Large solar plant photocatalytic water decontamination: Degradation of atrazine

Photocatalytic degradation of atrazine was successfully and efficiently carried out in a large modular flow trough system under solar light. The degradation leads to complete mineralization of the alkyl substituents of s-triazine, giving trihydroxy-s-triazine as a final product. An efficient detoxification can be attained. The presence of 1 × 10⁻³m of peroxydisulphate, kept constant during the treatment, is sufficient to remove 98% of atrazine with very short residence times (less than 6 min), and to convert the parent triazine to more than 90% of trihydroxy-s-triazine in less than 2 h. The peroxydisulphate is particularly advantageous when large amounts of polluted ground water have to be treated. The factors affecting the total efficiency are discussed in view of a simple model for the primary events in the photocatalytic system.     

Effect of climatic and operational parameters on the performance of an indirect solar still

A numerical study has been performed to evaluate the performance of a passive solar distillation system consisting of a flat-plate solar collector and a condensing chamber. Transfer equations, constructed on thermal and mass balances over various components of the still, have been solved using an implicit numerical scheme and the Diabolo Sablier method. Simulations were performed using meteorological data of Algiers (Algeria) and the Liu and Jordan method. Results show that the maximum amount of fresh water is produced in August, while the climatic conditions of May lead to the maximum daily efficiency of the condenser.     

Heterogeneous photocatalytic hydrogen generation in a solar pilot plant

Few studies have been published about large scale heterogeneous photocatalysis hydrogen generation with simultaneous removal of organic pollutants. The purpose of the present work was to study the simultaneous photocatalytic hydrogen production and organic pollutant removal under direct solar irradiation at pilot-plant scale. The experiments were performed in a Compound Parabolic Collector (CPC) at the Plataforma Solar de Almería (PSA). The efficiencies of two different photocatalytic systems, one based on a nitrogen doped and platinized TiO₂, and the other using a platinized CdS–ZnS composite were evaluated. Formic acid and glycerol were used as sacrificial electron donors. Also, experiments using real municipal wastewaters were carried out showing simultaneous hydrogen generation and partial water pollutant removal. The largest amounts of hydrogen were obtained with aqueous solutions of formic acid, although the experiments with real wastewater gave moderate amounts of hydrogen, pointing towards the possible future use of such waters for photocatalytic hydrogen generation.     

Anaerobic acidification of sugar-beet processing wastes: Effect of operational parameters

The objective of this study was to maximize the hydrolysis and acidification of sugar-beet processing wastewater and beet pulp for volatile fatty acid (VFA) production through acidogenic anaerobic metabolism. Experiments were conducted to determine the optimum operational conditions (HRT, waste-mixing ratio and pH) for effective acidification in daily-fed, continuously mixed anaerobic reactors. For this purpose, reactors were operated at 35 ± 1 °C with different combinations of HRT (2-4 days), wastewater-pulp mixing ratios (1:0-1:1, in terms of COD) and pH ranges (5.7-7.5). Increased OLRs, resulting from pulp addition, increased the amount of acidification products (VFAs) which led to relatively low operational pH values (5.7-6.8). In this pH range, methanogenic activity was successfully inhibited and the lowest methane percentages (5.6-16.3%) were observed in the produced biogas. The optimum operational conditions were determined to be 2-day HRT and 1:1 waste mixing ratio (in terms of COD) without external alkalinity addition. These operational conditions led to the highest tVFA concentration (3635 ± 209 mg/L as H-Ac) with the acidification degree of 46.9 ± 2.1%.     

New helio-photocatalytic-photovoltaic hybrid system for simultaneous water decontamination and solar energy conversion

Test results for a designed and installed hybrid photocatalytic-photovoltaic system (HPPS) are presented in this paper. The HPPS consists of one device with dual functions: The photocatalytic system uses UV radiation to promote degradation of organic pollutants, and beside it absorbs the IR radiation. The photovoltaic (PV) system converts the visible radiation into electricity, which can either be used directly by the recirculation pump or stored in a battery for other purposes. The suggested design aims to achieve an autonomous, environmentally friendly method for the treatment of biorecalcitrant pollutants. Two prototypes were erected: HPPS_P, using Plexiglas and HPPS_G using commercial glass. Both were tested outdoors to determine their impact on photovoltaic power production. Test results showed that PV power diminished to 14% and 22% for HPPS_G and HPPS_P respectively, compared to a PV panel alone.     

TiO2-fixed-bed reactor for water decontamination using solar light

A photocatalytic reactor using immobilized TiO₂ (Degussa P25) on a glass plate was studied on a bench scale using solar light as the source of radiation. The influence of parameters such as the slope of the plate, solar light intensity, flow rate and molar flow rate, as well as the geometry of the reactor, was studied using dichloroacetic acid (DCA) as a model compound. A linear dependence of degradation with solar light intensity, measured at 365 nm, was observed. Experiments with recirculation as well as a single pass of solution suggested no mass transfer limitations in this system. The mineralization of DCA resulted in the production of quantitative amounts of chloride ions. An initial concentration of 5 mmol/L of DCA decayed to 2 mmol/L in about 2 min of irradiation. An exponential decay of degradation was observed with an increase of the molar flow rate, achieving saturation around 1.5 mmol DCA/min.     

