Efficient Polyhydroxyalkanoates Production from a Waste-Activated Sludge Alkaline Fermentation Liquid by Activated Sludge Submitted to the Aerobic Feeding and Discharge Process

Abstract

It was reported in our previous publication that the accumulation of short-chain fatty acids (SCFA) was significantly enhanced when waste-activated sludge (WAS) was anaerobically fermented at pH 10.0 (Yuan, et al., Environ. Sci. Technol. 2006, 40, 2025-2029). In this paper, the production of polyhydroxyalkanoate (PHA) by activated sludge with an aerobic feeding and discharge (AFD) process was investigated by the use of WAS alkaline fermentation liquid as the carbon source. It was observed that compared with other PHA synthesis processes reported in the literature, the AFD process showed the highest PHA production. The PHA content in sludge reached 72.9% when activated sludge was submitted to the AFD process. This was the highest PHA content obtained so far by activated sludge using wastes as the renewable carbon source. Although nitrogen and phosphorus were released into the WAS alkaline fermentation liquid, their presence did not affect PHA synthesis, which indicates that it is unnecessary to remove the released nitrogen and phosphorus, and the fermentation liquid can be used directly for PHA production. The accumulated PHAwas mainly composed of 3-hydroxybutyrate (3HB) (73.5 mmol C%), 3-hydroxyvalerate (3HV) (24.3 mmol C%), and 3-hydroxy-2-methylvalerate (3H2MV) (2.2 mmol C%). Further investigation showed that SCFA rather than protein and carbohydrate in the alkaline fermentation liquid made the main contribution to PHA production. The PHA produced from WAS alkaline fermentation liquid had a molecular weight of 8.5 x 10(5) Da and a melting point of 101.4 degrees C. Analysis using the 16S rRNA gene clone library revealed that gamma-Proteobacteria, alpha-Proteobacteria, and beta-Proteobacteria were the dominant microorganisms in the PHA production system.

Challenges and Opportunities for Customizing Polyhydroxyalkanoates

“…The enriched cultures of glycogen accumulating organisms were reported to utilize VFA from fermented sugarcane molasses to produce copolymers having 3HB (56-70 mol%), 3HV (13-43 mol%), 3HHx (1-23 mol%), 3H2 MB (0-2 mol%) and 3H2MV (0-2 mol%) which varied with VFA composition [7]. In addition to 3HV, presence of propionate in media also promoted 3H2MB and 3H2MV in the polymer as these could be formed through the combination of acetyl-and propionyl-CoA [60,61]. Lactate is more likely to promote 3HB in a polymer by both pure and mixed cultures [7].…”

Unveiling PHA-storing populations using molecular methods

“…and Azoarcus sp., which was further confirmed and quantified by FISH (already discussed in the hybridization section). Jiang et al (2009) also used the PCR-based methodology to characterize a selected MMC with waste-activated sludge (WAS) alkaline fermentation liquid as carbon source under ADF conditions (Jiang et al 2009). A SBR was operated with 3 days of SRT and took 45 days to reach a steady state.…”

Effects of pentachlorophenol on the bacterial denitrification process

“…The N 2 O in gas was directly sampled and injected into the sample inlet of gC by a syringe, and the N 2 O in aqueous solution was detected after using headspace with equilibrium temperature and time of 25 °C and 3 h, respectively. [18] The detailed procedures for NAD + and NADH measurements were conducted according to the literature. [19] Duplicate samples (1 mL each) were centrifuged at 12,000 r/min for 5 min.…”

“…[25,26] The glucose utilization by P. denitrificans was measured according to previous publication. [27] The lactate dehydrogenase (LDH) was measured by cytotoxicity detection kit (LDH release assay) (Roche Molecular Biochemicals) according to the manufacturer's instruction. The measurements of NO …”