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.

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.

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 min15 min 20 min

89.46 %91.76 %93.05 %

2 ppm 0.5 gm0.75 gm 1.0 gm

25 min 15 min10 min

88.05 %90.42 %93.16 %

5 ppm 0.5 gm 0.75 gm1.0 gm

5 min5 min10 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

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.

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

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 .

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

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.

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

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.

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.

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

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.