Effect of alkalinity on bio-zeolite regeneration in treating cold low-strength ammonium wastewater via adsorption and enhanced regeneration.

Low temperature severely inhibits microbial activity, making biological method inefficient for ammonium removal from wastewater. A zeolite biological fixed-bed (ZBFB) was successfully established for 6.0-8.0 °C low-strength ammonium wastewater treatment via adsorption-regeneration. Ion exchange was a remarkable alternative and zeolite was mostly applied. Nevertheless, insufficient zeolite bio-regeneration rate was the key obstacle for economically sustainable utilization. By adsorption, effluent NH4+-N was around 1.5-2.5 mg/L. About 26% regeneration rate was obtained. With a ceramsite biological aerobic filter (CBAF) operated with ZBFB in series at the regeneration stage, the regeneration rate reached 95%, 3.5 times higher. Studies of alkalinity effects on bio-zeolite regeneration process indicated that Na2CO3 worked better than NaHCO3. Greater amount and one dose mode of alkalinity addition, higher regeneration rate could be obtained. The bio-zeolite regeneration process followed pseudo first-order kinetics with K = 0.0629 h-1. High-throughput sequencing analysis indicated the enriched nitrifying microorganisms in CBAF fully oxidized NH4+-N in regeneration solution, which accelerated desorption and conversion of NH4+-N by the circulation of regeneration solution between ZBFB and CBAF. The dynamic adsorption experiment proved that ZBFB-CBAF was feasible for cold low-strength ammonium wastewater treatment.