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Production of polyhydroxyalkanoates from olive oil mills wastewater

Final Report Summary - POLYVER (Production of polyhydroxyalkanoates from olive oil mills wastewater)

Olive oil production has significant impacts on the environment, due to toxic organic and inorganic compounds that are present in olive oil mills wastewater (OOMW). European legislation prohibited uncontrolled OOMW discharge into soil and water; hence current conventional disposal options consist of physical and chemical treatment, evaporation in open tanks and subsequent incineration of solid residuals and, finally, limited release on the ground for fertilisation purposes.

The POLYVER project aimed to develop and implement an innovative technology able to permit the conversion of OOMW from a dangerous waste to a renewable source for biopolymers production. The two main scientific and technological objectives of the project were to:
1. create a new process for OOMW treatment and production of polyhydroxyalkanoates (PHA);
2. apply the process on site so as to enable its utilisation for OOMW treatment in a large scale.

The proposal innovation relied on the conversion of pollutants to a commercially exploitable biopolymer, while available alternatives simply separated toxic compounds from purified water without reducing the polluting load. OOMW organic compounds acted as a source of nutrients for the biopolymer producing bacteria strains.

Firstly, the project requirements and technical specifications were defined, taking into account OOMW chemical properties, characteristics of the biofermentation process and recovery of the biopolymer in order to reduce environmental impact. Fermentation in particular was dependant on features that varied between region and producer. The chemical and physical characteristics of the final product were determined with respect to its potential industrial applications which were investigated through a preliminary market analysis.

The bacteria were therefore selected and the fermentation process was analysed through evaluation of numerous parameters and in accordance to the finalised specifications. PHA was produced using a multi step process and its recovery was considered in relation to the effects on the post-processing and the economical aspect of its production.

The obtained microbiological results were subsequently exploited for the pilot scale plant design and construction. Automation of the bioreactor cycles was achieved through the development of a personalised user interface. The prototype tests enabled the finalisation of pretreatment and post-treatment activities. Nevertheless, PHA production was only feasible at a low yield which ought to be improved. Bioreactor cycling and operation modes should also be refined prior to the process industrialisation.

In addition, life cycle assessment (LCA) of the proposal was performed, involving gross energy use and global warming potential parameters. LCA highlighted the necessity for optimisation of the technology in order to obtain competitive yields and reduce the electricity and solvents environmental costs.

Performance of water purification was taken into account after defining the most suitable method for polymer recovery. The relevant evaluation outlined the need of post-treatment, mainly using membranes, so as to completely remove the polluting compounds and reduce chemical oxygen demand (COD) before water disposal or reuse. Membrane process sequence, nanofiltration (NF) and reverse osmosis (RO) were examined for water treatment. Part of the purified water was then used for the dilution step of the PHA production process. Resulting water quality was satisfactory; nevertheless, suggestions for increased efficiency were formulated.

POLYVER technology was industrially exploitable, since the costs of PHA production and water treatment were lower than those required for OOMW disposal. However, in order to justify bioreactor investment, the production yield ought to be increased; hence further improvement of extraction and purification methods was necessary. An industrial scale production plant was conceptualised and a relevant economic analysis was elaborated. It appeared that part of the methodology could be adjusted to different qualities wastewater and by-products of the food industry. In addition, the membrane process was applicable to any industrial wastewater after incorporation of the exact case conditions.

POLYVER results were extremely innovative compared to the state of the art and offered the potential for numerous patents. Thus it was decided to limit as much as possible any publication related to sensible information. Nevertheless, knowledge was widely disseminated through scientific publications, construction and updating of the project website and preparation and implementation of an adequate dissemination plan.