Elimination of faecal indicator microorganisms from wastewater by combining constructed wetlands and heterogeneous photocatalysis: from laboratory to pilot-scale implementation

<div class="htmlview paragraph">Ozone and ultraviolet (UV) light have been shown to be effective in treating emerging pathogens that are not affected by the current standard treatment of chlorine. The hypothesis of this study was that a combined treatment of UV light and ozone would result in greater pathogen reduction than a large dose of either one individually. In the one-way studies for ozone and UV light, the ozone treatments took at least twice as long as the UV treatments to achieve the same extent of reduction in the microbial population. Specifically, 60 min for ozone and 30 min for UV light for a 4-log reduction in Heterotrophic plate counts (HPC's); 10 min for ozone and 3 min for UV light for a 3-log reduction in total coliforms and fecal coliforms; and, 6 min for ozone and 3 min for UV light for a 2-log reduction in coliphage. The ozone treatments, however, unlike the UV treatments, resulted in no positive re-growth in bacteria after treatment. Ozone and UV light acting simultaneously exhibited not merely additive, but synergistic effects, in reducing the microbial populations, with the exception of when low levels (2 min UV and 1 min ozone) of both factors were used. Specifically, the following treatment combinations yielded the maximum microbial reductions: low level of UV (1 min) and high level of ozone (4 min) for HPC's; high level of UV (2 min) and high level of ozone (4 min) for total Coliforms and fecal coliforms; and either one of the foregoing treatments for the overall microbial population. The synergistic effects between UV light and ozone allowed for lower UV and ozone levels to achieve the same extent of microbial reduction achieved by either factor acting separately. Thus, 2 min of ozone and 2 min of UV light applied simultaneously was just as effective as 6-8 min of ozone only or 2.5 min of UV light only. This synergistic effect should lead to reduced energy consumption while maintaining the level of disinfection required. If UV light and ozone were to be applied successively, the most effective sequence of application would be ozone first followed by UV light.</div>

Human activity in wilderness areas has the potential to affect aquatic ecosystems, including through the introduction of microorganisms associated with fecal contamination. We examined fecal microorganism contamination in water sources (lake outlets, snowmelt streams) in the popular Absaroka Beartooth Wilderness in the United States. Although the region is remote, increasing human visitation has the potential to negatively affect water quality, with particular concern about human-derived microorganism fecal contaminants. We used standard fecal indicator bacterial assays that quantified total coliform bacteria and Escherichia coli concentrations, together with more specific polymerase chain reaction-based microbial assays that identified possible human sources of fecal microorganisms in these waters. Total coliforms were detected at all lake outlets (21 of 21 sites), and E coli was detected at 11 of 21 sites. Droplet digital polymerase chain reaction assays revealed the presence of human feces-derived microorganisms, albeit at abundances below the limit of detection (<10 gene copies per milliliter of water) at all but 1 of the sampling sites. Our results suggest low prevalence of water-borne pathogens (specifically E coli and human-derived Bacteroides) in this popular wilderness area. However, widespread detection of total coliforms, Bacteroides, and E coli highlight the importance of purifying water sources in wilderness areas before consumption. Specific sources of total coliforms and E coli in these waters remain unknown but could derive from wild or domesticated animals that inhabit or visit the Absaroka Beartooth Wilderness. Hence, although contamination by human fecal microorganisms appears minimal, human visitation could indirectly influence fecal contamination through domesticated animals.

Photocatalytic degradation of pharmaceutical wastes by alginate supported TiO2 nanoparticles in packed bed photo reactor (PBPR)

The combination of heterogeneous photocatalysis with chemical and physical operations: A tool for improving the photoprocess performance

TiO2-photocatalytic treatment coupled with biological systems for the elimination of benzalkonium chloride in water

A practical demonstration of water disinfection using TiO 2 films and sunlight

To undertake a better water management in Oil&Gas sector, it is essential to decrease the wastewater generation by increasing the current reused water rates. Focused on this motivation, this study presents the performances of solar-assisted photo-Fenton and heterogeneous photo-catalysis on refinery wastewater treatment for reuse purposes with the aim of zero discharge. While initial tests were made on synthetic refinery wastewater, real case studies were performed with two types of refinery effluent in order to test the feasibility of using AOPs either as a secondary or tertiary treatment. Even though heterogeneous photo-catalysis and a combined process showed promising results for the treatment of the refinery effluents, photo-Fenton treatment revealed a superior effectiveness for application in both secondary and tertiary treatment, considering the improvements on TOC removal, toxicity and biodegradability. Photo-Fenton as secondary treatment resulted as efficient as the biological treatment, reaching final TOC values ca. 20 mg/L and 88% of COD removal presenting values lower than those achieved after the biological treatment. Moreover, a marked increase in the BOD5/COD ratio from 0.38 to 0.83 was obtained. Furthermore, as a tertiary treatment, photo-Fenton process either with H2O2/COD = 10 and H2O2/Fe2+ = 50 or H2O2/COD = 4 and H2O2/Fe2+ = 10 provided a final TOC value <4 mg/L. This result reveals the possibility to reuse the effluent in the refinery plant, thus increasing the sustainability.

