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As one of the main pollution sources in Hong Kong, the textile dyeing and finishing industry creates a significant proportion of water pollution in nearby harbour zones. Generally speaking, conventional biological treatment processes have difficulties in degrading many dye chemicals causing high COD and colour in dyeing wastwaters. Studies using physical and chemical processes to further reduce COD and colour from dyeing wastewater have been intensively reported. The use of a photocatalytic process in the presence of TiO2 to degrade many different types of dye chemicals has been confirmed. However, how to efficiently separate and reuse TiO2 from treated wastewater became a notable problem in the application of a TiO2 photo-oxidation process. This study aims to develop an advanced treatment process for dyeing wastewater treatment. In which dyeing wastewater was initially treated by an Intermittently Decanted Extended Aeration (IDEA) reactor to initially remove those biodegradable matters and further treated by a TiO2 photocatalytic reactor as advanced treatment for complete decolorization and high COD removal. Suspended TiO2 powder used in photooxidation was separated from slurry by a membrane filter and recycled to the photoreactor continuously. The results demonstrated that photocatalytic-oxidation process could degrade those non-biodegradable organic substances in the effluent treated by the biological treatment process and also remove the colour from the effluent completely. TiO2, as catalyst, was successfully recovered by a membrane filter and continuously reused in the photoreactor. The quality of dyeing wastewater treated by the advanced treatment process can be good enough for reuse in the textile dyeing processes.

Magnetite-immobilized cells of Pseudomonas putida 5-X can be used as biosorbent in copper removal from aqueous solutions. Dilute HCl pretreated magnetite-immobilized cells of Pseudomonas putida 5-X were used in this study for the treatment of wastewater streams containing copper (II) concentrations as high as 100 mg/L. The biosorbent removal and recovery operations were carried out using a series of three batch type biosorption reactors. It was observed that the dilute HCl pretreated magnetite-immobilized cells of Pseudomonas putida 5-X had higher biosorption capacity than that observed on the fresh cells of magnetite-immobilized cells of Pseudomonas putida 5-X. The removal and recovery rates of biosorbent were 96% and 95%, respectively. The process was reversible. The concentrations of copper ion (II) in the recovery solution could be as high as 1.4 g/L and could be successfully recovered using 0.6 N HCl.

Synthetic dyeing wastewater consisting of the three different commercial dyes with different strengths of COD (about 900 and 3000 mg/l respectively) was initially treated by an aerobic biological process, Intermittently Decanted Extended Aeration reactor (IDEA), for BOD removal, and then continuously treated by a TiO2 sensitised photoreactor for a further COD removal and decolorization. The catalysed photooxidation process can degrade those non-biodegradable organic substances in the effluent treated by the IDEA process and also decolorize the effluent completely. It is also found that some nonbiodegradable organic substances can be converted to biodegradable forms by the sensitized photo-oxidation reaction. A bio-photoreactor system was designed to combine this photocatalytic reactor with the IDEA reactor for the treatment of dyeing wastewater. The performance of this combined bio-photoreactor system with and without recirculation was investigated and compared. The system with recycled water has similar efficiency for decolorization and COD removal to that without recirculation, but has a high capacity to eliminate the effects caused by a shock loading, and also the system can treat dyeing wastewater with a higher organic concentration.

Intermittent decanted aerated reactors (IDARs) were used for biological treatment of eucalypt wood panel industrial wastewater. IDARs in extended aeration mode were effective for removal of 50-80 % of total COD and 90-96 % of total BOD5. Kinetic studies revealed a sludge yield of 0.45 (g biomass/g COD removed) and more effective treatment using a sludge age of greater than 20 days and F/M ratios less than 0.2. Colour increases of greater than 200 % resulted from biological treatment, but the average molecular weight of chromophoric species were reduced.

This study concentrated on the biological treatment and post-ozonation of mature eucalypt kraft bleachery effluents. The objectives were to optimise reduction of priority pollutants such as AOX, chlorate, high molecular weight chromophores and toxicity while maintaining high COD/BOD removals. Biological treatment was adequately modelled with Monod kinetics, using biodegradable COD. Sludge yields were of the order 0.76 g biomass/g BCOD. Treatment was most effective (70% total COD reduction and 95% BOD5 reduction) with sludge ages over 20 days and F/M ratios 0.2-0.3. Biological treatment did not reduce total AOX nor colour but reduced chlorate by 63% in preliminary trials. A fungal isolate, Aspergillus.p2 reduced colour by 54% when supplemented with glucose. Ozonation as a tertiary treatment reduced AOX by 60% and colour decrease followed first-order kinetics with respect to ozone consumption.