Determination of optimum operating conditions for production of polyhydroxybutyrate by activated sludge submitted to dynamic feeding regime

Abstract

Polyhydroxybutyrate (PHB) was produced by activated sludge in a two-stage process. In the first stage, the sludge with high storage potential was enriched in a sequencing batch reactor (SBR) operated by a dynamic feeding regime. The biosynthesis of PHB was sequentially accomplished in a batch reactor in the second stage. This article focused on the optimization of PHB content by evaluating the effects of three critical factors: Dissolved oxygen, pH and food-to-microorganism (F/M) ratio in the batch reactor. The results showed that the rate of substrate uptake, as well as the yield and content of PHB increased with the increase of dissolved oxygen concentration. The control of pH was not necessary under the weak alkaline condition for improvement of PHB content, except for the case in which the pH value was out of rang of 7.0 to 10.0. The enhanced F/M ratio favored PHB accumulation in the range of 1.0 to 4.5 C-mmol/C-mmol and the highest PHB content, 64%, was achieved at 4.5 C-mmol/C-mmol. When F/M ratio was enhanced to 6.0 C-mmol/C-mmol, the phenomenon of utilizing simultaneously intracellular PHB and external substrate by sludge was observed, which resulted in a sharp decrease of PHB content. The microscopic observation clearly confirmed that dynamic feeding regime was effective for selecting and enriching the sludge with a high storage potential.polyhydroxybutyrate, activated sludge, dynamic feeding regime, optimum operating conditions Conventional plastics have faced some severe problems, because of their persistency in the environment and non-biodegradability. Therefore, the biodegradable plastic has potentials in applications. Polyhydroxyalkanoates (PHAs) are the polyester of hydroxyalkanoates synthesized by numerous bacteria as intracellular carbon and energy storage compounds, and have similar mechanical properties to conventional plastics like polypropylene or polyethylene. Additionally, PHAs have the attractive features of being completely biodegradable, biocompatible, and produced from renewable sources. Polyhydroxybutyrate (PHB) is the most common and best characterized PHAs. For the economical production of PHAs, various bacterial strains, either wild-type or recombinant, and new fermentation strategies were developed with high content and productivity of PHAs [1,2]

Efficient polyhydroxyalkanoate (PHA) accumulation by a new continuous feeding mode in three-stage mixed microbial culture (MMC) PHA production process

“…(Fig. 2) The increase of reaction pH during the PHA accumulation stage has been reported by several researchers (Chua et al, 2003;Serafim et al, 2004;Qu et al 2009;Albuquerque et al, 2011). Dias et al (2006) has concluded that three processes affect the reaction pH: uptake of the substrate (decrease the concentration of H + in the solution), NH 3 assimilation and CO 2 production and transfer (both increase the concentration of H + in the solution).…”

Effect of dissolved oxygen and temperature on macromolecular composition and PHB storage of activated sludge

“…By contrast, another previous study focussing on PHB production by activated sludge in a two-stage 169 process revealed that the rate of substrate uptake, as well as the yield and content of PHB increased 170 with an increase in DO concentration. [12] The studies reported by Qu and Liu [12] also showed that an 171 enhanced F/M ratio favored PHB accumulation. 172 173…”

“…[11] 71 4 Many studies have been carried out on activated sludge to produce PHA, most of them using feast-72 famine regimes or nutrient pulses. [12] It has been observed that its production depends on operational 73 parameters such as the type of carbon source, C/N ratio, organic load, dissolved oxygen (DO) 74 concentration, pH, sludge retention time (SRT), temperature, magnetic field intensity, and nutrient 75 deficiencies such as nitrogen and phosphorus. [13][14][15] 76 There is currently great interest worldwide to produce various commercially usable macromolecules 77 from the WAS from sewage treatment plants.…”

What Has Been Trending in the Research of Polyhydroxyalkanoates? A Systematic Review

“…Activated sludge can be an alternative to pure cultures for PHA production due to many PHA-producing bacteria present in activated sludge (Yang et al, 2013 ). In the wastewater treatment process, the microorganisms from activated sludge display the ability to transform a biodegradable carbon source into PHA before using them for growth (Qu and Liu, 2009 ). Industrial-scale PHA production is based mainly on pure-culture systems with refined feedstock and sterile cultivation conditions.…”

“…Later studies (after 2000) focus on parameters such as carbon and nitrogen sources, their mutual quantitative relations in the fermentation reaction, and the impact of these parameters on process efficiency (Khardenavis et al, 2005 ). Further analysis on the example of PHB production describes the impact of critical factors such as dissolved oxygen, pH, and food to microorganism (F/M) ratio in the batch reactor on the reaction efficiency (Qu and Liu, 2009 ). Researchers also carried out physiochemical properties analysis of the polymers PHB and P(HB-co-HV) to identify production conditions that directly affect final product mechanical properties (Wallen and Rohwedder, 1974 ; Patel et al, 2009 ).…”