Microbial degradation of textile dyes to safe end-products

Gottlieb, A.L., 2003. Microbial degradation of textile dyes to safe end-products. PhD, Nottingham Trent University.

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Discharges from textile dyehouses often include large amounts of reactive azo dyes. These are recalcitrant to conventional wastewater treatment processes thus resulting in coloured waterways. Azo dyes can be decolourised biologically in bioreactors via fission of the azo (-N=N-) bonds to produce aromatic amines, but these are known to be toxic and/or genotoxic. This investigation concentrates on the toxicity and genotoxicity produced by decolourisation of a simulated textile effluent (STE) containing the reactive azo dye C.I. Reactive Black 5 in its hydrolysed form (RBOH). Two bioreactors were used, a batch-fill type Sequencing Batch Reactor (SBR) and continuous flow type Hybrid Anaerobic Baffled Reactor (HABR), operated under both anaerobic and anaerobic-aerobic conditions. The microflora of each bioreactor was studied in order to elucidate the interrelations between toxicity and/or genotoxicity, decolourisation efficacy and the microbial population.

Initially, the rapid bacterial toxicity and genotoxicity assays chosen were validated for their suitability before applying them to assessment of the SBR and HABR. High levels of decolourisation were observed in both bioreactors under all conditions (86-94%). Under anaerobic conditions, high levels of toxicity were observed in both bioreactors (EC50 values 0.24-0.46% of original concentration), whilst the toxicity was only significantly decreased (EC50 16.89-17.80%) after anaerobic-aerobic operation in the HABR due to mineralisation of aromatic amines. No significant genotoxicity was observed.

Microflora numbers and composition were assessed using Fluorescent in situ Hybridisation (FISH) and Denaturing Gradient Gel Electrophoresis (DGGE). It was concluded that both the SBR and HABR operated under anaerobic conditions could support a relatively diverse, thriving, stable bacterial and archaeal population, but that increasing bacterial diversity was encouraged by the compartmentalisation of the HABR. Operation under anaerobic-aerobic conditions showed greatest divergence and appearance of unique species adapted to the aerobic environment in the HABR, due to the different conditions that could be provided by a compartmentalised bioreactor. The predominant species identified by culturing and sequencing under both anaerobic and anaerobic-aerobic conditions were Clostridium and Bacteroides spp. in the SBR and Staphylococcus and Bacteroides spp. in the HABR. The archaeal population of the SBR was predominated by Methanosaeta sp. under anaerobic-aerobic conditions, and Actinomadura sp. was only observed in aerated samples. Several bacterial species were found to be unique to the aerobic sections of the HABR, and some were identified Nocardia and Rhodococcus spp.

Item Type: Thesis
Description: This research programme was funded by the EPSRC and carried out in conjunction with Loughborough University of Technology.
Creators: Gottlieb, A.L.
Date: 2003
ISBN: 9781369314861
Divisions: Schools > School of Science and Technology
Record created by: Linda Sullivan
Date Added: 30 Nov 2020 14:05
Last Modified: 03 Aug 2023 11:19
URI: https://irep.ntu.ac.uk/id/eprint/41711

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