Assessment and influence of operational parameters on the TiO2 photocatalytic degradation of sodium benzene sulfonate under highly concentrated solar light illumination

Sodium benzene sulfonate (BS) was decomposed in aqueous TiO₂ dispersions under highly concentrated solar light illumination to examine the photocatalytic characteristics of a parabolic round concentrator (PRC) reactor to degrade the pollutant without visible light absorption. The effects of such operational parameters as initial concentration, volume of the aqueous BS solution, oxygen purging, and TiO₂ loading on the kinetics of decomposition of BS were investigated. An effective photodegradation necessitates a suitable combination of initial volume and concentration of BS solution. Relative to atmospheric air, oxygen purging significantly accelerates the degradation process at high initial concentrations of BS (0.40 mM or 1.0 mM). Optimal TiO₂ loading was 9 g l⁻¹, greater than previously reported. Elimination of TOC (total organic carbon) followed pseudo first-order kinetics in the initial stages of the photodegradation process. The relative photonic efficiency for the photodegradation of BS is ζ_rel=1.0.     

Efficient solar hydrogen production by photocatalytic water splitting: From fundamental study to pilot demonstration

Photocatalytic water splitting with solar light is one of the most promising technologies for solar hydrogen production. From a systematic point of view, whether it is photocatalyst and reaction system development or the reactor-related design, the essentials could be summarized as: photon transfer limitations and mass transfer limitations (in the case of liquid phase reactions). Optimization of these two issues are therefore given special attention throughout our study. In this review, the state of the art for the research of photocatalytic hydrogen production, both outcomes and challenges in this field, were briefly reviewed. Research progress of our lab, from fundamental study of photocatalyst preparation to reactor configuration and pilot level demonstration, were introduced, showing the complete process of our effort for this technology to be economic viable in the near future. Our systematic and continuous study in this field lead to the development of a Compound Parabolic Concentrator (CPC) based photocatalytic hydrogen production solar rector for the first time. We have demonstrated the feasibility for efficient photocatalytic hydrogen production under direct solar light. The exiting challenges and difficulties for this technology to proceed from successful laboratory photocatalysis set-up up to an industrially relevant scale are also proposed. These issues have been the object of our research and would also be the direction of our study in future.     

Engineering of solar photocatalytic collectors

This paper briefly describes the different collectors used in solar photocatalysis for wastewater treatment and, based on prior experience, the main advantages and disadvantages of each. As the tubular-shape reactor configuration is the most appropriate for handling and pumping water, the compound parabolic collector (CPC) is proposed as an interesting combination of parabolic concentrators and flat static systems and constitutes a good option for solar photochemical applications. The design of compound parabolic concentrators for solar photocatalytic applications is described in detail and 25–50 mm is proposed as the optimum photoreactor diameter, based on the optical characteristics and optimum concentration of the two photocatalytic systems (TiO₂ and photo-Fenton) that can be used with sunlight for wastewater treatment. It has been demonstrated that since aluminium is the only metal that is highly reflective in the ultraviolet spectrum of solar radiation, aluminium-based mirrors are the best option. But, especially when exposed to outdoor conditions, aluminium must be protected and, therefore, at the present time, anodised and electropolished aluminium surfaces are considered the most suitable solutions. As the photochemical reactor contain the working fluid, including the catalyst, it must transmit UV sunlight efficiently and be able to work under enough pressure to handle the high volumes resulting from the large number of collectors in an industrial treatment plant, only low-iron glass is proposed as feasible for constructing the photoreactor (collector absorbers). Finally, ray-tracing algorithm simulations are presented as a design tool for the optical configuration of a particular reactor, drawing conclusions for its improvement and assisting in final engineering decision-making.     

Effect of interface recombination on solar cell parameters

A model is presented for p–n hetero-junction solar cells in which interface recombination is the dominant diode current transport mechanism. The model explains the large diode ideality factor (n>2) and the increased saturation current density in terms of increased density of interface states N_ir. Furthermore, the model allows us to explain the non-translation between illuminated and dark J–V characteristics. The explanation is based on the assumption that, for high interface state density values, both the depletion layer width and the diffusion voltage in the p- and n-side of the junction are functions of N_ir. The interface recombination leads to lower values of the open-circuit voltage, short-circuit current density, and fill factor. These results are illustrated by numerical calculations of solar cell parameters and compared with experimental data achieved for ZnO/CdS/CuGaSe₂ single-crystal solar cells.     

The effects of climatic,design and operational parameters on the performance of wick-type solar distillers

The theory of wick-type solar distillers has been modified. The effects of climatic, design and operating conditions on the modified factor have been investigated experimentally, and a correlation equation derived. The effects of these conditions on the production rate of distilled water have also been presented.     

