Research On Pha Production Using Crude Glycerol And Biological Process

With the rapid development of the global economy,the consumption of nonrenewable energy represented by fossil fuels has become increasingly serious.As a result,countries are increasingly concerned about renewable resources.Polyhydroxyalkanoate(PHA)is nontoxic and renewable.Crude glycerin is a byproduct of biodiesel and can be used in PHA production.Untreated crude glycerol has the characteristics of high pH and high salt content,which inhibits the growth of most microorganisms.In this study,crude PG was used as a substrate to enrich PHA synthetic bacteria and synthesize PHA.The microbial community structure succession law during the enrichment process,the gradual increase of crude glycerol ratio and the gradual reduction of crude glycerol ratio during microbial community structure and PHA synthesis ability were studied..In this study,PHA synthetic bacteria were first enriched with 50 % crude glycerol and 50 % sodium propionate as carbon source.The main operating parameters,PHA synthesis index parameters and microbial community during enrichment were studied.The results showed that the inoculating sludge entered the reactor and the reactor was stably operated after 60 days of enrichment.During the enrichment period,the sludge concentration and sludge settling ratio showed a shortterm rise and then decreased and finally remained stable.During the enrichment period,the analysis of PHA synthetic bacteria shows that Roseibacillus and Meganema can do minate the reactor in a "relay" form,and Meganema reaches the maximum when Roseibacillus is reduced to the lowest.Microorganisms are competitive.In addition,the Meganema,Thauera and Paracoccus can coexist,and the PHA ability of the system is maximized after the enrichment stabilized.It is known that these three microorganisms contribute a lot to the synthesis of PHA.At the same time,this experiment investigated the effect of gradually increasing the proportion of crude glycerol on the enrichment of PHAproducing bacteria under the condition of stable operation of 50 % crude glycerol.The ratios were set at 50 %,70 % and 100 %.The results showed that the proportion of crude glycerol would not increase gradually.The utilization rate of crude glycerol was reduced with accelerating the rate of ammonia nitrogen consumption in the sludge feast stage.With the gradual increase of the proportion of crude glycerol,there are 6 species,6 species and 7 species of top10 species at the genus level.The species diversity in the reactor is increased,but the PHA synthesis ability is reduced.In this experiment,the ratio of crude glycerol was gradually reduced to 70 % and 50 % under the condition of stable operation of 100 % crude glycerol.The results showed that with the gradual decrease of the ratio of crude glycerol,the rate of consumption of crude glycerol by microorganisms and the ammonia stage of activated sludge.The rate of consumption was accelerated.At the level of top10,there were 7 species,7 species and 5 species,respectively.The species diversity decreased and the PHA synthesis ability decreased.In addition,the relative abundance of Saccharibacteria_genera_incertae_sedis increased and it was an absolute do minant species at the three crude glycerol ratios,indicating that this microorganism is more competitive with glycerol.When the crude glycerol content is reduced,the microorganisms convert more of the substrate into the required growth,which has little effect on the PHA synthesis.In summary,compared with the 50 % and 100 % crude glycerolrich reactor,the PHA production of 100 % crude glycerol is higher.The change in the structure of the carbon source does not have a large effect on the structure of the PHA component,and the proportion of HB is greater than that of HV.The PHA synthetic bacteria enrichment process with crude glycerol can reduce the PHA synthesis and relieve the excess of crude glycerol.This study can provide theoretical support for the practical application of the new PHA plastic.