Assessment of the influence of counter ions on biosorption of copper cations in brewer's spent grain - Waste product generated during beer brewing process

Abstract

The influence that conditioning leached ground barley grain (known as “brewer's spent grain” (BSG)) has on the effectiveness of copper cation sorption was analysed. Saturation with counter ions of functional groups present on the grain surface was carried out in hydrochloric acid, sodium hydroxide, sodium and calcium chloride solutions. For comparison, BSG was also conditioned in demineralised water. Spent barley grain is a by-product of the brewing industry which can be used as a biosorbent in the removal of heavy metals from waste water. Emphasis is placed on the effect of competitive sorption of copper and hydrogen cations and the negative influence of a solution alkalinisation on sorption efficiency. It was demonstrated that the changes of Cu2+ and H+ concentration partition coefficients in the solution and BSG during the sorption process are not monotonic. It was also demonstrated that, compared to raw BSG, conditioning BSG in a hydrochloric acid solution improves sorption efficiency by approximately 40%, which is an important conclusion as regards application. Saturation of functional groups with Na+ and Ca2+ counter ions, which have weak affinity with functional groups, does not improve Cu2+ sorption efficiency; however, it considerably increases the efficiency of hydrogen cations sorption which, in consequence, increases the solution pH. Due to similar chemical characteristics of functional groups, the analyses can be applied in order to optimise sorption processes in other biosorbents. It has been confirmed that ion exchange is the main mechanism of heavy metal sorption in natural sorbents.