[Polyhydroxyalkanoate (PHA) Synthesis by Glycerol-based Mixed Culture and Its Relation with Oxygen Uptake Rate (OUR)].

Polyhydroxyalkanoate (PHA) is one of the most promising biopolymers with the advantages of biodegradable biocompatible and renewable. A glycerol-fed PHA-producing mixed culture was enriched in a feast-famine regime. The substrate versatility and PHA production capacity of the mixed culture were studied using acetate,propionate,butyric, glucose and lactate as substrate, respectively. The results showed a high PHA content with lactate and acetate as the sole substrate, respectively. When acetate and propionate were used as mixed substrates to produce PHA, the PHA contents increased with the proportion of acetate and the PHA content was the highest as the ratio acetate/propionate was 3:1.The results based on the modeling of simultaneously storage and growth and the linear fitting under three different acetate/propionate ratios showed that there was a linear relation between PHA synthesis and OUR. Thus, it is feasible to estimate PHA content based on in-situ real-time monitoring data of OUR.

[On-line Estimation for the Amount of Stored PHA in Activated Sludge Based on OUR-HPR Measurements].

Activated sludge process is an important approach for industrial Polyhydroxyalkanoate ( PHA ) production. Off-line measurement with a time lag and complex analysis, is a common method for PHA, but is not suitable for the process control of PHA production. Based on a model for simultaneous storage and growth-soluble microbial products (SSAG-SMP), it is assumed that there is the linear relationship between the PHA synthesized and OUR or HPR, respectively. Further, a novel method to estimate PHA content based on in-situ monitoring data of oxygen uptake rate (OUR) and hydrogen-ion production rate (HPR) is established in this paper. The results of modeling OUR and HPR under different substrate concentrations showed that oxygen consumption proportion (kPHA,OUR) and proton consumption proportion (kPHA,HPR) of PHA synthesis were 0.67 and 0.57, respectively. The predicted results based on the linear relationship were essentially consistent with measured ones, and indicated that the method is feasible

[Influencing factors of floc size distribution and fractal dimension of activated sludge].

Floc size distribution (FSD) and fractal dimension are the important parameters for activated sludge. FSD of aerobic activated sludge during flocculation process was measured by a laser particle size analyzer, and the influence of velocity gradient, VSS/ SS, EPS content and Zeta potential on FSD was investigated. The results showed that the floc volume-average size was negatively correlated to velocity gradient (R > 0. 80) , and the order-of-magnitude of the floc volume-average size was equivalent to that of Kolmogorov scale (their differences were dependent on sludge VSS/SS, floc strength and etc). At a fixing velocity gradient, the floc volume-average size was positively correlated to VSS/SS or EPS (R2 >0. 85) , whereas negatively correlated to Zeta potential. Organic matter and EPS played important roles on the flocculation of activated sludge by enhancing the floc strength and improving the flocculation effect. Compared with polysaccharides, proteins in EPS seemed to be more beneficial for the flocculation of activated sludge. Based on microscopy and image analysis, the 2D and 3D fractal dimension of aerobic activated sludge floc was determined to be 1.28-1.72 and 1.70-2.69, respectively. It was found that fractal dimension (2D and 3D)was decreased with increasing VSS/SS (or EPS content). For the same activated sludge, the 3D fractal dimension was decreased with increasing floc size, and the relationship between 3D fractal dimension and floc size could be approximately described by a power function.