Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach
Abstract
:1. Introduction
2. Materials and Methods
2.1. Substrate and Inoculum Preparation
2.2. Experiemental Set Up
2.3. Analytical Methods
2.4. Determination of the System Performance
2.5. Economic Estimation
3. Results and Discussion
3.1. Performance of Anaerobic Batch Reactor toward Pollutant Removal and Bio-CH4 Production from Dye Wastewater (Results of the First Experiment)
3.1.1. Effect of Mixing Ratio on Color and COD Removal Efficiencies
3.1.2. Effect of Mixing Ratio on Methane Production from Dye Wastewater and WS Substrate
3.1.3. COD Mass Balance for Validation of Bio-CH4 Production Data
3.2. Biochar Production (Results of the Second Experiment)
3.2.1. Morphology and Elemental Composition of Raw Sludge, Exhausted Sludge, and Biochar
3.2.2. Crystallographic Structure of Raw Sludge, Exhausted Sludge, and Biochar
3.2.3. Main Functional Groups of Raw Sludge, Exhausted Sludge, and Biochar
3.3. Economic Analysis for the Anaerobic Co-Digestion System Treating Dye Wastewater
4. Conclusions
Supplementary Materials
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Parameter | Unit | Value |
---|---|---|
Dye wastewater | ||
pH | - | 11.35 ± 0.53 |
Total COD | mg/L | 1810 ± 131 |
Soluble COD | mg/L | 1180 ± 59 |
Total organic carbon (TOC) | mg/L | 2954 ± 135 |
Ammonia nitrogen (NH4-N) | mg/L | 34.16 ± 0.56 |
Volatile fatty acids (VFA) | mg/L | 378.26 ± 17.39 |
Sludge inoculum | ||
Total solids | g/L | 21.35 ± 1.00 |
Volatile solids | g/L | 16.95 ± 0.85 |
Volatile suspended solids | g/L | 13.88 ± 0.71 |
Moisture content | (w/w%) | 85.65 ± 3.50 |
Ash content | (w/w%) | 17.50 ± 0.72 |
Mixing Ratios | 100/0 | 90/10 | 80/20 | 65/35 | 50/50 |
---|---|---|---|---|---|
SIR | 0.50 ± 0.03 | 0.31 ± 0.02 | 0.30 ± 0.02 | 0.29 ± 0.01 | 0.28 ± 0.01 |
C/N | 7.96 ± 0.54 | 11.6 ± 0.83 | 17.9 ± 1.22 | 24.12 ± 1.67 | 33.44 ± 2.39 |
Final pH | 5.19 ± 0.23 | 6.38 ± 0.25 | 6.77 ± 0.29 | 6.85 ± 0.29 | 6.82 ± 0.30 |
CODinitial total (mg/L) | 1810 ± 131 | 2240 ± 155 | 2610 ± 180 | 3050 ± 218 | 3530 ± 252 |
CODfinal total (mg/L) | 1320 ± 94 | 1040 ± 76 | 902 ± 60 | 960 ± 69 | 1470 ± 109 |
CODsoluble final (mg/L) | 987 ± 71 | 865 ± 64 | 850 ± 63 | 848 ± 63 | 1260 ± 91 |
VFA/alkalinity | 0.32 ± 0.02 | 0.27 ± 0.02 | 0.20 ± 0.01 | 0.19 ± 0.01 | 0.27 ± 0.02 |
CH4 yield (mL/g COD) | 75.90 ± 5.42 | 146.52 ± 10.37 | 176.73 ± 12.44 | 185.37 ± 12.58 | 151.78 ± 10.22 |
CH4 yield (mL/g CODremoved) | 280.36 ± 19.03 | 273.50 ± 19.25 | 270.06 ± 19.20 | 270.52 ± 19.14 | 260.09 ± 18.81 |
∆VSS (mg/L) | 125.44 ± 8.82 | 191.04 ± 13.07 | 252.21 ± 17.35 | 358.53 ± 25.80 | 369.15 ± 26.24 |
CODbiomass/CODinitial (%) | 9.84 ± 0.72 | 12.11 ± 0.82 | 13.72 ± 1.04 | 16.69 ± 1.37 | 14.85 ± 1.14 |
CODCH₄/CODinitial (%) | 21.69 ± 1.58 | 41.86 ± 3.03 | 50.49 ± 3.31 | 52.96 ± 3.61 | 43.37 ± 2.84 |
CODsoluble/CODinitial (%) | 54.53 ± 3.95 | 38.62 ± 2.52 | 32.57 ± 2.19 | 27.80 ± 2.11 | 35.69 ± 2.71 |
COD mass balance (%) | 86.06 ± 5.72 | 92.59 ± 6.82 | 96.78 ± 7.07 | 97.46 ± 7.22 | 93.91 ± 6.87 |
Item | Scenario#1 AD | Scenario#2 AD/Pyrolysis | Justification |
---|---|---|---|
Capital costs (USD) | |||
Construction | 10,000 | 10,000 | Included site footprint, screening unit, receiving tanks, anaerobic unit (assumed as 15 m3 of lightweight structural concrete with a foundation), piping, and fitting. Maintained 35–45% of the total capital costs |
Mechanical equipment | 9800 | 11,100 | Included the cost of pumps for lifting wastewater and sludge, a screw press for sludge dewatering, a heat exchanger, and a mixer. Maintained 40–44% of the capital costs |
Pyrolysis unit | 0 | 5000 | Purchase price and shipping of a pyrolysis unit. The price included an additional condenser, furnace, and gas cleaning equipment. |
