Yuancai Chen

Adsorption of Cu2+, Cd2+ and Ni2+ from aqueous single metal solutions on graphene oxide membranes

Novel, highly ordered layered graphene oxide (GO) membranes with larger interlayer spacing were prepared by induced directional flow and were used as adsorbents for the removal of Cu(2+), Cd(2+) and Ni(2+) from aqueous solutions. The effects of pH, ionic strength, contact time, metal ion concentration and cycle time on Cu(2+), Cd(2+) and Ni(2+) sorption were investigated. The results indicated that the adsorption of Cu(2+), Cd(2+) and Ni(2+) onto GO membranes was greatly influenced by the pH and weakly affected by the ionic strength. The adsorption isotherms for Cu(2+), Cd(2+) and Ni(2+) were well fitted by the Langmuir model. The maximum adsorption capacities of the GO membranes for Cu(2+), Cd(2+) and Ni(2+) were approximately 72.6, 83.8 and 62.3 mg/g, respectively. The adsorption kinetics of Cu(2+), Cd(2+) and Ni(2+) onto GO membranes followed the pseudo-second-order model. The adsorption equilibrium was reached in a shorter time. The GO membranes can be regenerated more than six times based on their adsorption/desorption cycles, with a slight loss in the adsorption capacity. The results demonstrated that the GO membranes can be used as effective adsorbents for heavy metal removal from water.

Enhancing biodegradation of wastewater by microbial consortia with fractional factorial design

Batch experiments were conducted on the degradation of synthetic and municipal wastewater by six different strains, i.e., Agrobacterium sp., Bacillus sp., Enterobacter cloacae, Gordonia, Pseudomonas stutzeri, Pseudomonas putida. By applying a fractional factorial design (FFD) of experiments, the influence of each strain and their interactions were quantified. An empirical model predicting the treatment efficiency was built based on the results of the FFD experiments with an R(2) value of 99.39%. For single strain, Enterobacter cloacae, Gordonia and P. putida (p=0.008, 0.009 and 0.023, respectively) showed significant enhancement on organic removal in the synthetic wastewater. Positive interaction from Enterobacter cloacae, Gordonia (p=0.046) was found, indicating that syntrophic interaction existed, and their coexistence can improve total organic carbon (TOC) degradation. Verification experiments were performed to evaluate the effect of bioaugmentation by introducing three selected strains into an activated sludge reactor for treating municipal wastewater. The removal efficiency of TOC with the bioaugmentation was increased from 67-72% to 80-84% at an influent TOC concentration of 200mg/L. The results derived from this study indicate that the FFD is a useful screening tool for optimizing the microbial community to enhance treatment efficiency.

Removal of heavy metal ions from aqueous solution by zeolite synthesized from fly ash

Zeolite was synthesized from coal fly ash by a fusion method and was used for the removal of heavy metal ions (Pb2+, Cd2+, Cu2+, Ni2+, and Mn2+) in aqueous solutions. Batch method was employed to study the influential parameters such as adsorbent dosage, pH, and coexisting cations. Adsorption isotherms and kinetics studies were carried out in single-heavy and multiheavy metal systems, respectively. The Langmuir isotherm model fitted to the equilibrium data better than the Freundlich model did, and the kinetics of the adsorption were well described by the pseudo-second-order model, except for Cd2+ and Ni2+ ions which were fitted for the pseudo-first-order model in the multiheavy metal system. The maximum adsorption capacity and the distribution coefficients exhibited the same sequence for Pb2+ > Cu2+ > Cd2+ > Ni2+ > Mn2+ in both single- and multiheavy metal systems. In the end, the adsorption capacity of zeolite was tested using industrial wastewaters and the results demonstrated that zeolite could be used as an alternative adsorbent for the removal of heavy metal ions from industrial wastewater.

Sorption/desorption behavior of triclosan in sediment-water-rhamnolipid systems: Effects of pH, ionic strength, and DOM.

