An analysis of the bacterial community in a membrane bioreactor fed with photo-Fenton pre-treated toxic water

Application of Photo-Fenton-Membrane Technology in Wastewater Treatment: A Review

Photo-Fenton coupled with membrane (photo-Fenton-membrane) technology offers great potential benefits in future wastewater treatment because it can not only degrade refractory organics, but also separate different pollutants from water; additionally, it often has a membrane-self-cleaning ability. In this review, three key factors of photo-Fenton-membrane technology, photo-Fenton catalysts, membrane materials and reactor configuration, are presented. Fe-based photo-Fenton catalysts include zero-valent iron, iron oxides, Fe-metal oxides composites and Fe-based metal-organic frameworks. Non-Fe-based photo-Fenton catalysts are related to other metallic compounds and carbon-based materials. Polymeric and ceramic membranes used in photo-Fenton-membrane technology are discussed. Additionally, two kinds of reactor configurations, immobilized reactor and suspension reactor, are introduced. Moreover, we summarize the applications of photo-Fenton-membrane technology in wastewater, such as separation and degradation of pollutants, removal of Cr(VI) and disinfection. In the last section, the future prospects of photo-Fenton-membrane technology are discussed.

Advanced membrane bioreactors systems: New materials and hybrid process design

Membrane bioreactor (MBR) is deemed as one of the most powerful technologies for efficient municipal and industrial wastewater treatment around the world. However, low microbial activity of activated sludge and serious membrane fouling still remain big challenges in worldwide application of MBR technology. Nowadays, more and more progresses on the research and development of advanced MBR with new materials and hybrid process are just on the way. In this paper, an overview on the perspective of high efficient strains applied into MBR for biological activity enhancement and fouling reduction is provided first. Secondly, as emerging fouling control strategy, design and fabrication of novel anti-fouling composited membranes are comprehensively highlighted. Meanwhile, hybrid MBR systems integrated with some novel dynamic membrane modules and/or with other technologies like advanced oxidation processes (AOPs) are introduced and compared. Finally, the challenges and opportunities of advanced MBRs combined with bioenergy production in wastewater treatment are discussed.

Impact of selected non-steroidal anti-inflammatory pharmaceuticals on microbial community assembly and activity in sequencing batch reactors

This study covers three widely detected non-steroidal anti-inflammatory pharmaceuticals (NSAIDs), diclofenac (DCF), ibuprofen (IBP) and naproxen (NPX), as NSAIDs pollutants. The objective is to evaluate the impact of NSAIDs at their environmental concentrations on microbial community assembly and activity. The exposure experiments were conducted under three conditions (5 μg L^-1 DCF, 5 μg L^-1 DCF+5 μg L^-1 IBP and 5 μg L^-1 DCF+5 μg L^-1 IBP+ 5 μg L^-1 NPX) in sequencing batch reactors (SBRs) for 130 days. Removals of COD and NH₄⁺-N were not affected but total nitrogen (TN) removal decreased. IBP and NPX had the high removal efficiencies (79.96% to 85.64%), whereas DCF was more persistent (57.24% to 64.12%). In addition, the decreased removals of TN remained the same under the three conditions (p > 0.05). The results of oxidizing enzyme activities, live cell percentages and extracellular polymeric substances (EPS) indicated that NSAIDs damaged the cell walls or microorganisms and the mixtures of the three NSAIDs increased the toxicity. The increased Shannon-Wiener diversity index suggested that bacterial diversity was increased with the addition of selected NSAIDs. Bacterial ribosomal RNA small subunit (16S) gene sequencing results indicated that Actinobacteria and Bacteroidetes were enriched, while Micropruina and Nakamurella decreased with the addition of NSAIDs. The enrichment of Actinobacteria and Bacteroidetes indicated that both of them might have the ability to degrade NSAIDs and thereby could adapt well with the presence of NSAIDs.

Effect of substrate characteristics on microbial community structure, function, resistance, and resilience; application to coupled photocatalytic-biological treatment

Advanced oxidation (AO) coupled with biodegradation is an emerging treatment technology for wastewaters containing biologically recalcitrant and inhibitory organics, including those containing chlorinated aromatic compounds. The composition of the AO effluent organics can vary significantly with reaction conditions, and this composition can affect the performance of subsequent biodegradation. Three synthetic effluents were used to mimic varying degrees of AO of 2,4,5-trichlorophenol: 4-chlorocatechol to mimic light transformation, 2-chloromuconic acid to mimic moderate transformation, and acetate to mimic extensive transformation. The substrates were fed to identical chemostats and analyzed at steady state for removal of chemical oxygen demand (COD) and dissolved organic carbon (DOC), biomass concentration, and bacterial diversity. The chemostat fed acetate performed best at steady state. The 2-chloromuconic acid chemostat was next in terms of steady-state performance, and the 4-chlorocatechol reactor performed worst, correlating with degree of AO transformation. A spike of 100 μM 2,4,5-trichlorophenol was then applied to each chemostat. The chemostat fed 4-chlorocatechol exhibited the best resistance to the perturbation in terms of maintaining consistent community structure and biomass concentration, whereas the performance of the acetate-fed chemostat was severely impaired in these categories, although it quickly regained capacity to remove organics near pre-perturbation levels demonstrating good resilience. The opposing trends for steady-state versus perturbed performance highlight tradeoffs inherent in coupled chemical-biological systems.

Coupled photocatalytic-biodegradation of 2,4,5-trichlorophenol: effects of photolytic and photocatalytic effluent composition on bioreactor process performance, community diversity, and resistance and resilience to perturbation

Sequentially coupled advanced oxidation-biodegradation systems have proven effective for treating a variety of wastewaters, but in several cases the pretreatment did not improve, or even hindered, subsequent biodegradation. Therefore, investigating the relationship between advanced oxidation pretreated effluent and subsequent bioreactor performance can help to optimize these systems. Here, a photocatalytic reactor was used to produce four unique effluents from 2,4,5-trichlorophenol (TCP) by varying light wavelength, catalyst presence, and reaction time, demonstrating that the conditions of photocatalytic pretreatment can be tuned to achieve a variety of treatment objectives. The photocatalytic effluents were characterized for chemical oxygen demand (COD), chloride release, aromaticity, and residual TCP concentration. The four effluents were normalized to 40 mg COD/L, combined with biological medium components, and fed to continuous bioreactors. Bioreactors were assayed for COD removal, TCP removal, optical density (OD), and microbial diversity via denaturing gradient gel electrophoresis. In general COD removal in the bioreactors increased as aromatic character of the photoeffluent decreased, but the least aromatic effluent performed poorly indicating the nuanced relationship between photoreactor effluent composition and bioreactor performance. While neither indicator of community diversity, richness nor evenness, correlated with COD removal or biomass accumulation, each effluent produced a unique community as indicated through similarity indices. All conditions demonstrated strong overall TCP removal. After two weeks at steady state, the reactors were perturbed with a 120-μM spike of TCP. Overall the most aromatic photoeffluent produced the most resistant community to the perturbation, while the optimum effluents at steady state produced communities with poor resistance in terms of biomass accumulation and COD removal. These results highlight the tradeoffs between steady state performance and resistance to perturbation that are necessary to optimize a combined advanced oxidation-biodegradation treatment strategy.