Microbial Fuel Cell | Bioremediation | Sewage treatment |

Use of Microbial Fuel Cell for Sewage Treatment

Introduction

Sewage treatment is the process of removing contaminants from wastewater and household sewage, both runoffs (effluents), domestic, commercial and institutional. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce an environmentally safe fluid waste stream (treated effluent) and a solid waste (treated sludge) suitable for disposal or reuse. The treatment of wastewater is not only important for our health but also to keep our environment clean and healthy [1] [2].

Discharge of untreated sewage water in the water body is a common practice in many countries. This is the common cause of pollution of surface and groundwater because there is a large gap between the generation and treatment of domestic wastewater in India [3] [4].

The treatment and disposal of sewage sludge is an expensive and environmentally sensitive problem that is growing worldwide. Sludge production is increasing whilst previously accepted methods for disposal are coming under pressure or even being phased out altogether so there is now an urgency to find cost-effective and innovative solutions that appease environmental and public pressures [5] [6].

keywords: Sewage treatment, Bioremediation, Microbial Fuel Cell, sewage treatment plant, sewage plant, Microbial fuel cell wastewater treatment, Microbial fuel cell for wastewater treatment and power generation, microbial fuel cell wastewater treatment, Microbial fuel cell advantages

What is sewage? 

Sewage is defined as water-carried waste, either in solution form or suspended form, intended to be removed or discarded from municipal communities, households or industries. Also referred to as wastewater, it consists of more than 99% water & is usually characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains [7]. 

The sewage or the wastewater has been adversely affected in quality by anthropogenic influence. The term wastewater should be separated from the term sewage. Wastewater mainly constitutes liquid waste discharged by domestic residences, commercial properties, industry, agriculture, which often contains some contaminants that result from the mixing of wastewater from different sources. 

Based on its origin wastewater can be further classified as sanitary, commercial, industrial, agricultural or surface runoff. On the other hand, sewage mainly includes domestic, municipal, or industrial liquid waste products. Domestic sewage is the primary source of pathogens and putrescible organic substances. Because pathogens are excreted in faces, all sewage from cities and towns is likely to contain pathogens of some type, potentially presenting a direct threat to public health [7]. 

It is very important to bring under notice that the use of untreated sewage in agriculture is of public concern due to possible phytotoxicity and/or incorporation of metal cations into the food gradients. Excess nitrogen and phosphorus in effluents can leach and pollute groundwater under continuous sewage effluent use for long periods. 

In conclusion, the growing population, urbanization, economic and industrial development are not only putting pressure on the water resources in terms of quantity, but the pressure is also increasing in terms of quality. Therefore, the importance of sewage treatment needs to be stressed upon along with the development of new and innovative methods.

Types of sewage 

There are three basic sewage types are: 

1. Domestic sewage – Water from houses and apartments

2. Industrial sewage – Water from manufacturing or chemical processes

3. Storm sewage – Runoff from precipitation

Principle pollutants in sewage are organic material, suspended solids, plant nutrients and microbes [8].

Domestic sewage consists of chemicals from daily use products. When they are added to the sewage supply, they can affect the health of all forms of life in the water. 

Industrial waste has been a problem since the industrial revolution. Industrial waste may be toxic, ignitable, corrosive or reactive. If improperly managed, this waste can pose dangerous health and environmental consequences. 

The BOD of storm sewage is of particular concern when it is mixed with domestic sewage in combined sewerage systems. It may contain higher concentrations of suspended solids than domestic sewage [8].

Another classification of sewage would be: 

1.Treated sewage -  Once wastewater or sewage is passed through a treatment plant it is referred to as treated sewage. It goes through several stages in the treatment process to ensure that any harmful bacteria, pollutants and contaminants are eliminated. 

2.Untreated Sewage- Untreated sewage is wastewater that contains harmful waterborne pathogens and bacteria. It has not gone through a sewage treatment plant [9].

