Photocatalytic inactivation of Flavobacterium and E. coli in water by a continuous stirred tank reactor (CSTR) fed with suspended/immobilised TiO2 medium

A photocatalytic continuous stirred tank reactor (CSTR) was built at laboratory scale to inactivate two environmental bacteria strains (Flavobacterium and E. coli) in tap water. Several parameters were found to impact reactor efficiency. Bacterial initial concentration is an important factor in inactivation rate. After 30 minutes of irradiation at 10(8)-10(9) CFU mL(-1) starting concentration, a >5 log reduction was achieved while at 10(4)-10(6) CFU mL(-1) only a 2 log reduction was observed. Water hardness and pH have an important influence on the photocatalytic inactivation process. Soft water, with low Ca(+2) and Mg(+2) at low pH approximately 5.3 resulted in increased inactivation of Flavobacterium reaching >6 orders of magnitude reduction. E. coli and Flavobacterium at pH 5 were inactivated by 3 logs more as compared to pH 7 under similar conditions. pH below TiO2 isoelectric point (approximately 5.6) supports better contact between bacteria and anatase particles resulting in superior inactivation. TiO2 powder suspension was compared with immobilised powder in sol-gel coated glass beads in order to exclude the need for particles separation from the treated water. TiO2 suspension was more effective by 3 orders of magnitude when compared to coated glass beads. An interesting observation was found between the two bacterial strains based on their hydrophobicity/hydrophilicity balance. The more hydrophobic Flavobacterium compared to E. coli was inactivated photocatalytically by >3 logs more then E. coli in the first 30 minutes of irradiation interval. The results indicate the importance of the parameters involved in the contact between TiO2 particles and microorganisms that govern the successful inactivation rate in CSTR.     

Activation of solgel titanium nanofilm by UV illumination for NOM removal.

The control of natural organic matter (NOM) in drinking water treatment plants is required in order to control (i) the formation of potentially harmful disinfection byproducts (DBPs), (ii) the regrowth of bacteria and (iii) pipe corrosion in the distribution system. Photocatalysis is a promising advanced oxidation technology due to its ability to mineralise chlorinated byproduct precursors such as humic acids (HAs) to carbon dioxide and water. In this study, the efficiency of HAs and NOM removal in terms of UV absorbance at 254 nm (UV254) was tested by means of a new photocatalytic reactor made of stacked polymethylmethacrylate (PMMA) rings coated by TiO2 nanofilm. Three different sets of rings were coated with TiO2 gel one, two and three times respectively to optimise the coating thickness according to UV254 removal efficiency. The titania sol was immobilised on the substrate by a low temperature procedure and after 8 months the reactors were reactivated by means of UV radiation before the experiments. The photocatalytic removal efficiency of humic acid in terms of UV254 was significantly higher after 1 hour for the reactor employed with high thickness TiO2 nanofilm (around 20%) compared to middle and low thickness reactors (6 and 1.4%, respectively). However, during the same reaction time only 10% of UV254 was removed with high thickness TiO2 nanofilm using raw surface water, probably owing to ionic species naturally occurring in the raw water sample. Finally, the activation of the TiO2 nanofilm may be effectively accomplished by means of UV radiation where calcination cannot be applied (e.g. thermally sensitive substrates).     

Novel tiO2 nanocatalysts for wastewater purification: tapping energy from the sun.

Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection.     

催化湿式氧化法处理高浓度对氯苯基异氰酸酯生产废水的研究

在固定床鼓泡式反应器连续反应装置上对对氯苯基异氰酸酯生产过程中产生的高浓度实际废水进行催化湿式氧化处理。实验表明:制备的复合负载型催化剂CuO-ZrO2-CeO2/TiO2在处理该废水时具有较好的催化活性。通过对反应温度、反应压力、反应空速、气液比和进水pH等工艺条件的考察,得出最佳的工艺条件为:反应温度T=240℃,反应压力P=6.5MPa,空速=2.0 h-1,V(气)∶V(水)=230∶1,进水pH=8,在此条件下CODCr去除率达到96.9%。     

Determination and occurrence of organic micropollutants in reverse osmosis treatment for advanced water reuse

