Treatment of dairy wastewater using anaerobic and solar photocatalytic methods

The present study was aimed to treat the dairy wastewater by using anaerobic and solar photocatalytic oxidation methods. The anaerobic treatment was carried out in a laboratory scale hybrid upflow anaerobic sludge blanket reactor (HUASB) with a working volume of 5.9 L. It was operated at organic loading rate (OLR) varying from 8 to 20 kg COD/m³ day for a period of 110 days. The maximum loading rate of the anaerobic reactor was found to be 19.2 kg COD/m³ day and the corresponding chemical oxygen demand (COD) removal at this OLR was 84%. The anaerobically treated wastewater at an OLR of 19.2 kg COD/m³ day was subjected to secondary solar photocatalytic oxidation treatment. The optimum pH and catalyst loading for the solar photochemical oxidation was found to be 5 and 300 mg/L, respectively. The secondary solar photocatalytic oxidation using TiO₂ removed 62% of the COD from primary anaerobic treatment. Integration of anaerobic and solar photocatalytic treatment resulted in 95% removal of COD from the dairy wastewater. The findings suggest that anaerobic treatment followed by solar photo catalytic oxidation would be a promising alternative for the treatment of dairy wastewater.     

Preferential CO oxidation on Ru/Al2O3 catalyst: An investigation by considering the simultaneously involved methanation

The CO removal with preferential CO oxidation (PROX) over an industrial 0.5% Ru/Al₂O₃ catalyst from simulated reformates was examined and evaluated through considering its simultaneously involved oxidation and methanation reactions. It was found that the CO removal was fully due to the preferential oxidation of CO until 383 K. Over this temperature, the simultaneous CO methanation was started to make a contribution, which compensated for the decrease in the removal due to the decreased selectivity of PROX at higher temperatures. This consequently kept the effluent CO content as well as the overall selectivity estimated as the ratio of the removed CO amount over the sum of the consumed O₂ and formed CH₄ amounts from apparently increasing with raising reaction temperature from 383 to 443 K when the CO₂ methanation was yet not fully started. At these temperatures the tested catalyst enabled the initial CO content of up to 1.0 vol.% to be removed to several tens of ppm at an overall selectivity of about 0.4 from simulated reformates containing 70 vol.% H₂, 30 vol.% CO₂ and with steam of up to 0.45 (volume) of dry gas. Varying space velocity in less than 9000 h⁻¹ did not much change the stated overall selectivity. From the viewpoint of CO removal the article thus concluded that the methanation activity of the tested Ru/Al₂O₃ greatly extended its working temperatures for PROX, demonstrating actually a feasible way to formulate PROX catalysts that enable broad windows of suitable working temperatures.     

Elimination of pesticides and their formulation products from drinking water using thin film continuous photoreactor under solar radiation

There is an urgent need for the development of inexpensive, but reliable and efficient photocatalyst which can work under solar radiation for drinking water application. Hence the treatment options to be tried out for drinking water contaminated with pesticides and their formulation products should be cost effective and affordable. In this study, we developed a cheap and efficient photocatalyst and continuous photoreactor for the removal of pesticides from drinking water under solar radiation. Continuous photodegradation experiments were carried out with synthetically prepared commercial grade methyl parathion (Folidon 50% E.C.), dichlorvos (DDVP 70% E.C.), and analytical grade lindane. Photodegradation of mixed pesticide was carried out using both Degussa P-25 TiO₂ and N-doped TiO₂ with identical mass concentrations (50 μg/L) of all the three pesticides under UV, visible and solar radiation. Continuous reactor was operated for more than 24 h (6 h each on 4 days) for mixed pesticide degradation. N-doped TiO₂ showed 100% degradation for all the three pesticide under solar radiation. Photodegradation of mixed pesticide showed methyl parathion, dichlorvos and lindane were degrading simultaneously. However, the rate of reaction was completely different from single pesticide degradation. N-doped TiO₂ showed higher photocatalytic activity under solar radiation compared to UV and visible light. GC–MS analysis of mixed pesticide degradation showed more than 16 peaks in the middle of the reaction. Among these peaks, three intermediates such as hexachloro-benzene and para-nitrophenol and dichlorovinyl-O-methyl phosphate were identified in the middle of the reaction. However, at the end of the reaction (reactor outlet) none of the intermediates were observed.     

