[Behavior and Degradation of Polycyclic Aromatic Hydrocarbons (PAHs) in Coking Wastewater of A/O2 and A/O/H/O Processes].

Polycyclic aromatic hydrocarbons (PAHs) are typical organic pollutants found in coking wastewater, and their behavior and reduction can be affected by different treatment processes. Based on these considerations, this study investigated the behaviors of PAHs in coking wastewater under A/O2 and A/O/H/O treatment processes, respectively. In order to evaluate variations in PAH removal under two different treatment processes, samples were taken from different treatment units for quantification of PAHs using gas chromatography-mass spectrometry. Results showed that PAHs were barely degraded in anaerobic tanks of either treatment process and accumulated much higher concentrations than in aerobic and hydrolytic tanks. While low molecular weight PAHs (LMW PAHs) in aqueous phase from anaerobic tanks were degraded effectively in aerobic tanks, high molecular weight PAHs (HMW PAHs) mostly accumulated in the sludge phase; these potentially pose a higher environmental risk and therefore need to be treated separately. Moreover, the A/O/H/O process showed higher degradation of PAHs bioavailability and higher removal effectiveness for PAHs with four or more benzene rings than the A/O2 process; this is attributed to the hydrolytic tank's ability to promote hydrolysis of macromolecular organic compounds and therefore improve biodegradability of PAHs. Comprehensive results from the study indicated that the A/O/H/O process is more advantageous for degradation of PAHs than the A/O2 process.

[Analysis of novel style biological fluidized bed A/O combined process in dyeing wastewater treatment].

A novel biological fluidized bed was designed and developed to deal with high-concentration refractory organic industrial wastewater. From 12 successful projects, three cases of dyeing wastewater treatment projects with the scale of 1200, 2000 and 13000 m3/d respectively were selected to analyze the principle of treating refractory organic wastewater with fluidized bed technology and discuss the superiority of self-developed biological fluidized bed from the aspects of technical and economic feasibility. In the three cases, when the hydraulic retention time (HRT) of biological system were 23, 34 and 21. 8 h, and the volume loading of influents (COD) were 1.75, 4.75 and 2.97 kg/(m3 x d), the corresponding COD removal were 97.3%, 98.1% and 95.8%. Furthermore the operating costs of projects were 0.91, 1.17 and 0.88 yuan per ton of water respectively. The index of effluent all met the 1st grade of Guangdong Province wastewater discharge standard. Results showed that the biological fluidized bed had characteristics of shorter retention time, greater oxygen utilization rate, faster conversion rate of organic pollutants and less sludge production, which made it overcome the shortcomings of traditional methods in printing and dyeing wastewater treatment. Considering the development of technology and the combination of ecological security and recycling resources, a low-carbon wastewater treatment process was proposed.

Dechlorination of chlorobenzene in subcritical water with Fe/ZrO2, Ni/ZrO2 and Cu/ZrO2.

To obtain information about dechlorination of organochlorine compounds in subcritical water catalyzed by metals assisted with ZrO(2), dechlorination of chlorobenzene has been investigated in the presence of Fe/ZrO(2), Ni/ZrO(2) and Cu/ZrO(2) catalysts. The dechlorination efficiency was increased with increasing residence time, temperature and pressure. The order of effectiveness of the catalysts was Cu/ZrO(2) < Ni/ZrO(2) < Fe/ZrO(2). The dechlorination of chlorobenze obeyed pseudo-first-order kinetics models. The rate constants in subcritical water were much greater than that in ambient-temperature water; the activation energies were obtained. ZrO(2) in the catalyst had the power to absorb chlorobenzene onto the catalyst surface and promoted the dechlorination ability of the metal. The primary mechanism for dechlorinaton of chlorobenzene involved the reduction of chlorobenzene by reaction with nascent hydrogen. The nascent hydrogen reacted with the chlorobenzene, which adsorbed on the catalyst in non-planar and co-planar form, and formed benzene and chloride ions.

[Adsorption process of organic contaminant in untreated coking wastewater by powdered activated carbon].