UV-A and UV-C induced photolytic and photocatalytic degradation of aqueous ciprofloxacin and moxifloxacin: Reaction kinetics and role of adsorption

Life cycle assessment of a coupled solar photocatalytic–biological process for wastewater treatment

Plasmonic photodegradation of textile dye Reactive Black 5 under visible light: a vibrational and electronic study

This research contributes to the study and development of a new degradation technique that couples solar and biological processes for the treatment of biorecalcitrant, nonbiodegradable, and/or toxic organic substances present in the aqueous medium. Efficient physicochemical pretreatments are necessary to modify the structure of the pollutants, by transforming them into less toxic and biodegradable intermediates, allowing then, a biological procedure to complete the degradation of the pollutant load in a shorter time and in a less expensive way. The strategy of coupling photochemical and biological processes implicates among others, the study of some fundamental physicochemical properties, the optimization of a coupled reactor at laboratory scale (2 litres), and the study of solar photocatalytic treatment efficacy under direct sunlight using parabolic collectors of 40 to 200 litres. The study of the structure effect on the photoreactivity via TiO2 catalysis is studied using several substituted phenols to cover a wide variety of electronic effects, ranging from strong electron-donating (activating) to strong electron-withdrawing (deactivating) groups and herbicides with very similar molecular structures (metobromuron, isoproturon, chlorbromuron, and chlorotoluron). The photoreactivity of these compounds is affected by the electronic nature of the substituents and their positions in the aromatic ring, being higher when there is a greater electronic density. The Hammett constant, which represents the effect that different substituents have on the electronic character of the aromatic studied compounds, appears to give an adequate descriptor of their photocatalytic degradability. One important consideration in the TiO2-photocatalysed reactions is the adsorption of the organic compound on the surface of semiconductor particles. The dark adsorption isotherms for complete p-halophenols series and four herbicides are measured and correlated with their photoreactivity. The results indicate that no direct correlation exists between the extents of adsorption and the initial photodegradation rates of the studied compounds. Concerning the optimization and utilization of an integrated photocatalytic-biological process at laboratory scale, two kinds of combined systems are developed using immobilized biomass for the biological step and either diluted Fe3+/H2O3 (Fenton reaction) or TiO2 supported on glass rings for the photocatalytic pre-treatment. The advantages of the latter system are that the catalyst can be re-used and that the pH of the solution remains at neutral values. The photo-Fenton reaction instead, renders the phototreated solution acidic making neutralization necessary. The photochemical-biological flow reactors mentioned above, are employed to completely mineralize an isoproturon-herbicide solution. Preliminary experiments concerning the chemical and biological characteristics of the phototreated solution, are carried out to determine the moment at which it becomes biocompatible. Two operation modes (continuous or semi-continuous) of the photo-Fenton-biological coupled reactor are compared by studying the efficiency of the photochemical, biological, and overall treatments of p-nitro-o-toluenesulfonic acid (p-NTS) in solution. The two main parameter affecting the performance of the photo-assisted reactor in continuous mode are related to the very low pollutant concentration that characterise this kind of operation mode and to the high residual H2O3 concentration after the pretreatment. Thus, a semi-continuous mode was applied to try to overcome these inconveniences. In these conditions, 50 to 70 litres of polluted water can be treated per day per litre of photoreactor. The last part of this thesis, addresses the study of the solar photocatalytic treatment efficacy under direct sunlight using parabolic concentrating (Helioman reactors) and nonconcentrating (CPC) collectors. This part, carried out at the "Plataforma Solar de Almería" (PSA) in Spain, indicates that the solar photocatalytic treatment is effective for the purification of water contaminated by herbicides and other substances of industrial origin like the p-NTS. It is demonstrated the utility of both homogeneous (based on Fe3+/H2O3 reaction) and heterogeneous photocatalysis (based on TiO2) as pretreatment methods that can be followed by a biological treatment. Using a coupled system, the treatment of 100 to 300 litres of polluted water per square metre of photoreactor can be envisaged in a sunny day. The low manufacturing, installation, and maintenance costs, and easy operation of the CPC, compared with Helioman collectors, suggest that the former ones are, at present, the best way to apply the solar detoxification technology.

Kinetics and mechanism of Paraquat's degradation: UV-C photolysis vs UV-C photocatalysis with TiO2/SiC foams.

