MHC bioregeneration
Donnan dialysis coupled with bio-denitrification was used to regenerate MHC. Before bioregeneration, MHC was saturated by NO3--N in repeated coagulation processes. Then the bioregeneration was carried out at room temperature and under anaerobic conditions in a Donnan dialysis setup. The setup was made of Plexiglas (Beijing, China), divided into two chambers by a JAM-I homogeneous anion exchange membrane. The spent MHC was added into the desorption chamber. Sludge, 0.3 mol/L NaCl, and 12.9 mol/L ethanol (as carbon source) were added to the stripping chamber. The solution pH in both chambers was adjusted to 7.0 ± 0.2. The solution was stirred continuously at 400 rpm. Throughout the 30 h regeneration process, samples were collected at regular intervals from both chambers and filtered through 0.22 μm nylon membranes for analysis of residual NO3--N. The sludge cultivation method is in the SI.