Need for sewage treatment

Wastewater treatment, also called sewage treatment, is the removal of impurities and suspended solids from wastewater, or sewage, before they reach aquifers or water bodies. Most of the water used by homes, industries and businesses must be treated before it is released back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the watering [10]. 

If the wastewater is not treated properly, then the environment and human health can be negatively impacted. It can cause harm to fish and wildlife populations, oxygen depletion, contamination of drinking water, eutrophication and even chlorination of water bodies [10] [11]. 

Primary treatment removes 60% of suspended solids from wastewater. This treatment also involves aerating the wastewater, to put oxygen back in.

Secondary treatment removes more than 90% of suspended solids.

By pairing wastewater treatment with biofuel production we can solve two environmental issues simultaneously [11]. 

Cities with the best and the worst sewage system

1. Pune

2. Chennai

3. Gurgaon

Cities with the worst sewage system are:

1. Mumbai

2. Bengaluru

3. Kolkata

Present techniques employed in a few STPs

Advanced water treatment technologies are currently being employed to separate wastes and decrease the pollution of wastewater. These methods can be advanced oxidative methods, chemical precipitation and bioremediation.

Most of the sewage treatment plants employ a three-stage system which consists of primary, secondary and tertiary treatment. Primary treatment includes removing solid wastes.  This is done in a series of tanks. The waste materials can either be floating or settle to the bottom by gravity. Some of the primary treatment techniques include sedimentation, screening, grit removal, comminution. The sludge is then sent to a digester for further processing [12].

Secondary waste treatment is done to attain good quality effluent. It is done to remove small suspended solids and the biochemical oxygen demand for 5 days i.e. BOD5. It can be done by using oxidative methods like biofiltration, aeration techniques, oxidation ponds etc. or by implementing microbes to break down suspended matter and provide good quality effluent. Nearly all suspended solids and 85% of BOD is removed at the end of this stage [12] [13].

The effluent will still contain nitrogen, phosphorus, heavy metals and microbes. To remove this, the effluent is sent to a tertiary treatment tank. Here, processes like activated carbon absorption, coagulation-sedimentation, membrane filtration, sand filtration, chemical oxidation, chlorination etc. are implemented to give good quality, treated effluent [12]. 

In high-end, advanced STPs, UV screening is employed to remove pathogens present in the water. This is also used to control algal growth, which was promoted by nitrogen and phosphorus content present in the effluent. 

Alum is used to remove phosphorus and also aggregates solid particles into flocs. The sand filter removes the solids and allows water to flow through by gravity separation. This is fed to the chlorination tank, where the water is chlorinated to remove microbes and is sent to a discharge tank. Any excess chlorine is removed from the water, in the discharge tanks, by adding a small quantity of sodium bisulfite to ensure there is no harm to any organism consuming the treated water [13].

These are the current techniques used in modern sewage treatment plants. If an STP is to be built on a low budget, the tertiary plant’s function is usually taken over by the secondary plant.

Bioremediation

There are so many pollutants but some are of environmental and public health concerns due to their toxicities, including heavy metals, nuclear wastes, pesticides, greenhouse gases, and hydrocarbons [14].

The objective of sewage treatment is to produce a disposable effluent without causing harm to the surrounding environment and also prevent pollution [15]. 

Bioremediation includes techniques and biological mechanisms to degrade, detoxify, transform or mineralize the pollutants to an innocuous state. Bioremediation has proven effective and reliable due to its eco-friendly and low nature. Bioremediation can either be carried out ex situ or in situ, depending on several factors including cost, site characteristics, type of pollutant, etc.

Choosing appropriate bioremediation techniques, which will effectively reduce pollutant concentrations to an innocuous state, is crucial for a successful bioremediation project [16].

Indigenous microorganisms present in polluted environments can themselves do biodegradation and bioremediation of polluting substances if environmental conditions are suitable for their growth and metabolism [17].

