Enhancement of wastewater treatment with microbial formation of poly (beta-hydroxyalkanoates) from activated sludges

Polyhydroxyalkanoates (PHAs) and related co-polymers have been discovered and emerged as environmentally-friendly materials. However, the microbial PHA production cost is too high at present, thus hampering the development of its manufacturing processes and widespread applications. It is know that bacteria indigenous to activated sludge can accumulate large quantities of PHA under environmentally controlled conditions. The main aim of this research project is to investigate the behaviour of the microorganism community from different activated sludge, capable of accumulating PHA by using real wastewater and removing pollutant in wastewater so as to offer a potentially more environmentally-effective method of PHA production.;The isolated biomasses from 9 Hong Kong activated sludge were further identified as Pseudomonas huttiensis, Bacillus cereus , Pseudomonas putida, Bacillus pumilus, Bacillus pumilus, Sphingopyxis terrae, Aeromonas ichthiosmia and Yersinia frederiksenii.;Sphingopyxis terrae and Aeromonas ichthiosmia accumulated more than 30% PHB as intracellular content under shake flask experiments.;SBR application showed that the feeding influent of real wastewater supported the growth of the identified PHA biomasses. Mono strains of Bacillus pumilus, Pseudomonas putida and Sphingopyxis terrae had better pollutant removal efficiency than other biomasses. With increasing the influence concentrations would increase the system stabilization time of bacteria to achieve over 90% pollutant removal and also affecting the PHA accumulation capabilities. Aeromonas ichthiosmia achieved the highest PHA accumulation with about 22% PHB and about 8% PHV achieved when influent concentration of 6,500ppm COD applied. There was a PHA production inhibition phenomenon found in all identified bacteria when 12,000ppm COD applied.;Mixed strains of Pseudomonas huttiensis & Bacillus pumilus and Pseudomonas huttiensis & Sphingopyxis terrae achieved 2 days less treatment time than the mono strain to achieve over 90% pollutant removal for the influent concentration ranging from 6,000ppm to 12,000ppm COD. The highest PHB production enhancement was found by mixing Pseudomonas putida with Yersinia frederiksenii. More than 130% PHB accumulation enhancement achieved by these 2 mixed strains. PHA accumulation inhibition also found when 15,000ppm influent COD was applied. The results showed that mixed strains could perform enhancement of pollutant removal and PHA accumulation under a higher organic loading environment than mono strain did.