Recent advances on biosorption by aerobic granular sludge.

Aerobic granular sludge is a form of microbial auto-aggregation, and a promising biotechnology for wastewater treatment. This review aims at providing the first comprehensive, systematic, and in-depth overview on the application of aerobic granules as biosorbents. The target pollutants encompass heavy metals (both cationic and oxyanionic), nuclides, dyes, and inorganic non-metal substances. Different granule types are discussed, i.e. intact and fragmented, compact and fluffy, original and modified, and the effects of granule surface modification are introduced. A detailed comparison is conducted on the characteristics of granular biomass, the conditions of the adsorption tests, and the resultant performance towards various sorbates. Analytical and mathematical tools typically employed are presented, and possible interactions between the pollutants and granules are theorized, leading to an analysis on the mechanisms of the adsorption processes. Original granules appear highly effective towards cationic metals, while surface modification by organic and inorganic agents can expand their applicability to other pollutants. Combined with their advantages of high mechanical strength, density, and settling speed, aerobic granules possess exceptional potential in real wastewater treatment as biosorbents. Possible future research, both fundamental and practical, is suggested to gain more insights into the mechanism of their function, and to advance their industrial application.

Mechanism of enhanced Sb(V) removal from aqueous solution using chemically modified aerobic granules.

Sb(V) removal using Fe-modified aerobic granules was investigated. Increasing the biomass dosage improved the Sb(V) removal rate, but lowered the adsorption quantity; the optimal biomass concentration was 20 g/L (wet basis). Adsorption equilibrium was obtained at 2h at 175 rpm; the adsorption quantity was 36.6 mg/g. NaCl and other salts inhibited Sb(V) adsorption on Fe-modified granules, and the mechanism possibly lied more with the anions. The adsorption isotherms were evaluated using the Langmuir, Freundlich, and Temkin models. The Langmuir model best described the adsorption process, and gave a maximum monolayer adsorption quantity of 125 mg/g. The ΔH value for adsorption was 16.1 kJ/mol, indicating endothermicity, and the negative ΔG values at various temperatures suggested spontaneous adsorption. Outer-sphere and inner-sphere complexations were involved in Sb(V) adsorption.

[Influence of carbon source on EBPR metabolism and microorganism communities].

A SBR was used in this study for investigating the influence of carbon source on EBPR metabolism and microorganism communities when feeding with acetate and propionate. The SBR was operated with a cycle time of 8 h and each cycle consisted of 4 min feeding, 2 h anaerobic period, 5 h aerobic period, 35 min setting, 15 min decanting and 6 min waiting. The COD of influent was kept at 300 mg/L during the experiment. Acetate and propionate were used as the sole carbon source for operation of 60 days, respectively. The phosphorus release/ COD consumption in the end of anaerobic phase were 0.35 and 0.27 when acetate and propionate were used as the carbon source, respectively. The PHA composition was different when different carbon source was dosed. PHB accounted for 92.6% in the end of anaerobic phase but the value for PHV was only 7.4% when acetate was selected as the carbon source. No PH2MV was detected during this process. The compositions of PHA were PHB (10.2%), PHV (35.8%) and PH2MV (54.0%) in the end of anaerobic cycle when propionate was used as the sole carbon source. There was variation of microorganism communities during this process for the results of DGGE combined with SEM micrographs and PHA staining. Coccus morphotype PAOs were accumulated in acetate-fed phase and rod morphotype PAOs were accumulated in propionate-fed stage. Different PAOs were accumulated and the metabolic pathways were different when different carbon sources were used, but good EBPR could be achieved during all these conditions.

Hydrodynamic characteristics of a four-compartment periodic anaerobic baffled reactor.

Periodic anaerobic baffled reactor (PABR) is a novel reactor based on the design concept of anaerobic baffled reactor (ABR). Residence time distribution (RTD) studies on both clean and working reactors at the same hydraulic residence time (HRT) of 2 d were carried out to investigate the dead spaces and mixing patterns in PABRs at different organic loading rates (OLRs) in various switching manners and frequencies. The results showed that the fraction of dead space in PABR was similar to that in ABR, which was low in comparison with other reactor designs. Dead space may be divided into two categories, hydraulic and biological. In RTD studies without biomass, the hydraulic dead space in the PABR run in an "every second" switching manner with T = 2 d was the lowest whereas that in the PABR run in a T = infinity (ABR) switching manner was the highest. The same trend was obtained with the total dead space in RTD studies with biomass no matter what the OLR was. Biological dead space was the major contributor to dead space but affected decreasingly at higher OLR whichever switching manner the PABR run in. The flow patterns within the PABRs were intermediate between plug-flow and perfectly mixed under all the conditions tested.

[Influence of organic pollutants on the bacterial community in Songhua River drainage area].

In order to investigate the potential influence of the organic pollutants on the microbial composition and diversity, terminal restriction fragment length polymorphism (tRFLP) and 16S ribosomal DNA (rDNA) clone libraries combined with water quality analysis were selected to compare the structure of bacterial communities in four water bodies contaminated by different degrees of organic matter. tRFLP profiles of the waters and sediments all showed complex patterns and high similarity, however, some certain populations enriched with the pollution enhanced. Especially, the similarity of communities accorded strictly with that of water quality. Principal component analysis (PCA) indicated that the terminal restriction fragments (TRF) of bacteria in the waters and sediments grouped into different clusters. 16S ribosomal DNA sequences in the Songhua River sediment fell into ten known phyla and Proteobacteria are predominant with 21.92% of clones (in which the beta-Proteobacteria accounts for 10.96%). The sediment seriously polluted by domestic wastewater comprised of only 7 phyla, in which Proteobacteria was predominant with 47.37% of clones (subdivisions a-Proteobacteria and delta/epsilon-Proteobacteria were 21.05% and 15.79%, respectively). This study demonstrated that the long-term drainage of organic wastewater reduced the microbial diversity, and some functional microbes that are responsible for the degradation of organic matter, became dominant.