Real-time PCR quantification of nitrite reductase (nirS) genes in a nitrogen removing fluidized bed reactor.

Molecular approaches were applied to identify and enumerate denitrifying bacteria subsisting in a fluidized bed reactor (FBR). The FBR was continuously operated as a unit for the removal of nitrogen from the effluents of domestic sewage treatment plant, with an additional supply of methanol as a carbon source. By denaturing gradient gel electrophoresis (DGGE) and sequence analysis of 16S ribosomal RNA genes, Thauera group was found to be dominant among the denitrifying bacteria in the FBR sludge. Oligonucleotide probe THA155 for fluorescence in situ hybridization (FISH) was newly designed for specifically targeting the Thauera group. However, the THA155 signal obtained from the sludge was only 0.9-5.7% of the DAPI-stained total cells. The real-time polymerase chain reaction (PCR) targeting the sequences of nitrite reductase (NIR) gene, a key enzyme of denitrification processes, was performed to quantify the cells of denitrifying bacteria cells including the Thauera group in FBR sludge. An excellent correlation was obtained between the numbers of nirS genes and the activity of denitrifiers in the FBR sludge.     

Photocatalytic removal of cyanide with illuminated TiO(2)

Effects of TiO(2) dosage, pH and initial cyanide concentration on the removal efficiency of cyanide from aqueous solutions with illuminated TiO(2) have been investigated. Adsorption and oxidation were recognized as significant processes for the elimination of cyanide. From the Langmuir isotherm, the maximum adsorption capacity was determined as 17.24 mg/g at pH 7. Adsorbed amount of cyanide slightly increased as the TiO(2) dosage increased. However, as no significant increase was observed above 1 g/L TiO(2), an optimum TiO(2) dosage was determined as 1 g/L. Photocatalytic oxidation efficiency of cyanide was greatly affected by the solution pH. It increased as the solution pH decreased. The photocatalytic oxidation efficiency after 120 min was 80.4% at pH 3 while it was only 20.4% at pH 11. Photocatalytic oxidation of cyanide was well described by the second-order kinetics. Photocatalytic reaction with illuminated TiO(2) can be effectively applied to treat industrial wastewater contaminated with cyanide.     

Formation mechanism of nitrifying granules observed in an aerobic upflow fluidized bed (AUFB) reactor.

The influences of trace metals in the wastewater and shear stress by aeration were particularly examined to clarify the formation mechanism of nitrifying granules in an aerobic upflow fluidized bed (AUFB) reactor. It was found that Fe added as a trace element to the inorganic wastewater accumulated at the central part of the nitrifying granules. Another result obtained was that suitable shear stress by moderate aeration (0.07-0.20 L/min/L-bed) promoted granulation. Furthermore, it was successfully demonstrated that pre-aggregation of seed sludge using hematite promoted core formation, leading to rapid production of nitrifying granules. From these results, a nitrifying granulation mechanism is proposed: 1) as a first step, nitrifying bacteria aggregate along with Fe precipitation, and then the cores of granules are formed; 2) as a second step, the aggregates grow to be spherical or elliptical in form due to multiplication of the nitrifying bacteria and moderate shear stress in the reactor, and then mature nitrifying granules are produced. Fluorescence in situ hybridization (FISH) analysis successfully visualized the change in the spatial distribution of nitrifying bacteria in the granules, which supports the proposed granulation mechanism.     

Enhanced biological wastewater treatment using sodium alginate-immobilized microorganisms in a fluidized bed reactor

In this study, a microbial consortium isolated from an activated sludge tank of a conventional wastewater treatment plant was immobilized using sodium alginate (SA) as a support material for contaminant biodegradation in wastewater. A volume of 500 mL of activated sludge was immobilized in the SA beads (with a mass concentration of 25 g/L). The resulting SA beads were characterized, introduced into a fluidized bed reactor, fed with 1000 mL of the sample, and characterized again after the treatment process. The SA-immobilized microorganisms were tested first for degradation of organic matter (expressed as chemical oxygen demand) and total phosphorous in domestic wastewater, achieving removal efficiencies of 71% and 93%, respectively, after 12 h. Subsequently, the SA-immobilized microorganisms were tested for degradation of a basic blue 9 (BB9) textile dye in a condition that simulated textile wastewater. The efficiency of the BB9 degradation was found to be as high as 99.5% after 2 h. According to these results, SA-immobilized microorganisms were found to be an environmentally friendly and cost-effective alternative for treatment of municipal and industrial wastewater effluents.     

Biological Cr(VI) reduction in indigenous sludge cultures from Gauteng, South africa.

