Removal of coliform bacteria from dairy wastewater using graphene-silver nanocomposite

Nanoparticles are widely used in removing bacteria from water and sewage. This study evaluated the effect of graphene/silver nanocomposite on the removal of coliform from a dairy effluent. The composition was synthesized and its properties were determined using different techniques such as SEM, XRD and FTIR. The effects of various factors, including pH, adsorbent dose and contact time on coliform removal from solution were studied. Antimicrobial activity of the nanocomposite was examined by pour plate method in a VRBL medium. After preparing the VRBL medium from the sewage effluent, 1 mL of nanocomposite solution and 1 mL of bacterial suspension containing 9×10^4 CFU/mL were added into each of the plates. According to the results, the rate of silver ion release is faster as pH decreases, which naturally results in the increase of disinfection. Moreover, a higher percentage of removal occurred with an increase in contact time and nanocomposite dose due to higher exposure to nanoparticles and their higher penetration into bacterial cell membrane. Therefore, nanoparticles produced by this method exhibited good antibacterial activity, so that 100% of bacteria were eliminated at a nanocomposite concentration of 3.4 g/L and pH=5, after 90 min.