Chaocheng Zhao

Tertiary treatment of textile wastewater with combined media biological aerated filter (CMBAF) at different hydraulic loadings and dissolved oxygen concentrations.

An up-flow biological aerated filter packed with two layers media was employed for tertiary treatment of textile wastewater secondary effluent. Under steady state conditions, good performance of the reactor was achieved and the average COD, NH(4)(+)-N and total nitrogen (TN) in the effluent were 31, 2 and 8mg/L, respectively. For a fixed dissolved oxygen (DO) concentration, an increase of hydraulic loading resulted in a decrease in substrate removal. With the increase of hydraulic loadings from 0.13 to 0.78m(3)/(m(2)h), the removal efficiencies of COD, NH(4)(+)-N and TN all decreased, which dropped from 52 to 38%, from 90 to 68% and from 45 to 33%, respectively. In addition, the results also confirmed that the increase of COD and NH(4)(+)-N removal efficiencies resulted from the increase of DO concentrations, but this variation trend was not observed for TN removal. With the increase of DO concentrations from 2.4 to 6.1mg/L, the removal efficiencies of COD and NH(4)(+)-N were 39-53% and 64-88%, whenas TN removal efficiencies increased from 39 to 42% and then dropped to 35%.

Laboratory investigation of oil-suspended particulate matter aggregation under different mixing conditions.

Oil-suspended particulate matter aggregation (OSA) has been recognized by the oil spill remediation community to effectively enhance the cleansing of spilled oil in the marine environment. While studies have investigated the application of mineral fines as an effective method to facilitate oil dispersion, decision-makers still lack information on the role of mixing energy in OSA formation and its significance to oil dispersion in real spills. This work studied the effect of level and duration of mixing energy on OSA formation using the standard reference material 1,941 b and Arabian light crude oil. The results showed that dispersed small oil droplets increased with an increase of both the level and duration of mixing energy to form multi-droplet OSAs. The sizes of the dispersed droplets varied between 5 and 10 μm under different conditions studied. The maximum oil trapping efficiency increased from 23% to 33%, the oil to sediment ratio increased from 0.30 to 0.43 g oil/g sediment, and the required shaking time decreased from 2.3 to 1.1h as the shaking rate increased from 2.0 to 2.3 Hz. Based on the size measurement results, a breakage effect on the formed OSAs and sediment flocs was confirmed under high mixing energy level.

Study of Interfacial Tension Between Oil and Surfactant Polymer Flooding

Abstract Surfactant polymer flooding is an important technology for enhancing oil recovery. It is generally thought that the lower the interfacial tension (IFT) between the combination flooding and oil is the higher oil recovery is. Some physical stimulation experiments have been conducted to show that a system with low IFT could bring better oil recovery than one with ultralow IFT in heterogeneous reservoirs. Emulsion experiments and visual experiments have also been carried out to determine the reason. This article presents results of those experiments and gives the possible mechanism of those results.

Biofouling characteristics and identification of preponderant bacteria at different nutrient levels in batch tests of a recirculating cooling water system

Understanding the influence of nutrient levels on biofouling control is an important requirement for management strategies in a recirculating cooling water system. Nutrient limitation may be one way to control biofouling development without increasing biocide dosing. Therefore, this study was carried out to investigate the effects of nutrient levels on biofouling characteristics and to identify the preponderant bacteria in the batch tests with a simulated cooling water system. The biofouling characteristics were assessed by varying the biofoulant mass and the bacteria respiratory activity, which was estimated by measuring oxygen uptake rates. According to the results obtained in nutrient factor experiments, the biofouling could be better controlled at carbon, nitrogen and phosphorus concentrations of 30 mg N/L, 8 mg N/L and 1.0 mg P/L, respectively. Increasing carbon concentrations shortened the biofouling initial growth period and resulted in higher biofoulant mass. The preponderant bacteria strains involved in biofouling under two culture conditions were identified by applying both physiological and biochemical tests and further molecular biology techniques with phylogenetic affiliation analysis. Enterobacter (family Enterobacteriaceae), Staphylococcus (family Micrococcaceae), Bacillus (family Bacillaceae), Proteus (family Enterobacteriaceae), Neisseria (family Neisseriaceae) and Pseudomonas (family Pseudomonadaceae) were dominant in the conditions of lower carbon concentration (30 mg/L). Enterobacter are autotrophs, but the other five bacteria are all heterotrophs. In the conditions of higher carbon concentration (70 mg/L), Klebsiella (family Enterobacteriaceae), Enterobacter and Microbacterium (family Microbacteriaceae) were dominant; Enterobacter and Microbacterium are heterotrophs.

The Isolation of Bioflocculant-producing Strains and the Application in the Oily Wastewater Treatment Process

Three bioflocculant-producing bacteria strains were isolated by the pyridine screening method. The flocculating rate of bioflocculant produced by KL9-1-3 on kaolin suspension (4.0g/L) reached as high as 98.2%. The strain KL9-1-3 was identified as Rhodococcus sp. according to its morphological, physiological, biochemical, and 16S rDNA sequence characteristics. It was deduced that the main component of purified bioflocculant was polysaccharide through infrared spectrophotometry and GC-MS analysis. The bioflocculant KL9-1-3 can effectively deal with oily wastewater, and the corresponding maximum removal rates of oil and COD for oily wastewater were 74.1% and 42.9%, respectively, under the optimum conditions of bioflocculant dosage 0.2 mL/L, pH 10.0, temperature 40°C, and Ca2+ as the coagulant.

Effect of diesel leakage in circulating cooling water system on preponderant bacteria diversity and bactericidal effect of biocides.

