Wenrong Hu

Allelopathic effects of Ailanthus altissima extracts on Microcystis aeruginosa growth, physiological changes and microcystins release

The use of allelochemicals has been proved an environmentally friendly and promising method to control harmful algal blooms. This study was conducted to explore the application potential of Ailanthus altissima (A. altissima) extracts in Microcystis aeruginosa (M. aeruginosa) control for the first time. Four treatments with A. altissima extractions (25mgL(-1), 50mgL(-1), 100mgL(-1), and 200mgL(-1) respectively) and a control group were built to investigate the effects of A. altissima on the growth, cellular microstructure and cell viability, physiological changes, and release of extracellular matters. Results showed that the cell density of M. aeruginosa was effectively inhibited by A. altissima extract, and the inhibition rates were dose-dependent within 5d. Especially for the treatment with 200mgL(-1) of extract, the inhibitory rates remains above 90% after 5d exposure. In addition, A. altissima effectively decreased the amount of extracellular cyanotoxin microcystins and destroyed the photosynthesis-related structure of algae cell during the experimental period. The results demonstrated the A. altissima extracts can be used as an effective and safe algicide to control algal blooms. However, it must be noted that specific compounds responsible for algicidal effect should be isolated and identified to explore inhibition mechanism of A. altissima in future study.

Beneficial changes in biomass and lipid of microalgae Anabaena variabilis facing the ultrasonic stress environment

This study investigated the beneficial effects of ultrasonic treatment on the biomass, lipid and protein of the microalgae Anabaena variabilis. The microalgae after 11days cultivation (initial algae) were treated at the powers of 200, 350 and 500W for 10min and then cultured continuously for 3days (day 12-14). The power of 200W induced the highest lipid content 37.8% on day 12. The subsequent experiments tested the ultrasonic treatment times of 5, 10, 20 and 40min at 200W in the initial algae. The significantly improved lipid content 46.9% and productivity 54.2mg/L/d were obtained almost 1.46 and 1.86times more than that of the control algae respectively after 1day of continuous cultivation at 5min. The proper ultrasonic treatment showed the feasibility and high efficiency in promoting lipid accumulation without negatively influencing the biomass, fatty acid profiles and protein content.

Mutual facilitations of food waste treatment, microbial fuel cell bioelectricity generation and Chlorella vulgaris lipid production.

Food waste contains large amount of organic matter that may be troublesome for handing, storage and transportation. A microbial fuel cell (MFC) was successfully constructed with different inoculum densities of Chlorella vulgaris for promoting food waste treatment. Maximum COD removal efficiency was registered with 44% and 25 g CODL(-1)d(-1) of substrate degradation rate when inoculated with the optimal initial density (150 mg L(-1)) of C. vulgaris, which were 2.9 times and 3.1 times higher than that of the abiotic cathode. With the optimum inoculum density of C. vulgaris, the highest open circuit voltage, working voltage and power density of MFC were 260 mV, 170 mV and 19151 mW m(-3), respectively. Besides the high biodiesel quality, promoted by MFC stimulation the biomass productivity and highest total lipid content of C. vulgaris were 207 mg L(-1)d(-1) and 31%, which were roughly 2.7 times and 1.2 times higher than the control group.

A promising application of chitosan quaternary ammonium salt to removal of Microcystis aeruginosa cells from drinking water

This work was aimed toward studying the new application of chitosan quaternary ammonium salt (HTCC), a water-soluble chitosan derivative, on removal of Microcystis aeruginosa (M. aeruginosa) cells during HTCC coagulation and floc storage. Results showed that all cells were removed without damage under optimum coagulation conditions: HTCC dosage 1.5mg/L, rapid mixing for 0.5min at 5.04g and slow mixing for 30min at 0.20g. The high removal efficiency was due to the large size and compact structure of flocs formed by HTCC, which readily settled. During floc storage, HTCC could induce production of reactive oxygen species (ROS), which would accelerate M. aeruginosa cell lysis. But the flocs, into which the cells aggregated, could protect cells from cellular oxidative damage caused by ROS, thus keeping the cells intact for a longer time.

