Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination--a review

Optimization of conventional Fenton and ultraviolet-assisted oxidation processes for the treatment of reverse osmosis retentate from a paper mill

According to current environmental legislation concerned with water scarcity, paper industry is being forced to adopt a zero liquid effluent policy. In consequence, reverse osmosis (RO) systems are being assessed as the final step of effluent treatment trains aiming to recover final wastewater and reuse it as process water. One of the most important drawbacks of these treatments is the production of a retentated stream, which is usually highly loaded with biorecalcitrant organic matter and inorganics; and this effluent must meet current legislation stringent constraints before being ultimately disposed. The treatment of biorefractory RO retentate from a paper mill by several promising advanced oxidation processes (AOPs) - conventional Fenton, photo-Fenton and photocatalysis - was optimized considering the effect and interaction of reaction parameters; particularly using response surface methodology (RSM) when appropriate (Fenton processes). The economical cost of these treatments was also comparatively assessed. Photo-Fenton process was able to totally remove the COD of the retentate, and resulted even operatively cheaper at high COD removal levels than conventional Fenton, which achieved an 80% reduction of the COD at best. In addition, although these optimal results were produced at pH=2.8, it was also tested that Fenton processes are able to achieve good COD reduction efficiencies (>60%) without adjusting the initial pH value, provided the natural pH of this wastewater was close to neutral. Finally, although TiO(2)-photocatalysis showed the least efficient and most expensive figures, it improved the biodegradability of the retentate, so its combination with a final biological step almost achieved the total removal of the COD.

Enhanced degradation of azo dye alizarin yellow R in a combined process of iron-carbon microelectrolysis and aerobic bio-contact oxidation

PURPOSE

With the aim of enhanced degradation of azo dye alizarin yellow R (AY) and further removal of the low-strength recalcitrant matter (LsRM) of the secondary effluent as much as possible, our research focused on the combination of aerobic bio-contact oxidation (ABO) with iron/carbon microelectrolysis (ICME) process.

MATERIALS AND METHODS

The combined ABO (with effective volume of 2.4 l) and ICME (with effectively volume of 0.4 l) process were studied with relatively short hydraulic retention time (HRT) of 4 or 6 h.

RESULTS

At the HRT of 6 h with the reflux ratio of 1 and 2, the AY degradation efficiency in the final effluent was >96.5%, and the total organic carbon (TOC) removal efficiency were 69.86% and 79.44%, respectively. At the HRT of 4 h and the reflux ratio of 2, TOC removal efficiency and AY degradation efficiency were 73.94% and 94.89%, respectively. The ICME process obviously enhanced the total AY removal and the generated micromolecule acids and aldehydes then that wastewater backflow to the ABO where they were further biodegraded.

CONCLUSION

The present research might provide the potential options for the advanced treatment azo dyes wastewater with short HRT and acceptable running costs.

Processes for the elimination of estrogenic steroid hormones from water: a review

Natural estrogens such as estrone (E1), 17β-estradiol (E2), estriol (E3), and the synthetic one, 17α-ethinylestradiol (EE2), are excreted by humans and animals and enter into environment through discharge of domestic sewage effluents and disposal of animal waste. The occurrence of these substances in aquatic ecosystems may affect the endocrine system of humans and wildlife so it has emerged as a major concern for water quality. Extensive research has being carried out during the last decades on the efficiency of the degradation and/or removal of these hormones in sewage treatment plants (STPs). Conventional and advanced treatments have been investigated by different authors for the elimination of estrogens from water. This paper aims to review the different processes and treatments that have been applied for the elimination of E1, E2, E3 and EE2 from water. With this purpose, physical, biological and advanced oxidation processes (AOP) have been addressed.

Evaluation of three reagent dosing strategies in a photo-Fenton process for the decolorization of azo dye mixtures

Three reagent dosing strategies used in the solar photo-assisted decolorization of a mixture of sulfonated dyes consisting of acid blue 113, acid orange 7 and acid red 151 were evaluated. Results demonstrated that the dosing strategy influenced both reagent consumption and the biodegradability and toxicity of the effluent. In one strategy (E(1)), the Fenton's reactants were dosed in a punctual mode, while in the other two strategies (E(2) an E(3)), the reactants were dosed continuously. In the E(2) strategy the reactants were dosed by varying the duration of the injection time. In the E(3) strategy, the reactants were dosed during 60 min at a constant rate, but with different concentrations. All cases showed that feeding the reactor between 40% and 60% of the maximal dose was sufficient to decolorize more than 90% of the mixture of azo dyes. The E(1) strategy was less effective for aromatic content reduction. Conversely, the continuous addition of the reagents (E(2) and E(3) strategies) improved the aromatic content removal. E(3) strategy was substantially more appropriate than E(1) strategy due to improved the effluent quality in two key areas: toxicity and biodegradability.

