Novel biomimetic membrane technologies for the application in water treatment and energy production

Abstract

In the light of global water scarcity and increasing water and energy demand, new ways to provide safe and clean water and renewable energy sources have to be found. This topic does not only affect developing countries, but affects industrialized countries as well. The perception of wastewater has changed in recent years, from being seen as waste to being seen as a resource for water, energy and valuable compounds. Membrane technology can be used to reclaim water from municipal and industrial wastewater. In recent years, forward osmosis (FO) has raised increasing interest as an emerging membrane technology, because of its ability to efficiently reject pathogens and almost all solutes in the wastewater. When forward osmosis is integrated into hybrid systems, for example in combination with reverse osmosis (RO), high-quality water can be recovered. FO can also be combined with anaerobic membrane bioreactors (FO-AnMBR) in order to simultaneously treat wastewater and produce biogas, which is a renewable energy source. The overall aim of this thesis is to evaluate biomimetic FO membranes for water recovery and biogas production. The goals are 1) to investigate the FO membrane performance in terms of water flux and nutrient rejection, both in stand-alone FO as well as in combination with RO 2) to analyse the fouling mechanisms and cleaning efficiency and 3) investigate process performance in terms of water flux and biogas production in FO-AnMBRs. The results show that a wide variety of wastewaters, ranging from anaerobically digested manure to microbial biomass, can be treated with FO, and high rejection of nutrients (ammonia, orthophosphate, chemical oxygen demand (COD)) can be achieved. The predominant fouling mechanisms in these cases were organic fouling, as well as biofouling. When FO was combined with RO, the double-barrier mechanisms achieved very high nutrient removal. Chemical cleaning was able to restore 75% of the initial water flux of the pristine membrane. When FO was integrated into an anaerobic membrane bioreactor, it was found that the methane production rate increased in comparison to the membrane-less start-up phase, indicating that a higher organic loading rate can be achieved due to the membrane. However, bioreactor performance in terms of methane production yield and rate remained unstable, possibly indicating shear stress or inadequate C/N ratio of the brewery wastewater. Taken together, these results show the feasibility of water recovery from wastewater and simultaneous biogas production, using biomimetic FO membranes. However, further work will be required in the future to optimise the processes and gain a deeper understanding with regards to fouling, cleaning and pretreatment strategies, as well as the optimisation of operational conditions in osmotic anaerobic membrane bioreactors.