Zaisheng Yan

Enhanced degradation of phenanthrene and pyrene in freshwater sediments by combined employment of sediment microbial fuel cell and amorphous ferric hydroxide

The degradation of phenanthrene and pyrene in freshwater sediment was investigated under three kinds of treatments (addition of amorphous ferric hydroxide to sediments, employment of sediment microbial fuel cell (SMFC), and the combination of ferric addition and SMFC employment). After 240 days of experiments, it was found that the combined treatment led to the highest removal efficiencies of phenanthrene (99.47 ± 0.15%) and pyrene (94.79 ± 0.63%), while the employment of SMFC could obtain higher removal efficiencies than Fe(III) addition. The combined approach improved potentials of phenanthrene and pyrene biodegradation in sediments under anaerobic pathways except methanogenic condition, and also stimulated humification of organic matters in sediments. At the end of experiments, ratios of humic acid to fulvic acid in sedimentary organic matters reached to 2.967 ± 0.240 in the combined treatment, and were only around 1.404-1.506 in the other treatments. Thus, organic matters in sediments in the combined treatment could adsorb tightly residual PAHs with less bioavailability. Considering both enhanced biodegradation and final sequestration of PAHs in sediments, the combined application of Fe(III) addition and SMFC employment offered a new promising remediation technology for contaminated sediments.

Analysis of the attached microbial community on mucilaginous cyanobacterial aggregates in the eutrophic Lake Taihu reveals the importance of Planctomycetes.

The phylogenetic diversity of the microbial community assemblage of the carpet-like mucilaginous cyanobacterial blooms in the eutrophic Lake Taihu was investigated. 16S ribosomal DNA clone libraries produced from the DNA of cyanobacterial assemblages that had been washed to remove unattached bacteria contained only cyanobacteria. However, a further treatment which included grinding the freeze-dried material to physically detach cells followed by the removal of larger cells by filtration allowed us to detect a large variety of bacteria within the cyanobacterial bloom community. Interestingly, the dominant members of the microbial community were Planctomycetes followed by Cytophaga–Flavobacterium–Bacteroides (CFB), Betaproteobacteria, and Gammaproteobacteria. The analysis of the 16S ribosomal DNA clone libraries made from enrichment culture revealed much higher phylogenetic diversity of bacteria. Dominant bacterial groups in the enrichment system were identified as members of the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria subdivisions, CFB group, and Planctomycetes. In addition, the clone libraries constructed from Planctomycetes-specific 16S ribosomal RNA primers also verified that the enrichment allowed a diversity of Planctomycetes to proliferate, although the community composition was altered after enrichment.

Complex Interactions Between the Macrophyte Acorus Calamus and Microbial Fuel Cells During Pyrene and Benzo[a]Pyrene Degradation in Sediments.

This study investigated the interaction of the macrophyte Acorus calamus and sediment microbial fuel cells (SMFC) during the degradation of high molecular weight-polycyclic aromatic hydrocarbons (HMW-PAHs) in sediments. Over 367-days, the combination of macrophyte and SMFC led to an increase in pyrene and benzo[a]pyrene degradation rates by at least 70% compared to SMFC or macrophyte alone. While either the macrophyte or SMFC increased redox potential in sediments, redox potentials near the anode (approximately 6 cm depth) in the macrophyte-SMFC combination were markedly lower than that in the only macrophyte treatment. Moreover, rhizospheric bacterial communities in macrophyte-SMFC and macrophyte treatments were distinctly different. Aerobic genera (Vogesella, Pseudomonas, Flavobacterium and Rhizobium) and anaerobic genera (Longilinea, Bellilinea, Desulfobacca and Anaeromyxobacter) became dominant in the rhizosphere in macrophyte and macrophyte-SMFC treatments, respectively. In addition, the macrophyte-SMFC combination improved the numbers of not only aerobic but anaerobic PAHs degraders in sediments. So, the SMFC employment facilitated the formation of anoxic zones in sediments with oxygen loss and exudates from the roots. As a result, cooperation of anaerobic/aerobic microbial metabolism for accelerating HMW-PAHs removal occurred within sediments after combining macrophytes with SMFC.

