Download Tackling Energy and Water Crisis: Renewable Energy Extracted

Tackling Energy and Water Crisis: Renewable Energy Extracted from
Wastewater to Drive Desalination.
Potential of Microbial Desalination Cells- A novel reactor for energy recovery,
wastewater treatment, and desalination.
Instructor : Oded Porat Department of Environmental Sciences
Abstract:
Water scarcity is of growing concern due to population growth, climate change,
pollution, and industrial development. It is estimated that in the next 20 years the average
per capita supply of clean water will decrease by one-third. Two of the prevailing methods
to combat this water deficit are the recovery of useable water from wastewaters, and
desalination of ocean and brackish waters. Both these methods are effective yet they are
energy intensive due to the power required for aeration, sludge treatment, high pressure
membrane operation, or thermally driven distillation. To meet the growing demand for
water in a sustainable fashion renewable sources of energy are being investigated to drive
the treatment and desalination processes. One promising area of research is the
development of bioelectrochemical systems (BES) which use microorganisms to create
energy in the form of electricity, hydrogen, and methane.
A Microbial Fuel Cell (MFC) is an example of a BES which uses exoelectrogenic
bacteria, bacteria that can transfer electrons extra-cellularly, to oxidize organic fuels and
create electricity. The oxidation of dissolved organic matter in wastewater occurs in an
anode chamber resulting in the release of protons and electrons (equation 1). The protons
diffuse across a cation selective membrane to the cathode chamber, while the electrons are
transferred to an anode. From the anode the electrons flow to the cathode through an
external circuit, thereby creating a current. In the majority of MFC’s the electrons combine
with protons and oxygen to form water (equation 2)-(figure 1).
Equation 1: Anodic Reaction with Acetate as substrate
𝐶𝐻3 𝐶𝑂𝑂− + 2𝐻2 𝑂 => 2𝐶𝑂2 + 7𝐻 + + 8𝑒 −
Equation 2: Cathodic Reaction with Oxygen as TEA.
𝑂2 + 4𝑒 − + 4𝐻 + => 2𝐻2 𝑂
1
Since MFCs need ion transport to maintain charge balance and generate electricity,
salts can be removed during the electricity-generating process. This realization gave birth to
a modified MFC reactor, which is called a microbial desalination cell (MDC).The device alters
the MFC design by inserting a pair of Ion Exchange Membranes(IEMs) between the anode
and cathode chambers. The addition of these membranes creates a middle or desalination
chamber. The Chloride [Cl−] ions present in the desalination cell migrate to the anode
chamber to balance positive charge resulting from the release of protons from the anodic
oxidation. Alternatively, the movement of Sodium [ Na+] to the cathode chamber balances
the negative charge that is created by the consumption of protons from the cathodic
reduction. This ion migration leads to desalination of the saline water without the use of an
external energy source (figure 2). The addition of the desalination chamber to the MFC gives
the MDC its novel functionality: simultaneous wastewater treatment, desalination, and
energy recovery.
The purpose of this research project is to gain understanding of how to build and
operate an MDC. Additionally participants will learn how to: monitor and improve reactor
performance, use analytical instruments to track compounds within the reactor, and
characterize membrane characteristics (permeability, adsorption potential).
Figure 1 MFC general description: Bacteria oxidize glucose under anaerobic conditions, an
releasing electrons and protons in the process. The electrons are passed to the anode and
transferred to the cathode were they meet the protons that diffused across the proton
exchange memrbane. On the cathode the protons and electrons combine with dissolved
oxygen to from water.The flow of electrons through a resistor allows for accesibale energy.
2
Figure 2 Schematic representation of an MDC reactor: Bacteria oxidize organic matter in an
anerobic anode chamber, releasing protons and electrons. The electrons are transferred to
the cathode chamber creating a potential gradient and making desalination of water
possible (middle chamber). The anode and cathode are separated from the salt solution by
means of AEMs and CEMs respectivley.
Figure 3 Reactor Setup in Lab: Computer with Labview program that is monitoring the two
reactors in right hand side of picture.
Student mission / Objective:
The purpose of this research project is to gain understanding of how to build and operate an
MDC. Additionally participants will learn how to: monitor and improve reactor performance,
use analytical instruments to track compounds within the reactor, and characterize
membrane characteristics (permeability, adsorption potential).
3
Students will learn to use peristaltic pumps, pH meter, dissolved oxygen meter, conductivity
meter, voltmeter. Additionally students will learn to build reactors, condition Ion Exchange
Membranes, plan flow rates, build electrical circuits.
Students will also learn analytical techniques including: solution preparation, standard
preparation, construction of calibration curves, interpretation of Total Organic Carbon, Ion
Chromatograph, and Liquid Chromatography/ Mass Spectrometry results.
Students will have the opportunity to learn how to use Lab View- a computer program used
to monitor reactors online.
Requirements
Students should have a good grasp of chemistry, biology, and physics. Participants should be
hard working, inquisitive, diligent, and organized. Students should be familiar with Excel and
feel comfortable working with basic hand tools. Students must also feel comfortable working
with bacteria.
Please read the following paper in order to get a sense of the project
"A New Method for Water Desalination Using MicrobialDesalination Cells"
Questions about the paper:
1. How is MDC performance monitored? What is charge transfer efficiency, how is it
calculated? Can you think of any way that this efficiency could exceed 100 percent?
2. Why is the low alkalinity of many wastewaters a potential problem for the MDC? How can
this problem be solved?
3. How does changing the external resistance of the reactor influence the voltage drop
across the reactor?
4. Compare current methods of desalination ( Reverse Osmosis, Electro Dialysis) to MDCs.
What are the costs associated with each process? How are the process similar/different?
We will discuss the answers when we meet at the dinner in the opening ceremony.
Please fill free to contact me with questions regarding the project at
[email protected]
4
Recommended reading material:
1. "Efficient Salt Removal in a Continuously Operated Upflow Microbial Desalination
Cell With an Air Cathode"
2. "Simultaneous Water Desalination and Electricity Generation in a Microbial
Desalination Cell With Electrolyte Recirculation for pH Control"
3. "Exoelectrogenic bacteria that power microbial fuel cells."
4. " A state of the art review on microbial fuel cells: A promising technology for
wastewater treatment and bioenergy"
5. "Energy consumption and water production cost of conventional and renewableenergy-powered desalination processes"
5