Behaviors of Microcystis aeruginosa cells during floc storage in drinking water treatment process.

This is the first study to systematically investigate the different behaviors of Microcystis aeruginosa in the sludges formed by AlCl3, FeCl3, and polymeric aluminium ferric chloride (PAFC) coagulants during storage. Results show that the viability of Microcystis aeruginosa in PAFC sludge was stronger than that of cells in either AlCl3 or FeCl3 sludge after the same storage time, while the cells’ viability in the latter two systems stayed at almost the same level. In AlCl3 and FeCl3 sludges high concentrations of Al and Fe were toxic to Microcystis aeruginosa, whereas in PAFC sludge low levels of Al showed little toxic effect on Microcystis aeruginosa growth and moderate amounts of Fe were beneficial to growth. The lysis of Microcystis aeruginosa in AlCl3 sludge was more serious than that in PAFC sludge, for the same storage time. Although the cell viability in FeCl3 sludge was low (similar to AlCl3 sludge), the Microcystis aeruginosa cells remained basically intact after 10 d storage (similar to PAFC sludge). The maintenance of cellular integrity in FeCl3 sludge might be due to the large floc size and high density, which had a protective effect for Microcystis aeruginosa.

Significantly enhanced dewatering performance of drinking water sludge from a coagulation process using a novel chitosan–aluminum chloride composite coagulant in the treatment of cyanobacteria-laden source water

The enhanced dewatering performance and the fate of cyanobacterial cells in the filtration of cyanobacteria-laden sludge, generated by a coagulation process using a novel composite chitosan–aluminum chloride (CTSAC) coagulant, were systemically studied. Two other cyanobacteria-laden sludge, aluminum chloride (AC) sludge and chitosan (CTS) sludge, were also studied to compare dewater performance with CTSAC sludge. Results showed that the dewatering process did not cause cell lysis and microcystins (MCs) release. The level of MCs and extracellular organic matter (EOM) in the filtrate were decreased by adsorption and sieving onto the cake layer formed on the membrane, but dewatering at high vacuum pressure reduced the rejection efficiency. The sludge from the coagulation process using the CTSAC composite displayed better sludge dewaterability and obtained a better quality of filtrate (fewer MCs and EOM) than those from AC and CTS coagulation processes independently. A three-dimensional excitation–emission matrix (EEM) fluorescence measurement indicated that protein-like substances in soluble extracellular polymeric substances (EPS) played a negative role on cyanobacteria-laden sludge dewatering. In addition, CTSAC sludge showed a more compact structure and larger floc sizes than AC sludge and CTS sludge for a strong improvement in the charge neutralization and bridge ability of AC by combining CTS in the composite coagulant. It was further observed that floc size played a more significant role on sludge dewaterability than the degree of compactness. Overall, the preferable dewater performance of CTSAC sludge demonstrated the CTSAC composite coagulant has great potential for the treatment of cyanobacteria-laden source water.

Adjusting irradiance to enhance growth and lipid production of Chlorella vulgaris cultivated with monosodium glutamate wastewater.

Light is one of the most important factors affecting microalgae growth and biochemical composition. The influence of illumination on Chlorella vulgaris cultivated with diluted monosodium glutamate wastewater (MSGW) was investigated. Six progressive illumination intensities (0, 30, 90, 150, 200 and 300μmol·m(-2)s(-1)), were used for C. vulgaris cultivation at 25°C. Under 150μmol·m(-2)s(-1), the corresponding specific light intensity of 750×10(-6)μmol·m(-2)s(-1) per cell, algae obtained the maximum biomass concentration (1.46g·L(-1)) on the 7th day, which was 3.5 times of that under 0μmol·m(-2)s(-1), and the greatest average specific growth rate (0.79 d(-1)) in the first 7days. The results showed the importance role of light in mixotrophic growth of C. vulgaris. High light intensities of 200 and 300μmol·m(-2)s(-1) would inhibit microalgae growth to a certain degree. The algal lipid content was the greatest (30.5%) at 150μmol·m(-2)s(-1) light intensity, which was 2.42 times as high as that cultured in dark. The protein content of C. vulgaris decreased at high light intensities of 200 and 300μmol·m(-2)s(-1). The effect of irradiance on carbohydrate content was inversely correlated with that on protein. The available light at an appropriate intensity, not higher than 200μmol·m(-2)s(-1), was feasible for economical cultivation of C. vulgaris in MSGW.