Effect of temperature on submerged macrophyte litter decomposition within sediments from a large shallow and subtropical freshwater lake

In shallow aquatic systems, the majority of organic matter mineralization occurs in the sediments. Several factors including temperature control mineralization rates, however, the underlying causes of the effects are not well understood in subtropical lakes. In this study, we determined the influence of temperature on organic matter degradation by taking sediments from four sites in a subtropical large shallow freshwater lake, and monitoring organic matter composition and enzymes in microcosm experiments at five temperatures from 5 to 40°C. Following a three-month incubation, it was found that the mineralization of submerged plants in sediments was strongly influenced by temperature. Removal efficiency of total organic carbon in sediments ranged from 4.3 to 22.6% at 5°C, and reached 46.7–55.5% at 40°C. In addition, the removal efficiency of organic matter and the relative recalcitrant carbon decomposition depended on sediment type. For sediments in the site located in the lake center, recalcitrant and labile carbon decomposition had equivalent responses to the different temperatures. For sediments with dominance of submerged macrophytes, the humic acids were low even at high temperature. Thus, the annual deposition of plant litter in sediments favored organic carbon decomposition rather than humification.

Cellulose degradation by one mesophilic strain Caulobacter sp. FMC1 under both aerobic and anaerobic conditions

Caulobacteria are presumed to be responsible for considerable mineralization of organic material in aquatic environments. In this study, a facultative, mesophilic and cellulolytic bacterium Caulobacter sp. FMC1 was isolated from sediments which were taken from a shallow freshwater lake and then enriched with amendment of submerged macrophyte for three months. This strain seemed to evolve a capacity to adapt redox-fluctuating environments, and could degrade cellulose both aerobically and anaerobically. Cellulose degradation percentages under aerobic and anaerobic conditions were approximately 27% and 10% after a 240-h incubation in liquid mediums containing 0.5% cellulose, respectively. Either cellulose or cellobiose alone was able to induce activities of endoglucanase, exoglucanase, and β-1,4-glucosidase. Interestingly, ethanol was produced as the main fermentative product under anaerobic incubation on cellulose. These results could improve our understanding about cellulose-degrading process in aquatic environments, and were also useful in optimizing cellulose bioconversion process for bioethanol production.

Various voltage productions by microbial fuel cells with sedimentary inocula taken from different sites in one freshwater lake.

In this study, single-chamber microbial fuel cells (MFCs) were inoculated with sedimentary samples taken from one freshwater shallow lake. After 98 days of operation, it was found that sedimentary inocula had strong effect on MFC performances, and Fe(III) contents in sediments were significantly related to voltage values produced from MFCs. Inoculation of the sedimentary sample from the site with the highest Fe(III) content led to the production of the highest voltage with a value of 580 mV, while voltage from the MFC inoculated with sediments from the site with the lowest Fe(III) concentration was less than 30 mV at the end of the experiments. In addition, microbial communities of anode biofilms from the MFCs with the highest and lowest voltages showed significant difference. This study will help enable scientific decisions to be made regarding the selection of freshwater sediments as MFC inoculum, and survey exoelectrogenic microorganisms within sediments.

Heterogeneity in metal binding by individual fluorescent components in a eutrophic algae-rich lake

Dissolved organic matter (DOM) affects the toxicity, mobility and bioavailability of metals in aquatic environment. In this study, the interactions between two metals of environmental concern [Cu(II) and Fe(III)] with DOM in a euthrophic algae-rich lake (Lake Taihu, China), including dissolved natural organic matter (NOM) and algal extracellular polymeric substance (EPS), were studied using fluorescence excitation-emission matrix (EEM) quenching titration combined with parallel factor (PARAFAC) analysis. Obvious protein-like peaks were detected in algal EPS matrix, while both protein- and humic-like peaks can be found in NOM. PARAFAC analysis identified four fluorescent components, including one humic-, one tryptophan- and two tyrosine-like components, from 114 EEM samples. It was shown that fluorescent tyrosine- (log K(M) > 5.21) and humic-like substances (log K(M) > 4.84) in NOM fraction exhibited higher metal binding capacities than those in EPS matrix, while algal EPS was characterized with a high metal-tryptophan-like substances affinity (log K(M) > 5.08). Moreover, for the eutrophic algae-rich lakes, fluorescent tryptophan- and humic-like substances were responsible for Cu transportation, whereas the mobility of Fe would be related with the tyrosine-like substances. The results facilitate a further insight into the biogeochemical behaviors of metals in eutrophic algae-rich ecosystems as well as other related aquatic environments.