Continuous flow photochemical reactor for solar decontamination of water using immobilized TiO2

A photochemical reactor is designed for solar decontamination of organic pollutants in water, where the nanocrystalline photocatalyst TiO₂ is immobilized on glass. The reactor modules could be connected in series and/or parallel to achieve desired flow rates under different conditions of illumination and degree of contamination. Methyl violet and phenol was found to completely degrade under solor irradiation and flow rates of 102–138 ml/h.     

Electricity and potable water from a solar tower power plant

The cogeneration of electricity and potable water utilising solar energy is studied, assuming solar tower power plants with the open volumetric PHOEBUS receiver. The results for alternative plant configurations show that the water production cost is about the same or even lower than the cost of water produced by conventionally fired systems. Furthermore, the integration offers a reduction of CO₂-emissions related to the water production of up to 50%, additionally to the environmental benefits of solar electricity production.     

Large area CIGS2 thin film solar cells on foils: nucleus of a pilot plant

In earlier research, conversion efficiency of 10.4% (AM1.5) and 9.9% (AM0) has been achieved on small area CuIn_xGa_1−xS₂ (CIGS2) solar cell on 127 μm thick stainless steel substrate. The area of research is mainly focused on studying CIGS2 thin films as solar cell absorber material and growing high efficiency cells on ultralightweight and flexible metallic foils such as 127 μm thick stainless steel and SiO₂ coated 25 μm thick Ti foils. This paper presents the scaling up process of CIGS2 thin film substrate from 2.5 × 2.5 cm² to 10 × 10 cm². Initial scaling up efforts focused on achieving uniform thickness and stress-free films. Process of scaling up consisted of refurbishment of selenization/sulfurization furnace, design and fabrication of scrubber and enlargement of new CdS deposition setup. The scaling up from 2.5 × 2.5 cm² to 10 × 10 cm² substrate size has laid the foundation for PV Materials Lab of Florida Solar Energy Center becoming the nucleus of a pilot plant.     

Decontamination of industrial cyanide-containing water in a solar CPC pilot plant

The aim of this work was to improve the quality of wastewater effluent coming from an Integrated Gasification Combined-Cycle (IGCC) power station to meet with future environmental legislation. This study examined a homogeneous photocatalytic oxidation process using concentrated solar UV energy (UV/Fe(II)/H₂O₂) in a Solar Compound Parabolic Collector (CPC) pilot plant. The efficiency of the process was evaluated by analysis of the oxidation of cyanides and Total Organic Carbon (TOC). A factorial experimental design allowed the determination of the influences of operating variables (initial concentration of H₂O₂, oxalic acid and Fe(II) and pH) on the degradation kinetics. Temperature and UV-A solar power were also included in the Neural Network fittings. The pH was maintained at a value >9.5 during cyanide oxidation to avoid the formation of gaseous HCN and later lowered to enhance mineralization. Under the optimum conditions ([H₂O₂] = 2000 ppm, [Fe(II)] = 8 ppm, pH = 3.3 after cyanide oxidation, and [(COOH)₂] = 60 ppm), it was possible to degrade 100% of the cyanides and up to 92% of Total Organic Carbon.     

Applied studies in solar photocatalytic detoxification: an overview

The technical feasibility and performance of photocatalytic degradation of four water-soluble pesticides (diuron, imidacloprid, formetanate and methomyl) have been studied at pilot scale in two well-defined systems which are of special interest because natural-solar UV light can be used for them: heterogeneous photocatalysis with titanium dioxide and homogeneous photocatalysis by photo-Fenton. The pilot plant is made up of compound parabolic collectors specially designed for solar photocatalytic applications. The initial concentration tested with imidacloprid, formetanate and methomyl was 50 and 30 mg/l with diuron, and the catalyst concentrations were 200 mg/l and 0.05 mM with TiO₂ and iron, respectively. Total disappearance of the parent compounds, 90% mineralisation and toxicity reduction below the threshold (EC₅₀) have been attained with all pesticides tested. All these results have contributed to an evaluation of photocatalytic treatment capacity and comments on the main parameters of TiO₂ and Fe separation from the treated water.     

荒漠中的发电站——太阳能烟囱发电站

一前言 太阳能烟囱发电技术是通过集热棚吸取太阳热能使棚内空气温度升高,根据烟囱的原理,在烟囱内将形成强大的气流,利用这股气流形成的风力驱动风机,带动发电机发电。太阳能烟囱发电系统主要由透光的采光大棚、烟囱及风力涡轮机构成,如图1所示。     

Effect of water emissivity on solar still efficiency

The proper installation of a solar still can reduce the heat loss from the basin to ambient and significantly increase the still efficiency. In this case, the use of a dye resulted in minimal improvement in still efficiency. The reduction in the water emissivity will reduce the radiation heat transfer from water to glass. This resulted in a substantial improvement in still efficiency and offers great potential for solar still usage. The two methods above are mutually exclusive and could be used concurrently for best results. The numerical predictions reported agree favorably with the most recently published experimental work in a similar configuration.