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BACKGROUND Nutrient removal via nitrite was investigated in a sequencing batch reactor ( SBR) treating reject water produced from the anaerobic digestion of sewage sludge and the subsequent dewatering process. The polyhydroxyalkanoate ( PHA) storage capacity of the biomass obtained under nitrifying (nitritation) and non-nitrifying aerobic conditions was investigated in batch reactors for biomass taken from the SBR. RESULTS In situ activity tests showed that the nitritation rate was not affected by the type of external organic carbon source that was added (i.e. propionic acid - HPr and sludge fermentation liquid - SFL). In contrast, the specific nitrite uptake rate ( sNUR) and the specific phosphate uptake rate ( sPUR) via nitrite were much higher when SFL was applied compared with HPr (22.39 ± 1.08 mgN g− 1VSS h−1 and 3.41 ± 1. 71mgP g− 1VSS h−1 when SFL was added compared with 7.80 ± 1. 23mgN g− 1VSS h−1 and 1.09 ± 0. 12mgP g− 1VSS h−1 when HPr was added). The majority of phosphorus removal was attributed to the normal growth of biomass rather than the activity of phosphorus accumulating organisms ( PAOs). The PHA yield was 0.65-0.67 C-mmol PHA/C-mmol short chain fatty acid ( SCFA) when nitrification was inhibited, and 0.60-0.63 C-mmol PHA/C-mmol SCFA when nitritation also occurred. CONCLUSION The PHA yield was not adversely affected under nitrifying conditions, demonstrating that nitritation can be integrated with the production of PHA. © 2014 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoate (PHA) production via mixed microbial cultures (MMCs) can potentially decrease process operational costs as compared to conventional pure culture techniques. However, the volumetric productivity of PHA by MMCs must be augmented to increase its cost competitiveness. For this purpose, a three-stage bioreactor system was operated in this study, with (i) anaerobic fermentation of molasses, (ii) culture selection, and (iii) PHA accumulation and harvesting stages. In stage 2, bioreactor operation with pH control at 8 led to twice the biomass concentration (up to 8 g VSS L−1, where VSS is the volatile suspended solids) as compared to operation without pH control (maximum pH 9). No loss in the specific PHA storage efficiency was observed (PHA content up to 57.5% and PHA storage rate up to 0.27 Cmol PHA Cmol X−1 h−1, where X is the active biomass), thereby resulting in twice the volumetric PHA production rate. The limited biomass growth at the higher pH level was not due to nutrient limitation, but likely to a shift in the microbial community. It is hypothesized that the increased enrichment of Azoarcus at pH 8 led to higher PHA productivity. pH control in the culture selection stage can lead to enhanced PHA production from MMCs, improving the viability of the process. [ABSTRACT FROM AUTHOR]

In enhanced biological phosphorus removal (EBPR) systems, polyphosphate-accumulating organisms (PAOs) are primarily responsible for removing phosphate from wastewater. Propionate is an abundant carbon substrate in many EBPR plants and has been suggested to provide PAOs an advantage over their carbon competitors--the glycogen-accumulating organisms (GAOs). The aerobic metabolism of PAOs enriched with a propionate carbon source is studied in this paper. A metabolic model is proposed and experimentally validated to characterize the aerobic biochemical transformations by PAOs. The model predicts very well the experimental data obtained from the enriched PAO culture through solid-, liquid-, and gas-phase analyses. This model may be combined with previously formulated metabolic models to better describe the biochemical activity of PAOs with acetate and propionate as the primary carbon sources. Furthermore, it can also facilitate the study of the effect of different carbon sources on PAO-GAO competition. Water Environ. [ABSTRACT FROM AUTHOR]