Accelerated removal of pyrene and benzo[a]pyrene in freshwater sediments with amendment of cyanobacteria-derived organic matter

The removal of pyrene and benzo[a]pyrene (BaP) were investigated in freshwater sediments with amendment of seven different organic matters including cyanobacteria-derived organic matter (COM), plant-derived organic matter (POM), and humic substances (HS). During the 210 days of experiments, the amendment of COM or HS enhanced significantly the removal of pyrene and BaP in sediments, especially with fresh COM (FCOM) treatment much superior to HS. On the contrary, degradation of these polycyclic aromatic hydrocarbons (PAHs) was not significantly improved and even inhibited in POM-amended sediments. The first-order rate constants of pyrene and BaP degradation in the FCOM-amended sediments reached 0.00540±0.00017d(-1) and 0.00517±0.00057d(-1), respectively, and were about three and five folds of those in the control treatment. The enhanced PAHs degradation in FCOM-amended sediments was related to higher PAH-degrading bacteria number and bioavailability with a result of biostimulation and priming effect by labile carbon and high-value nutrition in FCOM. Thus, this study improved our understanding about effects of settled biomass from cyanobacterial blooms, which occurred frequently in eutrophic aquatic ecosystems, on the natural attenuation of PAHs in sediments. Furthermore, this study would also help develop a new promising approach to remediate PAH-contaminated sediments through utilization of cyanobacterial bloom biomass.

Interconnection of Key Microbial Functional Genes for Enhanced Benzo[a]pyrene Biodegradation in Sediments by Microbial Electrochemistry

Sediment microbial fuel cells (SMFCs) can stimulate the degradation of polycyclic aromatic hydrocarbons in sediments, but the mechanism of this process is poorly understood at the microbial functional gene level. Here, the use of SMFC resulted in 92% benzo[a]pyrene (BaP) removal over 970 days relative to 54% in the controls. Sediment functions, microbial community structure, and network interactions were dramatically altered by the SMFC employment. Functional gene analysis showed that c-type cytochrome genes for electron transfer, aromatic degradation genes, and extracellular ligninolytic enzymes involved in lignin degradation were significantly enriched in bulk sediments during SMFC operation. Correspondingly, chemical analysis of the system showed that these genetic changes resulted in increases in the levels of easily oxidizable organic carbon and humic acids which may have resulted in increased BaP bioavailability and increased degradation rates. Tracking microbial functional genes and corresponding organic matter responses should aid mechanistic understanding of BaP enhanced biodegradation by microbial electrochemistry and development of sustainable bioremediation strategies.

Enhanced removal of organics and phosphorus in a hybrid coagulation/membrane bioreactor (HCMBR) for real textile dyeing wastewater treatment

Abstract In this work the performance of a hybrid coagulation/membrane bioreactor (HCMBR) was assessed for real textile dyeing wastewater advanced treatment. Poly-aluminum chloride (PACl) was selected and used in the experiments. Batch experiment results showed that the optimal dosage was 40 mg Al/L. During the pilot-scale experiment, the suitable dosage and dosing interval were once per day at the dosage of 40 mg Al per L of amount of mixed liquor into the HCMBR system. It was found that membrane fouling was effectively retarded by PACl addition in the running MBR system. Additionally, removal of pollutants according to influent and effluent quality was monitored. HCMBR achieved much higher removal efficiencies than membrane bioreactor (MBR) in CODcr, UV254, and total phosphate, due to PACl coagulation in the HCMBR bioreactor. And the application of PACl was effective in decreasing the content of extracellular polymeric substances and the membrane fouling resistances. The transmembrane pressure of HCMBR ...