Advanced treatment by ozonation and sonolysis for domestic wastewater reuse
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... Thus, alternative disinfectants such as ozone [12], ozone/UV [13], and chlorine dioxide/peracetic acid [14] have been attempted also to effectively remove DBPs precursors and trace organics. Advanced oxidation processes (AOPs) have gained importance and have been studied intensively to remove emerging pollutants such as pharmaceuticals, personal care products, pathogens, etc. from urban wastewater treatment plants (UWWTPs) effluent in recent years [15] [16]. AOPs results in the formation of extremely reactive species (such as hydroxyl radicals) capable of oxidizing a wide range of organics occurring in wastewater [16,17]. ...
... Anyhow, water reuse strategies are intended to address the problem of water scarcity without aggravating other environmental problems, thus reflecting the need of an environmental assessment-based approach [10] [21] as well as to minimize effluent toxicity [7] [11]. Color removal using ozone and ultrasonics [15] and particularly, the synergetic effect of ozonation and PCO processes in the organic matter mineralization and color removal from reclaimed water, were investigated [22]. However, none of these studies has dealt with DBPs' formation and ecotoxicity. ...
This study aimed to optimize two oxidation processes for wastewater reuse of an urban wastewater treatment plant (UWWTP) effluent intended for human consumption. Ozonation and TiO2 photocatalytic oxidation (PCO) processes were compared for their effectiveness in terms of organic matter degradation (measured as UV absorbance at 254 nm, UV254), disinfection by products formation (measured as trihalomethanes formation potential, THMFP), and ecotoxicity (evaluated by Daphnia magna and Lepidium sativum), on secondary treated wastewater collected from a UWWTP in the province of Salerno (southern Italy). Accordingly, ozonation experiments using 28 mg/L ozone dose and PCO experiments using 250 W lamp (emission range: 315–400 nm; emission peak: 14.7 μW/cm2 at 340 nm) and varying TiO2 dose from 1 to 3 g/L were carried out. Ozonation (t 1/2 = 71.6 min) was not found as effective as PCO for organic matter degradation at all TiO2 doses, and 3 g/L of TiO2 was found to be the most effective photocatalyst loading (t 1/2 = 41.8 min). Moreover, PCO-treated samples resulted in a lower THMFP compared to ozonation process. While ozonation did not increase toxicity to D. magna severely (10% of immobilization), PCO-treated samples exhibited varying toxicity end-points possibly due to formed oxidation intermediate products. However, Cl2 disinfection of treated wastewater samples played an improving role in toxicity of PCO-treated samples. In particular, in 30 min oxidized samples, toxicity to D. magna was decreased up to 50% (from 40 to 20% of immobilization) while germination index of L. sativum, a phytotoxicity test used for irrigation quality testing purpose, improved at 30% after Cl2 disinfection in 3 g/L of TiO2 treated sample.
... In the process of photocatalysis, the efficiency of photocatalyst increases with rising the surface species that work as trapping by adsorption themselves on the photo-catalyst surface, while photo electron-hole recombination is the significant factor that depresses efficiency. Three essential recombination mechanisms exist [20,21]: ...
... In the process of photocatalysis, the efficiency of photocatalyst increases with rising the surface species that work as trapping by adsorption themselves on the photo-catalyst surface, while photo electron-hole recombination is the significant factor that depresses efficiency. Three essential recombination mechanisms exist [20,21]: ...
The nanocomposites applications are very interesting in the fields of medicine, packaging, optical integrated circuits, drug delivery, coatings, sensors, aerospace, packaging materials, consumer goods, consumer goods adhesives. etc. This review includes new nanocomposite contain of polymer and oxide nanoparticle for photocatlytic applications with high activity, low cost and low weight. The results showed that the nanocomposite has high photocatalytic activity.
... The photo-reduction process occurs on the conductance band by electron-acceptor species such as O 2 , while the photo-oxidation process occurs on the valence band by electron-donor species such as -OH which the H 2 O originally, and produces the hydroxyl radical used for degradation and mineralization of pollutants [1,[50][51][52]. The essential processes under illumination of semiconductor particles are shown in the Figure 1 The advantages of heterogeneous photocatalysis process are low cost, have a high conversion efficiency and quantum yield, high stability, high activity, widely used fields such as industry and environment, and works in high range of spectra (UV and visible light), or solar light [49,53], but the recombination process regards a disadvantage of heterogeneous photocatalysis process, due to loss in the energy as heat. In photocatalysis process, the efficiency of photo-catalyst rises with increase in the surface species which acts as traps by adsorbing them on the photocatalyst surface, while the major factor which depresses the efficiency is photo electron-hole recombination. ...