Effects of pH, ionic strength and DOM on the sorption and desorption of triclosan (TCS) in sediment-water-rhamnolipid systems were systematically investigated through controlled batch experiments. Results showed that solubilization enhancement of TCS by rhamnolipid was higher in acid pH range than in alkaline pH range and was the highest at the ionic strength of 5×10(-2) M. Sorption of rhamnolipid onto sediment decreased with the increase of pH while the result was contrary to ionic strength. Moreover, the apparent distribution coefficients of TCS (Kd(*)) decreased from 73.35 to 32.30 L/kg with an increase of solution pH, as varying pH had significant influence on sorption of RL onto sediment and degree of ionization of TCS. Rhamnolipid presented the largest distribution capacity of TCS into the aqueous phase at moderate ionic strength (5×10(-2) M) with the Kd(*) of 17.26 L/kg. Further results also indicated that the presence of humic acid in aqueous phase could increase the desorption of TCS from contaminated sediment. The desorption enhancement was much higher in the system containing both rhamnolipid and DOM than in the single system. These findings provide meaningful information for enhanced migration of TCS from sediment to water by rhamnolipid.

Interaction among multiple microorganisms and effects of nitrogen and carbon supplementations on lignin degradation

The mutual interactions among the consortium constructed by four indigenous bacteria and five inter-kingdom fusants and the effects of nitrogen and carbon supplementations on lignin degradation and laccase activity were investigated. Analyzed by Plackett-Burman and central composite design, the microbial consortium were optimized, Bacillus sp. (B) and PE-9 and Pseudomonas putida (Pp) and PE-9 had significant interactions on lignin degradation based on a 5% level of significance. The nitrogen and carbon supplementations played an important role in lignin degradation and laccase production. The ultimate lignin degradation efficiency of 96.0% and laccase activity of 268U/L were obtained with 0.5g/L of ammonium chloride and 2g/L of sucrose. Results suggested that a stable and effective microbial consortium in alkalescent conditions was successfully achieved through the introduction of fusants, which was significant for its industrial application.

The microorganism community of pentachlorophenol (PCP)-degrading coupled granules

Coupled granules are self-immobilized aggregates of microorganisms under micro aerobic conditions, which have the dissolved oxygen (DO) level of 0.6 mg.L(-1). The effects of DO concentration on pentachlorophenol (PCP) reduction and its microbial community were investigated in a coupled anaerobic and aerobic reactor. Both the diversity and the dynamicity of the Eubacteria and Archaea community, which were responsible for PCP degradation, were evaluated by means of amplification by polymerase chain reaction (PCR) and separation using the denaturing gradient gel electrophoresis (DGGE) technique. The results demonstrated a major shift in the Eubacteria and Archaea community as the mixed aerobic and anaerobic seeding sludge (1:1 by volume) developed into coupled granules and finally acclimated with PCP throughout the experiment period within 60 days. The numbers of the Eubacteria population decreased from 20, 16 to 11; Shannon diversity index decreased from 2.75, 2.53 to 2.10. In contrast, the number of the Archaea population increased from 12, 14 to 18; and Shannon diversity index increased from 1.87, 1.88 to 2.43. Phylogenetic analysis based on 16SrDNA genes showed the dominance Sphingomonas, Desulfobulbus, Proteobacteria, Actinobacterium, Methanogenic and some uncultured bacteria in the PCP-degrading coupled granules. Microorganism community construction of coupled granules was also deduced.

Enhanced adsorption performance of MoS2 nanosheet-coated MIL-101 hybrids for the removal of aqueous rhodamine B

A MoS2 nanosheet-coated chromium terephthalate MIL-101 octahedron hybrid (denoted as MoS2/MIL-101) was prepared via a simple hydrothermal reaction. The obtained MoS2/MIL-101 hybrid exhibited a significantly enhanced adsorption ability toward rhodamine B (RhB) as compared with pure MoS2, MIL-101, and the physical mixture of the two. The results demonstrate that the MoS2/MIL-101 hybrid had a high uptake capacity (Qm ≈ 344.8mgg-1) and fast adsorption rate for the removal of aqueous RhB. The excellent adsorption performance is likely related to the synergism of hydrogen bonding, π-π stacking interactions, and direct coordination between the MIL-101 substrate and RhB, as well as electrostatic interactions between MoS2 nanosheets and RhB. In particular, the uniform distribution of MoS2 nanosheets along with the negative charges on MIL-101 could have a strong interaction with the positively charged RhB, thus leading to an improvement in adsorption performance as observed for the MoS2/MIL-101 hybrid. Furthermore, MoS2/MIL-101 displayed good regenerability and reusability, making it attractive for the adsorption removal of aqueous RhB.