Contingency | 2400 | 2400 | About 9% of the capital costs |
Total | 22,200 | 28,500 | The extra cost of purchasing and installing a pyrolysis unit increases the capital costs of scenario#2 by about 30% compared with scenario#1 |
Operating costs (USD/y) | |||
Electrical energy consumption | 1218 | 1819 | Energy consumption for maintaining mesophilic conditions (37 °C), drying, pyrolysis, and operating equipment (motors, pumps, lighting) computed by adding up individual energy demands assuming 0.05 USD/kWh electricity tariff |
Chemical utilization | 962 | 1062 | Chemicals and reagents, e.g., for pH adjustment, buffering, nutrients, for effective microbial degradation assuming a unit cost of 0.03 USD/kg |
Water utilization | 485 | 533 | Water for mixing substrates, cleaning assuming a unit cost of water 0.02 USD/m3 |
Maintenance | 380 | 420 | About 10% of the operating costs |
Overhead and Staff salaries | 535 | 620 | Taxes, process control, legal fees, insurance, and office supplies |
Total operating costs | 3580 | 4454 | Extra electrical energy consumption for scenario#2 for pyrolysis |
Profits (USD/y) | |||
Pollution reduction (COD removal) | 2107 | 2107 | Calculated from an organic load of 106.75 kg COD/d, COD removal efficiency of 68.52%, and 0.08 USD/kg COD removed. These values correspond to the design criteria of an organic loading rate of 7.12 kg/m3/d and an F/M ratio of 0.69 d–1 |
Biogas selling | 2850 | 2850 | Computed from the COD mass balance of CODCH4/CODin = 52.96% and assuming a unit cost of 0.4 USD/m3 of biogas |
Carbon credit (biogas) | 1277 | 1277 | The biogenic carbon emissions were calculated from CO2 trading of 10 USD/ton CO2 |
Biochar selling | 0 | 1246 | Derived from CODbiomass/CODinitial of 16.69%, biochar yield of 0.613 g/g, and 1.5 USD/kg biochar selling price |
Carbon credit (biochar) | 0 | 15 | Calculated from carbon content in biochar = 47.54% (see EDX characteristics in Figure 4c), and CO2/C molar ratio of 44/12. |
Sludge disposal | 0 | 1355 | Denotes transportation costs and fees paid for sludge disposal (without pyrolysis) in a landfill. The amount of sludge generated (10.04 kg/d) was based on an SRT of 15.49 d, which is considered suitable to avoid VFAs accumulation and maintain a balance between the faster-growing bacteria and the slower-growing groups [66] |
Total profits | 6233 | 8849 | Additional profits for scenario#2 from biochar selling and carbon credit from biochar |
Profitability criteria | |||
Net profit (USD/y) | 2653 | 4395 | Computed as the difference between the total annual revenues and the annual operating costs |
Payback period (PBP in y) | 8.4 | 6.5 | This time should be compared with the project lifetime (10 y) |
NPV (USD) | −4396 | 989 | Net present value is estimated using an 8% discount rate and a project lifetime of 10 years |
IRR (%) | 3.4% | 8.8% | Internal rate of return should be greater than or equal to the project discount rate (8%) |
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Tumanyisibwe, A.; Nasr, M.; Fujii, M.; Ibrahim, M.G. Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach. Water 2024, 16, 2025. https://doi.org/10.3390/w16142025
Tumanyisibwe A, Nasr M, Fujii M, Ibrahim MG. Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach. Water. 2024; 16(14):2025. https://doi.org/10.3390/w16142025
Chicago/Turabian StyleTumanyisibwe, Albert, Mahmoud Nasr, Manabu Fujii, and Mona G. Ibrahim. 2024. "Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach" Water 16, no. 14: 2025. https://doi.org/10.3390/w16142025
APA StyleTumanyisibwe, A., Nasr, M., Fujii, M., & Ibrahim, M. G. (2024). Anaerobic Digestion of Dye Wastewater and Agricultural Waste with Bio-Energy and Biochar Recovery: A Techno-Economic and Sustainable Approach. Water, 16(14), 2025. https://doi.org/10.3390/w16142025