Suggested changes to existing methods of sewage treatment

The common ways to treat wastewater include physical water treatment, biological water treatment, chemical treatment, and sludge treatment. But the disadvantages of the existing methods are - chemical consumption, ineffective in removal of the metal ions at low concentration, high sludge production, handling and disposal problems (management, treatment, cost) [18]. 

Requires management and maintenance of the microorganisms and/or physicochemical pre-treatment (inefficient on non-degradable compounds or when toxic compounds are present), slow process, hydraulic retention time, sludge retention time/recycling. The result has been the pursuit of alternative forms of sanitation such as pit latrines, composting toilets, Septic tanks, on-site disposal systems – chemical toilets, composting pits. These methods are more effective and more efficient than the current methods [18] [19]. One such way is the use of a microbial fuel cell (MFC).

Microbial Fuel Cell (MFC)

Microbial fuel cells (MFCs) is one of the latest bio-electrochemical processes that aim to produce electricity by using the electrons derived from biochemical reactions catalyzed by bacteria. The energy generated by MFCs is expected to supply enough energy to partially cover the energy demand in urban wastewater treatment plants (WWTPs) [20].

MFCs utilize the anaerobic respiration of microorganisms to convert organic waste (fuel) directly into useful electricity, which can then be used for practical applications. No commercial models have been developed so far. We have come up with methods that will aid its commercialization. 

Image A 

The anodic solution provides a good amount of resistance to the flow of electrons compared to the electrodes. To increase the efficiency of the MFCs, mediators like methyl viologen and humic acid are used to transport electrons from the anodic solution to the anode. These mediators act as shuttles for electrons, diffusing to the anode, discharging electrons, and then diffusing back to bacterial cells. But mediators are toxic to the environment [21].

Image B

The use of nanowire forming bacteria like Shewanella oneidensis, Geobacter sulfurreducens etc. in the anodic chamber can greatly increase the efficiency of the MFCs and significantly reduce the overall cost. 

Image C

Bacterial nanowires are electrically conductive filaments or appendages, that are now researched for their use in natural and engineered systems. These nanowires facilitate the direct transfer of electrons to the anode, hence greatly increasing efficiency and reducing significant costs. Many bacteria, most notably the Geobacter and Shewanella genera form these nanowires [22].

In the cathode, oxygen reduction reactions (ORRs) occurs. To catalyze this reaction, we generally use expensive catalysts like platinum. We suggest using bio-cathodes as a viable and cost-effective alternative of catalyst for ORRs.

Photoautotrophs like microalgae, which have a high rate of reproduction can be used. In the presence of sunlight, it can meet the oxygen level requirement for ORR and can also produce biomass for the feed.

Image D

Algal cathodes eliminate the need for a mechanical air supply at the cathode, therefore, lowering the running costs [23]. The ability to produce high current densities by Geobacter sulfurreducens in the MFC has been made very popular in the research community [24]. 

The availability of the complete genome sequence of Geobacter sulfurreducens, genetic system and the electron transfer ability to electrode has been proven that Geobacter sulfurreducens is a potential candidate for electricity generation in MFCs [25].

The use of metallic nano-particles enhances the electron turnover rate up to 8 folds as nano-particles act as nano-electrical connectors between the active site of the enzyme and an electrode [26].

Some microbes used in MFC

Our goal is to put MFCs into practical use and to make MFC plants that house a multitude of these cells. This will help us to gain electricity as well as degrade waste materials.

The country's largest sewage treatment plant (STP) is being constructed in Okhla, Delhi. The overall budget is estimated to be 900 crore rupees for this project. An STP of this size would require a huge amount of electricity to run. To save the costs for electricity, an MFC plant can be built surrounding the STP. Any excess electricity produced can also be provided to the city or surrounding settlements.

Conclusion

Sewage is defined as water-carried waste, either in solution form or suspended form, intended to be removed or discarded from municipal communities, households or industries. Principle pollutants in sewage are organic material, suspended solids, plant nutrients and microbes. If the wastewater is not treated properly, then the environment and human health can be negatively impacted.

