Research on enhancement of zero-valent iron on dissimilatory nitrate/nitrite reduction to ammonium of Desulfovibrio sp. CMX.

The process of nitrate dissimilation to ammonium (DNRA) is an important way for storing nitrogen in nature and DNRA is a key step in efficient recovery of nitrogen in wastewater. However, in view of the low conversion efficiency of DNRA, zero-valent iron (ZVI) was used to enhance the DNRA process of Desulfovibrio sp. CMX. ZVI can obviously promote the nitrate/nitrite reduction. The experiment indicated that 5 g/L 300 mesh ZVI could convert 5 mmol/L nitrate or nitrite to ammonium in 48 h or 36 h respectively, and the conversion ratio of NO2- to NH4+ could reach more than 90%. The ZVI provided a suitable growth environment for the Desulfovibrio sp. CMX through chemical reduction of nitrite, production of divalent iron (Fe2+), reduction of oxidation-reduction potential (ORP) and adjustment of pH, which strengthened the DNRA performance. This experiment is advantageous for increasing efficiency of DNRA and provides a new idea for efficient recovery of nitrogen resources.

Adsorption behavior of azo dye C. I. acid red 14 in aqueous solution on surface soils.

Azo dyes have received considerable attention because of their association with various human health problems. The aim of the investigation is to determine the adsorption behavior of azo dyes in aqueous solution on DG06, GSE17200, and GSE17201 soils using C. I. Acid Red 14 (AR14) as example. The experimental results indicate that the Freundlich model expresses the adsorption isotherm better than the Langmuir model and the pseudo-second-order model achieves adsorption of AR14 on the three soils well. Based on the pseudo-second-order model, the adsorption thermodynamic of AR14 on DG06 soil have been studied and the thermodynamics parameter of deltaG0 is determined and deltaG0 value shows the adsorption process of AR14 on DG06 is mainly physical in nature. Furthermore, the effects of temperature, pH and salinity (NaCl) on adsorption have been investigated. The decrease in pH or the increase in salinity enhances the adsorption of AR14 by DG06, GSE17200, and GSE17201.

[Performance of constructed wetland for municipal wastewater tertiary treatment: winter and summer comparison].

An improved three-stage vertical flow constructed wetland (CW) was used for tertiary treatment of effluent from two typical Dalian municipal wastewater treatment plants. The experiments were carried out under ambient condition in Dalian for the whole year. Performances of the CW for COD, TN, NH4(+) -N and TP removal in summer (Jun.-Aug.), winter (Nov.-Jan. the second year) and spring (Feb.-Apr.) were compared. In summer, the removal rates of COD, TN, NH4(+) -N and TP reached 88.5%, 76%, 100% and 98%, respectively. While in winter they reached 88%, 85.3%, 86.4% and 97%, respectively. In spring, the removal rates reached 87.7%, 76.7%, 70.3% and 95.5%, respectively. The effluent water quality for summer, winter and spring were: COD 2.8, 3.8 and 3.9 mg x L(-1), respectively; TP 0.02, 0.05, and 0.07 mg x L(-1), respectively; TN 6.8, 2.9, and 9.2 mg x L(-1), respectively; NH4(+)-N 0.01, 0.3, and 8.1 mg x L(-1), respectively. Results showed good performance of CW for Dalian municipal wastewater tertiary treatment, especially for COD and TP removal. The effluent COD and TP meet the needs of Environmental Quality Standard for Surface Water (GB 3838-2002) III, whereas the effluent TN and NH4(+)- N meet the needs of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) class I A and B, separately. The pollutant removal loads in summer, winter and spring were as flow: COD 4.9, 5.1, and 5.0 g x (m2 x d)(-1); TN 3.4, 3.0, and 5.5 g x (m2 x d)(-1); NH4(+) -N 0.2, 0.6, and 3.7 g x (m2 x d)(-1); TP 0.15, 0.30, and 0.28 g(m2 x d)(-1). It is indicated that no significant influence of seasons on pollutant removal is found by comparing the removal rates as well as pollutant removal loads in different seasons, however, the removal of NH4(+) -N and TN in CW is mainly influenced by influent pollutant loads.

Preparation and evaluation of molecularly imprinted solid-phase microextraction fibers for selective extraction of bisphenol A in complex samples.

Molecular imprinted polymer (MIP) as solid-phase microextraction (SPME) fibers coating has gained great attention in recent years. In this study, a simple preparation approach for bisphenol A (BPA) MIP coating with controlled thickness on fused-silica capillaries was developed. A capillary was inserted into a larger bore capillary to form a sleeve as mold. The prepolymer solution containing the template BPA was introduced into the interspace between the two capillaries for polymerization under photoirradiation. The larger bore capillary was removed away after the polymerization, and MIP coating with certain thickness on the surface of the inserted capillary was obtained. SPME conditions based on the MIP-coated fibers were optimized, and the extraction performance of the fibers with different thickness coating was compared. Finally, the MIP fibers were used for selective extraction of BPA spiked in tap water, human urine, and milk samples. The average recoveries of spiked BPA in the three samples were 92.5%, 81.6%, and 87.5%, respectively. The present analytical performance is not up to par for applicability to real environmental matrices. Further improvement will be necessary for analysis of real complex samples.

[Sorption-desorption of phosphate in wastewater by hydrous iron oxide].

FeCl3 was used t o prepare hydrous iron oxide (HIO) as a n absorbent for phosphate (P) sorption and desorption study. The results showed that as pH decreased, the sorption capacity of HIO increased, and the sorption kinetics followed the second-order model, and the sorption isotherm could be fitted by the Langmuir equation. A 50 g/L NaOH solution was used for desorption of P from HIO, and the desorption rate could be reached over 98% . No relation was found between desorption rate and adsorption capacity. Based on above results, HIO was applied to adsorption of P from supernatant of sludge thickener, and after desorption, more than 90% of P was recovered. According to the results obtained, an effective system for P removal and recovery from municipal wastewater was suggested, which includes the following processes: adsorption, desorption, regeneration of HIO, and of recovery of P from P-rich desorption solution.

Azoreductase from Rhodobacter sphaeroides AS1.1737 is a flavodoxin that also functions as nitroreductase and flavin mononucleotide reductase.

Previously reported azoreductase (AZR) from Rhodobacter sphaeroides AS1.1737 was shown to be a flavodoxin possessing nitroreductase and flavin mononucleotide (FMN) reductase activities. The structure model of AZR constructed with SWISS-MODEL displayed a flavodoxin-like fold with a three-layer alpha/beta/alpha structure. With nitrofurazone as substrate, the optimal pH value and temperature were 7.0 and 50 degrees C, respectively. AZR could reduce a number of nitroaromatic compounds including 2,4-dinitrotoluene, 2,6-dinitrotoluene, 3,5-dinitroaniline, and 2,4,6-trinitrotoluene (TNT). TNT resulted to be the most efficient nitro substrate and was reduced to hydroxylamino-dinitrotoluene. Both NADH and NADPH could serve as electron donors of AZR, where the latter was preferred. Externally added FMN was also reduced by AZR via ping-pong mechanism and was a competitive inhibitor of NADPH, methyl red, and nitrofurazone. AZR with broad substrate specificity is a member of a new nitro/FMN reductase family demonstrating potential application in bioremediation.