Savannah Stuart-Dahl Veera Gnaneswar Gude Mississippi State University 1
Outline Wastewater Treatment Water-Energy Nexus Microbial Desalination Experimental Studies Conclusions 2
Wastewater Treatment By conventional aerobic treatment Low-strength wastewaters such as domestic wastewater High capital expenditure Considerable operational and energy consumption costs Aeration energy demand of about 0.5 kwh/m 3 (up to 60% of total), amounting to an energy use of the order of 30 kwh per capita per year Large amounts of excess sludge (around 40%), requiring an appropriate treatment and disposal 3
US Energy Consumption U.S. consumes about 27, 230 trillion (10 12 ) BTUs of petroleum products in the transportation sector ( 28.7x10 12 MJ/year) with more than 60% being imported from foreign countries Water and Wastewater treatment accounts for about 3-4% of the U.S. electrical energy load, similar to that in other developed countries About $ 25 billions are spent for water and wastewater treatment annually in U.S. Over next 20 years, water and wastewater treatment infrastructure will require > 2 trillions for building, maintaining, and operating these systems 4
Wastewater: Energy & Water Resource Wastewater contains up to 10 times energy needed to treat (2% of U.S. electrical energy load) Wastewater has the substrate required for microbial electricity generation Treated wastewater can be reused for other beneficial purposes, NEWater Nutrients can be recovered as Struvite Water Resource Recovery Facility (WRRF) 5
Microbial Fuel Cells Substrates used in microbial fuel cells Synthetic Acetate Glucose Corn Stover Cellulose Actual Municipal wastewater Animal dairy wastewater Food wastewater Brewery wastewater Landfill Leachate 6
Why Microbial Fuel Cells? Energy available in Substrates Based on the calorific content of glucose, an MFC can theoretically (at % efficiency during metabolism) deliver 3 kwh for every kilogram of organic matter (dry weight) in one single step. As a comparison, bio-methanization yields 1 kwh of electricity and 2 kwh of heat per kilogram of COD removed. This means that during substrate conversion in MFCs, hardly any energy is released in the form of external heat, and that all biochemical energy in the waste can be potentially converted into electricity.
(Gude 2016) Thermodynamic Justification
Thermodynamic Justification Reactions with Standard Potential (E o ) and Actual Potential (E) (Hamelers et al. 2010) Hamelers, H. M., Ter Heijne, A., Sleutels, T. A., Jeremiasse, A. W., Strik, D. B., & Buisman, C. N. (2010). New applications and performance of bioelectrochemical systems. Applied Microbiology And Biotechnology, 85(6), 1673-1685.
Thermodynamic Justification Anodic Reaction Anaerobic degradation C 6 H 12 O 6 + 12 H 2 O Anodophilic Bacteria 6HCO 3- + 3OH - + 24e - E=-0.429 Cathodic Reaction - Algae Biocathode Photosynthetic reaction in algal biocathode nco a lg ae, hv 2 nh2o CH2O) n ( no 2 O 2 + 4H + + 4e Algae H 2 O E=0.805
Photosynthetic Microbial Desalination 11
Research Objectives Current issues in MDC research Reproducibility Process optimization Interdependence of process variables No studies on low substrate wastewaters
Process Optimization using RSM Central Composite Model A three factorial subset design proposed by Gilmour (6) Three levels on three factors Represented by a cube with six replications at the center The six replications at the center offer better approximation of the true error which statistically helps in determining significance of the variables. Its symmetry in design with regard to the center offers equal importance to all levels of all parameters. Process variables COD: 300 mg/l TDS: 10 30 mg/l Algae: 0.1 0.3 (absorbance) 13
Materials and Methods Anode: Microbial consortium from wastewater treatment plant in Starkville Medium used in anode chamber was a synthetic waste water containing: Glucose 468.7 mg/l, KH 2 PO 4 (4.4 g/l), K 2 HPO 4 (3.4 g/l), NH 4 Cl(1.5 g/l), MgCl 2 (0.1 g/l), CaCl 2 (0.1 g/l), KCl(0.1 g/l), MnCl 2 4.H 2 O( 0.005 g/l), and NaMo.O 4.2H 2 O(0.001 g/l) Cathode: Microalgae - Chlorella vulgaris CaCl 2 (25 mg/l), NaCl (25 mg/l), NaNO 3 ( mg/l), MgSO 4 (75 mg/l), KH 2 PO 4 (105 mg/l), K 2 HPO 4 (75 mg/l), and 3 ml of trace metal solution with the following concentration was added to 0 ml of the above solution: FeCl 3 (0.194 g/l), MnCl 2 (0.082 g/l), CoCl 2 (0.16 g/l), Na 2 MoO 4 *2H 2 O (0.008 g/l), and ZnCl 2 (0.005 g/l)
Materials and Methods MDC Reactors Plexiglass rectangular-shaped, V= 60 ml Carbon cloth as electrodes Cation exchange membrane (CEM, CMI 7000, Membranes international) Anion exchange membrane(aem, AMI 7001, Membranes international) Volume of desalination chamber=30 ml Initial NaCl = 10, 20, 30 g/l
