**6. Removal of cellulose using BES**

Cellulose is a β-1,4-linkaged polymer of Glucose. Cellulosic biomass, usually obtained from agricultural and industrial activities, can be considered as one of the highly available sources of renewable energy on earth. Cellulosic materials can be used in a process of sustainable energy production by transforming them to H2, ethanol, and methane. But due to economic and technical problems, it remains difficult to produce such products [57].

One of the main major downsides of Cellulose is that it's a moderately recalcitrant compound. It can be converted to different types of fuels such as bioethanol, methane and Hydrogen, but the energy recovery and treatment in waste water is difficult because of its low density in terms of energy and highly recalcitrant nature [58]. Another problem is that, cellulose is adhered with lignin or/and Hemicellulose. Lignin may cause problems by not allowing cellulases to digest cellulose material due to this tight adherence. However microbial fuel cells (MFCs) can be used to convert cellulosic materials to Electrical energy and it has been found to be an effective technology which can be used as an alternative. The microorganism or microorganisms must be able to breakdown cellulose anaerobically to sugar monomers and they should also be electrochemically active in order to directly convert liberated sugars to electricity in a Microbial Fuel Cell. Here, they should use an anode as an alternative electron acceptor. Metabolites of cellulose hydrolysis are oxidized in this manner to produce direct electrical energy [57].

Anaerobic microorganisms of facultative varieties can be found in the rumen. Through fermentation or anaerobic respiration, they hydrolyze cellulose while conserving energy significantly. Hence, Rumen microbial consortium can be used in Microbial Fuel Cells to generate electricity from cellulose [57]. Cellulose is different from other organic materials because, it needs this consortium to metabolize it [58]. When the Rumen consortia was used in Microbial Fuel cells, it showed the


*Expedited Biodegradation of Organic Pollutants and Refractory Compounds… DOI: http://dx.doi.org/10.5772/intechopen.99229*

#### **Table 4.**

*BES studies involving cellulose and the bioelectrochemical characteristics of the BES systems during cellulose remediation.*

presence of respiratory anaerobes & hydrolytic enzymes which involved in cellulose hydrolysis. Phylogenetic analysis was also used to understand this relationship [57].

*Clostridium cellulolyticum* and *Geobacter sulfurreducens* were used in one study to demonstrate the production of electricity in Microbial Fuel cells which used particulate MN301 Cellulose. Fluorescent *in situ* hybridization and quantitative PCR showed that most *Clostridium* cells were attached to cellulose which was there as a suspension. In the meantime, *Geobacter* cells were attached to the electrode. However, in contrast, use of soluble carboxymethyl cellulose caused bacteria to remain as suspension and biofilm. This explains that it is possible to improve electricity conversion from solution by decanting supernatant and settling Cellulose, as Cellulose hydrolysis can be improved by optimizing the reactor operations. Cellulose transformation performance can be increased with further research. The performance of the reactor with increasing biocatalyst density should be further analyzed. Hence, the effectiveness of decant and settling at cellulolytic density of higher concentration is one part which needs further focus to identify cellulose conversion extent [58]. Several previous studies have demonstrated the effectiveness of various BES types to biodegrade and convert the energy content of cellulose and its derivatives into electrical energy (**Table 4**).

#### **7. Removal of lignin its derivatives in BES**

Lignin is a phenolic polymer which is heterogenous in nature. It is made of renewable source of aromatic chemicals. Main components of Lignin are three alcohols namely phydroxyphenyl guaiacyl and syringyl. Different types of lignin in different plant components like grass, softwood and hardwood contain different amounts of methoxy groups depending on the degree of these three types of alcohols present in them. Microbial Fuel Cell (MFC) is a type of biological decomposition method which can be used to degrade lignin efficiently [59]. Microbial fuel cells are devices which produce electricity from catalysis of microorganisms by using chemical energy as their energy source [60]. They contain a cathode chamber which is aerobic and an anode chamber which is anaerobic. Both of these chambers are connected either by a salt bridge or a membrane where the protons can be exchanged. In the anode chamber, microorganisms like fermenting bacteria produce smaller fermentation products from larger organic molecules. CO2, protons, and electrons are produced by oxidation using anaerobic bacteria afterwards. The circuit is completed by electrons passing to the anode interface which are then transferred to the cathode through an external wire. The cathode reduces the oxygen molecules to either form water or H2O2. Here, H2O2 is produced by a two-step reaction consisting of a two-electron reaction [59]. The lignin undergoes hydrogen peroxide mediated oxidative depolymerization when introduced to the cathode. In aerobic, low pH conditions this oxidative reaction will proceed better as oxygen is required for H2O2 production. An effective method for H2O2 production has already been observed recently via a microbial electrochemical cell [61].