The growing demand on water resources has increased the interest in wastewater reclamation for multiple end-use applications such as indirect and direct potable reuse. In these applications, the removal of organic micropollutants is of a greater concern than in conventional wastewater treatment. This article presents a collection of data of trace organic micropollutants in an urban wastewater treatment plant (WWTP) in North East Spain using reverse osmosis (RO) membrane treatment. The RO rejection values of the organic molecules studied with a wide range of solute size and hydrophobicity were determined. Several chromatographic methods monitoring different endocrine disrupting chemicals (EDCs), pharmaceuticals and personal care products (PPCPs) were used. Results indicated that secondary effluents from this Spanish WWTP contained most of the studied organic compounds indicating incomplete removal of organics in the conventional treatment of the plant. However, the rejection of most micropollutants was high for all three RO membrane types (low energy, high rejection, fouling resistant) tested. It was observed that some selected micropollutants were less efficiently removed (e.g. the small and polar and the more hydrophobic) and the molecular weight and membrane material influenced removal efficiencies.     

The removal and degradation of pharmaceutical compounds during membrane bioreactor treatment

Pharmaceutical compounds such as non-steroidal anti-inflammatory drugs (NSAIDs) and antibiotics have been detected in sewage treatment plant (STP) effluents, surface and ground water and even in drinking water all over the world, and therefore have developed as compounds of concern. Membrane bioreactor (MBR) treatment has gained significant popularity as an advanced wastewater treatment technology and might be effective for an advanced removal of these pollutants. This paper evaluates the treatment of wastewater containing three NSAIDs (acetaminophen, ketoprofen and naproxen) and three antibiotics (roxithromycin, sulfamethoxazole and trimethoprim) performed in two MBRs with sludge retention times (SRTs) of 15 (MBR-15) and 30 (MBR-30) days over a period of four weeks. It was observed that NSAIDs were removed with higher efficiencies than the antibiotics for both MBRs, and the MBR-30 presented higher removal efficiencies for all the compounds than obtained by MBR-15. Removal rates ranged from 55% (sulfamethoxazole) up to 100% (acetaminophen, ketoprofen). Besides mineralisation biological transformation products of ketoprofen and naproxen produced by wastewater biocoenosis were identified in both MBR permeates using liquid chromatography coupled with mass spectrometry (LC-MS). The results indicated the importance of investigating the environmental fate of pharmaceuticals and their transformation products reaching the environment.     

Study on the treatment of Acid Red 4 wastewaters by a laminar-falling-film-slurry-type VUV photolytic process.

The purpose of this study is to develop the design equation of a laminar-falling-film-slurry-type (LFFS) photoreactor for the treatment of organic wastewaters (Acid Red 4) by 185 nm vacuum ultra-violet (VUV) related processes. The LFFS photoreactor is one of the most efficient reactor configurations for conducting heterogeneous photocatalytic reactions, particularly for wastewater treatment. The decomposition of Acid Red 4 dye wastewaters by VUV-based photo-oxidation process was studied under various UV light intensities, dosages of H2O2 and TiO2. By the treatment of the LFFS-VUV only process, it was found that the decomposition rates of the dye in aqueous solutions increased with the increasing of VUV light intensity, dosage of TiO2, dosage of H2O2. The apparent potential of OH. generation from the photolysis of used oxidants (i.e. OH. sources, H2O, H2O2, TiO2) to decompose the targeted dye wastewater was investigated and compared.     

Photochemical degradation of naproxen in the aquatic environment.

Naproxen belongs to the group of non-steroidal anti-inflammatory drugs. It is often used to treat pain of rheumatic and non-rheumatic diseases. The photochemical experiments of naproxen degradation were performed in the wastewater effluents from wastewater treatment plant (WWTP) Kloten/Switzerland at its real concentrations (without standard addition) and in drinking water containing naproxen standard, adjusted to pH = 7 and pH = 6. All performed experiments showed that within 5 min of photochemical oxidation, the disappearance of naproxen exceeded 90%. The first-order rate constants of naproxen degradation were determined. The maximal value of rate constant was observed by UV/H2O2 process in water samples at pH = 6 (k = 0.997 min(-1)).     

纳米TiO2光催化在废水治理中的研究与应用

介绍了纳米TiO2的光催化机理,讨论了其在废水处理中的不足之处以及近年来的改进手段。概述了光催化技术在处理含油废水、含药废水、印染废水、造纸废水、表面活性剂废水、重金属污染物废水等方面的最新应用研究进展,指出了其在废水处理中还存在阳光效率低、回收再利用困难、降解效率有限等问题及今后的研究趋势。     

Advanced oxidation process-biological system for wastewater containing a recalcitrant pollutant.

