ABSTRACT

To limit the carbon footprint, the future energy resources should be carbon neutral and renewable. Such sources include biomass as a sustainable resource for energy production. Algae can be considered as one of such potential feedstocks for bio-based economy (Gajda et al., 2015). During conventional wastewater treatment processes, a large quantity of carbon dioxide (CO2) is emitted into the atmosphere during oxidation of organic matter, and it causes a harmful effect on environment. If this amount of CO2 can be captured by algae for photosynthesis, huge algal biomass can be produced for production of value-added products (Gude et al., 2013). Such microalgal biomass can be further utilized for the production of methane, hydrogen, ethanol, butanol and electricity during anaerobic processes. Considering the energy value, the highest energy yields (kJ/g of dry wt. microalgal biomass) reported in the literature were 14.8 as ethanol, 14.4 as methane, 6.6 as butanol, 1.2 as hydrogen and electricity of 0.98 W/m2 (Lakaniemi et al., 2013). Microalgal biomass is considered as a potential substrate for anaerobic energy conversion processes, especially for methanogenic digestion, fermentation and for electrogenic bacteria (Lakaniemi et al., 2013). Additionally, algal biomass with/without pre-treatment serves as feedstock for bio-electrochemical systems (BES) for production of energy. The energy can be recovered in the form of direct electricity in microbial fuel cell (MFC) or in the form of hydrogen in microbial electrolysis cell (MEC) during treatment of organic matter. Also, CO2 released during anodic oxidation captured for photosynthesis with release of oxygen as terminal electron acceptor for cathodic reduction in microbial carbon capture cell (MCC) or with microbial solar cell (MSC). The algae grown in the photobioreactor (or in cathodic chamber) can serve as potential candidates for CO2 capture, biomass recovery, feedstock for anodic reactions, methanogen suppressors and by-product recovery in various aspects of BES (Jadhav et al., 2017; Rajesh et al., 2015), as discussed in Table 9.1. Utilization of Algae in MFC for Different Applications https://www.niso.org/standards/z39-96/ns/oasis-exchange/table"> Application MFC Details Findings References Algae as substrate for electricity generation Spirulina platensis algal biofilm on anode Current generation proportional to chlorophyll content Lin et al. (2013) Oxygen production for cathodic reactions Scenedesmus obliquus algal biocathode; H-type MFC 15.7 mg/L of oxygen used as terminal electron acceptor for MFC Kakarla and Min (2014) Methanogen inhibitor Clayware MFC with Chaetoceros pretreated inoculum

Long chain saturated

fatty acid from algae inhibits methane formation

Rajesh et al. (2015) CO2 sequestration Chlorella vulgaris biocathode; glucose as an anodic substrate CO2 generated during anaerobic process fixed at algal biocathode Wang et al. (2010) Ethanol and biodiesel production C. vulgaris algae

Ethanol = 2.13 g/L/hr;

biodiesel = 12 m3/year

Kerls (2012)