144
explored, which consists of mixing the polyhydroxyalkanoates-containing cells in
an immiscible solvent with water at high temperatures. Then, the polyhydroxyalkanoates are extracted by the addition of cold water. The advantage of this method
is the ability to recycle the solvent a number of times before disposing of it
(Visakh 2014).
To overcome the drawbacks of the solvent extraction method, the digestion
method was explored as a slightly more environmentally friendly alternative.
Sodium hypochlorite is used to dissolve non-polyhydroxyalkanoates biomass followed by centrifugation to recover polyhydroxybutyrate polymer. However, this
method can lower the polyhydroxyalkanoates content (Tan et al. 2014). To overcome this issue, an additional chemical, chloroform, is added to the solution to
protect the polyhydroxyalkanoates from degradation (Visakh 2014; Tan et al. 2014).
The solvent is then extracted and recovered via filtration. Other methods were
developed to enhance the mentioned routes such as solid shear (Visakh 2014) or
enzymatic digestion (Tan et al. 2014).
Enzymatic digestion was found to produce better results as it causes negligible
degradation of polyhydroxyalkanoates produced. It consists of enzymatic hydrolysis of the cells first, followed by polyhydroxyalkanoates recovery by centrifugation.
It was reported that polyhydroxyalkanoates with a purity of 90% were achieved via
the enzyme digestion method (Tan et al. 2014). Although this method is safer compared to its counterparts and has lower environmental footprint, its expensive price
increases the overall polyhydroxyalkanoates costs for a lower purity. More recently,
new methods have been explored for the recovery of polyhydroxyalkanoates including supercritical fluid disruption (Hejazi et al. 2003) and dissolved-air flotation (Van
Hee et al. 2006). Hejazi et al. were able to recover polyhydroxyalkanoates by the
disturbing Cupriavidus necator cells by the pressurization of a supercritical fluid
(CO 2 ) to the environment and increasing the temperature and pressure of the system
over the critical point of the supercritical fluid. After a period of time, the pressure
was released causing a pressure drop that disrupted the cells (Hejazi et al. 2003). For
the dissolved-air flotation recovery, Van Hee et al. diluted the fermentation broth
before putting it in a flotation column, then the bottom phase was freeze-dried to
recover polyhydroxyalkanoates granules (Van Hee et al. 2006) (Table 5.5).
The fourth step involves the accumulation of polyhydroxyalkanoates via precipitation, centrifugation, or filtration in order to concentrate the polyhydroxyalkanoates and remove the cellular debris (Kourmentza et al. 2017). The solution is
subjected to rotary evaporation followed by precipitation of polyhydroxyalkanoates
due to the addition of ice-cold ethanol or methanol depending on the chain length
(Tan et al. 2014). The last and final step is the purification, which involves processes
such as washing, drying, and polishing (Kourmentza et al. 2017).
A suitable polyhydroxyalkanoates extraction route selection depends on various
factors such as reaction time, pH and concentration, and recyclability of chemicals.
However, in order to reduce the costs of polyhydroxyalkanoates production and
environmental burdens, a system with a non-solvent harvesting recovery method is
the most beneficial (Visakh 2014).
S. Sali and H. R. Mackey
explored, which consists of mixing the polyhydroxyalkanoates-containing cells in
an immiscible solvent with water at high temperatures. Then, the polyhydroxyalkanoates are extracted by the addition of cold water. The advantage of this method
is the ability to recycle the solvent a number of times before disposing of it
(Visakh 2014).
To overcome the drawbacks of the solvent extraction method, the digestion
method was explored as a slightly more environmentally friendly alternative.
Sodium hypochlorite is used to dissolve non-polyhydroxyalkanoates biomass followed by centrifugation to recover polyhydroxybutyrate polymer. However, this
method can lower the polyhydroxyalkanoates content (Tan et al. 2014). To overcome this issue, an additional chemical, chloroform, is added to the solution to
protect the polyhydroxyalkanoates from degradation (Visakh 2014; Tan et al. 2014).
The solvent is then extracted and recovered via filtration. Other methods were
developed to enhance the mentioned routes such as solid shear (Visakh 2014) or
enzymatic digestion (Tan et al. 2014).
Enzymatic digestion was found to produce better results as it causes negligible
degradation of polyhydroxyalkanoates produced. It consists of enzymatic hydrolysis of the cells first, followed by polyhydroxyalkanoates recovery by centrifugation.
It was reported that polyhydroxyalkanoates with a purity of 90% were achieved via
the enzyme digestion method (Tan et al. 2014). Although this method is safer compared to its counterparts and has lower environmental footprint, its expensive price
increases the overall polyhydroxyalkanoates costs for a lower purity. More recently,
new methods have been explored for the recovery of polyhydroxyalkanoates including supercritical fluid disruption (Hejazi et al. 2003) and dissolved-air flotation (Van
Hee et al. 2006). Hejazi et al. were able to recover polyhydroxyalkanoates by the
disturbing Cupriavidus necator cells by the pressurization of a supercritical fluid
(CO 2 ) to the environment and increasing the temperature and pressure of the system
over the critical point of the supercritical fluid. After a period of time, the pressure
was released causing a pressure drop that disrupted the cells (Hejazi et al. 2003). For
the dissolved-air flotation recovery, Van Hee et al. diluted the fermentation broth
before putting it in a flotation column, then the bottom phase was freeze-dried to
recover polyhydroxyalkanoates granules (Van Hee et al. 2006) (Table 5.5).
The fourth step involves the accumulation of polyhydroxyalkanoates via precipitation, centrifugation, or filtration in order to concentrate the polyhydroxyalkanoates and remove the cellular debris (Kourmentza et al. 2017). The solution is
subjected to rotary evaporation followed by precipitation of polyhydroxyalkanoates
due to the addition of ice-cold ethanol or methanol depending on the chain length
(Tan et al. 2014). The last and final step is the purification, which involves processes
such as washing, drying, and polishing (Kourmentza et al. 2017).
A suitable polyhydroxyalkanoates extraction route selection depends on various
factors such as reaction time, pH and concentration, and recyclability of chemicals.
However, in order to reduce the costs of polyhydroxyalkanoates production and
environmental burdens, a system with a non-solvent harvesting recovery method is
the most beneficial (Visakh 2014).
S. Sali and H. R. Mackey