Storage Of Polyhydroxyalkanoate From Volatile Fatty Acid By Activated Sludge

A sequencing batch reactor was conducted by aerobic dynamic feeding with acetate as carbon source to domesticate activated sludge to enrich PHA -accumulating microorganisms. After being domesticated, the PHB accumulation was researched. The results showed that feeding by high acetate dosage of 931.5mg C/L; the activated sludge produced PHB. During feast period, 94% acetate was removed, in which a fraction of 53.4% of acetate was transformed to PHB. The PHB content of activeated sludge is 836mg/L.To improve the PHB content in activated sludge and to find the optimal condition for PHB synthesization. Three critical factors: F/M (food/microbiology), dissolved oxygen and nitrogen deficiency was evaluated. The results showed that:①with the F/M increasing, the maximum PHB production increased correspondingly. Feeding by a high dosage acetate with a F/M (Food to Microorganisms) of 2.5 mg C L-1/ mg C L-1, PHB production reached its maximum value of 1070mg/L at 8 h. when F/M ratio above 2.5 mg C L-1/ mg C L-1, PHB content didn't increase anymore because of the long time of storage reaction (excess 8 hour).②the rate of substrate uptake increased with the increase of dissolved oxygen concentration, but a moderate dissolved oxygen supply appears to be appropriate for the most efficient conversion of acetate to PHB. At a moderate dissolved oxygen supply rate of 80L/h(KLa 8.93 L/h), a much higher conversion of 0.76 was reached.③Subjected to nitrogen -limiting conditions, the growth of activated sludge is manly due to the storage of PHB, yet the residual cell biomass didn't increase. Under the nitrogen-limiting condition, the maximum value of PHB storage was 1598mg/L, 65.2% of activated sludge.To research the effect of carbon source on PHA stucture, unique carbon source aceatate, propionate, butyrate and mixed carbon of them was used to produce PHA, respectively. Results showed that using acetate or butyrate as carbon source, PHB was obtained, when the carbon source was propionate or mixed carbon, the terpolymer of HB/HV/HMV was obtained. And the HV content of PHA was linear with the propionate content.The production of PHA by starchy wastewater was investigated. The results showed that the starchy wastewater was almost acidificated to butyric, acetic, propionic, valeric acids and ethanol. At the second stage, activated sludge was fed by the organic acids discharged from the acidification reactor to produce PHA and 34.7% PHA of sludge was acquired, with a purity of 96.8%. The PHA in the sludge was extracted and its structure and thermal character were analyzed. The results showed that the PHA was composed of HB and HV and the PHA had HV content of 8.9 mol%. The results of thermal analysis showed that the melting point was 150℃and the thermal degradation temperature was 270℃. Therefore, feeding by the acidified starchy, the copolymer of 3HB and 3HV was produced by activated sludge, and the PHBV had the character of lower melting-temperature and good thermal stability.The acidogenic react was investigated for the optimal PHA production using the acidifitied starchy. Results showed that the degree of acidification was higher when temperature was controlled at 35℃. HRT influence the acetate and alcohol content and OLR influence alcohol content. However, the type of fermentation was maily influeced by pH. Propionic acid type fermentation occurred at pH about 5.5. Ethanol fermentation occurred at lower pH. Butyrate fermentation was dominant with a higher Ph value.therefore,improving the propionic acid content by control the fermentation condition make acidficited starchy a good carbon source for PHA synthesis.