Elsevier

Bioresource Technology

Volume 195, November 2015, Pages 25-30
Bioresource Technology

Characteristic changes in algal organic matter derived from Microcystis aeruginosa in microbial fuel cells

https://doi.org/10.1016/j.biortech.2015.06.014Get rights and content

Highlights

  • Algal organic matter (AOM) was degraded in microbial fuel cells (MFCs).

  • AOM degradation was more completely by MFC than by fermentation.

  • Changes in AOM compositions and structures during MFC treatment were characterized.

  • Several different methods are used in AOM characterization.

Abstract

The objective of this study was to investigate behavior of algal organic matter (AOM) during bioelectrochemical oxidation in microbial fuel cell in terms of compositions and structures. Study revealed that the AOM derived from blue-green algae Microcystis aeruginosa could be degraded more completely (82% COD removal) in microbial fuel cells (MFCs) than by anaerobic fermentation (24% COD removal) in a control reactor without closed-circuit electrode and electricity was produced simultaneously. A variety of techniques were used to characterize the changes in AOM compositions and structures during bioelectrochemical oxidation. The presence of syntrophic interactions between electrochemical active bacteria and fermentative bacteria to degrade large molecular organics into small molecular substances, which could be oxidized by electrode but not by fermentation. The dominant tryptophan protein-like substances, humic acid-like substances and Chlorophyll a in AOM were highly degraded during MFC treatment.

Introduction

Algae, being rich in lipid, protein and carbohydrate, is considered as a promising biomass energy due to its high growth rates, round year production, high bio-fuel yields, small occupied space, and other benefits (e.g. CO2 capture, wastewater nutrients removal) (Mata et al., 2010, Scott et al., 2010). To date, algal biomass has been mainly used to produce bio-fuels (e.g. bio-diesel and bio-ethanol), methane, and hydrogen via various physical, chemical and biological methods (Chisti, 2007, Hirano et al., 1998, John et al., 2011, Nath and Das, 2004, Singh and Gu, 2010).

Microbial fuel cells (MFCs) can directly generate electricity by oxidizing organic compounds with the help of bacterial electrochemical reactions (Logan et al., 2006). Many new technologies have recently emerged by integrating MFC with algae for renewable energy production and wastewater treatment. First, algae biomass including living cell, dry mass, algae residue produced from other water/wastewater treatment processes can be directly used as fuels in MFCs for current production (Kondaveeti et al., 2014, Velasquez-Orta et al., 2009, Wang et al., 2012b). In this way, pretreatment procedures (e.g. alkaline, heat, and microwave) are normally necessary to dissolve algae cell walls for improvement of performance (Gadhamshetty et al., 2013, Xiao and He, 2014). Second, algae as phototrophic microorganisms can also be used to supply MFC cathode with oxygen for electron reduction as well as to reduce CO2 and produce valuable biomass simultaneously (Wang et al., 2010, Xiao and He, 2014). Third, MFC can be integrated with an algal bioreactor with division of labor for removal of organics (in MFC) and nutrients (in the algal reactor) from wastewaters as well as bio-energy (electricity and biomass) production (Xiao et al., 2012).

In these algae/MFC systems, algae play a role of fuel or functional microorganism to facilitate the reactions in process. In any case, effluents would be produced and finally enter environment. It is necessary to evaluate their environmental risks before being discharged. Because algae biomass has complex chemical compositions and cell itself can generate extensive amount of algal organic matter (AOM), algal toxins, taste and odor compounds with its metabolic excretion, decay and autolysis (Henderson et al., 2010, Her et al., 2004). If these compounds can’t be degraded completely by MFC, they will deteriorate effluents to result in water body pollution or affect the performance of subsequent treatment processes. For example, harmful disinfection byproducts (DBPs) will be produced after the effluent containing AOMs through tertiary treatment (e.g. disinfection), and the DBPs toxicity are closely related to the compositions and structures of AOM. Characterization of AOM is necessary to evaluate the risk of effluent discharge. Bioelectricity production from blue-green algae coupled algal toxins (MC-RR and MC-LR) removal was achieved in a single chamber tubular MFC (Yuan et al., 2011). The genotoxic agents in the polluted lake water were almost completely removed in a single-chamber air–cathode MFC (He et al., 2013). Our previous studies showed that precursors of disinfection byproduct (trihalomethane) were effectively reduced in a two-chamber MFC (Wang et al., 2012a). However, few studies so far have systematically researched on changes in AOM during MFC treatment in terms of composition, molecular weight, structures and so on. Hur et al. (2014) have used acidifying dry algae (green algae, Scenedesmus obliquus) powder as MFC substrate to reveal that AOM compositions would sequentially change with order of proteins, acidic functional group, polysaccharides and amino.

This study aimed at examining the changes in the characteristics of AOM derived from M. aeruginosa. during MFCs operation, and further exploring the biodegradability of AOM in MFCs. In addition, results were compared with those in MFC operated in open circuit condition, which has not been investigated in previous studies. Several characterization methods including ultrafiltration, fluorescence EEM spectroscopy, FT-IR spectroscopy and UV–visible absorbance were used.

Section snippets

Preparation of AOM solution

M. aeruginosa (blue-green algae, Collection No. HB909) were obtained from the Culture Collection of Algae at the Institute of Hydrobiology, Chinese Academy of Sciences, and were grown using BG11 media in an air-conditioned light incubator at 30 ± 1 °C (GZX-250, Taisite Instruments Inc., China). Algae were extracted on day 33, corresponding to the growth phase of stationary. The algae cells in BG11 medium were broken by ultrasound (3.5 W/mL) using a sonicator (Sonics Vibracell VCX-130 PB, 130 W, 20 

Electricity generated from AOM

After 25 days of start-up, AOM derived from M. aeruginosa with a COD of 525 ± 11 mg/L was fed into the MFC. A maximum voltage of 580 ± 10 mV (1000 Ω resistor) and the stable voltage around 520 mV were obtained during each batch cycle with operating period of around 2 days. The maximum volumetric power densities was 4.2 ± 0.1 W/m3. The total COD removal rates were 82 ± 5% and 24 ± 3% for MFC working at closed circuit (MFC-CC) and MFC working at open circuit (MFC-OC), respectively. The COD removal in MFC-CC was

Conclusions

Degradation of AOM, mainly including protein-like and humic-like substances as well as Chlorophyll a, was more completely by bioelectrochemical oxidation in MFC with closed circuit than anaerobic fermentation in MFC with open circuit. The newly generated small molecular byproducts during AOM degradation could be oxidized by electrode but not by fermentation. The dominant tryptophan protein-like substances in AOM were degraded more quickly than aromatic protein during MFC treatment.

Acknowledgements

The authors would like to thank the Funds for Creative Research Groups of China (Grant No. 51121062), the National Natural Science Foundation of China (No. 50778048), and State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (No. 2014TS02) for their supports for this study.

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