Chemical oxygen demand reduction from coffee processing waste water – A comparative study on usage of biosorbents prepared from agricultural wastes

The utilization of three novel and distinct agricultural waste materials, namely casuarina fruit powder (CFP), sorghum stem powder (SSP) and banana stem powder (BSP) as low cost adsorbents for reducing chemical oxygen demand (COD) levels of coffee industry wastewater has been examined. Prepared adsorbents were characterized by scanning electron microscopy (SEM), Energy-dispersive x-ray spectroscopic (EDAX) and Fourier Transform Infrared Spectroscopy. The effects of parameters like adsorbent dose, pH, temperature, agitation rate and time of adsorption on the reduction of COD levels were analyzed for each adsorbent individually and the efficiency order is CFP>SSP>BSP. Based on the extent of compatibility to Freundlich/Langmuir adsorption isotherm and different models (pseudo-first order and second order, Boyd, Weber’s and Elovich), simultaneous occurrence of chemisorption and physisorption was proposed. Based on the observations, it is proposed that three kinetic stages involve in adsorption process viz., diffusion of sorbate to sorbent, intra particle diffusion and then establishment of equilibrium. As these three adsorbents exhibit adsorption capacity more than 80%, the adsorbents prepared from agricultural wastes have promising role towards reduction of COD from industrial wastewater to contribute environmental protection.