Two advanced oxidation processes (AOPs), ozonation and photo-Fenton, combined with a pilot aerobic biological reactor at field scale were employed for the treatment of industrial non-biodegradable saline wastewater (TOC around 200 mgL(-1)) containing a biorecalcitrant compound, alpha-methylphenylglycine (MPG), at a concentration of 500 mgL(-1). Ozonation experiments were performed in a 50-L reactor with constant inlet ozone of 21.9 g m(-3). Solar photo-Fenton tests were carried out in a 75-L pilot plant made up of four compound parabolic collector (CPC) units. The catalyst concentration employed in this system was 20 mgL(-1) of Fe2+ and the H2O2 concentration was kept in the range of 200-500mgL(-1). Complete degradation of MPG was attained after 1,020 min of ozone treatment, while only 195 min were required for photo-Fenton. Samples from different stages of both AOPs were taken for Zahn-Wellens biocompatibility tests. Biodegradability enhancement of the industrial saline wastewater was confirmed (>70% biodegradability). Biodegradable compounds generated during the preliminary oxidative processes were biologically mineralised in a 170-L aerobic immobilised biomass reactor (IBR). The global efficiency of both AOP/biological combined systems was 90% removal of an initial TOC of over 500 mgL(-1).     

Electro-Fenton as a feasible advanced treatment process to produce reclaimed water.

The feasibility of the electro-Fenton process to generate simultaneously both of the Fenton's reagent species (Fe2+/H2O2), was assessed as a potentially more economical alternative to the classical Fenton's reaction to produce reclaimed water. An air-saturated combined wastewater (mixture of municipal and laboratory effluents) was treated in discontinuous and continuous reactors at pH = 3.5. The discontinuous reactor was a 2 L electrochemical laboratory cell fitted with concentric graphite and iron electrodes. The continuous reactor tests used a pilot treatment system comprising the aforementioned electrochemical cell, two clarifiers and one sand filter. Several tests were carried out at different conditions of reaction time (0-60 min) and electrical current values (0.2-1.0 A) in the discontinuous reactor. The best operating conditions were 60 min and 1 A without filtration of effluents. At these conditions, in discontinuous and continuous reactors with filtration, the COD, turbidity and color removal were 65-74.8%, 77-92.3% and 80-100%, respectively. Fecal and total coliforms, Escherichia coli, Shigella and Salmonella sp. were not detected at the end of the pilot treatment system. Electrogeneration of the Fenton's reagent is also economical; its cost is one-fifth the cost reported for Advanced Primary Treatment.     

Simultaneous determination of several veterinary pharmaceuticals in effluents from urban, livestock and slaughterhouse wastewater treatment plants using a simple chromatographic method

Minocycline, oxytetracycline, tetracycline, enrofloxacin and ceftiofur, commonly used veterinary pharmaceuticals, were searched in four urban, two livestock and two slaughterhouse effluents from wastewater treatment plants (WWTPs) in the north of Portugal. A simple method that includes solid-phase extraction followed with analysis by high-performance liquid chromatography with diode array detector was established and applied to the simultaneous determination of the five pharmaceuticals in WWTP effluents. This method, which is expeditious, inexpensive and available in most laboratories, showed to be useful for screening for problematic levels of drugs in WWTP effluents. It is known that several livestock and slaughterhouse effluents (pre-treated or treated) are discharged to the urban network before discharge into the environment. The presence of these drugs in such effluents can constitute a significant environmental problem that should be addressed, by the monitoring of these drugs and by implementation of methodologies that contribute to their decrease/elimination from wastewaters. Minocycline (≤6 μg L(-1)), oxytetracycline (≤7 μg L(-1)), tetracycline (≤6 μg L(-1)) and enrofloxacin (<2 μg L(-1)) could be detected and/or quantified in three urban effluents. Detectable levels of enrofloxacin (<2 μg L(-1)) and quantifiable levels of tetracycline (≤15 μg L(-1)) were found in the slaughterhouse effluents.     

