3.7 Limitations
Phycoremediation of wastewater treatment has its limitations despite its simplicity,
effectiveness, and eco-friendly nature. These are explained in more detail below:
• Raw sewage has been studied broadly in the fields of microalgae culturing and
wastewater treatment. It is considered to be a suitable nutrient medium because of
its N/P ratios availability and low levels of toxicity (Li et al. 2011). Even though
agricultural wastewaters (such as manure-based wastewaters) are regarded as a
potential nutrient source for microalgae, the presence of pesticides in agricultural
wastewaters may be detrimental to a few microalgae species. Cyanobacteria
species are appropriate for pesticide bioremediation (usually at trace concentrations), but again the toxic cyanobacteria create a problem for the environment
(Caceres et al. 2008).
• In the case of effluent containing high organic and nutrient load (e.g., wastewater
from livestock, soybean processing, breweries, etc.), dilution is required prior to
microalgal treatment in order to prevent unwanted inhibitory effects of ammonium levels (Abeliovich and Azov 1976). At high nutrient concentrations, the
formation of chlorophyll a is excessive in microalgae, and it could have the effect
of reducing the amount of nutrients removed due to the limited amount of light
(4100 lux) (Aslan and Kapdan 2006).
• Though microalgae have demonstrated the ability to remove heavy metals (absolute concentration) from industrial effluents and simulated industrial effluents, a
high level of heavy metals can be harmful to algae growth. Also, some metal ions
(e.g., Fe
3+ , Cu
2+ , and Zn
2+ ) may precipitate phosphorus and reduce its availability
to microalgae (Zhen-Feng et al. 2011).
• Industrial effluents which are characterized by low nutrients and high toxic levels
require either added external nutrients or combined toxic industrial effluents with
municipal wastewater to support the microalgae growth (Chinnasamy et al.
2010).
• Microalgae can be cultivated either by batch mode or chemostat (continuous)
mode in which the continuous mode provides maximum efficiency compared to
that of batch mode since the nutrients are supplied continuously to the treatment
system. There are a twofold rise in biomass productivity, greater N and P removal
(> 99%), and higher bioenergy production (5.3–6.1 MJ m
À3 day
À1 ) from 1.33
days culturing of Scenedesmus sp. in municipal wastewater effluent (McGinn
et al. 2012). In spite of its advantages over the batch mode, this technique is yet to
be implemented in the industrial wastewater system, and most studies have been
conducted in batch or semi-batch mode (Kotteswari et al. 2012; Chinnasamy et al.
2010; Solovchenko et al. 2014; Mata et al. 2012).
• Phycoremediation requires comparatively high downstream processing costs.
Algae harvesting from wastewater after treatment remains a major problem to
the relevant industries, due to the size of algal cells and their diluted cultures
(most commonly 200–600 mg/l
À1 ) (Uduman et al. 2010). Also, the cost of algae
318
J. Umamaheswari et al.
Phycoremediation of wastewater treatment has its limitations despite its simplicity,
effectiveness, and eco-friendly nature. These are explained in more detail below:
• Raw sewage has been studied broadly in the fields of microalgae culturing and
wastewater treatment. It is considered to be a suitable nutrient medium because of
its N/P ratios availability and low levels of toxicity (Li et al. 2011). Even though
agricultural wastewaters (such as manure-based wastewaters) are regarded as a
potential nutrient source for microalgae, the presence of pesticides in agricultural
wastewaters may be detrimental to a few microalgae species. Cyanobacteria
species are appropriate for pesticide bioremediation (usually at trace concentrations), but again the toxic cyanobacteria create a problem for the environment
(Caceres et al. 2008).
• In the case of effluent containing high organic and nutrient load (e.g., wastewater
from livestock, soybean processing, breweries, etc.), dilution is required prior to
microalgal treatment in order to prevent unwanted inhibitory effects of ammonium levels (Abeliovich and Azov 1976). At high nutrient concentrations, the
formation of chlorophyll a is excessive in microalgae, and it could have the effect
of reducing the amount of nutrients removed due to the limited amount of light
(4100 lux) (Aslan and Kapdan 2006).
• Though microalgae have demonstrated the ability to remove heavy metals (absolute concentration) from industrial effluents and simulated industrial effluents, a
high level of heavy metals can be harmful to algae growth. Also, some metal ions
(e.g., Fe
3+ , Cu
2+ , and Zn
2+ ) may precipitate phosphorus and reduce its availability
to microalgae (Zhen-Feng et al. 2011).
• Industrial effluents which are characterized by low nutrients and high toxic levels
require either added external nutrients or combined toxic industrial effluents with
municipal wastewater to support the microalgae growth (Chinnasamy et al.
2010).
• Microalgae can be cultivated either by batch mode or chemostat (continuous)
mode in which the continuous mode provides maximum efficiency compared to
that of batch mode since the nutrients are supplied continuously to the treatment
system. There are a twofold rise in biomass productivity, greater N and P removal
(> 99%), and higher bioenergy production (5.3–6.1 MJ m
À3 day
À1 ) from 1.33
days culturing of Scenedesmus sp. in municipal wastewater effluent (McGinn
et al. 2012). In spite of its advantages over the batch mode, this technique is yet to
be implemented in the industrial wastewater system, and most studies have been
conducted in batch or semi-batch mode (Kotteswari et al. 2012; Chinnasamy et al.
2010; Solovchenko et al. 2014; Mata et al. 2012).
• Phycoremediation requires comparatively high downstream processing costs.
Algae harvesting from wastewater after treatment remains a major problem to
the relevant industries, due to the size of algal cells and their diluted cultures
(most commonly 200–600 mg/l
À1 ) (Uduman et al. 2010). Also, the cost of algae
318
J. Umamaheswari et al.