BackgroundUsing treated wastewater in agriculture irrigation could be a realistic solution for the shortage of fresh water in Iran, however, it is associated with environmental and health threats; therefore, effluent quality assessment is quite necessary before use. The present study aimed to evaluate the physicochemical and microbial quality of Shiraz wastewater treatment plant effluent for being used in agricultural irrigation. In this study, 20 physicochemical and 3 microbial parameters were measured during warm (April to September) and cold months (October to march). Using the measured parameters and the Canadian Water Quality Index, the quality of the effluent was determined in both warm and cold seasons and in all the seasons together.ResultsThe calculated index for the physicochemical parameters in the effluent was equal (87) in warm and cold months and it was obtained as 85 for the seasons all together. When the microbial parameters were used in order to calculate the index, it declined to 67 in warm and cold seasons and 64 in all the seasons together. Also, it was found that three physicochemical parameters (TDS, EC, and NO3) and three microbial parameters (Fecal coliform, Helminthes egg, and Total coliform) had the most contribution to the reduction of the index value.ConclusionsThe results showed that the physicochemical quality of Shiraz Wastewater Treatment Plant Effluent was good for irrigation in the warm, cold, and total of the two kinds of seasons. However, by applying the microbial parameter, the index value declined dramatically and the quality of the effluent was marginal.

Removal of hydrophobic organic pollutants from soil washing/flushing solutions: A critical review

The pulp and paper industry generates 10-250 m³ of wastewater per ton of pulp and paper products. Accordingly, it is the third largest wastewater-generating industry with more than 700 types of discharged toxic contaminants. These substances are difficult to degrade by natural means and present hazardous risks to the human health (e.g. carcinogenicity, mutagenicity and endocrine disruptors) and ecosystem (e.g. scum formation, thermal impact, and eutrophication). However, conventional biological treatment methods are incapable of degrading these complex and bio-recalcitrant substances. Therefore, the main objective of this research was to develop a more sustainable integrated treatment system (consisting of coagulation process and heterogeneous photocatalysis) to effectively remove suspended solids and persistent organic contaminants in the raw pulp and paper mill effluent (PPME). Firstly, a detailed preliminary study of utilizing Cassia obtusifolia (C. obtusifolia) seed gum as a natural coagulant to pre-treat raw and undiluted PPME was investigated. At recommended coagulation process conditions (initial effluent pH = 5, C. obtusifolia seed gum dosage = 0.75 g/L, slow-mixing velocity and time = 10 rpm and 10 min, respectively, and settling time = 1 min), C. obtusifolia seed gum removed high loadings of total suspended solids (TSS) and chemical oxygen demand (COD) of up to 86.9 and 36.2%, respectively. Following that, the interactive effects of coagulation process conditions were evaluated. Under optimal pre-treatment conditions (C. obtusifolia seed gum dosage = 0.17 g/L, alum dosage = 0.09 g/L, and slow-mixing time = 3.40 min), the combined use of C. obtusifolia seed gum and alum at natural pH of raw PPME (pH 7.2) yielded 89.6 and 55.4% of TSS and COD removals, respectively. Pre-treatment of raw and undiluted PPME using coagulation in the present work established that C. obtusifolia seed gum could be used as an alternative plant-based coagulant or as a potential coagulant aid in pre-treatment of complex industrial effluent. Photoactive Fe₂O₃-TiO₂ was synthesized in the absence of solvent and at ambient conditions using mechanochemical process (via ball milling) for the subsequent photocatalysis of pre-treated PPME. Detailed characterization studies revealed enhanced intrinsic properties of the fabricated Fe₂O₃-TiO₂. The highest photodegradation efficiency of pre-treated PPME (62.3% of COD removal) was achieved using Fe₂O₃-TiO₂ synthesized at 20 min of milling time, 250 rpm of milling speed, and 1 mol% of Fe₂O₃ loading. Then, the interactive influences of photocatalytic operating conditions and reusability of Fe₂O₃-TiO₂ were investigated. Under optimal photocatalytic conditions (initial effluent pH = 3.88, Fe₂O₃-TiO₂ dosage = 1.3 g/L, and air flow-rate = 2.28 L/min), 80.6% of COD was removed from pre-treated PPME using Fe₂O₃-TiO₂. The present study established that the mechanochemical process enabled a greener and facile synthesis of a highly photoactive, recyclable and retrievable Fe₂O₃-TiO₂ that could effectively degrade industrial PPME. Lastly, this research concluded that the studied integrated treatment system of raw PPME (using coagulation process and heterogeneous photocatalysis) achieved an overall treatment efficiency of 89.6 and 91.6% TSS and COD removals, respectively. This study has successfully demonstrated an effective and environmentally more sustainable integrated treatment system to degrade raw PPME.