Evaluation of biodegradability of biodegradable plastics in activated sludge

Biological polymers produced by microbial fermentation are naturally biodegradable and are potential environment-friendly substitutes for synthetic plastics. However, broader applications are restricted by high production costs. In this study, activated sludge bacteria in a conventional system treating a wastewater that contained xenobiotic organics were induced by nitrogen deficiency in the reactor liquor to accumulate intracellular storage polymers, which can be extracted as a low-cost source of biodegradable plastics. Chromatographic analysis of the extracted polymers revealed a composition of poly-hydroxyalkanoate and a number of related co-polymers. Alcaligene spp. in the activated sludge microbial consortium was identified as the main genus that accumulated these polymers. When the C:N ratio was increased from 20 to 140, specific polymer yield increased to a maximum of 0.39 g polymer/g dry cell while specific growth yield decreased to 0.26 g dry cell/g carbonaceous matter consumed. The highest overall polymer production yield of 0.11 g polymer/g carbonaceous matter consumed was achieved when the C:N ratio was maintained at a nitrogen- deficient level of 100. The specific polymer yield in the isolated Alcaligene spp. cells reached as high as 0.7 g polymer/g dry cell mass. While reducing the costs of biodegradable plastics, this technique also reduced the amount of excess sludge generated from the wastewater treatment process by 39%.

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PHA (polyhydroxyalkanoate) production potential of activated sludge treating wastewater

Water Science & Technology ◽

10.2166/wst.2002.0417 ◽

2002 ◽

Vol 45 (12) ◽

pp. 119-126 ◽

Cited By ~ 34

Author(s):

H. Takabatake ◽

H. Satoh ◽

T. Mino ◽

T. Matsuo

Keyword(s):

Wastewater Treatment ◽

Activated Sludge ◽

Organic Pollutants ◽

Wastewater Treatment Plants ◽

Recovery Process ◽

Biodegradable Plastics ◽

Operational Conditions ◽

Conventional Activated Sludge ◽

Dry Cell Weight ◽

Dry Cell

The main purposes of wastewater treatment systems are to remove organic pollutants, but it would be very attractive if there were a way to recover the organic pollutants as valuable organic materials. One of the possible ways to recover organic pollutants in wastewater is to convert them into polyhydroxyalkanoates (PHAs), which are biodegradable plastics. In this study, 18 activated sludge samples in 4 wastewater treatment plants (WWTPs) in Tokyo, Japan, were evaluated for their potential to produce PHAs by aerobic batch experiments with excess supply of acetate as the sole carbon source. The activated sludge samples tested had the capability to accumulate PHA up to 18.8% of dry cell weight on average, with the range of 6.0% to 29.5%. The results showed that the maximum PHA content was dependent on the influent more than on the operational conditions of the activated sludge, and that conventional activated sludge produced PHA as much as anaerobic-aerobic activated sludge did. The PHA content achieved in this study is still low, and further improvement is needed to put into practice the recovery process of organic pollutants as biodegradable plastics by activated sludge.

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