Removal of natural organic matter from water using chemically activated coffee husk

Abstract

Natural organic matters are one of the detrimental parameters to be considered in conventional drinking water treatment processes. The existence of high concentration of natural organic matter in raw and processed water can result in taste, color and odor problem, and facilitate bacterial regrowth in water distribution systems. Moreover, in conventional drinking water treatment systems where chlorine is used as disinfectant, they act as the precursor for the formation of disinfection by products such as trihalomethen, which have carcinogen effect on the health of human being. Hence, they have to be regulated by different treatment mechanisms beyond the conventional drinking water treatment systems. In this study, group of batch adsorption experiments were conducted to examine the HA adsorption capacity of chemically activated coffee husk as the function of contact time, pH of the solution, initial humic acid (as representative of NOM) concentration, adsorbent dose, agitating speed and desorption study parameters. The study revealed that adsorption capacity increased with time until equilibrium time reached 60 min and the maximum adsorption yield was 93.7%. The adsorption of HA was greatly dependent on pH of the solution. Generally, adsorption was remained at a maximum level within PH range 3-6, the optimum pH for maximum HA adsorption was revealed at pH = 3 with maximum adsorption 94.33% and above pH = 6 the HA uptake of the adsorbent dramatically decreased. The amount of HA adsorbed decreased with increasing the dose of adsorbent to 25 g/L. CACH reduced 10mg/L HA to 1.67mg/L which is below the WHO guideline value of 2 mg/L dissolved organic matter in drinking water to prevent formation of dis-infection by product, Hence the 1 g/L CACH was considered as an optimum dose. Also the amount of HA adsorbed increased with increasing the initial HA concentration from 0.5 mg/L to 20 mg/l. The adsorption kinetics data of HA adsorption followed well the pseudo-second order equation with the correlation coefficient R= 0.997 and Ks = 0.078. The equilibrium adsorption data were better represented by the Langmuir isotherm (R2 = 0.998, SSE = 0.006). The desorption experiment done using alkaline solution of 0.1M and 0.2 M of NaOH at pH >11, and the desorption capacity was 70.44 and 90.72% respectively. Thus CACH could be used as a media for HA removal.