Using Polymers to Improve Current Water Treatment Technologies: Contaminant Removal and Role of Microbial Communities
Membrane filtration and adsorption are two widely used water treatment technologies that have the potential to deliver clean water to meet the increasing demand worldwide. However, various issues, mainly fouling in membrane filtration, and obstacles in producing cheap, reusable, and high capacity adsorbent for adsorption, prevent these technologies to perform at their fullest capacity. Polymers are important players in both technologies from coating membranes to improve its antifouling properties, to the development of polymer composite adsorbents to remove more contaminants from water. Although their roles have been studied extensively, there are still a lot of knowledge gaps for polymers in membrane filtration and adsorption. Most of the studies on fouling of membrane have been done in conditions far from the reality, which possess complex water chemistries. More importantly, the combined effects of different parameters like antiscaling polymers, microbial communities, and calcium-containing crystals in bulk and on the surface of the membrane have been neglected. In this study, it was demonstrated that microbial communities from fresh water, wastewater, and seawater sources, not only could trigger the mineralization of calcium-containing crystals in undersaturated solutions, but also could determine the crystal structure. More importantly, this biotic-induced mineralization could not be inhibited by antiscaling polymers. Another knowledge gap about membrane filtration is how a coating of an antiscaling polymer, polyacrylic acid (PAA) along with an antimicrobial nanomaterial, graphene oxide (GO), would affect biofouling in seawater desalination. While GO gave the membrane antibiofouling property due to its antimicrobial property, PAA did not enhance biofouling resistance, although it made the surface more hydrophilic and negatively charged. Another application of polymers in water treatment was the investigation of polymers able to remove anionic pollutants. In this investigation, a positively charged polymer composite of chitosan and polyethyleneimine was synthesized by a facile method and used to adsorb nitrate in continuous mode and Cr(VI) in batch and continuous modes. A packed-bed column with the polymer composite showed excellent adsorption and recovery for nitrate, without losing the adsorption capacity after ten adsorption/desorption cycles. For Cr(VI) removal, the adsorbent had one of the highest Langmuir maximum adsorption capacities and was able to remove chromium from the complex chemistry of real electroplating wastewater in both batch and continuous modes.