Keywords:Bio-diatomite dynamic IntroductionThe dynamic membrane technology for wastewater treatment has gained great attention in recent years due to its cost-effective membrane module, reduced energy consumption and high effluent quality. Therefore, it is considered as a substitute to the conventional membrane bioreactor (MBR) (Kiso et al., 2004;Gander et al., 2000;Chu and Li, 2006). Dynamic membrane is formed on the underlying support mesh when filtering a solution containing fine particles, thus is also called secondary membrane (Kuberkar and Davis, 2000). The dynamic membrane formed on the relatively large-pore mesh increases the intrinsic membrane retention capacity (Alavi Moghaddam et al., 2002a,b), leading to a high solid-liquid separation efficiency and a high filtration flux (Seo et al., 2002(Seo et al., , 2007Fuchs et al., 2005). Dynamic membrane is also more convenient to clean than membrane reactor. Tap water backwash, air backwash or mechanical brushing can readily clean the dynamic membrane without using any chemical reagents (Al-Malack and Anderson, 1997;Fan and Huang, 2002;Ye et al., 2006). It was reported that diatomite particles could be used as carriers for microorganisms (Zhao et al., 2006). The microbial colonies can form zoogloeas on diatomite particles through microbial capsules and surface mucus and bio-diatomite is thus named. The bio-diatomite reactor, which combines * Corresponding author. Tel.: þ86 21 65982691; fax: þ86 21 65982313.E-mail addresses: chq123zl@hotmail.com (H. Chu), dbz77@tongji.edu.cn (B. Dong).A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s w a t e r r e s e a r c h 4 4 ( 2 0 1 0 ) 1 5 7 3 -1 5 7 9

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This study was conducted to examine the feasibility of using a moving‐bed‐biofilm reactor with internal circulation through aeration for the treatment of municipal wastewater. The attached film was a mixed‐microorganism consortium, which used composite‐refined‐diatomaceous earth as novel biomass carriers to form a diatomaceous‐earth‐moving‐bed‐biofilm‐reactor (DEMBBR) process. The startup of laboratory‐scale, continuous‐flow reactor was successfully achieved without seeding activated sludge. The DEMBBR process removed chemical oxygen demand, total phosphorus, ammonium‐nitrogen, and turbidity at the highest rate of 88.5, 83, 92.3, and 96.7%, respectively, with a hydraulic retention time of only 2.5 hours. The DEMBBR was less affected by interruption and adverse operation conditions than the conventional‐activated‐sludge reactor. Thus, the DEMBBR could be proposed to be a cost‐effective, small‐wastewater‐treatment‐process unit.

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The partial nitrification (PN) performance and the microbial community variations were evaluated in a sequencing batch reactor (SBR) for 172 days, with the stepwise elevation of ammonium concentration. Free ammonia (FA) and low dissolved oxygen inhibition of nitrite-oxidized bacteria (NOB) were used to achieve nitritation in the SBR. During the 172 days operation, the nitrogen loading rate of the SBR was finally raised to 3.6 kg N/m3/d corresponding the influent ammonium of 1500 mg/L, with the ammonium removal efficiency and nitrite accumulation rate were 94.12% and 83.54%, respectively, indicating that the syntrophic inhibition of FA and low dissolved oxygen contributed substantially to the stable nitrite accumulation. The results of the 16S rRNA high-throughput sequencing revealed that Nitrospira, the only nitrite-oxidizing bacteria in the system, were successively inhibited and eliminated, and the SBR reactor was dominated finally by Nitrosomonas, the ammonium-oxidizing bacteria, which had a relative abundance of 83%, indicating that the Nitrosomonas played the primary roles on the establishment and maintaining of nitritation. Followed by Nitrosomonas, Anaerolineae (7.02%) and Saprospira (1.86%) were the other mainly genera in the biomass.