Polyhydroxyalkanoates production alongside wastewater treatment by mixed microbial cultures

Abstract

The focus of this research work was conducted to analyse the three stages of a polyhydroxyalkanoates (PHA) production process alongside wastewater treatment. PHA are considered as potential substitutes of conventional plastics and the circular economy model, considers them as value-added products. However their production costs has limited their widespread, so currently many efforts are carried towards the development of cost-effective alternatives to enhance the PHA processes and reduce their costs. The process evaluated herein involves: 1. Acidogenic fermentation: Different wastes were evaluated in terms of their potential to produce volatile fatty acids (VFA) under acidogenic fermentation. Using wastes as non-expensive substrates for PHA production, can reduce the overall process costs. A lot of effort was carried on the determination of the VFA composition as it is a key parameter to determine the type of PHA synthesized and thus, their structure and properties. 2. Aerobic enrichment step: A mixed microbial culture (MMC) was used for the enrichment of PHA-accumulating microorganisms. MMC was used as an approach to reduce the costs related with the use of pure cultures. A sequencing batch reactor (SBR) was operated under feast/famine regimen. Firstly, acetic acid was used as sole carbon source and the effect over the PHA accumulation performance was studied by comparing the PHA content working at pH controlled (7. 5) and without pH controlled. A second SBR was inoculated to enrich a MMC using a synthetic fermented olive mill waste water (OMW). 3. PHA accumulation: The enriched-MMC was used for batch experiments to promote high PHA contents. The influence of several parameters on the PHA maximum accumulation were evaluated. The pH influence was assessed in a range from 4. 0 to 9. 0. PHA accumulation under N and P limitation or excess was determined. The effect of the feeding strategy was also evaluated and the substrate composition influence on the final PHA composition and contents were elucidated. 4. Downstream processing: PHA extraction was done using DMC as green solvent and the recovery results were compared with the results obtained when chloroform is used. The idea of using DMC is to overcome the toxic environmental and human concerns related with the use of chlorinated solvents. The impact on the PHA recovery of applying a pre-tretament to boost cell lysis with sodium hypochlorite (NaOCl) or use a precipitation with methanol at the end of the process were investigated.

Date of Award	24 Oct 2018
Original language	English
Supervisor	Maria Eugenia Suarez Ojeda (Director)