4-Nitrophenol is a raw material used by the textile and tannery industries. In this experiment, 18 strains of Bacteria were initially isolated from activated sludge wastewater treatment plant serving these industries in Samut Prakam Province. Strains AS107 and AS217, which are classified as Pseudomonas sp., were then selected for the next step in the experiment. Compared with the other strains, both have a higher capacity to utilize 4-nitrophenol as a carbon and nitrogen source together with other nutrients, which were available in medium. 4- nitrophenol inhibits the growth of strain AS107 in concentration greater than 0.026 mM. While strain AS217 was found to grow on the medium contaminated with 4-nitrophenol in concentration from 0.01 to 0.1 mM without inhibition. Optimal conditions for their growth were pH 7 and 30 °c. Strains AS 107, AS217 and mixed cultures were added to influent from the textile industry. According to monitoring data for a 2 weeks period, the pH of the first, second, third, and control batches declined from above 8 to approximately 7. A reduction in COD was also found to occur. The largest reduction in COD was in the first batch which was able to degrade COD by 92°/o. There was also a reduction in 4-nitrophenol in all of the experiment batches over the 2 week period. However, the level of 4-nitrophenol contamination in the control batch remained constant until day 12, after which it began to decline. In day 14, the last day of the experiment, there was 4-Nitrophenol residue in the control batch measuring 0.005 mM while there was no residue found in the experiment batches on this last day. 4-nitrophenol was eliminated in the experiment batches by strains AS107 and AS217 by day 13. In conclusion, both strains are appropriate for further development in the treatment of industrial wastewater.
