Process Stability Of Polyhydroxyalkanotes Production Using Acidogic Waste Water

Polyhydroxyalkanoates (referred to as PHAs or PHA) are a sort of bio-degrable andbio-renewable biological plastics, which was expected to take the place of traditionalpetrochemical-based plastics. Generally, it can be synthetized with PHA producingbacterias using Hydrolysis fermented liquid from organic waste. However, as for thehigh cost of substrate sterilization as well as microbal isolation and purificationoccurred during PHA production process, it was not easy to reduce the high cost of PHAproduct, which hindered it from mass application. The introduction of mixced microbalcultures(MMCs) in PHA production makes it possible for perfect cost control. In thiskind of new process, it owned an simple operation instruction and substrate sterilizationwas no longer needed, thus substrate cost was reduced while renewable carbon source inthe waste watwe was recorved. Thanks to this new technique, the environmental threatof abandoned pollutant was removed and high-value biological plastic PHA productswas obtained, which has a great significance to its cost reduction and vast application.3-stage MMC based PHA production process is widely adopped in recentresearches.It contains3main steps of acidogic of waste carbon source, culture selectionof MMCs and PHA accumulation. Of all the3steps, culture selection is the decisivestep as it will directly affect the synthetic efficiency and process cost in PHA production.To come up with a solution of sludge bulking occurred in step2and optimize cultureextraction time in order to provide stedy and efficient MMCs for PHA production iscritical problem needed to cope with.This research is based on typical3-stage PHA production process using acidogicsugar cane as substrate. We took out a series of experiments to investgate therelationship within organic loading, sanitary sewage feeding, sludge stability and enrichefficiency. Otherwise, we introduced a set of continuous flow reactor to test itslong-term slection efficiency and working stability as enrichment reactor.Test result showed that when SBR was used as enrichment reactor, different influentsubstrate concentration and sanitary sewage addition radio could make a difference tosludge stability and slection efficiency during reactor setup. It was showed that organicfeeding mixed with10%of sanitary sewage had a better performance on sludge stabilitythan organic feeding mixed with20%of sanitary sewage and organic feeding mixedwith no sanitary sewage. However, this advantage was not so obvious as the sludgebulked in the end. On the other hand, influent substrate concentration had a greaterinfluence on sludge stability. Long-term observation showed that medium influent substrate concentration（of about1100mgCOD/L）could maintain a high MLSS(ofabout3000mg/L) under low SRT (SRT=10d) as well as high culture selection efficiency.During batch experiment conducted on the94thday of enrichment, a PHA conversionrate of0.7145COD/COD as well as PHA synthesis rate of0.1912mg COD PHA/mgX/h was achieved. By the way, we proved that the continuous flow reactor will not helpto improve sludge settlebality, and it was not as flexable as SBR once sludge bulkingoccurred. As a consequence, it is not wise of us to choose continuous flow reactor asenrichment reactor. At last, we proved that intracellular glycogen level had a similartrend with its PHA synthesis ability. So we can use glycogen level to indicate cultureselection efficiency in enrichment step, and optimize the timing to introduce PHAsynthesis.