Most of the sewage treatment plants employ a three-stage system which consists of primary, secondary and tertiary treatment. Primary treatment includes removing solid wastes. Secondary waste treatment is done to attain good quality effluent. Tertiary treatment is used to remove any remaining waste and disinfects the water to make it fit for use.

Bioremediation is the process of using microbes, like fungi and bacteria to remove pollutants and clean the environment. Our project uses the principle of rhizo-degradation to help inefficient treatment of sewage while simultaneously producing electricity. Microbial fuel cells (MFCs) is one of the latest bio-electrochemical processes that aim to produce electricity by using the electrons derived from biochemical reactions catalyzed by bacteria. MFCs utilize the anaerobic respiration of microorganisms to convert organic waste directly into useful electricity.

The overall performance of an MFC depends on the microorganism, materials used for making the electrode, appropriate cell designs and optimizing process parameters. These factors can accelerate the commercialization of MFCs in near future. An MFC plant set up along with an STP will benefit both the STP and the nearby villages, town or city as the current can be shared by both the parties.

In conclusion, the growing population, urbanization, economic and industrial development is not only putting pressure on the water resources in terms of quantity, but the pressure is also increasing in terms of quality. Therefore, the importance of sewage treatment needs to be stressed upon along with the development of new and innovative methods. The modified MFC can help in reducing the stress of sewage treatment and can help in the generation of electricity, thereby tackling the energy crisis as well. 

by Anant Kumar

R. Nakul

Other Contributors

Sania Nadkarni

S Sneha

Rishika Basu

Anwesha Maity

Kaviya Aditi

Rai Das

https://replicoo.blogspot.com/2021/07/regenerative-medicine-for-nervous-system-and-heart_01273350084.html

https://replicoo.blogspot.com/2021/06/stem-cell-therapy-for-corona-patients.html

https://replicoo.blogspot.com/2021/07/toll-like-receptors.html

References: 

[1] – Biniwale, R.B., (2012), Application of Natural Methods for Sewage Treatment and Polishing of Treated Wastewater, National Environmental Engineering Research Institute (NEERI), pp (216-218).

[2] – Central Pollution Control Board, Guidelines on construction, operation and application of Root Zone Treatment systems for the treatment of municipal and industrial wastewater, (2003), Central Pollution Control Board, pp (21- 29). 

[3] – A study of the effectiveness of sewage treatment plants in Delhi region, March 2012, Applied Water Science 3(1) , DOI: 10.1007/s13201-012-005

[4] – Gautam, S.K., Sharma, D., Tripathi, J.K. et al. A study of the effectiveness of sewage treatment plants in Delhi region. Appl Water Sci 3, 57–65 (2013). https://doi.org/10.1007/s13201-012-0059-9 

[5] – https://www.sciencedirect.com/book/9780080402710/alternative-uses-for-sewage-sludge

[6] – Alternative Uses For Sewage Sludge Edited by J.E. HALL, WRc Medmenham, U.K. Proceedings of a Conference Organised by WRc Medmenham and Held at the University of York, UK on 5-7 September 1989

[7] – http://sciencejournal.in/data/documents/SCIENCE-VOL-1-2-4.pdf

[8] – Nathanson, J. A., & Ambulkar, A. (July 2019). Wastewater treatment. Retrieved October 27, 2020, from https://www.britannica.com/technology/wastewater-treatment

[9] – What are the different types of Sewage? (2018, May 09). Retrieved October 27, 2020, https://www.cleansafeservices.co.uk/what-are-the-different-types-of-sewage/

[10] – https://www.usgs.gov/special-topic/water-science-school/science/wastewater-treatment-water-use?qt-science_center_objects=0#qt-science_center_objects

[11] – Moses, H. (1945). The Reasons for Sewage Treatment and the Responsibilities of the Operator. Sewage Works Journal, 17(5), 980-984. Retrieved October 27, 2020, from http://www.jstor.org/stable/25030104

