A homogeneous reagent for Ni2+ capture from wastewater: The phase transition mechanism and impact evaluation for aerobic sludge

Heterogeneous process with low mass transfer rate is limited in the treatment of large-volume Ni-containing wastewater. The homogeneous reaction provides a promising strategy to solve this problem, but phase transition process of Ni 2+ removal and its potential impact on activated sludge system are rarely explored. Herein, the Ni 2+ removal efficiency and process were firstly investigated in detail by using S-containing reagent with dithioamino groups. When the dosage of reagent concentration was controlled at 5–10:1(Ni), Ni 2+ can be rapidly and completely removed within 1 min. Additionally, other coexisting Cu 2+ , Co 2+ , Cd 2+ , and Pb 2+ could be synchronously removed with more reagent adding, while the typical organics (e.g., humic/citric acid) in water and high concentration of chemical oxygen demand (3800 mg L −1 ) in actual wastewater, exhibited negligible inhibition for Ni 2+ capture. The phase transition was visually investigated by charge coupled device camera and paticle size change. Experimental characterizations demonstrate that the dithioamino groups in capture reagent could efficiently chelate with Ni 2+ , which can be validated by the theoretical calculations. Vitally, the utilization of reagent cannot affect the nitrification activity of aerobic sludge system through short-term experiment and 29 months of operation while ensuring total Ni removal efficiency. These findings highlight an opportunity for using S-containing organic reagents to remove heavy metal ions from actual wastewater, especially in the application of the sewage treatment plant with bulky water.