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Hybrid-hollow-fiber membrane bioreactors were developed for the enhanced cometabolic biotransformation of phenol and 4-chlorophenol (4-cp) by Pseudomonas putida ATCC49451. Bioreactor performance was investigated, compared, and analyzed under batch and continuous operating modes. The spinning solutions contained polysulfone (PS), N-methyl-2-pyrrolidone, and various weight ratios of granular activated carbon (GAC) (GAC: PS of 0, 1:4, and 1:2). The bioreactor fabricated with 1:2 GAC hybrid-hollow-fiber membranes demonstrated the best performance for the removal of phenol and 4-cp, both under batch and continuous operations. Under batch operation, 500 mg [L.sup.-1] phenol and 4-cp were completely removed within 23 h in the bioreactor, compared with 26 and 30 h for the 1:4 GAC and GAC free bioreactors. Sorption, biotransformation, desorption, and bioregeneration were identified as the four steps for substrate removal during batch operation. The 1:2 GAC hollow-fiber membrane bioreactor also manifested superiority over the other two during continuous operation for start up and the transient phase after shock loadings of the feed. 300 mg [L.sup.-1] phenol and 4-cp were completely removed in the 1:2 GAC hybrid-hollow-fiber membrane bioreactor whereas 4-cp was not completely removed in the other two bioreactors at a feed rate of 30 mLh [h.sup.-1]. From the experimental results, it was inferred that at steady state, biotransformation was achieved through the dynamic equilibrium among sorption, desorption, and biotransformation rates established within the bioreactors. DOI: 10.1061/(ASCE)0733-9372(2007)133:4(404) CE Database subject headings: Hybrid method; Reactors; Transformations: Biological treatment; Phenol.

An immobilized cell hollow fiber membrane bioreactor was operated continuously for the cometabolic transformation of 4-cp in the presence of phenol. In contrast to the batch operation of the bioreactor in which the immobilized cells were exposed to decreasing substrate concentrations, at high substrate concentrations, under continuous operation, dissolved oxygen was found to be a limiting nutrient. It was found that substrate degradation was enhanced by aerating the feed with pure oxygen. It was also found that the optimum number of hollow fibers in the bioreactor was 25, ca. 30% bioreactor volume. This occurred due to a balance of the pore space available for cell immobilization in the fibers against the extracapillary space available for suspension cell growth. During continuous operation, regardless of feed rate (21-60 mL x [h.sup.-1]), the maximum substrate loading was found to be 9 x [h.sup.-1] each of phenol and 4-cp in order that both substrates were completely transformed. In anticipation of reduced provision of phenol as a specific growth substrate for 4-cp cometabolic transformation, it was concluded that complete transformation of 4-cp could be effected through a minimum substrate concentration ratio of phenol:4-cp of 1:1.8. DOI: 10.1061/(ASCE)0733-9372(2006)132:3(309) CE Database subject headings: Biodegradation; Membranes; Biological treatment: Phenol.

The cometabolic transformation of high concentrations of 4-chlorophenol (4-cp) in the presence of phenol (growth substrate) was investigated in an immobilized cell hollow fiber membrane bioreactor. The biotransformation rates of 4-cp and phenol by free cells and immobilized cells were compared and it was found that biotransformation by immobilized cells was more efficient than that by freely suspended cells, especially at high substrate concentrations. Even when the initial substrate concentrations were both 1,000 mg [L.sup.-1], the substrates could still be transformed completely within 45 h in the hollow fiber membrane bioreactor. It was found that removal rates of the substrates were dependent not only on absolute substrate concentration, but also on the concentration ratios of 4-cp to phenol. With increased concentration ratios, phenol depletion rate decreased while 4-cp depletion rate increased. This was attributed to increased competitiveness of 4-cp in the competitive inhibition with phenol since the membranes had relatively better sorption for 4-cp over phenol. The bioreactor was operated batchwise for 18 times to investigate the feasibility of the bioreactor for long term operation. It was found that there was no significant decrease in the bioactivity, which demonstrates a potential for continuous operation. CE Database subject headings: Biodegradation; Biological treatment; Batch processing; Phenol; Membranes.

A characterization study on synthetic wastewaters containing various commercially available ink-jet inks was conducted. Analysis of this resulted in the identification of seven high-risk noncompliance parameters, namely, chemical oxygen demand (COD), biochemical oxygen demand at 5 days (BO[D.sub.5]), total dissolved solids (TDS), phenols, copper, iron, and sulphate concentrations. Of these, COD reduction was found to be the most stringent treatment criterion based on the industry-accepted standard Fenton's oxidation reaction for treatment. TDS and COD were also proposed as critical parameters for the initial assessment of the quality of untreated ink effluents. To provide for rapid and robust indications of the TDS and COD of the untreated ink effluents, a correlation for TDS as a function of conductivity and turbidity was obtained. Furthermore, a deterministic approach based on Beer's law of absorbance additivity was developed for determining COD of mixtures of ink effluents using absorbance measurements at 210, 436, 525, and 620 nm. These were validated successfully against experimental data. Based on an in-depth analysis of the compositions of ink effluents, a list of simple and rapid on-site water quality parameters was proposed for monitoring the quality of the treated ink wastewater. This consisted of measurements of UV-absorbance at 210 nm, conductivity, pH, turbidity, and color. Based on the discharge limits imposed by a particular country, one can then develop a range of values for these quality parameters in order to meet the discharge regulations of that country. The Singapore context was used as a case study to illustrate this approach. In addition, it was found that the copper content in the cyan ink effluents was substantially reduced by more than 96% along with the standard Fenton's reaction. Through the course of investigating the Fenton's oxidation reaction, it was found that measurements of oxidation-reduction potential and/or temperature are suitable indicators of the progress of the reaction. CE Database subject headings: Wastewater treatment; Effluents; Oxidation; Oxygen demand; Parameters; Assessment.