High-temperature sulfuric acid decomposition over complex metal oxide catalysts

Activity and stability of FeTiO₃, MnTiO₃, NiFe₂O₄, CuFe₂O₄, NiCr₂O₄, 2CuO·Cr₂O₃, CuO and Fe₂O₃ for the atmospheric decomposition of concentrated sulfuric acid in sulfur-based thermochemical water splitting cycles are presented. Catalyst activity was determined at temperatures from 725 to 900 °C. Catalytic stability was examined at 850 °C for up to 1 week of continuous operation. The results were compared to a 1.0 wt% Pt/TiO₂ catalyst. Surface area by nitrogen physisorption, X-ray diffraction analyses, and temperature programmed desorption and oxidation were used to characterize fresh and spent catalyst samples.Over the temperature range, the catalyst activity of the complex oxides followed the general trend: 2CuO·Cr₂O₃ > CuFe₂O₄ > NiCr₂O₄ ≈ NiFe₂O₄ > MnTiO₃ ≈ FeTiO₃. At temperatures less than 800 °C, the 1.0 wt% Pt/TiO₂ catalyst had higher activity than the complex oxides, but at temperatures above 850 °C, the 2CuO·Cr₂O₃ and CuFe₂O₄ samples had the highest activity.Surface area was found to decrease for all of the metal oxides after exposure to reaction conditions. In addition, the two complex metal oxides that contained chromium were not stable in the reaction environment; both leached chromium into the acid stream and decomposed into their individual oxides. The FeTiO₃ sample also produced a discoloration of the reactor due to minor leaching and converted to Fe₂TiO₅. Fe₂O₃, MnTiO₃ and NiFe₂O₄ were relatively stable in the reaction environment. In addition, CuFe₂O₄ catalyst appeared relatively promising due to its high activity and lack of any leaching issues; however it deactivated in week-long stability experiments.Complex metal oxides may provide an attractive alternative to platinum-based catalyst for the decomposition of sulfuric acid; however, the materials examined in this study all displayed shortcomings including material sintering, phase changes, low activity at moderated temperatures due to sulfate formation, and decomposition to their individual oxides. More effort is needed in this area to discover metal oxide materials that are less expensive, more active and more stable than platinum catalysts.     

The effect of ZnO-coating on the performance of a dye-sensitized solar cell

This study investigates the effect of a ZnO-coated TiO₂ working electrode on the power conversion efficiency of a dye-sensitized solar cell (DSSC). This electrode was designed and fabricated by dipping the TiO₂ electrode with the TiCl₄ treatment in a solution of zinc acetate dehydrate [Zn(CH₃COO)₂·2H₂O] and ethanol. The effects of the concentration of Zn(CH₃COO)₂·2H₂O and the duration of dipping on the band gap of a working electrode and the power conversion efficiency of a DSSC were also examined. The band gap of the working electrode increases to 3.75 eV [TiO₂ electrode dipped in 0.05 M Zn(CH₃COO)₂·2H₂O) for 3 min] from 3.22 eV (TiO₂ electrode). Interestingly, the power conversion efficiency of the DSSC with a Zn-coated TiO₂ electrode (6.7%) substantially exceeds that of the conventional DSSC with a TiO₂ electrode (5.9%), and it may be originated from an increased energy barrier between ZnO and TiO₂ that reduces the electron recombination rate.     

