Synthesis Of Polyhydroxyalkanoates(PHA) By Bacterial Consortium From Excess Sludge Fermentation Liquid

The synthesis of biodegradable plastics, polyhydroxyalkanoates (PHA) is ofimportant significance to reduce cost of PHA production and to recycle (and reduce)waste sludge. PHA is synthesized via mixed bacterial method, using waste sludgefermentation liquid as substrate. Sludge composition and condition of anaerobicdigestion process have a great effect on composition of fermentation liquid, and furtherinfluence of efficiency of PHA synthesis and composition of PHA. Therefore, in thispaper, I did research on influences of hydrolysis of waste sludge production affected bycomposition and concentration of sludge, patterns and synthesis process conditions ofPHA by bacterial consortium using sludge fermentation liquid, to provide theoreticalbasis and technical support for the combination of waste sludge utilization and PHAproduction process.Studies show that within sludge concentration range VS=10-50g/L, the higher thewaste sludge concentration, thermophilic anaerobic digestion of organic matter (SCOD)and VFAs are both higher in dissolved hydrolysis liquid, and the reason is that underhigher temperature and anaerobic conditions, more soluble protein and saccaridesubstances are released in highly concentrated sludge, which are further decomposedinto smaller organic acid molecules. Using initial concentration of sludge (VS), SCODand VFAs can be calculated via following formulae: y=4.9743x+94.892and z=4.2425x-2.706(x: VS-g/L，y: maxSCOD-mg/L VS，z: maxVFAs-mgSCOD/L VS),which have been verified. Protein and total saccaride contents have great influences onconcentration and variation of VFAs, high protein content in sludge leads more valericand acetic acids. High saccaride content in sludge leads more butyric and acetic acids.Sludge concentration has little effect on sludge reduction, and sludge organic matterreductions are both30%.Next, sludge fermentation liquid is used to acclimate bacteria in ADF for PHAsynthesis, and further to obtain high PHA synthesis rate SH-24mixed strains. Studiesshow that under high initial carbon source concentration (SCOD=5,000mg/L) in thesludge fermentation liquid, CDW is2.35g/L, PHA synthesis rate reaches30.74%, andPHA production is0.72g/L. Bacterial group SH-24consumes VFAs first for PHAsysthesis and cell growth. SH-24can take advantage of the six different VFAs to produce PHA monomers, including HB, HV and H2MV, high content of isovaleric acidhelps synthesize HV and H2MV, while HB is the most among all synthetic products bySH-24using VFAs.Finally, it is to optimize the main culture conditions, which would influence. Moredigestive inhibitors (thiourea) would promote bacterial growth, and slow down PHAdegradation. Change of feast-famine proportion (F/F) could improve PHA synthesis rate:when F/F is1:2, more HV monomers are synthesized, and PHA synthesis rate reaches37.2%, which is8.9%higher than the rate when F/F rate is1:3. Cell growth and PHAsyntheses are effected at different levels, when F/F rates are too high, or too low.