Nitrogen removal via core-shell bio-ceramic/Zn-layer double hydroxides synthesized with different composites for domestic wastewater treatment

Powdered layer double hydroxides are small with low density, which results in problems when they are applied to constructed wetlands. The removal efficiency of many original substrate materials tends to decrease with nitrogenous saturation. To overcome these defects, a co-precipitation method was used to prepare modified bio-ceramic coated with ZnFe-layer double hydroxides (Zn:Fe =1:1, 2:1, 3:1) and ZnAllayer double hydroxides (Zn:Al =1:1, 2:1, 3:1) under alkaline conditions. Different molar ratios were firstly considered in bio-ceramic/Zn-layer double hydroxides to screen for the best modification methods. Fourteen simulated columns were produced to treat the nitrogen-containing domestic wastewater, and these columns were filled with different modified bio-ceramics and original bioceramics. The nitrogen removal rates of modified bio-ceramic improved. Group A was the experimental group, and group B was the control group. Group B had chloroform added to influent wastewater to retard the microbial growth. The NH4+-N removal rates in group A were higher than group B. Nitrates accumulated and fluctuated throughout the purification experiments due to the dominance of dissolved oxygen in the vertical-flow simulated columns. Isothermal adsorption tests were subsequently performed. The nitrogen adsorption capacity and microbial action were measured to verify the best modified coating method for bio-ceramics and to explore the mechanisms of nitrogen removal. Bioceramic/ZnFe (2:1)-layer double hydroxides were the best coating for the bio-ceramics. The treated water met Class 1A level for Chinese discharge standards from municipal wastewater treatment plant (GB18918-2002) in the aspect of the NH4--N concentration. The reagent cost of the bio-ceramic/ZnFe (2:1)-layer double hydroxides was RMB 0.07/kg. Within an assumed service cycle of one year, bioceramican-layer double hydroxides could increase the cost to 0.3500/m(3) wastewater, while the NH4+-N removal rates improved 15.11%. In summary, the layer double hydroxides-coating modification of the original bio-ceramic is an economical and promising strategy for new types of highly efficient, durable, and stable substrates. It enhances the adsorption capacity and improves the microbial effect. (C) 2018 Elsevier Ltd. All rights reserved.