Adsorption of paraquat herbicide in water using humic acids supported on sludge from tap water production entrapped in alginate beads

Abstract

Adsorption of paraquat in water using humic acids supported on sludge from tap water production or alum sludge entrapped in alginate beads has been studied. The adsorbent was characterized by Fourier transform infrared spectroscopy showing that it composes of humic acids, alum sludge and alginate in beads. Afterwards, the type and amount of adsorbents were studied including bare alginate beads, humic acids-alginate beads, alum sludge-alginate beads, alum sludge-humic acids-alginate beads-1 and alum sludge-humic acids-alginate beads-2. These adsorbents were subjected to the paraquat adsorption study in aqueous solutions. The results showed that all adsorbents can adsorb paraquat, especially the alum sludge-humic acids-alginate beads that can adsorb paraquat with the maximum adsorption percentage of 93.6%. After that, the adsorption efficiency of the alum sludge-humic acids-alginate beads was investigated in batch system. The optimal pH of adsorption was 4-10. The adsorption kinetics was fitted to the pseudo-first order kinetic model. The adsorption behavior of paraquat obeyed the Freundlich adsorption isotherm. The maximum adsorption amount from experiment was more than 94.5 mg/g. In column study, the efficiency of paraquat absorption decreased with the increasing flow rate of the solution. The result of the effect of eluent concentration showed that hydrochloric acid and nitric acid can elute the paraquat from the adsorbent but it can also destroy the adsorbent surface. Meanwhile, sodium chloride can elute paraquat from the adsorbent without destroying the adsorbent surface. In addition, the alum sludge-humic acids-alginate beads were applied to the real water samples collected from agricultural areas at Suphan Buri, Lopburi and Chachoengsao provinces. The adsorbent has a potential to remove paraquat from real water samples.