Continuous adsorption of ammonium from primary and digester effluents using biosolids-derived biochar and cation exchange resin

Abstract

Conventional biological treatment of wastewater can remove ammonium in the form of nitrogen gas, thus the opportunity of recovering the nutrient is lost. This study explored the continuous adsorption of ammonium from wastewater (primary and digester effluents) using biochar and cation exchange resin. The biochar was produced via the pyrolysis of biosolids (stabilised sewage sludge), and its ammonium adsorption performance was compared with a commercial cation exchange resin. Adsorption studies suggested that ammonium removal from synthetic wastewater was higher than from real effluents due to the competitive uptake of other components in the stream. Biochar with 100–500 μm particle size gave an ammonium adsorption capacity of 0.17 and 0.53 mg g−1 for primary and digester effluents, respectively. However, resin outperformed biochar with an estimated adsorption capacity of 17.96 and 28.38 mg g−1 for primary and digester effluents, respectively. Furthermore, the biochar bed was saturated in a few seconds, while the resin bed had a breakthrough time of 3 and 21 h, depending on the conditions applied. Therefore, it was proposed to treat the wastewater with biochar to obtain N-laden biochar and then send the resulting effluent to a series of resin columns for complete ammonium removal. The economic analysis of the process generated a net present value of $6 M and $0.6 M and a payback period of 6 and 10 years using primary and digester effluents, respectively. The profitability result is highly sensitive to the products sale price, the number of regeneration cycles of resin, and biosolids management cost.