our approved and associated vendors provide such infrastructure to the client.