Research on photocatalytic H2 production from acetic acid solution by Pt/TiO2 nanoparticles under UV irradiation

The Pt/TiO₂ particles have been prepared by the photodeposition of Pt on TiO₂ surface and characterized by X-ray diffraction. Photocatalytic H₂ production from acetic acid (HAc) over Pt/TiO₂ in aqueous solution has been studied at ambient temperature under UV irradiation. The effects of operational variables such as Pt loading, photocatalyst concentration, HAc concentration, and solution pH, have been systematically investigated. The optimum conditions for H₂ production from HAc by Pt/TiO₂ were Pt loading 1.0 wt.%, Pt/TiO₂ concentration 0.22 g/L, HAc concentration 6.52 g/L and pH 1.0. The H₂ yield is 0.27 mol-H₂/mol-HAc obtained under prolonged time irradiation. Experimental results showed that the photocatalytic H₂ production activity could be enhanced remarkably by depositing a suitable amount Pt on TiO₂ surface. Based on our results, a new process for H₂ production from biomass can be achieved by coupling fermentative H₂ production with photocatalytic H₂ production. The process also provides a method for degradation of organic pollutants with simultaneous H₂ production. A possible mechanism for photocatalytic decomposition of HAc over Pt/TiO₂ was also proposed.     

Inactivation of Enterococcus sp. by photolysis and TiO2 photocatalysis with H2O2 in natural water

This paper presents research carried out into the disinfectant power of a series of treatments based on the individual application and possible combinations of TiO₂ (1 g/L), H₂O₂ (0.04 mM) and irradiation (290–800 nm and 320–800 nm) on Enterococcus sp., a faecal bacterial indicator used in water analysis. The main aims are the determination of the influence of the UVB range on the inactivation of Enterococcus sp. in natural water, the mode of application of irradiation (intermittent or continuous) and the capacity of bacterial recovery after the application of the treatments in darkness conditions. The results show that when the irradiation includes the UVB range, a very high degree of inactivation is obtained in an Enterococcus sp. solution in natural water (N₀ = 10⁸ CFU 100 mL^?1) by irradiation alone. Neither the addition of TiO₂ nor of H₂O₂ are very relevant in these conditions. However, if the irradiation does not include the UVB range, the bactericidal action of photolysis is practically nonexistent, highlighting the positive effect of TiO₂ and H₂O₂ on the irradiation, the photocatalysis and photocatalysis/H₂O₂ treatments obtaining a higher degree of disinfection. Continuous and intermittent illumination give rise to similar inactivation levels in all the treatments studied, except for photolysis in which a significant increase in inactivation is observed when the irradiation is continuous. During 3 h of darkness following application of the treatments, there is no change or else a slight recovery of the bacterial population.     

Solar photocatalysis—a possible step in drinking water treatment

Possibility of the use of solar radiation for reduction of Natural Organic Matter (NOM) content in natural lake water, as a source for drinking water preparation, was the topic of this research. Solar radiation alone does not have enough energy for sufficient degradation of NOM, but in combination with heterogeneous photocatalyst-titanium dioxide (TiO₂), with or without other chemicals, the degradation potential could increase. In specific geographical conditions in Republic of Croatia, e.g. Adriatic islands or Dalmatia, solar radiation could be used for photocatalytic degradation of natural organic matter (NOM) in surface waters and therewith lighten the process of preparing them to the potable water. Specific quality of the geographical locality appears in fact that it is a very attractive tourist destination, especially in period June–September. In this period the drinking water demand is the biggest and, fortunately, the intensity of the solar radiation, too. So, there is a proportion between the drinking water demand and solar radiation available for the use in drinking water treatment.A number of tests with lake water exposed to solar radiation in non-concentrating reactors were performed and photodegradation of NOM for various combinations of doses and crystal forms of TiO₂ with H₂O₂ was studied. Irradiation intensity was estimated from global solar radiation measurements. The best performance for the NOM degradation had combination of 1 g/L TiO₂ both anatase and rutile+solar radiation+H₂O₂, but—economically—it was not the best combination. An estimation of the biodegradation potential of dissolved organic matter after the photocatalytic step is given, too.     

Decolouration of textile dyes in wastewaters by photocatalysis with TiO2

The photocatalytic removal of colour of a synthetic textile effluent, using TiO₂ suspensions under solar radiation, has been studied at pilot plant scale. A synthetic dye solution was prepared by a mix of six commercial textile dyes. A photochemical reactor of parallel CPC reflectors with UV-transparent tubular receivers was used. The study of photodegradation was carried out using the Taguchi’s parameter design method. Following this methodology, the reaction was conducted under different flow conditions, pH and H₂O₂ concentrations. The results show that all dyes used in the experiences can be degraded successfully by photo-oxidation. The process shows a significant enhancement when it is carried out at high flows, alkaline media and high H₂O₂ concentration. Colour removal from the effluent was reached at 55 min operating time.     