Formation of chlorinated by-products during photo-Fenton degradation of pyrimethanil under saline conditions. Influence on toxicity and biodegradability

This study evaluated the formation of chlorinated transformation products during photo-Fenton treatment of pyrimethanil (PYR-20 mg L(-1)) in two water matrices, demineralised water (DW) and water containing 5 g L(-1) of NaCl (DW(NaCl)). All experiments were carried out in compound parabolic collectors (CPC) at an initial Fe(2+) concentration of 5 mg L(-1) and H(2)O(2) concentration of 150-350 mg L(-1). Dissolved Organic Carbon (DOC), High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD), Liquid Chromatography-Time-Of-Flight Mass Spectrometry (LC-TOF-MS), toxicity and biodegradability tests were conducted to control the photocatalytic treatment. In DW, PYR was completely eliminated after 11.8 min of illumination and initial DOC was reduced 50% after 79 min of illumination with 33 mM of H(2)O(2) consumed. On the other hand, in DW(NaCl) water matrix, the same reduction in DOC took 110 min of illumination and H(2)O(2) consumption of 39 mM, and total degradation of PYR was observed at 12 min of illumination. PYR transformation products (TPs) were identified by LC-TOF-MS. It was demonstrated that photo-Fenton in a DW(NaCl) produces some chlorinated TPs in addition to the non-chlorinated TPs identified during degradation in the DW. All TPs formed were eliminated during photo-Fenton. Additionally, the presence of chlorinated TPs does not increase the toxicity of the water, and TPs formed are more biodegradable than PYR.

Use of iron oxide nanomaterials in wastewater treatment: a review

Nowadays there is a continuously increasing worldwide concern for the development of wastewater treatment technologies. The utilization of iron oxide nanomaterials has received much attention due to their unique properties, such as extremely small size, high surface-area-to-volume ratio, surface modifiability, excellent magnetic properties and great biocompatibility. A range of environmental clean-up technologies have been proposed in wastewater treatment which applied iron oxide nanomaterials as nanosorbents and photocatalysts. Moreover, iron oxide based immobilization technology for enhanced removal efficiency tends to be an innovative research point. This review outlined the latest applications of iron oxide nanomaterials in wastewater treatment, and gaps which limited their large-scale field applications. The outlook for potential applications and further challenges, as well as the likely fate of nanomaterials discharged to the environment were discussed.

Degradation of 32 emergent contaminants by UV and neutral photo-fenton in domestic wastewater effluent previously treated by activated sludge

This study focuses on the removal of 32 selected micropollutants (pharmaceuticals, corrosion inhibitors and biocides/pesticides) found in an effluent coming from a municipal wastewater treatment plant (MWTP) based on activated sludge. Dissolved organic matter was present, with an initial total organic carbon of 15.9 mg L(-1), and a real global quantity of micropollutants of 29.5 μg L(-1). The treatments tested on the micropollutants removal were: UV-light emitting at 254 nm (UV(254)) alone, dark Fenton (Fe(2+,3+)/H(2)O(2)) and photo-Fenton (Fe(2+,3+)/H(2)O(2)/light). Different irradiation sources were used for the photo-Fenton experiences: UV(254) and simulated sunlight. Iron and H(2)O(2) concentrations were also changed in photo-Fenton experiences in order to evaluate its influence on the degradation. All the experiments were developed at natural pH, near neutral. Photo-Fenton treatments employing UV(254), 50 mg L(-1) of H(2)O(2), with and without adding iron (5 mg L(-1) of Fe(2+) added or 1.48 mg L(-1) of total iron already present) gave the best results. Global percentages of micropollutants removal achieved were 98 and a 97% respectively, after 30 min of treatments. As the H(2)O(2) concentration increased (10, 25 and 50 mg L(-1)), best degradations were observed. UV(254), Fenton, and photo-Fenton under simulated sunlight gave less promising results with lower percentages of removal. The highlight of this paper is to point out the possibility of the micropollutants degradation in spite the presence of DOM in much higher concentrations.

Biodegradation of phytosanitary products in biological wastewater treatment

Agricultural activity generates two types of waste: firstly, biodegradable organic effluents generally treated by biological processes and, secondly, phytosanitary effluents which contain residues of plant protection products. The latter are collected and treated. Current technological solutions are essentially based on concentration or physical-chemical processes. However, recent improvements in the biodegradability of pesticides open the way to the consideration of alternative, biological, treatment using mixed liquor from wastewater plant activated sludge. The feasibility of the biological treatment of viticultural effluents has been evaluated by the application of pesticides to activated sludge. The necessity for selection of a pesticide-resistant biomass has been highlighted. The elimination of the phytosanitary products shows the potential of a resistant biomass in the treatment of pesticides. The aerated biological storage ponds at three wineries, followed by a sand or reed-bed filter, were used for the treatment of the total annual volume of the viticulture effluents and validate the laboratory experiments. The results show that the biological purification of pesticides by activated sludge is possible by allowing approximately 8 days for biomass adaptation. Stability of purification occurs between 20 and 30 days.