Petroleum products leakage results in adverse effect on the normal operation of a circulating cooling water system. However, relatively little research has been done to explore the effect of petroleum products leakage on circulating cooling water quality and biofilm preponderant bacteria diversity. Also, normal biocides application modes cannot fulfil the need for biofilm control. In this study, diesel oil was used as the experimental subject representing leaking petroleum products; the effect of diesel addition on biofilm preponderant bacteria diversity and the bactericidal effect of chlorine dioxide and tetradecyl dimethyl benzyl ammonium chloride (1427) was investigated. Bacterial community structures were examined by PCR-denaturing gradient gel electrophoresis and PCR cloning of 16S rDNA genes. Except for 100 mg/L diesel, increasing diesel concentration enhanced the biofilm detachment ratio compared with the control test. The microstructure of biofilm samples with 0, 300 and 900 mg/L diesel addition was observed. The species of preponderant bacteria in the biofilm sample with 300 mg/L diesel addition were more and the bacterial distribution was more uniform than those in the biofilm sample with 900 mg/L diesel addition. With ClO2 and 1427 addition, chemical oxygen demand increased, lipid phosphorus and bacterial count first decreased and then remained stable, and the bactericidal ratio first increased and then remained stable. Diesel addition variation has more obvious effect on ClO2 than 1427.

˙OH-initiated heterogeneous oxidation of methyl orange using an Fe–Ce/MCM-41 catalyst

In this study, a simple and active Fe3O4–Fe2O3–CeO2/MCM-41 (Fe–Ce/MCM-41) catalyst was fabricated, using iron and cerium species that were simultaneously immobilized on a MCM-41 zeolite surface, and employed as a heterogeneous Fenton-like catalyst for the oxidation of methyl orange (MO) for the first time. The activity of the Fe–Ce/MCM-41 catalyst was evaluated based on the degradation of MO, and the effects of the operating conditions (i.e., pH value, catalyst addition, hydrogen peroxide (H2O2) concentration and MO concentration) on degradation performance were investigated. The kinetics results indicated that MO removal followed pseudo-first order kinetics. Based on the analysis of metal leaching, X-ray photoelectron spectroscopy, and the effects of radical scavengers, MO in the bulk solution was primarily oxidized by surface-bound ˙OH, which was generated by the reaction of Fe2+ and Ce3+ species with H2O2 on the catalyst surface. The as-prepared Fe–Ce/MCM-41 catalyst exhibited excellent performance without the aid of ultrasonic and UV light irradiation, which can decrease the operating costs. In addition, this process may be promising for application in practical wastewater treatment.

Investigation of the kinetics of oil–suspended particulate matter aggregation

The process of oil-suspended particulate matter aggregation (OSA) has been recognized by the oil spill remediation community to enhance the natural cleansing of oiled shorelines. A laboratory study was conducted to investigate the kinetics of OSA formation under various mixing intensities using the standard reference material 1941b and Arabian heavy crude oil. The results showed that formation of OSAs increased exponentially with mixing time and reached a maximum within 5h. The maximum oil trapping efficiency increased from 24% to 47%, and the required shaking time decreased from 4.5 to 1.2h as the sediment concentration and mixing energy increased. The maximum oil-to-sediment ratio reached 0.24-0.68 g oil/g sediment within 5h. Most of the formed OSAs were solid OSAs and single droplet OSAs with low mixing energies, and multi-droplet OSAs with high mixing energies. The sizes of the dispersed oil droplets and OSAs were also investigated.

Comparison study of BiVO4 heterojunctions photocatalyst with different carbon materials

Abstract MWCNT/BiVO4 and RGO/BiVO4 heterojunctions were synthesized by the sol–gel method, and the photocatalytic activity of MWCNT/BiVO4 and RGO/BiVO4 were evaluated by monitoring the degradation of RhB in a heterogeneous photocatalytic reactor. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results indicated that a series of heterojunction structure composites were successfully synthesized, the heterojunction structure playing a crucial role in the electron–hole recombination. The crystal structure of BiVO4 was still monoclinic after the doping of MWCNT and RGO according to the XRD analysis, while the active sites of MWCNT/BiVO4 and RGO/BiVO4 were more than pure BiVO4. The RGO with a two-dimensional carbon sheet expressed higher performance than MWCNT with a one-dimensional carbon sheet for BiVO4 because the layered structure of the RGO had a stronger electron-trapping capability than MWCNT. The optimal MWCNT content was 2%, and the 6% RGO/BiVO4 showed the highest photocatalytic degradation efficiency of RhB. The photocatalytic degradation efficiency remained above 80% after five cycle tests.

Regenerable g-C3N4–chitosan beads with enhanced photocatalytic activity and stability

In this study, a series of regenerable graphitic carbon nitride–chitosan (g-C3N4–CS) beads were successfully synthesized via the blend crosslinking method. The prepared beads were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The structural characterization results indicate that the g-C3N4 granules were uniformly distributed on the surface of the chitosan matrix, and the structures of g-C3N4 and CS are maintained. In addition, the prepared g-C3N4–CS beads exhibited efficient MB degradation and stability. The optimum photocatalytic activity of our synthesized g-C3N4–CS beads was higher than that of the bulk g-C3N4 by a factor of 1.78 for MB. The improved photocatalytic activity was predominantly attributed to the synergistic effect between in situ adsorption and photocatalytic degradation. In addition, the reacted g-C3N4–CS beads can be regenerated by merely adding sodium hydroxide and hydrogen peroxide. Additionally, the regenerated g-C3N4–CS beads exhibit excellent stability after four runs, while the mass loss is less than 10%. This work might provide guidance for the design and fabrication of easily regenerated g-C3N4-based photocatalysts for environmental purification.