This work consists of five parts. The first part is concerned with
the preparation of metalized TiO2 nanoparticales. Metalized TiO2 was
prepared by photodeposition of different percentage of platinum (Pt) or
gold (Au) on the surface of TiO2 Hombikat (UV 100) surface. The
properties of prepared photocatalysts were investigated by Atomic
absorption (A.A) analysis, Fourier transform infrared (FT-IR) analysis,
X-ray diffraction (XRD) analysis and Atomic force microscope (AFM)
analysis.
Scherrer equation and modified Scherrer equation were used to
calculate the mean crystallite sizes and crystallite sizes of bare and
metalized TiO2 via XRD data. The calculated mean crystallite sizes and
crystallite sizes of bare TiO2 decreased with the increasing of metal
percentage. The AFM images indicated that the shape of bare and
metalized TiO2 is spherical. The particle size was found ranged between 9
and 11 crystallite size.
The band gap energy values for bare TiO2, Pt(0.5)/TiO2 and
Au(0.5)/TiO2 were calculated after applying the Kubelka-Munk
transformation. The results show shifting ultra violet absorption to visible
light absorption (red shift) and band gap narrowing. The band gap of bare
TiO2 was reduced from 3.289 eV to 3.263 eV for Pt(0.5)/TiO2 and to
3.246 eV for Au(0.5)/TiO2 too.
The second part deals with the studying the effect of different
parameters on photocatalytic oxidation of methanol by using bare and
metal loaded on TiO2 surface. The parameters include: weight of catalyst,
types of metal, percentage of loaded metal, methanol concentration, pH
of solution and temperature. However the third part deals with the
studying the effect of the same parameters in the second part on
photocatalytic dehydrogenation of methanol by using bare and metal
loaded on TiO2 surface. The photocatalytic activities of bare and
metalized nanoparticles have been assessed by formaldehyde formation
and hydrogen evolution from aqueous methanol solution.
The emerging technologies for wastewater treatment for water recovery and reuse in pulp and papermaking are presented in this chapter. Advanced oxidation processes (AOPs), treatment with microorganisms and enzymes, sequential biotreatment (anaerobic and aerobic), internal circulation (IC) reactor, the FlooBed bioreactor process, membrane processes, etc., are discussed.
In the past there was a prevailing feeling in industry that power ultrasound would be too expensive to use for water treatment on an industrial scale. This was based on calculations involving the direct scale up of power consumption in small-scale (generally batch) laboratory experiments. In recent times this attitude has changed somewhat as a result of the installation of a number of ultrasonic devices in operational water or sewage treatment plants. In our laboratories we have investigated the decontamination of water under the influence of ultrasound alone and in conjunction with other treatments. The results, particularly when applied to flowing systems, indicate a real future for sonochemistry in water treatment.
Some species of bacteria produce colonies and spores which agglomerate in spherical clusters (Bacillus subtilis) and this serves as a protection for the organisms inside against biocidal attack. Flocs of fine particles e.g. clay can entrap bacteria which can also protect them against the biocides. It is because of problems such as these that alternative methods of disinfecting water are under active investigation. One such method is the use of power ultrasound, either alone or in combination with other methods. Ultrasound is able to inactivate bacteria and deagglomerate bacterial clusters or flocs through a number of physical, mechanical and chemical effects arising from acoustic cavitation. The aim of this study was to investigate the effect of power ultrasound at different powers and frequencies on Bacillus subtilis. Viable plate count techniques were used as a measure of microbial activity. Results showed a significant increase in percent kill for Bacillus species with increasing duration of exposure and intensity of ultrasound in the low-kilohertz range (20 and 38 kHz). Results obtained at two higher frequencies (512 and 850 kHz) indicated a significant increase in bacteria count suggesting declumping. In assessing the bacterial kill with time under different sonication regimes three types of behaviour were characterized: High power ultrasound (lower frequencies) in low volumes of bacterial suspension results in a continuous reduction in bacterial cell numbers i.e. the kill rate predominates. High power ultrasound (lower frequencies) in larger volumes results in an initial rise in cell numbers suggesting declumping of the bacteria but this initial rise then falls as the declumping finishes and the kill rate becomes more important. Low intensity ultrasound (higher frequencies) gives an initial rise in cell numbers as a result of declumping. The kill rate is low and so there is no significant subsequent decrease in bacterial cell numbers.
Two approaches for modelling the formation of filamentary structures in cavitation bubble fields are presented. The first one describes the interaction of the sound field and the distribution of microbubbles in terms of a set of two coupled partial differential equations that determine the evolution of the sound-field amplitude and the bubble density. The second approach consists of a quasideterministic aggregation model, where the bubbles are treated as pulsating particles which experience radiation forces due to the sound-fields radiated from the other pulsating bubbles. Results of numerical simulations are presented for both models. The validity and limitations of both approaches are discussed.