[12] – Jayashree Dhote, Sangita Ingoleb, Arvind Chavhan, 2012, Review On Waste water Treatment Technologies, INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH & TECHNOLOGY (IJERT) Volume 01, Issue 05 (July 2012), 

[13] – W. R. Abma, W. Driessen, R. Haarhuis, M. C. M. van Loosdrecht; Upgrading of sewage treatment plant by sustainable and cost-effective separate treatment of industrial wastewater. Water Sci Technol 1 April 2010; 61 (7): 1715–1722. doi: https://doi.org/10.2166/wst.2010.977 

[14] – Srinivasa Rao, Devarakonda. (2013). BIOREMEDIATION OF SEWAGE USING SPECIFIC CONSORTIUM OF MICROORGANISMS. 

[15] – Igwenyi, Ikechuku. (2012). Sewage management and its benefits to man. International Research Journal of Biotechnology. 3. 2141-5153.

[16] – Azubuike CC, Chikere CB, Okpokwasili GC. Bioremediation techniques-classification based on site of application: principles, advantages, limitations and prospects. World J Microbiol Biotechnol. 2016;32(11):180. doi:10.1007/s11274-016-2137-x

[17] – Verma JP, Jaiswal DK. Book review: advances in biodegradation and bioremediation of industrial waste. Front Microbiol. 2016;6:1–2. doi: 10.3389/fmicb.2015.01555. 

[18] – Crini, G., Lichtfouse, E. Advantages and disadvantages of techniques used for wastewater treatment. Environ Chem Lett 17, 145–155 (2019). https://doi.org/10.1007/s10311-018-0785-9

[19] – https://genesiswatertech.com/blog-post/7-disadvantages-of-using-an-activated-sludge-process-for-your-municipality-or-company/

[20] – M. Ruscalleda Beylier, ... R.-C. Wang, in Comprehensive Biotechnology (Second Edition), 2011.

[21] – Ghangrekar MM, Shinde VB. Performance of membrane-less microbial fuel cell treating wastewater and effect of electrode distance and area on electricity production. Bioresour Technol. 2007 Nov;98(15):2879-85. doi: 10.1016/j.biortech.2006.09.050. Epub 2006 Nov 14. PMID: 17107789. 

[22] – Lal D. (2013). Microbes to generate electricity. Indian journal of microbiology, 53(1), 120–122. https://doi.org/10.1007/s12088-012-0343-2

[23] – Gajda, I., Greenman, J., Melhuish, C., & Ieropoulos, I. (2015). Self-sustainable electricity production from algae grown in a microbial fuel cell system. Biomass And Bioenergy, 82, 87-93. doi: 10.1016/j.biombioe.2015.05.017

[24] – Mehta T, Childers SE, Glaven R, Lovley DR, Mester T. A putative multicopper protein secreted by an atypical type II secretion system involved in the reduction of insoluble electron acceptors in Geobacter sulfurreducens. Microbiology (Reading, England). 2006 Aug;152(Pt 8):2257-2264. DOI: 10.1099/mic.0.28864-0. 

[25] – Lloyd, J. R., Leang, C., Hodges Myerson, A. L., Coppi, M. V., Cuifo, S., Methe, B., Sandler, S. J., & Lovley, D. R. (2003). Biochemical and genetic characterization of PpcA, a periplasmic c-type cytochrome in Geobacter sulfurreducens. The Biochemical journal, 369(Pt 1), 153–161. https://doi.org/10.1042/BJ20020597 

[26] - Xiao, Y., Patolsky, F., Katz, E., Hainfeld, J. F., & Willner, I. (2003). "Plugging into Enzymes": nanowiring of redox enzymes by a gold nanoparticle. Science (New York, N.Y.), 299(5614), 1877–1881. https://doi.org/10.1126/science.1080664

keywords: Sewage treatment, Bioremediation, Microbial Fuel Cell, sewage treatment plant, sewage plant, Microbial fuel cell wastewater treatment, Microbial fuel cell for wastewater treatment and power generation, microbial fuel cell wastewater treatment, Microbial fuel cell advantages