Effect of high-temperature stress on microalgae at the end of the logarithmic phase for the efficient production of lipid

ABSTRACT Efficient production of microalgae lipid is significant for the production of renewable biodiesel. In the present study, the high temperature of 40°C as stress environment was tested for stimulating lipid accumulation after the microalgae (Scenedesmus quadricauda) cells in suitable conditions grew to the end of the logarithmic phase. Different stress cultivation times of 1, 2, 3, 4, 5 and 6 days were studied. Interestingly, the lipid content and productivity reached 33.5% and 23.2u2005mg/Lu2005d after one day stress cultivation, showing substantial improvements of 39.6% and 33.3% compared with that in the untreated (day 0) microalgae cells, respectively. Longer stress time led to the decrease of biomass and lipid content compared with the untreated microalgae. However, a maximum protein content of 58.7% was obtained after six days. The stress cultivation at the end of the microalgae exponential phase for one day at a high temperature of 40°C could be a very useful industrial approach for efficiently promoting lipid content and biodiesel production.

Degradation mechanism of hydrogen-terminated porous silicon in the presence and in the absence of light

Si is well-known semiconductor that has a fundamental bandgap energy of 1.12 eV. Its photogenerated electrons in the conduction band can react with the ubiquitous oxygen molecules to yield ⋅O2− radicals, but the photogenerated holes in the valance band can’t interact with OH− to produce ⋅OH radicals. In this paper, we study the degradation of methyl orange (MO) by hydrogen-terminated porous Si (H-PSi) in the presence and in the absence of light. The absorption spectra of the degraded MO solutions indicated that the H-PSi had superior degradation ability. In the dark, the reduction of dye occurs simply by hydrogen transfer. Under room light, however, some of the dye molecules can be reduced by hydrogen transfer first and then decomposed in the conduction and valance bands. This result should be ascribed to its wide band gap energies centered at 1.79-1.94 eV.

The enhanced reduction of C- and N-DBP formation in treatment of source water containing Microcystis aeruginosa using a novel CTSAC composite coagulant

This study investigated the effect of a chitosan-aluminium chloride (CTSAC) composite coagulation process on reducing the formation of algal organic matters (AOM) related carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs), by removing or adsorbing their precursors. Compared with aluminium chloride (AC) and chitosan (CTS) alone, CTSAC significantly enhanced the removal of dissolved organic matter (DOC), polysaccharide, protein and humic acids, attaining removals of 64.95%, 80.78%, 70.85% and 44.50%, respectively. Notably, the three-dimensional excitation and emission matrix (3D-EEM) combined with molecular weight (MW) fractionation analysis revealed that CTSAC was not only effective for removing high-MW AOM, but also for the low-MW fractions that are important in forming DBPs. In addition, the CTSAC coagulation was proven to enhance the removal of aromatic polypeptide/amino acid-like materials and aliphatic amines, which have high N-nitrosodimethylamine formation potential. Efficient AOM removal by the CTSAC coagulation resulted in significant reduction of both AOM-related C-DBPs (63.54%) and N-DBPs (71%), while AC coagulation did not substantially reduce the formation of tribromomethane, 1,1,1-trichloropropanone or N-nitrosodimethylamine, and CTS coagulation alone did not achieve any obvious reduction in trichloronitromethane. Fourier transform infrared (FT-IR) spectroscopy analysis confirmed the interaction of CTS and AC in the CTSAC composite coagulation, which contributed to the improved AOM removal performance of CTSAC, and, in this case, reduced the formation of C- and N-DBPs.