The Cr(VI) reducing capability of an acclimated indigenous culture cultivated from primary sludge was evaluated in batch and packed-bed bioreactor systems. Performance evaluation was carried out in unmodified cultures, cultures modified by substituting terminal organisms in the consortium by a known Cr(VI)-reducing organism (Escherichia coli ATCC 33456), and pure cultures of Cr(VI)-reducing organisms. A high Cr(VI) reduction rate was observed in modified cultures and in the pure culture of the Cr(VI)-reducing bacteria (Bacillus sp.). Furthermore, the Bacillus sp. pure culture outperformed both the unmodified and modified consortium cultures in reducing Cr(VI). Abiotic Cr(VI) reduction activity was evaluated in heat-killed and azide (N3) inactivated control cultures. No significant Cr(VI) reduction was observed in the controls. This study is part of the continuing research to identify synergistic culture systems for treating toxic compounds from polluted environments.     

Simultaneous removal of carbon and nitrogen in an anaerobic inverse fluidized bed reactor.

The evaluation of simultaneous removal of carbon and nitrogen in an anaerobic inverse fluidized bed reactor is described. Continuous and batch experiments were used, with synthetic wastewater and glucose as the carbon source with two different nitrate concentrations of 100 and 250 mg N-NO3/L. The evolution of substrates and the concentrations of intermediary products in the gas phase were followed. Results indicate that the use of the biofilm in the inverse fluidized bed reactor allows the expression of denitrification and methanization activities simultaneously without physical or time separation. The removal of nitrogen with both the feeding of 100 and 250 mgN-NO3/L was higher than 90%, while the removal of carbon was 65% on average for the feeding with 100 mgN-NO3/L and 70% on average for the feeding with 250 mg N-NO3/L. This carbon degradation is equivalent to that obtained during the operation of the reactor in the period previous to the nitrate feeding. It was found that by using high values of the COD/N ratio, the dissimilative reduction of nitrates is favoured. Denitrification and anaerobic digestion occurs simultaneously under low values of COD/N.     

Removal of Cr(VI) by magnetite nanoparticle.

Magnetite nanoparticles were synthesized by sol-gel method. The highly crystalline nature of the magnetite structure with diameter of around 10 nm was characterized with transmission electron microscopy and X-ray diffractometry. The surface area was determined to be 198 m2/g. Batch experiments were carried out to determine the adsorption kinetics and mechanism of Cr(VI) by these magnetite nanoparticles. The Cr(VI) uptake was mainly governed by physico-chemical adsorption. The adsorption process was found to be pH and temperature dependent. The adsorption data fit well with the Freundlich isotherm equation. The Freundlich constants were calculated at different temperatures. The adsorption capacity increased with rising temperature. Preliminary results indicate that magnetite nanoparticles may be used as an adsorbent for removal of Cr(VI) from wastewater.     

Mechanistic evidence and efficiency of the Cr(VI) reduction in water by different sources of zerovalent irons.

The objective of this research was to assess the mechanism and effectiveness of the zerovalent iron (ZVI) to remediate the Cr(VI) contaminated water. The mechanism of Cr(VI) reduction by ZVI was evaluated by characterising surface properties and chemical compositions of Fe and Cr products using SEM-EDS, XRD and XPS analyses. The effectiveness of ZVI in Cr(VI) reduction was assessed by the luminescent bacteria (Photobacterium Phosphoreum). The Cr(VI) was reduced to Cr(III), when the reactive Fe(o) was oxidised to Fe(II, III), showing the presence of Fe2O3, (Fe-Cr)2O3 and FeOOH. The SEM-EDS analysis showed that ZVI with a higher reducing capacity was more subject to changes of surface and morphological properties due to ionisation of ZVI. The Cr and Fe in precipitates subsisted exclusively in the Cr(III) or Fe(III) states with the respective forms of Cr(OH)3 or Cr2O3 and FeOOH or Fe2O3. Electrons produced from ZVI oxidation reduced Cr(VI) to Cr(III), thus resultantly Cr(III) precipitated or co-precipitated with Fe(III) to form Fe(III)-Cr(III) hydroxide or Fe(III)-Cr(III) oxyhydroxide. Toxicity of water reacted with ZVI was significantly lower than that of the untreated water.     