Micropollutants removal in an anaerobic membrane bioreactor and in an aerobic conventional treatment plant

The paper expresses an attempt to tackle the problem due to the presence of micropollutants in wastewater which may be able to disrupt the endocrine system of some organisms. These kinds of compounds are ubiquitously present in municipal wastewater treatment plant (WWTP) effluents. The aim of this paper is to compare the fate of the alkylphenols-APs (4-(tert-octyl)) phenol, t-nonylphenol and 4-p-nonylphenol and the hormones (estrone, 17β-estradiol and 17α-ethinylestradiol) in a submerged anaerobic membrane bioreactor (SAMBR) pilot plant and in a conventional activated sludge wastewater treatment plant (CTP). The obtained results are also compared with the results obtained in a previous study carried out in an aerobic MBR pilot plant. The results showed that the APs soluble concentrations in the SAMBR effluent were always significantly higher than the CTP ones. Moreover, the analyses of the suspended fraction revealed that the AP concentrations in the SAMBR reactor were usually higher than in the CTP reactor, indicating that under anaerobic conditions the APs were accumulated in the digested sludge. The aerobic conditions maintained both in the CTP system and in the aerobic MBR favoured the APs and hormones degradation, and gave rise to lower concentrations in the effluent and in the reactor of these systems. Furthermore, the results also indicated that the degradation of APs under aerobic conditions was enhanced working at high solid retention time (SRT) and hydraulic retention time (HRT) values.     

Optimised photocatalytic degradation of a mixture of azo dyes using a TiO(2)/H(2)O(2)/UV process

The aim of the present study was to optimise the photocatalytic degradation of a mixture of six commercial azo dyes, by exposure to UV radiation in an aqueous solution containing TiO(2)-P25. Response surface methodology, based on a 3(2) full factorial experimental design with three replicates was employed for process optimisation with respect to two parameters: TiO(2) (0.1-0.9 g/L) and H(2)O(2) (1-100 mmol/L). The optimum conditions for photocatalytic degradation were achieved at concentrations of 0.5 g TiO(2)/L and 50 mmol H(2)O(2)/L, respectively. Dye mineralisation was confirmed by monitoring TOC, conductivity, sulfate and nitrate ions, with a sulfate ion yield of 96% under optimal reactor conditions. Complete decolorisation was attained after 240 min irradiation time for all tested azo-dyes, in a process which followed a pseudo-first kinetic order model, with a kinetic rate constant of approximately 0.018 min(-1). Based on these results, this photocatalytic process has promise as an alternative for the treatment of textile effluents.     

Photocatalytic oxidation of low concentration 2,4-D solution with new TiO2 fiber catalyst in a continuous flow reactor.

Environmental pollution by low concentrations of 2,4-Dichlorophenoxyacetic acid (2,4-D) is a concern these days due to ever increasingly stringent regulations. Photocatalysis with immobilized TiO2 fiber is a promising oxidation method. Laboratory experiments on photocatalytic degradation of 0.045 mmol l(-1) 2,4-D with the world's first high-strength TiO2 fiber catalyst were carried out in a continuous flow reactor in which the degradations were, in general, similar to those with high 2,4-D concentrations investigated elsewhere. Degradation and mineralization of 2,4-D were significantly enhanced with no initial pH adjustments. The rate constants for total organic carbon (TOC) without pH adjustment were about two-fold bigger than the pH adjustment cases. CO2 gas measurement and carbon mass-balance were carried out for the first time, where about 34% organic carbon converted into CO2 gas during four-hour oxidation. 2,4-Dichlorophenol (2,4-DCP), phenol, benzyl alcohol and two unknowns (RT = 2.65 and 3.78 min.) were detected as aromatic intermediates while Phenol was the new aromatic in HPLC analysis. Dechlorination efficiencies were high (> 70%) in all the cases, and more than 90% efficiencies were observed in chloride mass balance. Bigger flow rates and solution temperature fixed at 20 degrees C without pH adjustment greatly enhanced 2,4-D mineralization. These results can be an important basis in applying the treatment method for dioxin-contaminated water and wastewater.     

Water reuse for urban landscape irrigation: aspersion and health related regulations.

The Mediterranean seaside resort of Le Grau du Roi includes 40 hectares of landscaped areas spray irrigated with river water supplied through a separate network. Wastewater collected from several municipalities is treated in an activated sludge wastewater treatment plant (WWTP) and polished in waste stabilization ponds (WSPs). Planned substitution of treated wastewater for river water is hindered by spray irrigation prohibition within a 100 m distance from houses and recreational areas. WWTP and WSP effluents were monitored for pathogens with a particular attention to Legionella in Spring and Summer 2006. Helminth eggs, salmonellae and enteroviruses were never detected neither in WWTP effluent nor in the ponds. Legionella spp content was slightly higher or of the order of magnitude of river water contents. Regarding Legionella pneumophila contents, WSP effluent did not significantly differ from the river water. E.coli and enterococci contents in WSP effluents complied with the "excellent quality" criteria of the European Directive for coastal bathing waters. Therefore, substituting WSP effluents to river water is unlikely to alter health risks related to spray irrigation and, in this case, the buffer zone required by the French water reuse guidelines appears being short of support.     