Hydrogen production from steam and autothermal reforming of LPG over high surface area ceria

Steam and autothermal reforming reactions of LPG (propane/butane) over high surface area CeO₂ (CeO₂ (HSA)) synthesized by a surfactant-assisted approach were studied under solid oxide fuel cell (SOFC) operating conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to the conventional Ni/Al₂O₃. These benefits of CeO₂ are due to the redox property of this material. During the reforming process, the gas–solid reactions between the hydrocarbons present in the system (i.e. C₄H₁₀, C₃H₈, C₂H₆, C₂H₄, and CH₄) and the lattice oxygen (O_O^x) take place on the ceria surface. The reactions of these adsorbed surface hydrocarbons with the lattice oxygen (C_nH_m + O_O^x → nCO + m/2(H₂) + V_O + 2e′) can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reactions (C_nH_m ⇔ nC + 2mH₂). Afterwards, the lattice oxygen (O_O^x) can be regenerated by reaction with the steam present in the system (H₂O + V_O + 2e′ ⇔ O_O^x + H₂). It should be noted that V_O denotes as an oxygen vacancy with an effective charge 2⁺.At 900 °C, the main products from steam reforming over CeO₂ (HSA) were H₂, CO, CO₂, and CH₄ with a small amount of C₂H₄. The addition of oxygen in autothermal reforming was found to reduce the degree of carbon deposition and improve product selectivities by completely eliminating C₂H₄ formation. The major consideration in the autothermal reforming operation is the O₂/LPG (O/C molar ratio) ratio, as the presence of a too high oxygen concentration could oxidize the hydrogen and carbon monoxide produced from the steam reforming. A suitable O/C molar ratio for autothermal reforming of CeO₂ (HSA) was 0.6.     

Transient phenomenon of step switching for current or voltage in PEMFC

The transient phenomenon of fuel cell with 5 cm² active area is investigated in this study by current density step increase and switching voltage under different conditions. It is found that there is an undershoot when the current density step increase is at the loading of 60% RH anode cathode, 3 stoic., 70 °C, 15 psi for automobile applications. The voltage is almost zero under 0.2 step increase to 1.0 A/cm² due to the H⁺ transport in membrane or H₂/O₂ in catalyst layer is almost used up. The undershoot phenomenon is more serious under gases stoichiometries of 3.0/3.0 when H₂ is fully humidified due to low gas concentration or flooding on the electrode. This phenomenon would induce the degradation of fuel cell components.     

Syngas production by gasification of aquatic biomass with CO2/O2 and simultaneous removal of H2S and COS using char obtained in the gasification

Applicability of gulfweed as feedstock for a biomass-to-liquid (BTL) process was studied for both production of gas with high syngas (CO + H₂) content via gasification of gulfweed and removal of gaseous impurities using char obtained in the gasification. Gulfweed as aqueous biomass was gasified with He/CO₂/O₂ using a downdraft fixed-bed gasifier at ambient pressure and 900 °C at equivalence ratios (ER) of 0.1–0.3. The syngas content increased while the conversion to gas on a carbon basis decreased with decreasing ER. At an ER of 0.1 and He/CO₂/O₂ = 0/85/15%, the syngas content was maximized at 67.6% and conversion to gas on a carbon basis was 94.2%. The behavior of the desulfurization using char obtained during the gasification process at ER = 0.1 and He/CO₂/O₂ = 0/85/15% was investigated using a downdraft fixed-bed reactor at 250–550 °C under 3 atmospheres (H₂S/N₂, COS/N₂, and a mixture of gases composed of CO, CO₂, H₂, N₂, CH₄, H₂S, COS, and steam). The char had a higher COS removal capacity at 350 °C than commercial activated carbon because (Ca,Mg)S crystals were formed during desulfurization. The char simultaneously removed H₂S and COS from the mixture of gases at 450 °C more efficiently than did activated carbon. These results support this novel BTL process consisting of gasification of gulfweed with CO₂/O₂ and dry gas cleaning using self-supplied bed material.     