Ultrasonic irradiation has been one of the advanced oxidation methods for natural organic matter (NOM) removal. Its application simplicity and no production of toxic by-products make the system attractive. It has been shown that high power ultrasound produces strong cavitation in aqueous solution causing shock wave and reactive free radicals by the violent collapse of the cavitation bubble. These effects should contribute to the physical disruption and inactivation of microbial structures as well as to the decomposition of toxic chemicals in the water. The objective of this research was to investigate the effectiveness of low frequency – high power sonication for NOM removal (measured by both means of UV 254 absorbance and TOC) as well as controlling DBPs formation by varying irradiation time, light intensity, NOM concentration. Temperature, pH, conductivity, redox potential, and turbidity were monitored to evaluate the experimental study. The results indicate a strong capacity of sonication for NOM removal. The preliminary experiments showed that NOM removal is influenced by the intensity and time of sonication. Ultrasound, applied under such conditions, may be a realistic possibility for large-scale treatment; however, further studies should be performed to evaluate its effectiveness on different water sources.
This study aimed to evaluate the potential reuse of a leather tanning district and an urban wastewater treatment plant (UWWTP) effluents. The UWWTP discharges into the Sarno river which is one of the most polluted river in Europe. A water restoration program covering the rationalisation of the water use between industry and irrigation is in progress for this river. However, no use for fire protection which gains the most importance in summer season in the river catchement area as well as in all over Italy, was considered.
The evaluation of potential reuse in this study included industrial reuse and storage for fire protection. Chlorine is suggested as disinfectant before fire protection use while UV is for the non-contact industrial use. The existing water reuse limits in Italy are discussed. Finally, the establishment of compliance limits for each reuse alternative is emphasised.
The sonolytic inactivation of Escherichia coli (E. coli) is reported. The impact of power intensity, dissolved gas and ultrasonic frequency on the germicide effectiveness of sonification has been explored. The inactivation of E. coli exhibits pseudo-first order behavior, and depends moderately on total power and power intensity at a frequency of 20 kHz. The rate coefficients in an oxygenated solution vary from 0.031 to 0.046 min−1 when the power intensity ranges from 4.6 to 74 W cm−2. Inactivation occurs most readily at the highest sound intensity, 74 W cm−2. Three dissolved gases were investigated: oxygen, argon, and an argon/oxygen mixture. The nature of the dissolved gas does not strongly influence the magnitude of the inactivation coefficients which varied from k=0.027 min−1 to 0.047 min−1. Ultrasonic frequency, within the limits of 205–1017 kHz, displays a strong influence on the rate of E. coli inactivation in oxygenated solutions. The rate coefficients vary from 0.030 to 0.078 min−1. The most effective ultrasonic frequency for E. coli innovation is 205 kHz; the rate coefficient (k=0.078 min−1) is greater than the coefficient at 1071 kHz (k=0.030 min−1) by a factor of 2.6 and 358 kHz (k=0.064 min−1) also demonstrates a greater efficiency than either 618 kHz (k=0.041 min−1) or 1017 kHz.
Recent studies have shown that there is no loss of cell viability when the cells are subjected to ultrasonic standing wave fields in acoustic cell retention systems. These systems are characterised by waves that spatially vary in pressure amplitude in the direction of sound propagation. In this work an anechoic 'one-dimensional' sonication chamber has been developed that produces propagating waves, which differ from standing waves in that the pressure amplitude remains constant as the wave travels in a medium with negligible attenuation. The viability of yeast cell suspensions as a function of treatment time was investigated during exposure to both standing and propagating wave fields with frequencies slightly above 2 MHz. The influence of 12% (vol/vol) of ethanol in water on the spatial arrangement of the cells in suspension was also studied. Changes in yeast cell morphology caused by the different types of suspension media and the ultrasonic treatment were examined by transmission electron microscopy (TEM). The agglomeration of yeast cells within the pressure nodal planes appears to minimise damaging effects due to ultrasonic fields.
Ultrasonic inactivation of Escherichia coli XL1-Blue has been investigated by high-intensity ultrasonic waves from horn type sonicator (27.5 kHz) utilizing the "squeeze-film effect". The amplitude of the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The inactivation of the E. coli cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant gradually increased with increasing amplitude of the vibration face and showed rapid increase above 3 microm (p-p). In contrast, the H2O2 formation was not observed below 3 microm (p-p), indicating that the ultrasonic shock wave might be more important than indirect effect of OH radicals formed by ultrasonic cavitation in this system. The optimal thickness of the squeeze film was determined as 2 mm for the E. coli inactivation. More than 99% of E. coli cells was inactivated within 180-s sonication at the amplitude of 3 microm (p-p) and 2 mm of the thickness of the squeeze film.