Aerobic dynamic feeding (ADF) strategy was applied in sequencing batch reactor (SBR) to accumulate polyhydroxyalkanoate (PHA) in aerobic granules. The aerobic granules were able to remove 90% of the COD from palm oil mill effluent (POME). The volatile fatty acids (VFAs) in the POME are the sole source of the PHA accumulation. In this work, 100% removal of propionic and butyric acids in the POME were observed. The highest amount of PHA produced in aerobic granules was 0.6833mgPHA/mgbiomass. The PHA formed was identified as a P (hydroxybutyrate-co-hydroxyvalerate) P (HB-co-HV).
The polyhydroxyalkanoate (PHA) accumulation dynamics in aerobic granules that undergo the growth-disintegration cycle were investigated. Four sequencing batch reactors (SBR) were inoculated with aerobic granules at different stages of development (different sizes). Different sizes of aerobic granules showed varying PHA contents. Thus, further study was conducted to investigate the diffusion of substrate and oxygen on PHA accumulation using various organic loading rates (OLR) and aeration rates (AR). An increase in OLR from 0.91 to 3.64kg COD/m(3)day increased the PHA content from 0.66 to 0.87g PHA/g CDW. Meanwhile, an AR increase from 1 to 4L/min only accelerated the maximum PHA accumulation without affecting the PHA content. However, the PHA composition only changes with AR, while the hydroxyvalerate (HV) content increased at a higher AR.
Polyhydroxyalkanoate (PHA) recovery from aerobic granules was investigated using four cell digestion agents, namely, sodium hypochlorite, sodium hydroxide, acetone and sodium chloride. Simultaneously, the removal of extracellular polymeric substances (EPS) and its effect on PHA yield were investigated. The highest PHA recovery yield was obtained using sodium hypochlorite, accounting for 89% cell dry weight (CDW). The highest PHA was recovered after the sodium hypochlorite completely removed the EPS from the aerobic granules. The average molecular weight (Mw) of the PHA recovered using sodium hypochlorite was 5.31 × 10(5)g/mol with only 1.8% molecular weight degradation. The energy and duration analysis for PHA recovery revealed that the sodium hypochlorite method required the least amount of energy and time at 0.0561 MJ/g PHA and 26 h, respectively. The PHA that was recovered was a P3(HB-co-HV) co-polymer.
Microalgae-based biodiesel has gained widespread interest as an alternative energy source. Low-cost microalgae harvesting technologies are important for economically feasible biodiesel production. This study investigated, for the first time, the impact of adaptation period and height to diameter (H/D) ratio of a reactor on the growth and self-flocculation of microalgae, without the addition of bacteria. Six reactors were grouped into three sets of experiments, and each reactor was operated for 30 days at similar operating conditions (volume exchange ratio = 25% and settling time = 30 min). In set 1, two 8-L reactors, H5a (H/D ratio: 5) and H8a (H/D ratio: 8), were operated under batch operation. In set 2, reactors H5b and H8b were operated as sequential batch reactors (SBRs) without an adaptation period. In set 3, the reactors H5c and H8c were operated as SBRs with an adaptation period. The findings showed a threefold improvement in biomass productivity for the higher H/D ratio (H8c) and a reduction in biomass loss for microalgae. The H8c reactor exhibited 95% settling efficiency within 5 days, in comparison to 30 days for the H5c reactor. This study demonstrated that a higher H/D ratio and the introduction of an adaptation period in SBR operation positively influences growth and self-flocculation of enriched mixed microalgae culture.