Phosphorus recovery from anaerobic digester supernatant by struvite crystallization: model-based evaluation of a fluidized bed reactor

This paper is an attempt to model the UBC (University of British Columbia) MAP (Magnesium Ammonium Phosphate) fluidized bed crystallizer. A mathematical model is developed based on the assumption of perfect size classification of struvitre crystals in the reactor and considering the movement of liquid phase as a plug flow pattern. The model predicts variation of species concentration of struvite along the crystal bed height. The species concentrations at two extreme ends (inlet and outlet) are then used to evaluate the reactor performance. The model predictions provide a reasonable good fit with the experimental results for both PO4-P and NH4-N removals. Another important aspect of this model is its capability of predicting the crystals size and the bed voidage at different height of the reactor. Those predictions also match fairly well with the experimental observations. Therefore, this model can be used as a tool for performance evaluation of the reactor and can also be extended to optimize the struvite crystallization process in the UBC MAP reactor.     

Biofilm development during the start-up of a sulfate-reducing down-flow fluidized bed reactor at different COD/SO4(2-) ratios and HRT

In sulfate-reducing reactors, it has been reported that the sulfate removal efficiency increases when the COD/SO4(2-) ratio is increased. The start-up of a down-flow fluidized bed reactor constitutes an important step to establish a microbial community in the biofilm able to survive under the operational bioreactor conditions in order to achieve effective removal of both sulfate and organic matter. In this work the influence of COD/SO4(2-) ratio and HRT in the development of a biofilm during reactor start-up (35 days) was studied. The reactor was inoculated with 1.6 g VSS/L of granular sludge, ground low density polyethylene was used as support material; the feed consisted of mineral medium at pH 5.5 containing 1 g COD/L (acetate:lactate, 70:30) and sodium sulfate. Four experiments were conducted at HRT of 1 or 2 days and COD/SO4(2-) ratio of 0.67 or 2.5. The results obtained indicated that a COD/SO4(2-) ratio of 2.5 and HRT 2 days allowed high sulfate and COD removal (66.1 and 69.8%, respectively), whereas maximum amount of attached biomass (1.9 g SVI/L support) and highest sulfate reducing biofilm activity (10.1 g COD-H2S/g VSS-d) was achieved at HRT of 1 day and at COD/sulfate ratios of 0.67 and 2.5, respectively, which suggests that suspended biomass also played a key role in the performance of the reactors.     

High nitrification rate at low pH in a fluidized bed reactor with chalk as the biofilm carrier.

A typical steady state bulk pH of about 5 was established in a nitrifying fluidized bed with chalk as the only buffer agent. In spite of the low pH, high rate nitrification was observed with the nitrification kinetic parameters in the chalk reactor similar to those of biological reactors operating at pH>7. Various methods were used to determine the reasons for high rate nitrification at such low pH including (i) determination of bacterial species, (ii) microsensor measurements in the biofilm, and (iii) comparison of nitrification performance at low pH with a non-chalk fluidized bed reactor. Fluorescence in situ hybridization (FISH) using existing 16S rRNA-targeted oligonucleotide probes showed common nitrifying bacteria in the low pH chalk reactor. The prevalent nitrifying bacteria were identified in the Nitrosomonas oligotropha, Nitrosomonas europeae/eutropha, Nitrosospira and Nitrospira related groups, all well known nitrifiers. Microelectrode measurements showed that the pH in the biofilm was low and similar to that of the bulk pH. Finally, reactor performance using a non-chalk biofilm carrier (sintered glass) with the same bacterial inoculum also showed high rate nitrification below pH 5. The results suggest that inhibition of nitrification at low pH is highly overestimated.     

Adsorption of Cr(VI) in wastewater using magnetic multi-wall carbon nanotubes

Magnetic multi-wall carbon nanotubes were prepared with wet chemical treatments and characterized by a transmission electron microscope (TEM) and X-ray diffraction (XRD). They were used as adsorbents for the removal of Cr(VI) in aqueous solutions. The effects of adsorbent dosage, the concentration of Cr(VI) in aqueous solution, temperature, and pH value on the removal efficiency were studied. Results showed that the adsorption capacity of the magnetic multi-wall carbon nanotubes increased with the initial Cr(VI) concentration, but decreased with the increase of adsorbent dosage. The adsorption amount increased with contact time. The adsorption kinetics were best represented by the pseudo second-order kinetic model, and the adsorption isotherms indicated that the Langmuir model better reflected the adsorption process. The obtained calculation results for the Gibbs free energy revealed that the adsorption was a spontaneous and endothermic process. The enthalpy deviation was 3.835 kJ·mol⁻¹. The magnetic multi-wall carbon nanotubes showed significant potential for application in adsorption of heavy metal ions.     

