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

Abstract

Conventional plastics are inherently non-biodegradable and are posing a serious threat to our environment. Polyhydroxyalkanoates (PHAs) and related co-polymers have been discovered and emerged as environmentally-friendly materials. A wide variety of microorganisms can synthesize an optically active polymer of D(-)-3-hydroxybutyric acid as intracellular carbon and energy sources under certain specific production conditions. However, the 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 microbial communities of 9 activated sludge from different industries in Hong Kong were investigated to confirm their feasibility of PHA accumulation. R2A agar successfully screened out PHA biomasses in the activated sludges. The biomasses were then identified as Pseudomonas huttiensis, Bacillus cereus, Pseudomonas putida, Bacillus pumilus, Bacillus pumilus, Sphingopyxis terrae, Aeromonas ichthiosmia and Yersinia frederiksenii. Accord to the community study with shake flask experiments, Sphingopyxis terrae and Aeromonas ichthiosmia accumulated more than 30% PHB as intracellular content. Bacillus pumilus could accumulate up to 20% PHV as cellular content. 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 BOD and COD removal efficiency than other biomasses. Results showed that increasing the influence concentrations would increase the system stabilization time of bacteria to achieve over 90% COD, BOD and KN removal and also affecting the PHA accumulation capabilities. Aeromonas ichthiosmia achieved the highest PHA accumulation. The bacteria accumulated more than 22% PHB and more than 8% PHV of intracellular content when influent concentration of 6,500ppm COD applied. Although increasing of organic loading resulted in higher PHA yield, there was an 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 stabilize the system in achieving over 90% COD, BOD and KN removal for the influent concentration ranging from 6,000ppm to 12,000ppm COD. The results suggested that highest PHB production enhancement found by mixing Pseudomonas putida with Yersinia frederiksenii. A maximum yield of 25% PHB of intracellular contents was produced by mixing these 2 bacteria. It reflected more than 130% PHB accumulation enhancement achieved by mixed strains of Pseudomonas putida & Yersinia frederiksenii. A decrease in PHA accumulation occurred 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.