Quantification of dissolved methane in UASB reactors treating domestic wastewater under different operating conditions

This paper aimed at measuring the concentration of methane dissolved in effluents from different UASB reactors (pilot-, demo- and full-scale) treating domestic wastewater, in order to calculate the degree of saturation of such greenhouse gas and evaluate the losses of energetic potential in such systems. The results showed that methane saturation degrees, calculated according to Henry's law, varied from ～1.4 to 1.7 in the different reactors, indicating that methane was oversaturated in the liquid phase. The overall results indicated that the losses of dissolved methane in the anaerobic effluents were considerably high, varying from 36 to 41% of total methane generated in the reactor. These results show that there is considerable uncontrolled loss of methane in anaerobic wastewater treatment plants, implying the need of research on technologies aimed at recovering such energetic greenhouse gas.     

Phenol wastewater remediation: advanced oxidation processes coupled to a biological treatment.

Nowadays, there are increasingly stringent regulations requiring more and more treatment of industrial effluents to generate product waters which could be easily reused or disposed of to the environment without any harmful effects. Therefore, different advanced oxidation processes were investigated as suitable precursors for the biological treatment of industrial effluents containing phenol. Wet air oxidation and Fenton process were tested batch wise, while catalytic wet air oxidation and H2O2-promoted catalytic wet air oxidation processes were studied in a trickle bed reactor, the last two using over activated carbon as catalyst. Effluent characterisation was made by means of substrate conversion (using high liquid performance chromatography), chemical oxygen demand and total organic carbon. Biodegradation parameters (i.e. maximum oxygen uptake rate and oxygen consumption) were obtained from respirometric tests using activated sludge from an urban biological wastewater treatment plant (WWTP). The main goal was to find the proper conditions in terms of biodegradability enhancement, so that these phenolic effluents could be successfully treated in an urban biological WWTP. Results show promising research ways for the development of efficient coupled processes for the treatment of wastewater containing toxic or biologically non-degradable compounds.     

Effect of the disinfection agents chlorine, UV irradiation, silver ions, and TiO2 nanoparticles/near-UV on DNA molecules

Extracellular DNA in municipal wastewater and effluents from hospitals and R&D laboratories contains antimicrobial resistance and recombinant genes that are today considered as a new class of emerging contaminants. The objective of this research was to investigate the effect of disinfection agents on the integrity of DNA molecules by using real-time PCR. Escherichia coli cell suspensions and genomic DNA in aqueous solution were exposed to increasing doses of disinfection systems, including chlorination, UV irradiation, silver ions, and TiO2 nanoparticles/near-UV. The doses resulting in damage of DNA (16S rDNA) were determined using real-time PCR and compared with the doses resulting in the inactivation of bacterial cells. Our results showed that the disinfection agents chlorine, UV, and silver significantly inhibited the amplification of a fragment of 16S rDNA, but only when applied at doses much higher than the lethal doses for E. coli bacteria. The inactivation doses of TiO2 nanoparticles/near-UV were of the same order of magnitude for both DNA and living cells. Our results raise questions about the efficacy of disinfection processes to destroy and prevent the dispersion of DNA pollutants into the environment. In addition, the damage of DNA by high levels of disinfectants may have implications for the utilization of PCR-based methods for bacterial detection.     

An integrated approach for improving the wastewater discharge and treatment systems

Since treatment plants have been built all over Germany during the last decades, the water quality of receiving streams has been improved remarkably. But there are still a lot of quality problems left, which are caused e.g. by combined sewer overflows (CSO), treatment plant effluents or rainwater discharges from separate sewer systems. At present different efforts are undertaken to control sewer systems in order to improve the operation of urban drainage systems or more generally, design processes. The Emschergenossenschaft and Lippeverband (EG/LV) are carrying out research studies, which are focusing on a minimization of total emissions from sewer systems both from wastewater treatment plant (WWTP) effluents and from CSO. They consider dynamic interactions between rainfall, resultant wastewater, combined sewers, WWTP and receiving streams. Therefore, in an advanced wastewater treatment, a model-based improvement of WWTP operation becomes more and more essential, and consequently a highly qualified operational staff is needed. Some aspects of the current research studies are presented in this report. The need and the use of an integrated approach to combine existing model components in order to optimize dynamic management of combined sewer systems (CSS) with a benefit for nature are outlined.