Optimization of Green Extraction and Purification of PHA Produced by Mixed Microbial Cultures from Sludge

Abstract

Sludge from municipal wastewater treatment systems can be used as a source of mixed microbial cultures for the production of polyhydroxyalkanoates (PHA). Stored intracellularly, the PHA is accumulated by some species of bacteria as energy stockpile and can be extracted from the cells by reflux extraction. Dimethyl carbonate was tested as a solvent for the PHA extraction at different extraction times and biomass to solvent ratios, and 1-butanol was tested for purifying the obtained PHA at different purification times and PHA to solvent ratios. Overall, only a very small difference was observed in the different extraction scenarios. An average extraction amount of 30.7 ± 1.6 g of PHA per 100 g of biomass was achieved. After purification with 1-butanol, a visual difference was observed in the PHA between the tested scenarios, although the actual purity of the resulting samples did not present a significant difference. The overall purity increased from 91.2 ± 0.1% to 98.0 ± 0.1%.

Ethylic Esters as Green Solvents for the Extraction of Intracellular Polyhydroxyalkanoates Produced by Mixed Microbial Culture

“…In alternative to chlorinated hydrocarbons, which are the best solvents for PHAs, many research studies address the use of green solvents, with low or no toxicity and possibly derived from biochemical conversion, to overcome ecological issues, limitations involving worker safety or stringent regulations on solvent traces in goods for particular applications [ 25 ]. Solvents characterized by low toxicity, including ethers [ 26 , 27 ], esters [ 25 , 27 , 28 , 29 ], carbonates [ 29 , 30 , 31 , 32 ] and ketones [ 28 , 33 , 34 ], have been identified as appealing alternatives to chlorinated hydrocarbons. Their suitability is evaluated by taking into account their recyclability, the need for biomass pretreatment, polymer recovery yield, the quality of the extracted polymer in terms of purity and possible molecular weight reduction, as well as process cost and environmental performances [ 35 , 36 ].…”

Novel alternative recovery of polyhydroxyalkanoates from mixed microbial cultures using microwave‐assisted extraction

“…With respect to time, the efficiency increases significantly when the time decreases, at an S/B ratio of 1 volume, and less at 20 volumes. Several authors have stated that the S/B ratio was more significant than the time in PHA recovery 37,40 . Kumar et al 37 .…”

Established and advanced approaches for recovery of microbial polyhydroxyalkanoate (PHA) biopolyesters from surrounding microbial biomass

“…After purification with 1-butanol, a visible difference was observed for PHA samples obtained by the different tested scenarios (whitest product obtained after 0.5 h treatment at a PHA-to-solvent ratio of 1/100), although the measured purity (determined via TGA) of the obtained samples did not differ significantly. The overall purity after 1-butanol treatment increased from 91.2 ± 0.1% to 98.0 ± 0.1% (35).…”