Photocatalytic treatment of toxic organics in wastewater: Toxicity of photodegradation products

Manilal, V. B.; Haridas, Ajit; Alexander, Regi; Surender, G. D.

doi:10.1016/0043-1354(92)90138-t

Cited by 73 publications

(33 citation statements)

References 9 publications

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“…TiO 2 -photocatalysis has been extensively studied for transformation and degradation of a wide variety of toxic organics, including many chlorinated aromatics (Agrios et al, 2003;Choi and Hoffmann, 1997;Stafford et al, 1993Stafford et al, , 1997, and it has been used as a pretreatment in coupled systems for herbicides and chlorophenols (Manilal et al, 1992;Shang et al, 2002), but never in an intimately coupled system.…”

Section: Introductionmentioning

confidence: 99%

Intimate coupling of photocatalysis and biodegradation in a photocatalytic circulating‐bed biofilm reactor

Marsolek¹,

Torres²,

Hausner³

et al. 2008

Biotech & Bioengineering

119

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Coupling advanced oxidative pretreatment with subsequent biodegradation demonstrates potential for treating wastewaters containing biorecalcitrant and inhibitory organic constituents. However, advanced oxidation is indiscriminate, producing a range of products that can be too oxidized, unavailable for biodegradation, or toxic themselves. This problem could be overcome if advanced oxidation and biodegradation occurred together, an orientation called intimate coupling; then, biodegradable organics are removed as they are formed, focusing the chemical oxidant on the non-biodegradable fraction. Intimate coupling has seemed impossible because the conditions of advanced oxidation, for example, hydroxyl radicals and sometimes UV-light, are severely toxic to microorganisms. Here, we demonstrate that a novel photocatalytic circulating-bed biofilm reactor (PCBBR), which utilizes macro-porous carriers to protect biofilm from toxic reactants and UV light, achieves intimate coupling. We demonstrate the viability of the PCBBR system first with UV only and acetate, where the carriers grew biofilm and sustained acetate biodegradation despite continuous UV irradiation. Images obtained by scanning electron microscopy and confocal laser scanning microscopy show bacteria living behind the exposed surface of the cubes. Second, we used slurry-form Degussa P25 TiO2 to initiate photocatalysis of inhibitory 2,4,5-trichlorophenol (TCP) and acetate. With no bacterial carriers, photocatalysis and physical processes removed TCP and COD to 32% and 26% of their influent levels, but addition of biofilm carriers decreased residuals to 2% and 4%, respectively. Biodegradation alone could not remove TCP. Photomicrographs clearly show that biomass originally on the exterior of the carriers was oxidized (charred), but biofilm a short distance within the carriers was protected. Finally, we coated TiO2 directly onto the carrier surface, producing a hybrid photocatalytic-biological carrier. These carriers likewise demonstrated the concept of photocatalytic degradation of TCP coupled with biodegradation of acetate, but continued TCP degradation required augmentation with slurry-form TiO2.

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Section: Introductionmentioning

confidence: 99%

Intimate coupling of photocatalysis and biodegradation in a photocatalytic circulating‐bed biofilm reactor

Marsolek¹,

Torres²,

Hausner³

et al. 2008

Biotech & Bioengineering

119

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“…These methods allow compounds with complex structures to be transformed into simpler and/or less harmful compounds that can be biodegraded more readily by microorganisms. (Manilal et al 1992;Sakthivel et al 2001;Wang et al 2003;Enriquez et al;Reddy et al 2004;Mohanty et al 2005, Marsolek et al 2008. In particular, photocatalytic or photolytic oxidation (together denoted photo(cata)lysis) has been shown to be a good pre-treatment before biodegradation (Balcioglu and Arslan 1998;Li and Zhao 1999;Hu and Wang 1999;Li et al 2005;Suryaman et al 2006;Alinsafi et al 2007).…”

Section: Introductionmentioning

confidence: 97%

Photobiodegradation of phenol with ultraviolet irradiation of new ceramic biofilm carriers

et al. 2010

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Activated sludge acclimated to biodegrade phenol was allowed to attach on and in light porous ceramic carriers and to function as a biofilm in a photolytic circulating-bed bioreactor (PCBBR). Phenol degradation in the PCBBR was investigated following three protocols: photolysis with ultraviolet light alone (P), biodegradation alone (B), and the two mechanisms operating simultaneously (P/B). Phenol was degraded at approximately equal rates by B and P/B, each of which was much faster than the rate by P. Furthermore, phenol was mineralized to a significantly greater extent with P/B than with either P or B. SEM showed that the biofilm survived well inside macropores that presumably shaded the microorganisms from UV irradiation, even though the UV light greatly reduced biofilm on outer surface of the carriers in the P/B experiments. Rapid biodegradation of phenol, enhanced mineralization, and survival of bacteria inside macropores demonstrated that being in a biofilm inside the porous carriers protected the bacteria from UV-light toxicity, allowing intimate coupling of photolysis and biodegradation.

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“…First, it takes a long time for phenols to be fully mineralized by AOPs. Second, the intermediates formed during AOP mineralization of phenol are mostly harmful [17][18][19]. In this study, photolysis and biodegradation were suitably combined as one process for the treatment of recalcitrant wastewater, in which the recalcitrant compounds were degraded effectively [22,23].…”

Section: Introductionmentioning

confidence: 99%

Biofilm coupled with UV irradiation for phenol degradation and change of its community structure

Xia

Yan

Zhu

et al. 2011

Bioprocess Biosyst Eng

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The extensive use of phenol compounds and the inability to remove these compounds during wastewater treatment have resulted in the widespread occurrence of phenols in the natural environment. Phenols have been linked to serious risks to human and environmental health. Hence, the need to develop technologies that can effectively remove phenols from wastewater and source waters is a pressing challenge. In this study, light ceramic particles were immersed in activated sludge acclimated to degrade phenol, and microorganisms were allowed to attach to the particles surface to form biofilm. Then the ceramic particles with biofilm were moved into the photolytic circulating-bed biofilm reactor made of quartz glass, which was used for the degradation of phenol by three protocols: photolysis with UV light alone (P), biodegradation alone (B), and the two mechanisms operating simultaneously (photobiodegradation, P&B). The experimental results indicated that phenol removal rate was quickest by B experiment. However, P&B experiment gave more complete mineralization of phenol than that by other protocols. During P&B experiment, the microorganisms grown on porous ceramic carrier still kept the bioactivity degrading phenol, even under UV light irradiation. However, the dominant members of the bacterial community changed dramatically after the intimately coupled photobiodegradation, according to molecular biological analysis to the biofilm. Whereas Beijerinckia sp. was the dominant strain in the inoculum, it was replaced by Thauera sp. MZ1T that played a main role on degrading phenol during P&B experiment.

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Photocatalytic treatment of toxic organics in wastewater: Toxicity of photodegradation products

Cited by 73 publications

References 9 publications

Intimate coupling of photocatalysis and biodegradation in a photocatalytic circulating‐bed biofilm reactor

Intimate coupling of photocatalysis and biodegradation in a photocatalytic circulating‐bed biofilm reactor

Photobiodegradation of phenol with ultraviolet irradiation of new ceramic biofilm carriers

Biofilm coupled with UV irradiation for phenol degradation and change of its community structure

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