Experimental Studies - Reproducibility Voltage (V) 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 350 300 50 0 0 10 20 30 40 50 Time (hours) Cumulative (V) Process Conditions COD: mg/l TDS: 20 mg/l Algae: 0.2 (A) Time 48 hours Voltage (V) 0.2 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 300 50 0 0 10 20 30 40 50 Time (hours) Cumulative (V)
Experimental Studies Continued Voltage (V) 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 350 300 50 0 0 10 20 30 40 50 Time (hours) Cumulative Voltage (V), 20, 0.3 Series1, 10, 0.3 Series4, 20, 0.2 Series7 300, 20, 0.2 Series10, 20, 0.3 Series3, 10, 0.3 Series6, 20, 0.2 Series9 300, 20, 0.2 Series12 Voltage (V) 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 80 60 40 20 0 0 10 20 30 40 50 Time (hours) 160 140 120 Cumulative Voltage (V) 300, 30, 0.1 Series1 300, 30, 0.3 Series2, 20, 0.2 Series3 300, 10, 0.1 Series4 300, 30, 0.1 Series6 300, 30, 0.3 Series7, 20, 0.2 Series8 300, 10, 0.1 Series9
Experimental Studies - Polarization COD, TDS, ABS - 300, 10, 0.3 COD, TDS, ABS - 300, 10, 0.3 Power (W/m 3 ) 400 350 300 50 0 50 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0 0.05 0.1 0.15 0.2 0.25 0.3 Current (I) Current (I) Power (W/m 3 ) 400 350 300 COD, TDS, ABS - 300, 10, 0.3 Power (W/m 3 ) 350 300 50 0 0 0.05 0.1 0.15 0.2 Current (I)
Experimental Studies RSM optimization Total Voltage (V) 30 Total Voltage (V) 0.3 Total Voltage (V) 25 0.25 B: TDS (mg/l) 20 6 C: Algae Absorbance 0.2 6 15 0.15 10 0.1 300 10 15 20 25 30 A: COD (mg/l) B: TDS (mg/l)
Experimental Studies RSM optimization Total Voltage (V) Design-Expert Software Factor Coding: Actual Total Voltage (V) Design points above predicted value Design points below predicted value 325 70 X1 = B: TDS X2 = A: COD Actual Factor C: Algae Absorvance = 0.2 350 300 Total Voltage (V) 50 300 30 25 20 A: COD (mg/l) 15 B: TDS (mg/l) 10
Experimental Studies RSM optimization Total Voltage (V) Design-Expert Software Factor Coding: Actual Total Voltage (V) Design points above predicted value Design points below predicted value 325 70 X1 = C: Algae Absorbance X2 = B: TDS Actual Factor A: COD = 350 300 Total Voltage (V) 50 30 0.3 25 0.25 20 0.2 B: TDS (mg/l) 15 0.15 C: Algae Absorbance 10 0.1
Experimental Studies RSM optimization 30 Volume Increase (%) Water Recovery 300 Volume Increase (%) 18 16 16 25 16 B: TDS (mg/l) 20 14 12 6 A: COD (mg/l) 8 10 12 6 14 15 10 6 8 10 0.1 0.15 0.2 0.25 0.3 10 15 20 25 30 C: Algae Absorvance B: TDS (mg/l)
Experimental Studies RSM optimization Water Recovery Design-Expert Software Factor Coding: Actual Volume Increase (%) Design points above predicted value Design points below predicted value 21.9 6.3 X1 = A: COD X2 = B: TDS Actual Factor C: Algae Absorvance = 0.2 Volume Increase (%) 25 20 15 10 5 30 300 25 20 B: TDS (mg/l) 15 A: COD (mg/l) 10 23
Experimental Studies RSM optimization TDS Removal (%) 30 TDS Removal (%) 0.3 TDS Removal (%) 24 22 24 25 30 0.25 B: TDS (mg/l) 20 26 6 28 C: Algae Absorvance 0.2 26 6 28 15 0.15 30 24 22 10 20 0.1 32 300 10 15 20 25 30 A: COD (mg/l) B: TDS (mg/l)
Experimental Studies RSM optimization TDS Removal (%) Design-Expert Software Factor Coding: Actual TDS Removal (%) Design points above predicted value Design points below predicted value 33.3 9 X1 = A: COD X2 = B: TDS Actual Factor C: Algae Absorvance = 0.2 35 30 25 TDS Removal (%) 20 15 10 5 30 300 25 20 B: TDS (mg/l) 15 A: COD (mg/l) 10 25
Experimental Studies RSM optimization Algae Growth 300 Algae Growth 300 0.03 Algae Growth 0.04 0.04 0.04 A: COD (mg/l) 0.08 0.07 0.06 0.05 A: COD (mg/l) 0.05 0.04 0.04 0.04 0.1 0.15 0.2 0.25 0.3 10 15 20 25 30 C: Algae Absorbance B: TDS (mg/l)
Experimental Studies RSM optimization Algae Growth Design-Expert Software Factor Coding: Actual Algae Growth 0.1 0.02 X1 = A: COD X2 = B: TDS Actual Factor C: Algae Absorvance = 0.186486 0.1 0.08 Algae Growth 0.06 0.04 0.02 30 300 25 20 B: TDS (mg/l) 15 A: COD (mg/l) 10 27
Potential Applications Applications (A) septic tanks in decentralized and remote communities; (B) integration with wetlands; (C) Activated sludge systems in centralized systems; and (D) Industrial wastewaters (Gude 2016)
Conclusions RSM is a useful tool for understanding the interdependence and simultaneous responses of process variables in MDCs. Low substrate wastewaters such as agricultural wastewaters, effluents from anaerobic digesters and septic tanks and wetlands can be ideal for MDCs. Reproducibility and reliability can be achieved with proper protocols and experience. Simultaneous energy and water recovery can be feasible but large scale studies are required for proper evaluation of techno-economic feasibility. 29
Acknowledgement US Environmental Protection Agency Department of Civil and Environmental Engineering Bagley College of Engineering at Mississippi State University 30