Grantee Research Project Results
Final Report: Integrated Desalination and Wastewater Treatment Systems for Enhanced Water and Energy Recovery
EPA Grant Number: SU835721Title: Integrated Desalination and Wastewater Treatment Systems for Enhanced Water and Energy Recovery
Investigators: Gude, Veera Gnaneswar , Kokabian, Bahareh , Blair, Matthew , Morrero, Morgan , Khani, Hadi
Institution: Mississippi State University
EPA Project Officer: Hahn, Intaek
Phase: I
Project Period: August 15, 2014 through August 14, 2015
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2014) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Safe and Sustainable Water Resources , P3 Awards , Sustainable and Healthy Communities
Objective:
The objective of this project is to design and develop an integrated microbial desalination system to treat wastewater for electricity generation with nitrogen removal and to produce desalinated water simultaneously. The anode chamber with wastewater (substrate, electron donor) and cathode chamber with anammox process (nitrite/nitrate as electron acceptor) separated by a desalination chamber, will accommodate for simultaneous wastewater and saline water treatment due to ion migration between the anode and cathode chambers along with electricity generation and nitrogen removal.
Summary/Accomplishments (Outputs/Outcomes):
Current wastewater treatment systems are not sustainable since they consume enormous amounts of chemical and electrical energy for secondary treatment and yet release nutrients. Currently, commonly used activated sludge systems consume about 25-60% of total energy for aeration with excess sludge formation and disposal issues. Advanced wastewater treatment systems that have potential to produce net energy and remove nutrients are actively sought to solve the water quality and energy issues associated with wastewater treatment. Anaerobic treatment has proven to be beneficial from treatment, energy and environmental perspectives. In this category, microbial fuel cells provide efficient wastewater treatment while generating electricity. Understanding these systems further for potential increase in power production and high quality effluent recovery is critical to development of sustainable wastewater treatment systems.
Energy-neutral or energy-independent wastewater treatment system design is a major challenge. 2-5% of the total electricity load in the U.S. is used for water supply and wastewater treatment. Anaerobic treatment of wastewater is a viable alternative since the process reduces the sludge volumes. We are developing an integrated microbial desalination and anammox process unit where nitrogen rich treated wastewater effluent from the anaerobic treatment (from anode chamber) of MDC is passed through the cathode chamber to provide a carbon source and nitrogen removal. The design needs to optimize the flows of wastewater and saline water in the anode and middle chambers to maintain the limits of salt concentration and pH in the treated effluent.
Microbial consortium used in anode compartment was collected from the aerobic sludge of the wastewater treatment plant in Starkville, Mississippi. First, the sludge was allowed to acclimatize to anaerobic conditions in synthetic wastewater containing 300 mg/l of COD. Some part of this sludge was transferred into the anode chamber of an air cathode microbial full cell (MFC) to grow electroactive bacteria. The cylindrical-shaped MFC chambers were made of plexiglass with a diameter of 7.2 cm. The anode and cathode chambers were separated by an ion exchange membrane. Graphite papers were used as cathode and anode electrodes. The volume of the anode and cathode chambers was 180 ml after inserting the electrodes. The voltage for the air cathode MFC increased slowly for the first 60 hours of operation which can be related to the lag phase for microorganisms to establish their mechanisms for extracellular electron transfer and form a biofilm on the electrodes. The maximum open circuit value difference between the cathode and anode of the air cathode MFC was 0.425 V. When a 10 kΩ resistor was applied in the external circuit a maximum power of 1.33 mW/m2 was achieved for the air cathode MFC. About 40% of the organic matter in the synthetic wastewater in this first test was degraded to produce electrons which again confirms the ability of MFC technology to be used for in situ environmental remediation applications.
After successful demonstration of air cathode MFC for several months, the electrochemically active bacteria were transferred to microbial desalination cells. The MDC reactors were prepared by inserting a desalination chamber between anode and cathode chambers in MFC reactors. Cation exchange membrane (CEM, CMI 7000, Membranes international) separated the cathode and desalination part while an anion exchange membrane (AEM, AMI 7001, Membranes international) separated the anode and desalination chambers.
Fig. I shows the electricity generated by one of these cells for three batch experiments. Since we did not provide any chemical catalyst or aeration in the cathode chamber, the production of electricity indicates the effective role of anammox bacteria as biocathode and Nitrite/Nitrate as electron acceptor. Increase of maximum power for the third batch experiment compared to the first and second test demonstrates the formation of biofilm and the adaptation of bacteria to exoelecroactive bacteria that contribute more in electricity generation. The maximum produced voltage was 0.0896 V which is equal to power density of 0.114 W/m3. We believe that electricity generation by these cells has the potential to improve by several batch tests and formation of the biofilms on the electrodes. We are planning to improve our system in order to achieve at least twice of this power. About 29% of the organic carbon in the anode chamber was removed to generate electron. The calculated columbic efficiency for test 3 was very high compared to the second and first test (52.72% compared to 6.02% and 3.4%). Due to the higher electricity production and longer operation time salinity removal was also higher for the third test which was about 55%. The pH in the cathode chamber usually goes high due to the hydrogen consumption in the cathode chamber associated with the Nitrate reduction and due to the consumption of acidity during anammox process (Liu et al., 2008).
ANXMDC
Fig. I. Current generation profiles in Anammox-MDCs tests
Conclusions:
ANXMDCs have brought new perspective of wastewater treatment plants (WWTPs) to perform beyond just wastewater treatment. MDCs may improve the overall sustainability of these systems by not only treating wastewater but also including onsite energy generation and nutrient recycling. Wastewater treatment by anaerobic digestion can generate an electrical energy equivalent of 0.09–0.14 kWh/m3 through biogas production. Contrary to conventional desalination methods, MDC is considered an energy gaining process. It is estimated that about 1.8 kWh of bioelectricity can be generated in MDCs by treating 1 m3 of wastewater while a reverse osmosis technology requires 2.2 kWh of electricity for the same amount of water desalination. This suggests that desalination combined with MDCs has the potential to become a sole power generator along with wastewater treatment. Combining the energy produced by MDCs and the energy saved by desalination, a total 4 kWh/m3 of energy savings can be realized. However, the performance of current MDC systems needs to improve and exceed 500 W/m3 to outcompete existing anaerobic treatment technology.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 4 publications | 1 publications in selected types | All 1 journal articles |
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Gude VG. Energy and water autarky of wastewater treatment and power generation systems. Renewable and Sustainable Energy Reviews 2015;45:52-68. |
SU835721 (Final) |
Exit Exit |
Supplemental Keywords:
Microbial desalination cells, clean electricity, anaerobic treatment, anammox process, nitrification-denitrification, wastewater treatment, and sustainabilityThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.