137
location-dependent economic and environmental constraints, such as the cost of
energy. In general, a microbial mixed culture requires three steps: (1) fermentation
of complex substrate to readily biodegradable substrates such as volatile fatty acids,
(2) culture enrichment, and (3) polyhydroxyalkanoates accumulation. In certain circumstances, enrichment and accumulation phases may be possible to perform
together. A summary of the various overarching modes of process design is described
in Table 5.4 for enrichment and accumulation.
The anaerobic-aerobic method was the first method discovered to induce polyhydroxyalkanoates storage and was associated with biological phosphorus removal.
Depending on the nature of the substrate and whether fermentation is required or
sufficient in the anaerobic stage, a preceding fermenter may be necessary. The
anaerobic-aerobic method has the advantage that aeration is reduced, especially if
the famine phase is conducted under anoxic conditions. While accumulation is typically low, values up to 60% cell dry weight have been reported (Albuquerque et al.
2007) and have the added benefit that it can be coupled with phosphorus removal.
For compatibility with existing treatment processes, the anaerobic-aerobic method
may be a preferred choice. Aerobic-anoxic and anoxic-aerobic systems rely on similar integration with existing wastewater treatment processes where in the former
denitrification occurs on stored polyhydroxyalkanoates. Both can reduce aeration
requirements. While the former has achieved limited polyhydroxyalkanoates storage (Kourmentza et al. 2017), anoxic-aerobic systems have reported accumulation
as high as 60% g-polyhydroxyalkanoates/g-VSS (Anterrieu et al. 2014). Such systems have been enhanced through integration with fixed-film processes such as
moving bed biofilm reactor carriers or integrated fixed-film activated sludge systems to separate the long sludge retention times required for nitrification where this
process is still required for treatment from the short sludge retention times desired
for high-rate polyhydroxyalkanoates production (Anterrieu et al. 2014; Bengtsson
et al. 2017).
The three-step process is another type of continuous flow process. The first step
consists of conversion of carbohydrates to volatile fatty acids under anaerobic fermentation. This step is often carried out under acidic conditions to help promote
acidogenic bacteria and ensure inhibition of methanogenic bacteria that will compete for acetate that has been produced. The second step of the process consists of
the enrichment of activated sludge for the production of polyhydroxyalkanoatesaccumulating bacteria, most often, under aerobic dynamic feeding (ADF) conditions. The last step of the process consists of the polyhydroxyalkanoates accumulation
process under aerobic conditions in a fed-batch reactor (Kourmentza and Kornaros
2016). Aerobic dynamic feeding methods are the most commonly reported methods
from studies to induce polyhydroxyalkanoates accumulation and in general achieve
higher accumulation levels than the methods relying on alternating redox conditions
with values of 90% cell dry weight being reported (Jiang et al. 2011d). The alternating feast-famine conditions promote cultures with strong ability to produce polyhydroxyalkanoates during substrate-rich conditions.
One issue with aerobic dynamic feeding systems is the high aeration requirements and the need for sufficient famine conditions that may reduce overall
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…
location-dependent economic and environmental constraints, such as the cost of
energy. In general, a microbial mixed culture requires three steps: (1) fermentation
of complex substrate to readily biodegradable substrates such as volatile fatty acids,
(2) culture enrichment, and (3) polyhydroxyalkanoates accumulation. In certain circumstances, enrichment and accumulation phases may be possible to perform
together. A summary of the various overarching modes of process design is described
in Table 5.4 for enrichment and accumulation.
The anaerobic-aerobic method was the first method discovered to induce polyhydroxyalkanoates storage and was associated with biological phosphorus removal.
Depending on the nature of the substrate and whether fermentation is required or
sufficient in the anaerobic stage, a preceding fermenter may be necessary. The
anaerobic-aerobic method has the advantage that aeration is reduced, especially if
the famine phase is conducted under anoxic conditions. While accumulation is typically low, values up to 60% cell dry weight have been reported (Albuquerque et al.
2007) and have the added benefit that it can be coupled with phosphorus removal.
For compatibility with existing treatment processes, the anaerobic-aerobic method
may be a preferred choice. Aerobic-anoxic and anoxic-aerobic systems rely on similar integration with existing wastewater treatment processes where in the former
denitrification occurs on stored polyhydroxyalkanoates. Both can reduce aeration
requirements. While the former has achieved limited polyhydroxyalkanoates storage (Kourmentza et al. 2017), anoxic-aerobic systems have reported accumulation
as high as 60% g-polyhydroxyalkanoates/g-VSS (Anterrieu et al. 2014). Such systems have been enhanced through integration with fixed-film processes such as
moving bed biofilm reactor carriers or integrated fixed-film activated sludge systems to separate the long sludge retention times required for nitrification where this
process is still required for treatment from the short sludge retention times desired
for high-rate polyhydroxyalkanoates production (Anterrieu et al. 2014; Bengtsson
et al. 2017).
The three-step process is another type of continuous flow process. The first step
consists of conversion of carbohydrates to volatile fatty acids under anaerobic fermentation. This step is often carried out under acidic conditions to help promote
acidogenic bacteria and ensure inhibition of methanogenic bacteria that will compete for acetate that has been produced. The second step of the process consists of
the enrichment of activated sludge for the production of polyhydroxyalkanoatesaccumulating bacteria, most often, under aerobic dynamic feeding (ADF) conditions. The last step of the process consists of the polyhydroxyalkanoates accumulation
process under aerobic conditions in a fed-batch reactor (Kourmentza and Kornaros
2016). Aerobic dynamic feeding methods are the most commonly reported methods
from studies to induce polyhydroxyalkanoates accumulation and in general achieve
higher accumulation levels than the methods relying on alternating redox conditions
with values of 90% cell dry weight being reported (Jiang et al. 2011d). The alternating feast-famine conditions promote cultures with strong ability to produce polyhydroxyalkanoates during substrate-rich conditions.
One issue with aerobic dynamic feeding systems is the high aeration requirements and the need for sufficient famine conditions that may reduce overall
5 Integration of Polyhydroxyalkanoates Production with Industrial Wastewater…