A hybrid algal photosynthesis and ion-exchange (HAPIX) process for side stream wastewater treatment: Experimental and modeling studies

A hybrid ion-exchange and algal photosynthesis (HAPIX) process was used for treatment of side stream centrate from an anaerobic digester treating waste activated sludge. Although the high NH4⁺-N concentration of the centrate (~1180 mg/L) inhibited algal growth in unamended controls, addition of zeolite reduced the ammonia toxicity due to its ion exchange capacity. Na⁺ was the major cation exchanged with NH4⁺. Growth of algae further reduced the NH4⁺-N concentrations. Different zeolite dosages (60, 150, and 250 g/L) resulted in different concentrations of NH4⁺-N in solution. Algae grown in lower zeolite dosage (60 g/L) had high protein contents. A mathematical model that combined ion-exchange and algal photosynthesis processes predicted the aqueous NH4⁺-N concentration well. The HAPIX process is feasible for treatment of high NH4⁺-N strength side stream wastewaters while regulating intracellular algal biomass contents by adjusting zeolite dosages.