A Homogeneous Reagent for Ni2+ Capture from Wastewater : The Fast Removal Kinetics, 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-contained 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 reagents with dithioamino groups. When the dosage of reagent concentration was controlled at 5-10:1(Ni), the 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 water, exhibited negligible inhibition for Ni 2+ capture. The phase transition was visually investigated by charge coupled device camera and paticle size change. Experimental characterizations demonstrated that dithioamino groups in capture reagent could efficiently chelate with Ni 2+ , which was validated by theoretical calculations. Vitally, the treatment by reagents cannot affect the nitrification activity of aerobic sludge system through short-term experiment and 29 months of operation while ensuring total Ni removal effect. These findings highlight opportunities for using S-containing organic reagents to remove heavy metal ions from wastewater, particularly in sewage treatment plant with bulky water