Evaluation of solar photo-Fenton parameters on the pre-oxidation of leachates from a sanitary landfill

The main purpose of this work is to study the treatment of a leachate after preliminary aerated lagooning by a solar photo-Fenton process, using a photocatalytic reactor with compound parabolic collectors (CPCs). The influence of different process parameters in the reaction rate was evaluated, such as, the type of acid used in the acidification step (H₂SO₄, HCl, H₂SO₄ + HCl); type of iron salt (FeSO₄, FeCl₃) and respective iron concentration (60, 80, 100 and 140 mg Fe²⁺/L); temperature; and ratio of illuminated to total volume (25 L/35 L; 25 L/72 L). DOC abatement in the acidification procedure is independent of the type of acid used and temperature, and is related principally with the precipitation of humic acids. The use of HCl alone or in combination with H₂SO₄ leads to a substantially increase of the chloride ions, leading to the formation of less reactive chloride radicals when compared with sulfate radicals, decreasing the photo-Fenton reaction rate. The use of ferrous ions instead of ferric ions influenced positively the photo-Fenton reaction. Meteorological conditions favoring higher temperature of the leachate enhance the photo-Fenton reaction. Alternating dark and illumination intervals has shown a negligible effect on the illumination time needed to achieve the same mineralization, indicating that the Fenton process that takes place in dark zones is not efficient, even in the degradation of intermediate compounds resulting from the light-enhanced reaction. According to biodegradability tests, the optimum energy dose, necessary to obtain a biodegradable effluent, is 57.4 kJ_UV/L, consuming 120 mM of H₂O₂ and leading to a final DOC of 284 mg/L which corresponds to approximately 66% of mineralization.     

Formation and consumption of NO in H2 + O2 + N2 flames doped with NO or NH3 at atmospheric pressure

Flat premixed burner-stabilized H₂ + O₂ + N₂ flames, neat or doped with 300–1000 ppm of NO or NH₃, were studied experimentally using molecular-beam mass-spectrometry and simulated numerically. Spatial profiles of temperature and concentrations of stable species, H₂, O₂, H₂O, NO, NH₃, and of H and OH radicals obtained at atmospheric pressure in lean (? = 0.47), near-stoichiometric (? = 1.1) and rich (? = 2.0) flames are reported. Good agreement between measured and calculated structure of lean and near-stoichiometric flames was found. Significant discrepancy between simulated and measured profiles of NO concentration was observed in the rich flames. Sensitivity and reaction path analyses revealed reactions responsible for the discrepancy. Modification to the model was proposed to improve an overall agreement with the experiment.     

Solid oxide fuel cells operated by internal partial oxidation reforming of iso-octane

Two types of solid oxide fuel cells (SOFCs), with thin Ce_0.85Sm_0.15O_1.925 (SDC) or 8 mol% Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes, were fabricated and tested with iso-octane/air fuel mixtures. An additional Ru–CeO₂ catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density without anode coking. Thermodynamic analysis and catalysis experiments showed that H₂ and CO were primary reaction products at ≈750 °C, but that these decreased and H₂O and CO₂ increased as the operating temperature dropped below ≈600 °C. Power densities for YSZ cells were 0.7 W cm⁻² at 0.7 V and 790 °C, and for SDC cells were 0.6 W cm⁻² at 0.6 V and 590 °C. Limiting current behavior was observed due to the relatively low (≈20%) H₂ content in the reformed fuel.     

100 t/a-Scale demonstration of direct dimethyl ether synthesis from corncob-derived syngas

Direct conversion of biomass-derived syngas (bio-syngas) to dimethyl ether (DME) at pilot-scale (100 t/a) was carried out via pyrolysis/gasification of corncob. The yield rate of raw bio-syngas was 40–45 Nm³/h with less than 20 mg/Nm³ of tar content when the feedrate of dried corncob was 45–50 kg/h. After absorption of O₂, S, Cl by a series of absorbers and partial removal of CO₂ by the pressure-swing adsorption (PSA) unit sequentially, the obtained bio-syngas (H₂/CO≈1) was directly synthesized to DME over Cu/Zn/Al/HZSM-5 catalyst in the fixed-bed tubular reactor. CO conversion and DME space-time yield (STY) were 67.7% and 281.2 kg/m_cat³/h respectively at 260 °C, 4.3 MPa and 3000 h^?1(GHSV, syngas hourly space velocity). Synthesis performance would be increased if the tail gas (H₂/CO > 2) was recycled to the reactor when GHSV was 650–3000 h^?1.     