Study on the treatment of the sulfite pulp CEH bleaching effluents with the coagulation–anaerobic acidification–aeration package reactor

The coagulation-anaerobic acidification-aeration package reactor was designed for the treatment of pulp CEH bleaching effluents, the efficiencies in CODcr, BOD(5), AOX and toxicity removal achieved were 88.1%, 81.0%, 98.4% and 92.0%, respectively, with 15 h HRT. The toxicity and AOX were removed mainly through coagulation and anaerobic process, while the COD and BOD(5) were removed mainly through coagulation and aerobic process. The pretreatment of coagulation precipitation decreased the following organic load, which decreased the following treatment retention time and increased the stability of the system. The results of GC-MS showed: pollutants of wastewater were mainly chlorinated organics, most of AOX and the toxicity were removed by reductive dechlorination and acidified hydrolysis in anaerobic unit, the high COD removal in aerobic unit showed further degradation of pollutants. Chlorine atoms in the ortho position were preferentially dechlorination, that in para position were difficult to remove from chlorinated phenols during biological treatment.

Synthesis of SiO2 coated zero-valent iron/palladium bimetallic nanoparticles and their application in a nano-biological combined system for 2,2′,4,4′-tetrabromodiphenyl ether degradation

Polybrominated diphenyl ethers (PBDEs) are emerging persistent organic pollutants and the degradation of PBDEs is still a significant challenge owing to their extreme persistence and toxicity. In this study, the remediation of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) was investigated by employing a nano-biological combined system with SiO2-coated zero-valent iron/palladium bimetallic nanoparticles (SiO2-nZVI/Pd) as a reductant and Pseudomonas putida as a biocatalyst. The SiO2-nZVI/Pd exhibited much lower toxicity to the P. putida strain and higher reactivity in debromination than nZVI/Pd. The strain could grow well when the dosage was up to 1.0 g L−1. During the combined process, BDE47 (5 mg L−1) was completely debrominated to diphenyl ether (DE) within 2 h by SiO2-nZVI/Pd (1.0 g L−1) and then DE was completely degraded by P. putida after 4 days in sequential aerobic biodegradation. All the possible intermediates in the whole process were identified by ultra performance liquid chromatography (UPLC) and gas chromatography-mass spectrometer (GC-MS) analyses. The detection of BDE17, BDE7, BDE1 and DE indicated that rapidly stepwise debromination preferentially occurred at para positions in the anaerobic stage. Moreover, during aerobic biodegradation by P. putida, a number of phenolic compounds, such as phenol, catechol and hydroquinone were generated via ring opening by dioxygenation and further mineralized through the tricarboxylic acid cycle (TCA). Importantly, this combined process achieved rapid mineralization of PBDEs and avoided the generation of some highly toxic products like bromophenols and HO–PBDEs, which might have promising application prospects in the remediation of halogenated POPs.

Effect of oxygen availability on the removal efficiency and sludge characteristics during pentachlorophenol (PCP) biodegradation in a coupled granular sludge system.

This study systematically investigated the metabolism of pentachlorophenol (PCP) in batch experiments using coupled sludge granules under various dissolved oxygen concentrations. Results indicated that the oxygen condition in serum bottles has a significant effect on the microorganism metabolism. A greater degree of mineralization of PCP was achieved under oxygen-limited conditions (e.g., 40 and 60 initial headspace oxygen percentage (IHOP)), producing trichlorophenol (TCP), dichlorophenol (DCP) and monochlorophenol (MCP) as intermediates and chloride as one of the final products. Reductive dechlorination was identified as the primary pathway for the PCP degradation. Under strictly anaerobic or slightly oxidative conditions (0 and 20 IHOP), the reductive dechlorination of PCP led to an accumulation of TCP. Under aerobic conditions (80 and 100 IHOP), PCP degradation was less significant due to the hindered reductive chlorination in the presence of oxygen. It is also observed that cell hydrophobicity, protein (PN) concentration, settling velocity and specific gravity of the sludge granules decreased with IHOP from 0 to 60, and then increased with IHOP from 60 to 100. Specific methanogenic activity (SMA) and specific oxygen uptake rate (SOUR) confirmed that degradation of PCP was achieved by methanogenic and methanotrophic populations coexisting in a single granule. Because of a combination of reductive and oxidative degradation mechanisms, aerobic or facultative bacteria were found to oxidize the intermediates of PCP degradation products produced by methanogens and strict anaerobes during fermentation.