The article investigated the removal of organic contaminant from coking wastewater in adsorption process using powdered activated carbon as adsorbent. The dose of activated carbon, temperature, pH and reaction time were studied, and UV-Vis and GC/MS were used to carry out the qualitative and semiquantitative analysis of organic compositions in wastewater. The results showed that the optimum conditions for pretreatment of coking wastewater were 6 g activated carbon per liter, 30 degrees C, pH = 9 and reaction for 20 min, under which the removal efficiency of organic pollutants are more than 70%. Among the 56 kinds of organic compounds, 45 kinds such as dolichoalkanes, polynucleation aromatic series, azacyclo compounds could be removed, and the removal ratios of amidobenzene, hydroxybenzene, indoleacetic, acid-2-methyl-phenyl-ester are 63.5%, 42.6%, 88.1%, 28.1% respectively, while cresol and xylenol are more than 70% and 85%. In the adsorption process of multi-composition system in wastewater, macromolecules with low-pole and major -delta G0 as polynuclear aromatic hydrocarbons and azacyclo compounds could be adsorbed preferentially and completely in tacho-absorption period, while micromolecule with hadro-pole and inferior -delta G0 as amidobenzene and hydroxybenzene were adsorbed ambly.

Characteristics of high-sulfate wastewater treatment by two-phase anaerobic digestion process with Jet-loop anaerobic fluidized bed.

A new anaerobic reactor, Jet-loop anaerobic fluidized bed (JLAFB), was designed for treating high-sulfate wastewater. The treatment characteristics, including the effect of influent COD/SO4(2-) ratio and alkalinity and sulfide inhibition in reactors, were discussed for a JLAFB and a general anaerobic fluidized bed (AFB) reactor used as sulfate-reducing phase and methane-producing phase, respectively, in two-phase anaerobic digestion process. The formation of granules in the two reactors was also examined. The results indicated that COD and sulfate removal had different demand of influent COD/SO4(2-) ratios. When total COD removal was up to 85%, the ratio was only required up to 1.2, whereas, total sulfate removal up to 95% required it exceeding 3.0. The alkalinity in the two reactors increased linearly with the growth of influent alkalinity. Moreover, the change of influent alkalinity had no significant effect on pH and volatile fatty acids (VFA) in the two reactors. Influent alkalinity kept at 400-500 mg/L could meet the requirement of the treating process. The JLAFB reactor had great advantage in avoiding sulfide and free-H2S accumulation and toxicity inhibition on microorganisms. When sulfate loading rate was up to 8.1 kg/(m3 x d), the sulfide and free-H2S concentrations in JLAFB reactor were 58.6 and 49.7 mg/L, respectively. Furthermore, the granules, with offwhite color, ellipse shape and diameters of 1.0-3.0 mm, could be developed in JLAFB reactor. In granules, different groups of bacteria were distributed in different layers, and some inorganic metal compounds such as Fe, Ca, Mg etc. were found.

Supercritical gasification for the treatment of o-cresol wastewater.

The supercritical water gasification of phenolic wastewater without oxidant was performed to degrade pollutants and produce hydrogen-enriched gases. The simulated o-cresol wastewater was gasified at 440-650 degrees C and 27.6 MPa in a continuous Inconel 625 reactor with the residence time of 0.42-1.25 min. The influence of the reaction temperature, residence time, pressure, catalyst, oxidant and the pollutant concentration on the gasification efficiency was investigated. Higher temperature and longer residence time enhanced the o-cresol gasification. The TOC removal rate and hydrogen gasification rate were 90.6% and 194.6%, respectively, at the temperature of 650 degrees C and the residence time of 0.83 min. The product gas was mainly composed of H2, CO2, CH4 and CO, among which the total molar percentage of H2 and CH4 was higher than 50%. The gasification efficiency decreased with the pollutant concentration increasing. Both the catalyst and oxidant could accelerate the hydrocarbon gasification at a lower reaction temperature, in which the catalyst promoted H2 production and the oxidant enhanced CO2 generation. The intermediates of liquid effluents were analyzed and phenol was found to be the main composition. The results indicate that the supercritical gasification is a promising way for the treatment of hazardous organic wastewater.