Mechanisms of removing pollutants from aqueous solutions by microorganisms and their aggregates: a review

With the public's enhanced awareness of eco-safety, environmentally benign measures based on microorganisms and microbial aggregates have become more accepted as methods of removing pollutants from aquatic systems. In this review, the application of microorganisms and microbial aggregates for removing pollutants from aqueous solutions is introduced and described based on mechanisms such as assimilation, adsorption, and biodegradation. The advantages of and future studies regarding the use of microorganisms and microbial aggregates to remove pollutants are discussed. Due to the limitation of a single microorganism species in adapting to heterogeneous conditions, this review demonstrates that the application of microbial aggregates consisting of multiple photoautotrophic and heterotrophic microorganisms, is a promising method of removing multiple pollutants from complex wastewaters and warrants further research.

Removal of nalidixic acid and its degradation products by an integrated MBR-ozonation system

Chemical-biological degradation of a widely spread antibacterial (nalidixic acid) was successfully obtained by an integrated membrane bioreactor (MBR)-ozonation process. The composition of the treated solution simulated the wastewater from the production of the target pharmaceutical, featuring high salinity and a relevant concentration of sodium acetate. Aim of treatment integration was to exploit the synergistic effects of chemical oxidation and bioprocesses, by adopting the latter to remove most of the COD and the ozonation biodegradable products. Integration was achieved by placing ozonation in the recirculation stream of the bioreactor effluent. The recirculation flow rate was three-fold the MBR feed, and the performance of the integrated system was compared to the standard polishing configuration (single ozonation step after the MBR). Results showed that the introduction of the ozonation step did not cause relevant drawbacks to both biological and filtration processes. nalidixic acid passed undegraded through the MBR and was completely removed in the ozonation step. Complete degradation of most of the detected ozonation products was better achieved with the integrated MBR-ozonation process than using the sequential treatment configuration, i.e. ozone polishing after MBR, given the same ozone dosage.

Removal of organics and degradation products from industrial wastewater by a membrane bioreactor integrated with ozone or UV/H₂O₂ treatment

The treatment of a pharmaceutical wastewater resulting from the production of an antibacterial drug (nalidixic acid) was investigated employing a membrane bioreactor (MBR) integrated with either ozonation or UV/H(2)O(2) process. This was achieved by placing chemical oxidation in the recirculation stream of the MBR. A conventional configuration with chemical oxidation as polishing for the MBR effluent was also tested as a reference. The synergistic effect of MBR when integrated with chemical oxidation was assessed by monitoring (i) the main wastewater characteristics, (ii) the concentration of nalidixic acid, (iii) the 48 organics identified in the raw wastewater and (iv) the 55 degradation products identified during wastewater treatment. Results showed that MBR integration with ozonation or UV/H(2)O(2) did not cause relevant drawbacks to both biological and filtration processes, with COD removal rates in the range 85-95%. Nalidixic acid passed undegraded through the MBR and was completely removed in the chemical oxidation step. Although the polishing configuration appeared to give better performances than the integrated system in removing 15 out of 48 secondary organics while similar removals were obtained for 19 other compounds. The benefit of the integrated system was however evident for the removal of the degradation products. Indeed, the integrated system allowed higher removals for 34 out of 55 degradation products while for only 4 compounds the polishing configuration gave better performance. Overall, results showed the effectiveness of the integrated treatment with both ozone and UV/H(2)O(2).

An integrated MBR-TiO2 photocatalysis process for the removal of Carbamazepine from simulated pharmaceutical industrial effluent

This paper aims to demonstrate that integrating biological process and photocatalytic oxidation in a system operated in recycling mode can be a promising technology to treat pharmaceutical wastewater characterized by simultaneous presence of biodegradable and refractory/inhibitory compounds. A lab-scale system integrating a membrane bioreactor (MBR) and a TiO(2) slurry photoreactor was fed on simulated wastewater containing 10mg/L of the refractory drug Carbamazepine (CBZ). Majority of chemical oxygen demand (COD) was removed by the MBR, while the photocatalytic oxidation was capable to degrade CBZ. CBZ degradation kinetics and its impacts on the biological process were studied. The adoption of a recycling ratio of 4:1 resulted in removal of up to 95% of CBZ. Effluent COD reduction, sludge yield increase and respirometric tests suggested that the oxidation products were mostly biodegradable and not inhibiting the microbial activity. These results evidenced the advantages of the proposed approach for treating pharmaceutical wastewater and similar industrial effluents.