Experimental and modeling investigations of a hybrid upflow anaerobic sludge-filter bed (UASFB) reactor

A 9.8-L hybrid UASFB reactor, in which the lower half was occupied by a sludge blanket and the upper half by small floating polyethylene media, was evaluated using wine distillery vinasse as substrate. The reactor was operated for a total period of 232 days at 33 + 1 degrees C. Continuous feeding of the reactor was started with an initial OLR of 2.9 g COD/L.d and then it was increased step wise to 19.5 g COD/L.d by increasing the feed COD, while maintaining a constant HRT (1.05 d). The reactor was equipped with a continuous internal recirculation system from top to the bottom at the rate of 9 L/h (upflow velocity = 0.83 m/h) upto day 159 and then it was reduced to about half on day 160 onwards. It was observed that the reduced recirculation rate did not affect the performance of the reactor with an average COD(t) and COD(s) removal efficiencies of 82 and 88%, respectively. A maximum gas production rate of 6.7 L CH(4)/L(reactor).d was achieved for the highest OLR applied. The specific activity analysis depicts that the activity of the attached biomass was more than 2 times higher than that of the granular sludge. The efficiency of liquid mixing was good through out this study. The packing medium had a dual role in the retention of the biomass inside the reactor: i.e. entrapment of biomass within the support and filtration of the granular biomass, preventing it from going out of the reactor. ADM1_10 model simulated well the dynamic evolutions of the main variables in the liquid as well as in the gas phases.     

绿茶还原制备纳米铁对模拟地下水中Cr(Ⅵ)的去除效果

利用绿茶提取液还原制备的纳米铁(GT-NIP)对水中六价铬具有良好的去除效果的原理,通过向含水层中注入GT-NIP可望实现六价铬在地下水中的原位去除,但尚未得到验证。为此,首先利用绿茶提取液还原法制备纳米铁,然后考察了其对水中六价铬的还原效果,再利用柱试验研究GT-NIP对模拟地下水中六价铬的去除效果。结果表明:利用绿茶提取液制备的纳米铁为圆球形,大小均匀,直径约为10～20nm,且分散性较好,其中Fe2+含量为55.6%,Fe3+含量为44.4%。GT-NIP悬浮液在水中对Cr(Ⅵ)具有良好的降解能力,当GT-NIP浓度为1.0g/L时,反应1h,初始浓度为100mg/L的Cr(Ⅵ)去除率达到96.8%;在柱试验中,GT-NIP可以顺利穿透砂柱,平均出流百分比为68.6%。浓度为100mg/L的Cr(Ⅵ)溶液流过该纳米铁砂柱后,流出液中Cr3+浓度约为0.20mg/L,Cr6+浓度为0.10～0.25mg/L,即六价铬去除率达到99%以上。     

壳聚糖基印迹水凝微球对Cr (VI)的选择性吸附研究

目前水环境污染物成分复杂,常用的化学沉淀法已很难将重金属污染物分类去除并资源化利用,由此产生了大范围的危废污染环境,需要进行二次处理。利用离子印迹技术对壳聚糖基水凝微球进行改性,制备具有对Cr (VI)特异识别性能的吸附材料(CTS-IGB）,对其在单一Cr (VI)溶液和模拟电镀废水中的吸附行为特征进行研究。研究结果表明:在20 ℃、pH值为3时,CTS-IGB在单一Cr (VI)溶液和模拟电镀废水中Cr (VI)的吸附量在180 min内分别达到37.4 和44.3 mg/g,半饱和吸附时间仅分别为5.8和23.5 min;吸附行为符合准二级动力学。吸附等温线拟合表明吸附过程符合Freundlich模型;热力学参数表明吸附过程是放热反应,且吸附后无序度减小;相比于未改性壳聚糖水凝微球,CTS-IGB在共存离子（模拟电镀废液及其他双组份溶液）工况下对Cr (VI)的选择性提高32%~74%。该材料可作为潜在的吸附材料用于污染水环境中Cr (VI)的分离及回收。     

Volatile organic compound adsorption in a gas-solid fluidized bed.

