Dapeng Liang

The degradation of linear alkylbenzene sulfonate (LAS) in the presence of light and natural biofilms: the important role of photosynthesis.

Photosynthesis of algae usually changes the chemical conditions of microenvironment in natural waters. However, few studies have been carried out to examine the effects of diurnal variation and photosynthesis on behavior of organic pollutants in aquatic environments. In this study, linear alkylbenzene sulfonate (LAS) was selected as a representative of non-persistent organic pollutants to investigate the degradation of this type of pollutants in the presence of light and natural biofilms by laboratory batch experiments, with special emphasis on the effect of photosynthesis of the biofilms. The maximum decrease of LAS was observed in the coexistence of both illumination and fully active biofilms, and about 75% of the LAS were removed after a 36-h degradation experiment. The removal of LAS was found to be dominated by photosynthesis of the biofilms, with lesser roles attributed to biodegradation and adsorption by the biofilms, and the role of direct photolysis was negligible. The production of some reactive oxygen species might account for the role of photosynthesis in decomposing the LAS. The study confirms the important roles of algae biofilms and their photosynthesis in determining the fate of organic pollutants in aquatic environments.

Ammonia nitrogen removal and recovery from acetylene purification wastewater by air stripping

Ammonia nitrogen (NH4-N) contaminated wastewater has posed a great threat to the safety of water resources. In this study, air stripping was employed to remove and recover NH4-N from acetylene purification wastewater (APW) in a polyvinylchloride manufacturing plant. Investigated parameters were initial APW pH, air flow rate, APW temperature and stripping time. The NH4-N removal by air stripping has been modeled and the overall volumetric mass transfer coefficient (KLa) of the stripping process has been calculated from the model equation obtained. In addition, the ability of H2SO4 solution to absorb the NH3 stripped was also investigated. The results indicated that under the experimental conditions, the APW temperature and its initial pH had significant effects on the NH4-N removal efficiency and the KLa, while the effects of other factors were relatively minor. The removal efficiency and residual concentration of NH4-N were about 91% and 12 mg/L, respectively, at the optimal operating conditions of initial APW pH of 12.0, air flow rate of 0.500 m3/(h·L), APW temperature of 60 °C and stripping time of 120 min. One volume of H2SO4 solution (0.2 mol/L) could absorb about 93% of the NH3 stripped from 54 volumes of the APW.

Ammonia nitrogen removal from acetylene purification wastewater from a PVC plant by struvite precipitation

Acetylene purification wastewater (APW) usually contains high concentrations of ammonia nitrogen (NH4-N), which is generated during the production of acetylene in a polyvinylchloride manufacturing plant. In this study, a struvite precipitation method was selected to remove NH4-N from the APW. Laboratory-scale batch experiments were performed to investigate the effects of the initial APW pH, phosphate (PO4(3-)) concentration, magnesium (Mg(2+)) concentration, and sources of PO4(3-) and Mg(2+) on NH4-N removal. The results indicated that the initial APW pH had a significant effect on the removal of NH4-N, while the other factors had relatively minor effect. The NH4-N could be effectively removed at an optimum initial APW pH of 9.5, when Na2HPO4·12H2O and MgSO4·7H2O were both applied to NH4-N at a ratio of 1.2. Under these conditions, the efficiency of removal of NH4-N, total nitrogen and chemical oxygen demand were 85%, 84% and 18%, respectively. The X-ray diffraction analysis indicated that the precipitates were dominated by struvite. The scanning electron microscopy analysis of the precipitates showed a typical morphology of stick-like and prismatic crystals with coarse surface. The energy dispersive spectroscopy analysis indicated that the precipitates contained P, O, Mg and Ca.

Effects of tubificid bioturbation on realease of Cd and Zn from capping sediments

Laboratorial microcosm experiments were carried out to estimate the effects of the bioturbation induced by tubificid disturbance on release of Cd and Zn from capping lacustrine sediment. The farmland soil (5mm, 20mm) and uncontaminated sediment (5mm, 20mm) were collected as cap materials. Bioturbation effects on the pH of overlying water and the concentration of cadmium and zinc in the overlying water were studied in order to analyze the release flux of heavy metal in contaminated sediment disturbed by tubificid. The results showed that the capping decrease the release of heavy metals and the resuspension of sediment significantly and bioturbation could accelerate the release of Cd and Zn from capping sediment. With increasing of biomass, the release flux of Cd and Zn showed an upward-downward-upward tendency with no capping. The concentrations of Cd and Zn in overlying water declined with capping, and the release flux of Cd and Zn from sediment to overlying water decreased when the thickness of covering layer increased. The effects of capping and the transfer of heavy metal in sediment depended on the types and characteristics of cap materials. Generally, the inhibition for the release of heavy metal from polluted sediment capped by uncontaminated sediment is more significant. The release flux of Cd and Zn goes up with disturbance time increases. Meanwhile, there was adsorption of heavy metal by particles resuspending into overlying water under the tubificid reworking.

Measurement of freely dissolved PAH concentrations in overlying water and sediment using low density polyethylene

A method based on spiking performance reference compounds (PRCs) into low density polyethylene (LDPE) to measure freely dissolved Hydrophobic organic compounds (HOCs) in overlying water and sediment was introduced. Equilibration time of PRCs migrate to LDPE was determined and freely dissolved concentrations of three PAHs (acenaphthene, phenanthrene, pyren) in overlying water and sediment pore water were sampled and measured by the method. The results indicated that the concentrations of PRCs in LDPE were about constant after 64h. The measurement and subsequent calculation showed that freely dissolved concentrations of PAHs in the overlying water were 0.045µg/L, 0.087µg/L and 0.01175µg/L for acenaphthene, phenanthrene and pyren, respectively, and their concenreations in the sediment pore water were 0.112µg/L, 0.080µg/L and 0.0174µg/L, respectively.