Manufacturing technologies
Plastic, Wastewater treatment, Circular economy

Development of a bioplastic production systemusing waste activated sludge as biocatalyst
Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering
Associate Professor Daisuke Inouehttps://researchmap.jp/DaisukeINOUE

Abstract
Wastewater treatment by activated sludge processes generatehuge amounts of waste activated sludge (WAS) which mainly comprises a variety of microorganisms. The enhanced transformationof WAS to high value-added materials is still a big challenge forsustainable wastewater treatment. Therefore, we plan to use WAS
as the biocatalyst to produce polyhydroxyalkanoates (PHA), which
are biodegradable and biocompatible thermoplastic substancessynthesized by bacteria, from industrial wastewater/wastes as
feedstock for establishment of a PHA production system in wastewater treatment plants. To achieve this goal, we have been working
to establish the fundamental technologies, such as the methods torapidly enrich PHA-accumulating bacteria in WAS, and to efficiently
recover PHA stored in WAS.

Manufacturing technologies▍ Background & Results
Although WAS can produce PHA from various substrates, its
PHA production capability is not necessarily high owing to theco-existence of PHA-accumulating and non-PHA-accumulating
bacteria. Consequently, the enrichment of PHA-accumulating
bacteria is a key step for efficient PHA production using WAS as
the biocatalyst. However, the long enrichment duration in previous
methods is a significant obstacle limiting the beneficial use of daily
generated WAS in wastewater treatment plants (WWTPs). Therefore, we have studied the methods to achieve high enrichmentof PHA-accumulating bacteria within a short period (i.e., several
days during which WAS is pooled in WWTPs). With this aim, weemployed an aerobic dynamic discharge (ADD) process that
selectively enriches PHA-accumulating bacteria by imposing an
ecological selective pressure with the feast-famine regime and aphysical selective pressure based on the increased cell density byintracellular PHA storage. Till date, we have succeeded in obtaining mixed microbial cultures (MMCs) with a very high PHA accumulation capability within several days, using acetate or glucose
as the enrichment substrate. Especially, MMCs capable of storingas much as nearly 70 wt% of PHA could be obtained within only 2
d when acetate was used as the substrate. We have also studied
and gained knowledge on the environmentally-friendly method torecover PHA stored in the MMCs with high yield and purity, without
losing the physical properties as practically acceptable plastic materials.

applicable in a multitude of fields. PHA production with low costand energy input, which is aimed in this study, will also be of great
importance in the light of environmental protection.

Concept of evolving a wastewater treatment plant as the bio-refinery to produce
PHA

Flow of PHA production using WAS as the biocatalyst▍ Significance of the research and Future perspective
WWTPs are indispensable urban infrastructure for public health,aquatic environmental conservation, and sustainable water use.
Our goal is to evolve WWTPs as a core facility to create future circular society by adding the function of bio-refinery to produce PHA
and other high value-added materials from wastewater/wastes.
Realization of this idea will contribute largely to the carbon neutral
society. Additionally, PHA is a promising alternative plastic material

Principle of the aerobic dynamic discharge process applied for rapid enrichmentof PHA-accumulating bacteria from WAS

P a t e n tInoue, Daisuke; Fukuyama, Atsushi; Ike, Michihiko et al. Optimization of aerobic dynamic discharge process for very rapid enrichment ofpolyhydroxyalkanoates-accumulating bacteria from activated sludge. Bioresource Technology. 2021, 336, 125314, doi: 10.1016/j.biortech.2021.125314
Ike, Michihiko; Okada, Yukihiro; Inoue, Daisuke et al. Potential of waste activated sludge to accumulate polyhydroxyalkanoates and glycogen using
industrial wastewater/liquid wastes as substrates. Water Science and Technology. 2019, 80 (12), 2373-2380, doi: 10.2166/wst.2020.059
http://www.see.eng.osaka-u.ac.jp/wb/ikelab/URL
https://see.eng.osaka-u.ac.jp/topics/staff/3724.html
K e y w o r d waste activated sludge, biocatalyst, bioplastic, polyhydroxyalkanoates
Tr e a t i s e