Zhao Jianfu

Conductometric nitrate biosensor based on methyl viologen/Nafion/nitrate reductase interdigitated electrodes.

A highly sensitive, fast and stable conductometric enzyme biosensor for determination of nitrate in water is reported for the first time. The biosensor electrodes were modified by methyl viologen mediator mixed with nitrate reductase (NR) from Aspergillus niger by cross-linking with glutaraldehyde in the presence of bovine serum albumin and Nafion((R)) cation-exchange polymer. The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH, the enzyme loading and time of immobilization in glutaralaldehyde vapor were investigated with regard to their influence on sensitivity, limit of detection, dynamic range and operational and storage stability. The biosensor can reach 95% of steady-state conductance value in about 15s. Linear calibration in the range of 0.02 and 0.25 mM with detection limits of 0.005 mM nitrate was obtained with a signal-to-noise ratio of 3. When stored in 5 mM phosphate buffer (pH 7.5) at 4 degrees C, the sensor showed good stability over 2 weeks.

Conceptual mechanism of hydrodynamic impacts on freshwater algae for flow management

Numerous studies have shown that low flow condition is the main trigger of algae bloom and flow management is widely acknowledged as a strategy for inhibiting bloom development based on critical flow velocity and replacement. Due to the underlying intervention mechanism is still not clear,long-term practices of flow management are not very effective. Based on the research progress and a series of studies through long-term observation,enclosure and laboratory experiments,we present the conceptual mechanism that there existed three different mechanisms of hydrodynamic impacts on freshwater algae:( 1) low turbulent flow results in the thickness of cell diffuse layer thinner in favor of nutrients transport from water phase to algae cell,which is preferred by algae growth;( 2) medium turbulent flow is harmful to nutrients absorption and light availability of algae and inhibits the algae growth;( 3) high shear force can damage the algae cell walls,which are individually determinant in different levels of flow intensity. According to theories,critical flow velocity should be applied from two different aspects of water replacement and cytology in flow management. The results will be of great scientific significance in order to control algle bloom and remain the water quality in flow management.

On the light absorption characteristics of colored dissolved organic matter in Lake Dianshan

This paper focuses on the spectral absorption characteristic of colored dissolved organic matter (CDOM) in Lake Dianshan,which is the source of Huangpu River in Shanghai.The relationships between CDOM and water quality parameters,including chlorophyll a (Chl.a),turbidity and chemical oxygen demand (COD) were investi- gated.Spectral absorption shapes in different bands were studied to find precise S values (absorption spectrum slope coefficient).The results show that absorption coefficients of CDOM are not high,absorption coefficients at 355 nm range from 6.95 to 10.28 m~(-1) and absorption coefficients in the south lake is higher than that in the north lake.Corrections of CDOM and water quality parameters are not high,which show that CDOM mainly comes from urban sewage and industry wastewater.Spectral absorption coefficients of CDOM in the bands from 300 nm to 500 nm exponentially decrease with wavelength increasing while decrease linearly after 500 nm.The S values in the bands from 300 nm to 500 nm changes from 11.7μm~(-1) to 14.8μm~(-1).Absorption coefficients after 500 nm de- crease 0.0021 m~(-1) per.

Comparative study on synchronous adsorption of arsenate and fluoride in aqueous solution onto MgAlFe-LDHs with different intercalating anions

In this study, a series of MgAlFe-LDHs (Cl−, NO3−, intercalation, and calcined products of a CO32− interlayer) was synthesized and used for adsorption of arsenate and fluoride in individual contaminants and coexisting pollutant systems. Effects of various factors such as initial pH of solution, dosage of materials, coexisting ions, contact time, and initial pollutant concentrations were evaluated. Experimental results showed that different intercalating anions had a significant effect on adsorption performance of arsenate and fluoride in water. The adsorption of arsenate and fluoride on MgAlFe-CLDH, MgAlFe–Cl-LDH or MgAlFe–NO3-LDH can be described by different adsorption isotherm equations. During the simultaneous removal process, arsenate and fluoride competed for adsorption sites of the adsorbent materials, and the fluoride ions had advantages in the competitive adsorption on MgAlFe–Cl-LDH and MgAlFe–NO3-LDH. MgAlFe–NO3-LDH was used to adsorb arsenate and fluoride in coexisting pollution systems (the concentration of each pollutant was 2 mg L−1, the adsorbent dosage was 1.5 g L−1). The remaining arsenic concentration was reduced to less than 10 μg L−1 and the remaining fluoride ion concentration to below 20 μg L−1 which meets the World Health Organizations, EPAs and Chinas drinking water standards for arsenic and fluoride limits. A possible mechanism is discussed with support from further XRD, SEM, and XPS analysis of the materials after their adsorption.

Pollution status of organochlorines and heavy metals in surface sediment of southern Lake Taihu

Concentration and distribution of 19 organochlorines and 6 heavy metals in the surface sediment of southern Lake Taihu were studied and the relevant risk assessment was carried out.The results showed the concentrations of organochlorine pesticides(OCPs) and polychlorinated biphenyls(PCBs) detected ranged from 0.51-4.98ng/g(dw) and 1.49-15.15ng/g(dw),respectively,which was at a low contamination level compared to other fresh water sediments in China.The congener of α-hexachlorocyclohexane(α-HCH) was the dominant pollutant among OCPs and CB194,and CB28 were the dominant PCBs.The concentration rangesof Cu,Zn,Cr,Ni,Pb and Cd in the surface sediments of southern Lake Taihu were 14.4-79.7mg/kg,69.3-214mg/kg,65.0-99.5mg/kg,24.8-48.7mg/kg,12.3-39.2mg/kg and 0.015-0.563mg/kg,respectively.Effects range low(ERL) and effects range median(ERM) were used to evaluate the ecological risk of organochlorines.It was found that 90% of the sampling sites had a dichlorodiphenyltrichloroethanes(DDTs) value lower than the ERL,and the γ-HCH and PCBs values of all sites were lower than the ERL.The risk assessment was completed on heavy metals in sediments by using the potential ecological risk index(RI).The results indicated that the overall ecological risk caused by heavy metals was low.The potential ecological risk index of Cd was relatively higher,and the RIs of several heavy metals in XMK-0 were relatively higher than that in other sites.Although the concentration levels of the above organochlroine and heavy metal pollutants in the surface sediments of southern Lake Taihu were low and no serious threat has been observed to the ecological system,the prevention to these contaminations should not be ignored for their accumulative effect and toxicity in the environment.