[Effect of Membrane Wettability on Membrane Fouling and Chemical Durability of SPG Membranes].

Shirasu porous glass (SPG) membranes have been applied for microbubble aeration in aerobic wastewater treatment. In the present study, both hydrophilic and hydrophobic SPG membranes were used in a microbubble-aerated biofilm reactor with online chemical cleaning, and their membrane fouling and chemical durability were determined to be strongly dependent on the membrane wettability. The fouling layer formed on the surface of both membranes was confirmed to be mainly organic fouling, and the hydrophobic membrane showed a relatively stronger resistance to the organic fouling. The severe chemical corrosion of the hydrophilic membrane was observed due to exposure to the alkaline sodium hypochlorite solution used for chemical cleaning, which resulted in significant increases in the median pore diameter and the porosity. On the other hand, the pore structure of the hydrophobic membrane changed slightly when exposed to the alkaline sodium hypochlorite solution, suggesting its strong alkali-resistance due to the non-wetting surface. However, the surface hydrophobic groups of hydrophobic membrane could be oxidized by sodium hypochlorite solution, resulting in more wettable membrane surface. The hydrophobic membrane also showed better performance in the respects of oxygen transfer, contaminant removal and energy-saving. Therefore, the hydrophobic membrane seemed more appropriate to be applied for microbubble aeration in aerobic wastewater treatment process.

[Atrazine wastewater treatment in a SPG membrane-aerated genetically engineered microorganism biofilm reactor].

Membrane-aerated biofilm reactor (MABR) represent a novel membrane-biological wastewater treatment technology. In addition, bioaugmented treatment using genetically engineered microorganism (GEM) biofilm in MABR is proposed to improve refractory pollutant removal. In the present study, a SPG membrane aerated-biofilm reactor (SPG-MABR) with GEM biofilm formed on the SPG membrane surface was applied to treat atrazine wastewater. The influences of air pressure, biofilm biomass and liquid velocity on the performance of the SPG-MABR were investigated. The variation of GEM biofilm during the SPG-MABR operation was observed. The results indicated that the increased air pressure could promote atrazine and COD removal as well as re-oxygenation by increasing oxygen permeability coefficient. A higher biofilm biomass could also enhance atrazine and COD removal, but simultaneously reduce the re-oxygenation rate because biofilm thickness and oxygen transfer resistance increased. When liquid velocity in the SPG-MABR was decreased under laminar flow condition, atrazine and COD removal was improved due to the facilitated contaminant diffusion from wastewater to biofilm. The atrazine removal efficiency reached to 98.6% in the SPG-MABR after 5d treatment at air pressure of 300 kPa, biofilm biomass of 25 g x m(-2) and liquid velocity of 0.05 m x s(-1). The microbial polymorphism of GEM biofilm was observed during the SPG-MABR operation. The surface of GEM biofilm was gradually covered by other microbial cells and the distribution of GEM cells reduced, but inside the GEM biofilm, the GEM cells were still dominant.

[Simultaneous nitrification and denitrification in a microbubble-aerated biofilm reactor].

Simultaneous nitrification and denitrification (SND) is a new wastewater treatment process for biological nitrogen removal, which shows some significant advantages compared with conventional biological nitrogen removal processes. The SND process in a fixed bed biofilm reactor with microbubble aeration was investigated in this study. The removal efficiencies of COD and nitrogen were determined under different operational conditions and the functional bacterial populations for nitrogen removal in the biofilm were detected. The results showed that efficient SND process could be achieved in the biofilm reactor with microbubble aeration. The SND could be improved at lower dissolved oxygen (DO) concentration and larger porosity of packing bed when the COD loading rate and C/N ratio were increased. The removal efficiencies of COD and total nitrogen (TN) were 97.6% and 70.2%, respectively, at a COD loading rate of 0.86 kg x (m3 x d)(-1), a TN loading rate of 0.10 kg x (m3 x d)(-1), and a packing bed porosity of 81%, indicating the simultaneous efficient removal of COD and TN. Under these conditions, the oxygen utilization efficiency reached as high as 91.8% due to the enhanced oxygen mass transfer by microbubble aeration. In addition, the biofilm activity and the abundance of nitrifiers and denitrifiers were consistent with the removal capacity of COD, ammonia and TN under different operational conditions.