Developing a sustainable PHB extraction method from Synechocystis sp. grown on whey

Abstract

Most plastic products in circulation worldwide are based on fossil petroleum and are not biodegradable,which is known to be one of the biggest burdens and threats to the environment. One possible solution to this problem could be the use of bio-based and biodegradable polyhydroxybutyrate (PHB). Undernitrogen and phosphate depletion, Synechocystis sp. PCC 6714 produces PHB. As a positive side-effect,this method also binds the greenhouse gas CO2 through photosynthesis.This thesis analyses the results of a series of experiments carried out as part of basic research to better understand a possible PHB production process. The main goal was to investigate the effects of different lactose concentrations between 1 and 10 g/L from concentrated whey on the microorganism,particularly on the PHB production. The following three main results were obtained:Firstly, the cyanobacterium strain used could not metabolise lactose and even showed lower growth andPHB content of 2.2% at 1 g/L lactose compared to 4.2% without the addition of whey in the shake flaskexperiment. When upscaling in a photobioreactor, the same ratios were observed between cultivationswith and without whey, with the PHB content doubling to 6.5 and 10.5% (volumetric productivity 7.7and 21.1 mg/L/day).Secondly, the standard hydrolysation method for PHB quantification with concentrated sulfuric acid was compared with the alkaline sodium hydroxide method using a multivariate data analysis.Subsequently, the more promising acidic method was further optimised to reduce viscosity of sulfuricacid, gaining an optimum at 160 min, 14 M H2SO4, 100°C.Thirdly, as an alternative to the state of the art methods for recovering PHB, which use, e.g. the harmful chloroform, three ionic liquids based on the cation 1-Ethyl-3-methylimidazolium with three differentanions Dimethylphosphate, Acetate or Chloride were tested to dissolve the biomass but not thebiopolymer. 1-Ethyl-3-methylimidazolium Dimethylphosphate completely dissolved the biomass at75°C after 1 h and did not decompose or dissolve the PHB so that it could be implemented in a complete recovery process.