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Production of polyhydroxyalkanoates (PHA) in the pilot plant

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Production of polyhydroxyalkanoates (PHA) in the pilot plant

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Samenvatting

In this graduation project, the production of polyhydroxyalkanoates (PHA) was studied in relation to the pilot plant, which uses the wastewater from the chocolate factory of Mars Nederland B.V. in Veghel, in the biopolymer research project of the umbrella project of the STW: Waste-to-resource.
PHA is a biopolymer produced from waste, usable as raw material for the production of bioplastics, biochemicals and biofuel. PHA is a carbon storage molecule for various microorganisms, produced from organic content, preferably volatile fatty acids with a short chain length. The raw material PHA is currently only produced on industrial scale with pure cultures in aseptic conditions, which is a costly endeavour.
At the Delft University of Technology, in the department of Environmental Biotechnology, the production of PHA on open and mixed cultures was researched and is promising to reduce costs for PHA production. The process utilizes selective pressure on the carbon source to enrich the culture on PHA producing microorganisms: ecology applied to an industrial process. The bacterium P. acidivorans was discovered for its superior fatty acid uptake and PHA storage. The developed production process utilizes a three step system in the pilot installation: anaerobic fermentation of organic content to wastewater to volatile fatty acids, enrichment of an open and mixed culture in a sequencing batch reactor on the mixed substrate feedstock from the fermentation process, and PHA maximization in cell content of the enriched culture on the same mixed substrate in a fed-batch reactor. The aim of this project was to identify the parameters and criteria of the PHA production process in the pilot installation for the production of 1 kilogram equivalent quantities of PHA, which would represent a successful process worth upscaling. The parameters and criteria have been identified, but no kilogram equivalent was produced. Criteria of major import are identified for 1) feedstock production: application of a HRT of 50 hours or more, in 4.9 < pH < 6, and a temperature of 30˚C for production high VFA content of the feedstock with high concentrations of butyrate and valerate content used in 2) culture enrichment with parameters: sustained selective pressure in sequential cycles through a stable SRT of 1 day (with 2 cycles) for stable growth conditions and for stable enrichment conditions, and a nutrient excess environment with a ratio equal to or lower than 8 Cmol/Nmol, pH close to 7, at a temperature of 30˚C. The high enriched biomass is then needed in 3) PHA maximization with: nutrient depletion of the PHA maximization process, pH close to 7, high amounts of enriched biomass to reach high levels of PHA, at a temperature of 30˚C, on butyrate and valerate in the mixed substrate.
In the pilot installation, the fermentation product contained an average of 6 gram soluble COD per litre with 0.9 gram COD in solids. The soluble COD contained mostly VFA as acetate, propionate, butyrate and valerate, where the presence of ethanol indicated some incomplete fermentation at low HRT and low temperatures. An 62% enrichment (on a maximum of 55% PHA, TSS basis) was achieved on a substrate consisting of 77% volatile fatty acids (in soluble COD), containing 51% butyrate and valerate of the soluble COD. The enrichment was identified to be greater on high concentrations of butyrate and valerate in the feedstock, which was in turn identified to be produced in a high HRT fermentation process, where the achieved 51% was on a HRT of about 50 hours. Furthermore, the achieved enrichment took place on a nutrient dosage of 6.4 Cmol/Nmol. On a different culture, a maximum of 61wt% PHA on TSS basis was reached after 6.6 hours in an accumulation experiment in the laboratory of Environmental Biotechnology at the Delft University of Technology, constituting an enrichment of 28% P. acidivorans in the accumulator. The accumulation experiment in the pilot installation achieved 57% PHA on TSS basis after 4 hours, without reaching a maximum, producing 91.5 grams of PHA. The nutrient concentration of the effluent from the enrichment process was such that active biomass and ash content increased by 218%, which is a major improvement option: nutrient depletion.

Further optimization options and research considerations were identified.

Toon meer
OrganisatieAvans Hogeschool
OpleidingEnvironmental Science for Sustainable Energy and Technology-Breda
AfdelingATGM Academie voor de technologie van Gezondheid en Milieu
PartnersTU Delft, Mars Nederland B.V.
Datum2013-07-01
TypeBachelor
TaalEngels

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