Production of poly-3-(hydroxybutyrate-co-hydroxyvalerate) by Haloferax mediterranei using rice-based ethanol stillage with simultaneous recovery and re-use of medium salts

Abstract

Haloferax mediterranei holds promise for competitive industrial-scale production of polyhydroxyalkanoate (PHA) because cheap carbon sources can be used thus lowering production costs. Although high salt concentration in production medium permits a non-sterile, low-cost process, salt disposal after process completion is a problem as current environmental standards do not allow total dissolved solids (TDS) above 2000 mg/l in discharge water. As the first objective of this work, the waste product of rice-based ethanol industry, stillage, was used for the production of PHA by H. mediterranei in shake flasks. Utilization of raw stillage led to 71 ± 2% (of dry cell weight) PHA accumulation and 16.42 ± 0.02 g/l PHA production. The product yield coefficient was 0.35 while 0.17 g/l h volumetric productivity was attained. Simultaneous reduction of BOD5 and COD values of stillage by 83% was accomplished. The PHA was isolated by osmotic lysis of cells, purification by sodium dodecyl sulfate and organic solvents. The biopolymer was identified as poly-3-(hydroxybutyrate-co-15.4 mol%-hydroxyvalerate) (PHBV). This first report on utilization of rice-based ethanol stillage for PHBV production by H. mediterranei is currently the most cost effective. As the second objective, directional properties of decanoic acid together with temperature dependence of water solubility in decanoic acid were applied for two-stage desalination of the spent stillage medium. We report for the first time, recovery and re-use of 96% of the medium salts for PHA production thus removing the major bottleneck in the potential application of H. mediterranei for industrial production of PHBV. Final discharge water had TDS content of 670 mg/l.

Production of Polyhydroxyalkanoate (PHA) Biopolyesters by Extremophiles?

“…Additionally, about 29 % of yeast extract, an expensive growth additive needed as nitrogenand phosphate source for efficient cultivation of the strain, can be replaced by cell debris from previous cultivations [64]. Similar strategies were followed by Bhattacharyya and colleagues [65], who used waste stillage from the rice-based ethanol production for Hfx. mediterannei mediated PHB production.…”

Study on the Production and Re-use of Poly(3-hydroxybutyrate-co-3- hydroxyvalerate) and Extracellular Polysaccharide by the Archaeon Haloferax mediterranei Strain DSM 1411

“…Production of these valued compounds was described starting from carbon sources like glucose 16 , hydrolyzed lactose from dairy waste 9,10 , starchy residues 17,18 , vinasse 19 , rice-based ethanol stillage 20 , or glycerol from biodiesel production 21 . Already in 1995, the high potential of this organism to be implemented in "White Biotechnology", especially for bioplastic production, was discussed 22 , whereas only a few years ago, the application of the strain for PHA production explicitly from different agro-industrial waste streams was suggested by several authors 9,10,[17][18][19][20][21] . A comprehensive overview of the biotechnological potential of H. mediterranei and related halophilic species was provided by Quillaguamán and colleagues 23 .…”

Biocompounds from Haloarchaea and Their Uses in Biotechnology

“…Cheap carbon sources such as glycerol [89,90], rice bran [91], rice-based ethanol stillage [92], cheese whey [93], and olive mill wastewater (the effluent of the olive oil industry) have been tested using multistage processes [94,95] or only one-stage process ( …”