Conclusion

The experimental results show that coffee husk is an excellent alternative for the removal of Cr (VI) from aqueous solutions. The biosorption of Cr (VI) was dependent on pH, contact time, adsorbent dosage and initial metal concentration. Both Langmuir and Freundlich isotherms were followed by the adsorption of Cr (VI). The infra red spectral analysis showed that the functional groups like carboxyl and hydroxyl ions played an important role in the biosorption of Cr (VI). As the coffee husk is easily available from coffee processing units, its utility as biosorbent will be economical and be viewed as part of waste management strategy. Containing very less amount of protein (N = 0.63), coffee husk is advantageous over the protein rich algal and fungal biomass projected as metal biosorbents, since proteinous materials are likely to putrefy under moist conditions.  Moreover, the desorption experiments show that the metals can be desorbed after adsorption and Cr (VI) can be recovered.  The present adsorbent can be used at an industrial scale to remove chromium ions from the effluents before discharging into the environment. Coffee husk can replace the expensive activated carbon in the adsorption process. Most of the electroplating effluents contain chromium as one of the major contaminant, which can be removed in a cost-effective and efficient manner by coffee husk.