| Organic wastes,including food waste,sewage sludge and food waste,could be used to produce polyhydroxyalkanoate(PHA)for the lower production cost of PHA,thus replacing the high-price feedstock(glucose and plant oils).However,animal wastes,as an important part of agricultural wastes,were seldom studied for PHA production,although much carbon content are available in these wastes.In this study,by using the lactic acid fermentation broth from anaerobic fermentation of pig manure as the feedstock,the technique of PHA synthesis from lactic acid fermentation broth without extra purification was investigated;mixed microbial culture(MMC)with highly efficient PHA synthesizing bacteria were enriched under different aerobic sludge and solid retention times(SRTs),and effectively recovered and maintained to obtain the pig manure source MMC;the major process parameters were optimized to further achieve the higher performance of PHA synthesis.The conclusions of this study could provide theoretical support for the practical production of PHA from the lactic acid fermentation broth,thus developing the new route of pig manure utilization.The main conclusions of this study are as follows:(1)Put forward the technique of synthesizing PHA from lactic acid fermentation broth without extra purification by using MMC.Lactic acid fermentation broth was produced from co-fermentation of pig manure and fruit residues,and can be utilized to produce PHA,by using the three-stage fermentation mode,namely,LA broth production–bacteria enrichment–PHA synthesis.Under the broth concentrations of 3.44?36.58 g COD /L,PHA can be effectively synthesized from lactic acid fermentation broth.(2)Acclimating pig farm sludge with lactic acid fermentation broth under SRT of 8 days was the best enrichment strategy of achieving highly efficient MMC.Two types of aerobic sludge(pig farm sludge and municipal sludge)were selected to acquire MMCs in the enrichment process with SRTs of 2 and 8days using the lactic acid fermentation broth.Results showed that pig farm sludge was acclimated to the superior MMC during the enrichment process with SRT of 8 days and the dominant bacteria of MMC were genus paracoccus with abundance of 35.31?41.45%.(3)The optimal operational parameters for PHA synthesis using lactic acid fermentation broth were found.Results showed that the maximum PHA content of 30.29–38.84% and PHA yield of 0.54–0.61 gPHA-COD/g-COD can be achieved when the lactic acid concentration and p H in lactic acid fermentation broth was 20 g/L and 4.5–8.5,respectively.When p H of the lactic acid fermentation broth was 3.5,microbial activity in the reactor was inhibited,resulting in the very low PHA synthesis rate.In the microbial diversity,concentrations of lactic acid fermentation broth significantly impacted the bacterial groups during the PHA synthesizing process and except the treatment with p H of 3.5,p H of the broth did not significantly impact the microbial diversity.In summary,lactic acid fermentation broth from pig manure can directly synthesize PHA without need of broth separation and purification.Use of active sludge from pig farm facilitated the enrichment of highly effective MMC,and the PHA synthesis effects were improved by optimizing the important parameters of PHA synthesizing process(include feedstock concentrations and p H),thus providing the theoretical basis and data support for using lactic acid fermentation broth derived from pig manure for PHA synthesis. |