Fluidization finds many process applications in the areas of catalytic reactions, drying, coating, combustion, gasification and microbial culturing. This work aims to compare the dynamic adsorption characteristics and adsorption rates in a bubbling fluidized bed and a fixed bed at the same gas flow-rate, gas residence time and bed height. Adsorption with 520 ppm methanol and 489 ppm isobutane by the ZSM-5 zeolite of different particle size in the two beds enabled the differentiation of the adsorption characteristics and rates due to bed type, intraparticle mass transfer and adsorbate-adsorbent interaction. Adsorption of isobutane by the more commonly used activated carbon provided the comparison of adsorption between the two adsorbent types. With the same gas residence time of 0.79 seconds in both the bubbling bed and fixed bed of the same bed size of 40 mm diameter and 48 mm height, the experimental results showed a higher rate of adsorption in the bubbling bed as compared to the fixed bed. Intraparticle mass transfer and adsorbent-adsorbate interaction played significant roles in affecting the rate of adsorption, with intraparticle mass transfer being more dominant. The bubbling bed was observed to have a steeper decline in adsorption rate with respect to increasing outlet concentration compared to the fixed bed. The adsorption capacities of zeolite for the adsorbates studied were comparatively similar in both beds; fluidizing, and using smaller particles in the bubbling bed did not increase the adsorption capacity of the ZSM-5 zeolite. The adsorption capacity of activated carbon for isobutane was much higher than the ZSM-5 zeolite for isobutane, although at a lower adsorption rate. Fourier transform infra-red (FTIR) spectroscopy was used as an analytical tool for the quantification of gas concentration. Calibration was done using a series of standards prepared by in situ dilution with nitrogen gas, based on the ideal gas law and relating partial pressure to gas concentration. Concentrations up to 220 ppm for methanol and 75 ppm for isobutane were prepared using this method.     

Biosorption and bioreduction of Cr(VI) by locally isolated Cr-resistant bacteria.

Cr(VI) biosorption and bioreduction ability of locally isolated Cr-resistant bacteria was investigated using the shake-flask technique. A mixture of S. epidermidis and B. cereus showed the highest minimum inhibitory concentration (MIC) level at 750 mg/L Cr(VI) followed by S. aureus and Bacillus sp. of 250 mg/L, and A. haemolyticus of 70 mg/L. From the Langmuir adsorption isotherm, the treatment of cells with heat-acid resulted in the highest amount of Cr(VI) adsorped (78.25 mg/g dry wt. for S. epidermidis) compared to heat-acetone (67.93 mg/g dry wt. Bacillus sp.), heat only (36.05 mg/g dry wt. S. epidermidis) or untreated cells (45.40 mg/g dry wt. S. epidermidis and B. cereus). FTIR analysis showed the involvement of amine groups in Cr(VI) adsorption. In the bioreduction study, A. haemolyticus was able to completely reduce Cr(VI) up to 50 mg/L.     

循环流化床锅炉燃烧的优化调整

燃烧优化调整对循环流化床锅炉运行具有重要的指导意义。结合河南联孚电厂实际运行情况,经过长期的试验,对影响锅炉燃烧的各个运行参数进行了优化,得到了合适的运行参数,对燃烧调整优化方案的实施有借鉴意义。     

Catalytic wet peroxidation of phenol in a fixed bed reactor.

Iron-containing mesostructured materials (Fe-SBA-15) are suitable for continuous treatment of phenolic aqueous solutions by means of catalytic wet peroxide oxidation (CWPO) in a packed-bed reactor. These materials were successfully extruded, crushed and sieved with a particle size ranging from 1 to 1.6 mm using mineral clay and methyl cellulose as binders. Non-significant changes have been found in the textural and structural properties of the extruded material in comparison to the parent powder Fe-SBA-15 material. Activity of extruded catalyst in terms of phenol degradation and TOC reduction has been monitored in a continuous mode. The increase of residence time enhances significantly the TOC degradation. The catalyst stability, taking into account the loss of iron species from the catalyst into the aqueous solution, has also been examined. The catalytic results of Fe-SBA-15 material in comparison to a homogeneous catalytic test prove the relevant role of the solid catalyst in the oxidation process.     

Radial distribution modeling of liquid-phase phenol concentration in a liquid-solid fluidized bed photoreactor

A fluidized bed photoreactor with titanium dioxide-immobilized spherical activated carbon particles was examined. The light intensity profile was modeled using the Lambert-Beer rule for the modeling of the radial distribution of liquid-phase phenol concentration in the fluidized bed photoreactor, when considering the reactor composed of numerous differential annular drums and no mass transfer between drums. The model could be well matched with the experimental data which indicated the liquid flow rate of 13.8 L/min was the optimum in the balance of flow rate-related light penetration and photocatalyst concentration. By integration of liquid-phase phenol concentration along the radius, photocatalytic oxidation performance of the photoreactor was evaluated in comparison with the experimental data and model prediction. The results showed that the errors were less than 30% for most of the predictions. It is suggested that mass transfer and flow rate difference along the radial direction should be considered to obtain more precise prediction.