Chromium is the most common metal found in wastewater discharge of petrochemicals and leather industries. It is also used in metal alloys,pigments,paints,cement,paper,rubber materials. Due to its high toxicity it is very harmful either at high or low level exposure. Thus removal of hexavalent chromium ions from wastewater is essential. It commonly removed by Chemical Precipitation,Ion Exchange,Reverse Osmosis. In this project we try to remove it by simple adsorption process using charcoal and sawdust as adsorbents and achieve upto 97% removal. First we prepare Cr reach solution using K2Cr2O7 of 1 to 10ppm concentration range,various amount of adsorbent added in a well stirred vessel for specific time period. Then the samples taken to Spectrophotometer,measuring pink violet complex formed by 1,5-diphenylcarbazide at 541 nm. We also compare this value with membrane separation. Experimentally we prove that removal percentage of Cr using sawdust is better than using charcoal as adsorbent.

3.  Commonly removed by chemical
precipitation, ion exchange, reverse osmosis
and charcoal adsorption.
 Treatment methods differ depending on the
conditions of the process and properties of
wastewater.

4.  Lab grade activated carbon (300 mesh) was used
as adsorbent.
 All the solutions (1-10 ppm) were prepared using
the reagent-grade K2Cr2O7 and distilled water.
 Adsorption was done from 100 ml K2Cr2O7
solution using various amount of adsorbent in a
well stirred vessel for a specific time period.
 The chromium content in the fluid phase was
determined by UV absorption
spectrophotometer.

5. Conc.
of Cr
Amount of
adsorbent
(gm)
Time for
optimum
adsorption
Maximum
Cr removal
percentage
1 ppm 0.5 gm
0.75 gm
1.0 gm
60 min
15 min
20 min
89.46 %
91.76 %
93.05 %
2 ppm 0.5 gm
0.75 gm
1.0 gm
25 min
15 min
10 min
88.05 %
90.42 %
93.16 %
5 ppm 0.5 gm
0.75 gm
1.0 gm
5 min
5 min
10 min
87.68 %
90.27 %
94.49 %
5 ppm
(Regenerated
Charcoal)
1.0 gm
10 min 65.06 %
Percentage removal of chromium from solutions of different
Concentration using various amount of activated charcoal

6.  With the increase of adsorbent amount from per
100 ml solution , the percentage removal of
chromium increases from 86% to 94 % .
 As the surface area of the adsorbent increases
with the increase of adsorbent resulting higher
percentage of solute removal.

7. Figure 1. Effect of adsorbent amount and contact time on percentage removal of Cr from 1 ppm solution

8.  89 % adsorption was achieved using 0.5gm /100
ml 1 ppm solution.
 Removal percentage increased up to 93% within
very short contact time (20min ) when amount of
adsorbent doubled .

9. Figure 2. Effect of adsorbent amount and contact time on percentage removal of Cr from 5 ppm solution

10.  87 % adsorption was achieved using 0.5gm /100
ml 5 ppm solution.
 94 % adsorption was achieved only within 10
min when the amount of adsorbent doubled.

11. Figure 3. Effect of solute concentration and contact time on percentage removal of Cr from various
solution (using 1 gm adsorbent)

12.  Removal of Cr percentage from 5 ppm is
comparatively higher than 1ppm solution.
 Removal tendency decreases after attaining an
optimum adsorption, which is quite natural for
de-sorption after a certain amount of adsorption.

13. Membrane Separation
Process
Figure 4. Experimental set up for UF/RO
membrane unit.
 Separation of Cr has been done
using specified UF and RO unit
Results of UF are not significant
but RO is quite satisfactory.

14. Figure 5. Variation of permeate flow with
trans-membrane pressure drop.

15.  Permeate flow rate increased from 7.6 to 9.0 LPM
with the increase of trans-membrane pressure drop
from 12 psi to 15 psi.
 Removal percentage of Cr increased from 82 % to
98.5 % with the increase of trans-membrane pressure
drop.
 Rejection percentage may be increased by
maintaining proper trans-membrane pressure drop.