Modelling of a photobioreactor with algammox and zeolite treating concentrated ammonium wastewater

Removing nitrogen from wastewater has been done in different ways including chemical and biological methods. The latter ones include traditional approaches like nitrification-denitrification, but also more contemporary methods including the combination of algae and bacteria/archaea in the same system. Specifically, when dealing with concentrated ammonium streams, the incorporation of an additional process like ion exchange with zeolite may reduce the inhibitory conditions caused by free ammonia and therefore allow the biological process to run at optimal conditions. To understand how the combination of different processes may work, modelling is a useful tool. For instance, some models have been developed to represent algae and bacteria consortium for nitrogen removal treatment; and some others to represent zeolite and bacteria in a system also with the objective of removing nitrogen from water. Nevertheless, no outcome regarding algammox and zeolite processes together were found in the literature, neither in an experimental phase, nor in modelling. In this research a photobioreactor with algal-bacteria biomass and zeolite (clinoptilolite) were used to treat an influent with 1,700 mg N-NH4+/L. Results showed a complete bioregeneration of zeolite, and a good inorganic nitrogen removal efficiency (97%), but with slow ammonium removal rate principally due to a slow ammonium desorption process during aerobic phases. The main processes that remove ammonium from the system are nitritation, causing more than 50% of the ammonium removal, and anammox with more than 35%. Results obtained in the experimental phase were introduced in a model in the AQUASIM platform in which ion exchange, algal growth and decay, and bacterial growth and decay (AOB, NOB, OHO, anammox) were considered. Ion exchange processes were represented based on the Langmuir kinetic equation, the algal processes in accordance with Rada-Ariza (2018), and the bacterial biomass in accordance with ASM3. Results show a good prediction of the ion exchange ...