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

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.     

Catalase activity in human erythrocytes: effect of phenoxyherbicides and their metabolites

The effects of exposure to different concentrations of phenoxyherbicides and their metabolites were studied in human erythrocytes, with particular attention to catalase (CAT-EC. 1.11.1. 6- hydrogen peroxide: hydrogen peroxide oxidoreductase). 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dimethylphenol (2, 4-DMP) and 2,4-dichlorophenoxyacetic acid (2,4-D) did not affect CAT activity, but 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) decrease its activity, the latter being the more inhibitory.     

Novel fluorescent sensor using molecularly imprinted silica microsphere‐coated CdSe@CdS quantum dots and its application in the detection of 2,4,6‐trichlorophenol from environmental water samples

In this study, a high fluorescence sensitivity and selectivity, molecularly imprinted nanofluorescent polymer sensor (MIP@SiO₂@QDs) was prepared using a reverse microemulsion method. 2,4,6‐Trichlorophenol (2,4,6‐TCP) was detected using fluorescence quenching. Tetraethyl orthosilicate (TEOS), quantum dots (QDs) and 3‐aminopropyltriethoxysilane (APTS) were used as cross‐linker, signal sources and functional monomer respectively. The sensor (MIP@SiO₂@QDs) and the non‐imprinted polymer sensor (NIP@SiO₂@QDs) were characterized using infra‐red (IR) analysis, X‐ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The selectivity of MIP@SiO₂@QDs was examined by comparing 2,4,6‐TCP with other similar functional substances including 2,4‐dichlorophenol (2,4‐DCP), 2,6‐dichlorophenol (2,6‐DCP) and 4‐chlorophenol (4‐CP). Results showed that MIP@SiO₂@QDs had better selectivity for 2,4,6‐TCP than the other compounds. Fluorescence quenching efficiency displayed a good linear response at the 2,4,6‐TCP concentration range 5–1000 μmol/L. The limit of detection (LOD) was 0.9 μmol/L (3σ, n = 9). This method was equally applicable for testing actual samples with a recovery rate of 98.0–105.8%. The sensor had advantages of simple pretreatment, good sensitivity and selectivity, and wide linear range and could be applied for the rapid detection of 2,4,6‐TCP in actual samples.     

Toxicants inhibiting anaerobic digestion: A review

Anaerobic digestion is increasingly being used to treat wastes from many sources because of its manifold advantages over aerobic treatment, e.g. low sludge production and low energy requirements. However, anaerobic digestion is sensitive to toxicants, and a wide range of compounds can inhibit the process and cause upset or failure. Substantial research has been carried out over the years to identify specific inhibitors/toxicants, and their mechanism of toxicity in anaerobic digestion. In this review we present a detailed and critical summary of research on the inhibition of anaerobic processes by specific organic toxicants (e.g., chlorophenols, halogenated aliphatics and long chain fatty acids), inorganic toxicants (e.g., ammonia, sulfide and heavy metals) and in particular, nanomaterials, focusing on the mechanism of their inhibition/toxicity. A better understanding of the fundamental mechanisms behind inhibition/toxicity will enhance the wider application of anaerobic digestion.