Low concentrations of polycyclic aromatic hydrocarbons promote the growth of Microcystis aeruginosa.

There is an increasing need to describe the growth characteristics of cyanobacteria exposed to polycyclic aromatic hydrocarbons (PAHs) because the presence of PAHs in lakes is known to affect the growth of this kind of microorganisms. In this work, the effects of low concentrations of PAHs on Microcystis aeruginosa (M. aeruginosa) were investigated. M. aeruginosa were cultivated in the medium with a mixture of PAHs (0.486 mg L(-1) naphthalene, 0.049 mg L(-1) phenanthrene, and 0.0015 mg L(-1) pyrene) and different concentrations of nitrogen and phosphorus. During 31 d of incubation, profiles of cell number and chlorophyll-a content were determined. The results indicated that when the concentration of an individual PAH was below its no observed effect concentration (NOEC), the exposure of M. aeruginosa to a mixture of PAHs markedly promoted cell density after 7d of culture. Low concentrations of nutrients in the medium improved the growth of M. aeruginosa in the presence of PAHs. When concentrations of both phosphorus and nitrogen were 50% lower than those of the control, the specific growth rate of M. aeruginosa increased by 100% when exposed to PAHs, and the generation time decreased from 10.5 to 5.3d. The chlorophyll-a content in medium also increased from 2.23 to 3.18 µg mL(-1), which was attributed to an increase in cell numbers.

Cosorption of phenanthrene and mercury(II) from aqueous solution by soybean stalk-based biochar.

Soybean [Glycine max (L.) Merr.] stalk-based biochar was prepared using oxygen-limited pyrolysis. We evaluated phenanthrene (PHE) and Hg(II) sorption, from single and binary component solutions, onto prepared biochar. We found that the prepared biochar efficiently removed PHE and Hg(II) from aqueous solutions. The isotherms for PHE and Hg(II) sorption could be described using linear and Tóth models, respectively, both with high regression coefficients (R(2) > 0.995). When PHE and Hg(II) coexisted in an aqueous solution, we observed direct competitive sorption, each one suppressing another. Our results provide insight into the recycling of agricultural residues, and also a new application for removal of polycyclic aromatic hydrocarbons and heavy metals from contaminated water utilizing biochar from agricultural residue.

Removal of polycyclic aromatic hydrocarbons from aqueous solution on soybean stalk-based carbon.

Soybean [ (L.) Merr.] stalk-based carbons were prepared by phosphoric acid activation at different carbonization temperatures. Characteristics of the prepared carbon, including specific surface area, iodine number, and amount of methylene blue sorption, were determined. Experiments on phenanthrene, naphthalene, and acenaphthene, as representatives of polycyclic aromatic hydrocarbons (PAHs), removal from aqueous solution by the prepared carbon were conducted at different levels of carbon addition. The results indicated that the specific surface area, iodine number, and amount of methylene blue sorption increased with an increase of carbonization temperature. The maximum values were observed at 700°C and were 287.63 m g, 508.99 mg g, and 90.14 mg g, respectively. The removal efficiencies of phenanthrene, naphthalene, and acenaphthene tended to increase with increasing carbon amounts and carbonization temperature. The optimal removal performance was obtained under the experimental conditions of carbon concentrations of 0.04 g 32 mL and carbonization temperature of 700°C, and the removal efficiencies of phenanthrene, naphthalene, and acenaphthene were 99.89, 100, and 95.64%, respectively. The performance of the prepared carbon was superior to that of commercial activated carbon. Additionally, for the same carbon concentrations, the removal efficiency of PAHs on prepared carbons followed the order: phenanthrene > naphthalene > acenaphthene. Results obtained from this work provide some insight into the reuse of an agricultural residue, and also provide a new application for the treatment of PAHs in contaminated water utilizing activated carbon prepared from agricultural residues.

[Preparation method of stalk environmental biomaterial and its sorption ability for polycyclic aromatic hydrocarbons in water].

The soybean, sesame and corn stalks were pyrolyzed and charred for 8 h at 300-700 degrees C to obtain stalk environmental biomaterials. The BET specific surface areas, methylene blue, and iodine adsorption capacity of the stalk environmental biomaterials were determined. The sorption efficiency of these materials on single polycyclic aromatic hydrocarbon (PAH) and mixing PAHs were investigated. The BET specific surface areas of stalk biomaterials enlarged, and the sorption ability on methylene blue and iodine enhanced with increasing the treatment temperature. The obtained stalk biomaterials could effectively remove the PAHs from water. For instance, 91.28%, 89.01% and 99.66% of naphthalene, acenaphthene, and phenanthrene in 32 mL water were removed by 0.01 g biomaterials obtained by soybean stalk at 700 degrees C. The removal efficiencies of biomaterials for mixed PAHs in water were in the order of phenanthrene > naphthalene > acenaphthene. However, the sorption ability of produced stalk biomaterials differed significantly, and followed the order of corn > soybeans > sesame for the removal of naphthalene and acenaphthene, and soybean > corn > sesame for phenanthrene removal in water. Results of this work would provide some insight into the reuse of crop stalks, and also open a new view on the treatment of organic polluted water utilizing biomaterials.