Decolourization of reactive dyes by thin film immobilized surface photoreactor using solar irradiation

The photocatalytic degradation of four reactive dyes using TiO₂ was investigated in suspended and immobilized systems under solar irradiation. Batch degradation experiments were carried out at initial concentrations ranging from 25 to 100 mg l⁻¹ and at a catalyst loading of 0.5–1 g l⁻¹. The studies on batch photocatalytic degradation of four dyes, showed about 30–70% colour removal depending on the initial dye concentration, dye structure (functional group and reactivity of dyes) and the amount of catalyst. The thin film immobilized surface photoreactor was able to give nearly 90–98% colour removal depending on the initial concentration and exposure time. Flow rate has noticeable effect on colour removal particularly at higher concentration (100 mg l⁻¹). High colour removals obtained with solar radiation indicated effectiveness of this process and its potential for practical application.     

RuxCrySez electrocatalyst loading and stability effects on the electrochemical performance in a PEMFC

The present paper presents a study of the Ru_xCr_ySe_z chalcogenide electrocatalyst based on physical–chemical characterization through scanning electron (SEM), atomic force (AFM) microscopy and energy dispersion elemental analysis (EDS), thermal stability using differential scanning calorimeter (DSC), electrochemical kinetics towards the oxygen reduction reaction (ORR) in acid media by rotating ring-disk electrode (RRDE) and single and three-stack membrane-electrode assembly (MEA) performance as a function of catalyst loading (10%, 20% and 40% W from 0.2 to 2 mg cm⁻²). Results indicate an electrocatalyst with chemical composition of Ru₆Cr₄Se₅. AFM images showed 80–160 nm nanoparticle agglomerates. Good thermal stability of the cathode Ru₆Cr₄Se₅ was established after 100 h of continuous operation. The electrochemical kinetics study (RRDE) resulted in a electrocatalyst with high activity towards the ORR, preferentially proceeding via 4e⁻ charge transfer pathway towards water formation (i.e., O₂+4H⁺+4e⁻→2H₂O), with a maximum of 2.8% H₂O₂ formation at 25 °C. Finally, MEA tests revealed a maximum power density of 220 mW cm⁻² with a catalyst loading of 20 wt% at 1.6 mg cm⁻².     

Effects of dilution with carbon dioxide on the laminar burning velocity and flame stability of H2–CO mixtures at atmospheric condition

The objective of this investigation was to study the effect of dilution with CO₂ on the laminar burning velocity and flame stability of syngas fuel (50% H₂–50% CO by volume). Constant pressure spherically expanding flames generated in a 40 l chamber were used for determining unstretched burning velocity. Experimental and numerical studies were carried out at 0.1 MPa, 302 ± 3 K and ? = 0.6–3.0 using fuel-diluent and mixture-diluent approaches. For H₂–CO–CO₂–O₂–N₂ mixtures, the peak burning velocity shifts from ? = 2.0 for 0% CO₂ in fuel to ? = 1.6 for 30% CO₂ in fuel. For H₂–CO–O₂–CO₂ mixtures, the peak burning velocity occurred at ? = 1.0 unaffected by proportion of CO₂ in the mixture. If the mole fraction of combustibles in H₂–CO–O₂–CO₂ mixtures is less than 32%, then such mixtures are supporting unstable flames with respect to preferential diffusion. The analysis of measured unstretched laminar burning velocities of H₂–CO–O₂–CO₂ and H₂–CO–O₂–N₂ mixtures suggested that CO₂ has a stronger inhibiting effect on the laminar burning velocity than nitrogen. The enhanced dilution effect of CO₂ could be due to the active participation of CO₂ in the chemical reactions through the following intermediate reaction CO + OH ? CO₂ + H.