Study of polyhydroxyalkanoates production using acetic, propionic and butyric acids

Abstract

Nowadays, to replace the use of plastic is needed due to its low degradation capacity and its low efficiency in recycling, which usually leads to pollutants and toxic substances. To promote a circular system, the use of a bio-polymer such as polyhydroxyalkanoates (PHA) is proposed. This bio-polymer is produced from a four-stage system: fermentation, selection of microorganisms, accumulation of intracellular PHA and extraction, using wastewater or other wastes as the municipal waste organic fraction as substrates. In this work, a selection of PHA-producing microorganisms with an organic loading ratio of 3.5 g COD · L-1·d-1 with synthetic feeding is carried out in a 3L reactor where the ratio carbon- nitrogen is decreased (56.39 g COD /g N, 48.59 g COD / g N and 43.00 g COD / g N) to find the appropriate ratio. The process is performed with an HRT of 1.16 days and an SRT of 4.87 days. Accumulation test have also been carried out in a 1 L reactor where a ratio of 43.00 g COD / gN is worked. The pH, oxygen concentration, ammonium concentration and volatile fatty acids consume are monitored along the process. Moreover, the effect of added the PHA production process in a wastewater treatment plant where secondary sludge is mixed with municipal organic fraction has studied. The results obtained are to see the evolution of a system that it is trying to stabilize. Nevertheless, a reactor that works with a coupled feeding have a volatile suspended solid and totals ratio lower than another that works with an uncoupled feeding. In addition to that, the microorganism PHA content is twice as many in a reactor with coupled feeding as in an uncoupled feeding, according to the bibliography. However, it is observed that the microorganisms have the same maxim PHA content independent of the organic rate load, according to the bibliography. Regarding the nitrogen limitation, a correlation is observed between the increase in biomass and the increase in the nitrogen dose. Besides the C-N ratios of this study were insufficient. It is also observed that the acid consumption speed on the number of carbon in the molecular chain. Lastly, it has been concluded that the PHA production process could be implemented in a municipal wastewater treatment plant using VFA produced by the acidogenic fermentation of waste secondary sludge and squeezed OFMSW