Determination of biopolymer storage conditions from industrial wastewater by biological method

Petroleum-derived plastics having limited resources, resistence to biodegradation in the environment and hazardous character for living organisms can be replaced by bioplastics which stand out with their advantages such as being non-toxic, biocompatible with the living body and low carbon footprint. Although they are accepted as alternatives to petroleum-derived plastics, their production has not yet reached the industrial level. Bioplastics are plastics derived from renewable biological resources such as organic solid waste, plants, animals and microorganisms. Poly-ß-hydroxybutyrate (PHB) biopolymer is synthesized and stored by pure and mixed culture microorganisms in the presence of carbon source and nutrient and trace metal deficiency. Among the alternative carbon sources in the production of PHB are the organic contents of industrial wastewater. In particular, the use of food industry wastewaters as the carbon source can reduce production costs. During the production phase, parameters such as C/N ratio, sludge age, temperature and dissolved oxygen concentration are regulated. The main purpose of this study is to determine the optimum process conditions that can be applied to obtain the maximum level of PHB biopolymer with mixed culture by using the fruit juice industry wastewater as a carbon source. In addition to the synthetic sour cherry juice production wastewater, domestic wastewater was used as the nitrogen and phosphorus source. Mixed sludge culture obtained from the municipal wastewater treatment plant was used for the aerobic biological study, in a sequential batch reactor with feast and famine phases, using 2 cycles per day, 3 different temperature levels (20, 28 and 30°C), C/N ratio 30, 40 and 60 g COD/g N, sludge retention time (SRT) of 1, 2, 5 and 10 d. As a result of the study, optimum conditions for maximum PHB biopolymer production were determined as 28°C, C/N 40 and SRT 5 d. By increasing the temperature to 28°C, PHB production increased at C/N 30, 40 and 60. As the temperature increased, the PHB production rate also increased. In the periods conducted for SRT 1, 2, 5 and 10 d, the highest PHB production occurred for SRT 5 d. There was no PHB production in some samples for SRT 1 d. Biomass had a lower PHB production rate for SRT 10 d than 5 d. The highest production rate was obtained at C/N 40 among 30, 40 and 60 g COD/g N. Bacteria used carbon in the environment for growth and reproduction at low C/N ratios (C/N 30) while their PHB accumulation was adversely affected by the high carbon content.