A rapid determination method of chemical oxygen demand in printing and dyeing wastewater using ultraviolet spectroscopy.

A rapid method to determine chemical oxygen demand (COD) in printing and dyeing wastewater using ultraviolet (UV) spectroscopy was developed in this study. The UV method has several advantages compared to the chemical method, such as shortened analysis time, convenience, no requirement of expensive and toxic reagents, and good reproducibility. It was established that the magnitude of COD and, to a certain extent, pH and suspended solids of the sample have effects on the accuracy and precision of the method. The results showed the fitting range of COD(Cr) (COD determined by the dichromate method) was 0 to 360 mg/L(-1) And the pH ranged from 2.45 to 9.22. If the UV(365) (UV absorbance at 365 nm) is measured and is subtracted from UV(254) (UV absorbance at 254 nm), then the effects of suspended solids was eliminated. A control experiment of COD(Cr) determination using the rapid method and the standard dichromate method was carried out, which validated the former.

Pretreatment of textile dyeing wastewater using an anoxic baffled reactor.

A study on pretreatment of textile dyeing wastewater was carried out using an anoxic baffled reactor (ABR) at wastewater temperatures of 5-31.1 degrees C. When hydraulic retention time (HRT) was 8h, the color of outflow of ABR was only 40 times at 5 degrees C and it could satisfy the professional discharge standard (grade-1) of textile and dyeing industry of China (GB4287-92). The total COD removal efficiency of ABR was 34.6%, 47.5%, 50.0%, 53.3%, 54.7% and 58.1% at 5, 9.7, 14.9, 19.7, 23.5 and 31.1 degrees C, respectively. Besides, after the wastewater being pre-treated by ABR when HRT was 6h and 8h, the BOD5/COD value rose from 0.30 of inflow to 0.46 of outflow and from 0.30 of inflow to 0.40 of outflow, respectively. Experimental results indicated that ABR was a very feasible process to decolorize and pre-treat the textile dyeing wastewater at ambient temperature. Moreover, a kinetic simulation of organic matter degradation in ABR at six different wastewater temperatures was carried through. The kinetic analysis showed the organic matter degradation was a first-order reaction. The reaction activation energy was 19.593 kJ mol(-1) and the temperature coefficient at 5-31.1 degrees C was 1.028.

Performance of combined process of anoxic baffled reactor-biological contact oxidation treating printing and dyeing wastewater.

A study of the treatment of printing and dyeing wastewater was carried out using the combined process of anoxic baffled reactor-biological contact oxidation. The results showed the pH ascended continuously and the oxidation-reduction potential dropped gradually from compartment 1-6 in ABR. When hydraulic retention time was 12h, color removal efficiency was 92% and the color of effluent of ABR could satisfy the professional emission standard (grade-1) of textile and dyeing industry of China. The total COD removal efficiency of the combined process was 86.6% and the COD of effluent could satisfy the professional emission standard (grade-2) of textile and dyeing industry of China.

Determination of bulk mass transfer coefficient of biosorption on sludge granule based on liquid membrane mass transfer mechanism.

A bulk mass transfer coefficient (BMTC) equation was derived from the mechanism of mass transfer in surface liquid membrane in this study, which was based on the analysis of biosorption process, conservation of mass in sludge granule and the unification of the dimension. A biosorption experiment was carried out in which anoxic sludge from an anoxic baffled reactor for printing and dyeing wastewater treatment was used to adsorb Acid Red GR dye. The results showed that there was a linear regression curve between ln[qe/(qe-q)] (qe and q were the amount adsorbed at equilibrium and at time t, respectively.) and time t. There was also a good agreement between the adsorbate amount measured and that predicted by the equation of BMTC. The BMTC of Acid Red GR dye adsorbed by anoxic sludge was 6.816 kgm(-3)min(-1). Experimental results indicated that the BMTC determined by a simple adsorptive experiment using this equation was credible. It could be a feasible and effective way to determine BMTC of activated sludge for biosorption performance.