Hybrid algal photosynthesis and ion exchange (HAPIX) process for high ammonium strength wastewater treatment

A hybrid algal photosynthesis and ion exchange (HAPIX) process was developed that uses natural zeolite (chabazite) and wild type algae to treat high ammonium (NH₄⁺) strength wastewater. In the HAPIX process, NH₄⁺ is temporarily adsorbed from the liquid, which reduces the free ammonia (FA) concentration below the inhibitory level for algal growth. The slow release of adsorbed NH₄⁺ subsequently supports the continuous growth of algae. In this study, a HAPIX reactor reduced NH₄⁺-N concentrations in centrate from an anaerobic digester from 1180 mg L⁻¹ to below 10 mg L⁻¹ without dilution. Chabazite doses of 60 g L⁻¹ produced more algal biomass, with higher protein and starch contents, than doses of 150 g L⁻¹ and 250 g L⁻¹. Approximately 67–70% of fatty acids in the algal biomass harvested from HAPIX reactors were unsaturated. A mathematical framework that couples a homogeneous surface diffusion model with a co-limitation algal kinetic growth model reasonably predicted the algal biomass production and NH₄⁺-N concentrations in the HAPIX reactors. The HAPIX process has the potential to serve a two-fold purpose of high NH₄⁺-N strength wastewater treatment and agricultural or commercial biopolymer production.