Biochar Amendment in Green Roof Substrate: A Comprehensive Review of the Benefits, Performance, and Challenges
Abstract
:Featured Application
Abstract
1. Introduction
2. Biochar—Preparation and Unique Physiochemical Characteristics
3. Benefits of Biochar Amendment in Green Roofs
3.1. Runoff Retention
3.2. Runoff Quality Improvement
3.3. Thermal Reduction
3.4. Plant Health and Microbial Diversity
3.5. Air Quality Improvement
3.6. Soil Erosion Control
4. Barriers Limiting Biochar Amendment in GRs
4.1. Unpredictability Due to Inconsistent Research Findings
4.2. Limited Understanding of Optimal Biochar-Based Variables
4.3. Environmental Concerns
4.4. Economic Challenges
4.5. Policy Barriers
5. Future Research Opportunities
5.1. Further Investigations into the Performance of Biochar-Amended Green Roofs
5.2. Long-Term Observation Studies
5.3. Economic and Environmental Analysis
6. Conclusions
- (a)
- There is a clear trend indicating the benefits of biochar amendment in GRs. However, significant variation in parameters across biochar–GR studies make direct comparisons challenging. Additionally, the application of biochar in GRs is relatively new and not yet thoroughly studied, highlighting the need for further research to provide comprehensive insights.
- (b)
- Although some studies report contradictory findings, such as higher pollutant concentrations in runoff from biochar-amended GRs, the long-term improvement in runoff quality due to a significant reduction in runoff remains noteworthy.
- (c)
- The research on biochar amendment in GRs has been uneven, with the majority of studies focusing on runoff retention, improved runoff quality, enhanced plant performance, and microbial diversity. Certain other benefits of biochar for GRs, such as thermal reduction, carbon sequestration, and control of soil erosion, have received relatively less attention. Future studies should address this imbalance to provide a more comprehensive understanding of biochar’s full range of benefits.
- (d)
- Biochar-related variables such as particle sizes, processed forms, amendment rates, and application methods play an important role in determining the performance of biochar-amended GRs. However, contradictory findings in the literature highlight the need for further research to fully understand the impacts of these variables on the performance of green roofs.
- (e)
- The understanding of the long-term effects of biochar on GRs remains incomplete, likely due to the limited number of studies that conducted analysis with multiyear observations.
- (f)
- While biochar is well recognized to effectively sequester CO2, the integration of biochar into life cycle assessments (LCAs) is recommended to comprehensively understand its long-term environmental impacts.
- (g)
- It is also recommended to apply LCA to evaluate the cost aspects of biochar in GRs. This can provide deeper insights into the economic feasibility of biochar-amended GRs.
- (h)
- The utilization of biochar in GRs faces several barriers. In addition to inconsistent and limited research information, major challenges include high manufacturing costs, policy-related constraints, and environmental concerns. Addressing these issues is crucial for the widespread adoption of biochar in GRs.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Case Studies | Key Benefits of Biochar | Biochar Application Methods |
---|---|---|
[61] | Improved runoff quality, nutrient availability, and microbial community | Middle layer |
[62] | Improved runoff retention | Middle layer |
[63] | Improved runoff retention and plant performance | Top layer and mixing |
[64] | Improved runoff retention and runoff quality | Top layer and bottom layer |
[65] | Improved runoff retention | Top layer, mixing, and bottom layer |
[66] | Improved soil erosion | Mixing |
[67] | Improved carbon sequestration | Mixing |
[68] | Improved air quality | Mixing |
[69] | Improved temperature reduction | Mixing |
Reference | Approach | Substrate | Biochar Setup | Retention Rate without Biochar (%) | Retention Rate with Biochar (%) |
---|---|---|---|---|---|
[64] | Field-scale | Recycled, crushed brick, compost, crushed bark, and sphagnum moss | Buried biochar | 70 (summer), 50 (autumn) | 80 (summer), 64 (rainy autumn) |
Surface biochar | 75 (summer), 50 (autumn) | ||||
[65] | Pilot-scale | Light expanded clay aggregate, coir chips, and mulch | 7.5% mixed—medium biochar | 70 (summer), 50 (autumn) | 21.95–53.05 |
15% mixed—medium biochar | 27.44–58.54 | ||||
7.5% buried—medium biochar | 35.98–59.76 | ||||
7.5% mixed—fine biochar | 24.39–68.29 | ||||
7.5% surface—fine biochar | 36.59–67.48 | ||||
[70] | Pilot-scale | Topsoil | NA | 32.1 | 46.6 |
[71] | Pilot-scale | Gravel, sand, silt, clay, pumice, Fiber Life compost, and paper fiber | NA | Not saturated: 19.3–32.9 | Not saturated: 29.6–32.5 |
Saturated: 7.1–8.2 | Saturated: 8.5–12.6 | ||||
[72] | Pilot-scale | Peat, vermiculite, perlite, and sawdust | NA | 72.54 | 72.08 |
[73] | Soil column | Natural clay soil | NA | 45.5 | 69.3 |
[74] | Pilot-scale | Peat, vermiculite, perlite, and sawdust | NA | Substrate (5, 10, 15, and 20 mm): 47.1, 52.71, 56.99, and 62.64 | Substrate (5, 10, 15, and 20 mm): 47.7, 53.99, 60.42, and 66.5 |
[75] | Software modeling | Scoria (≤8 mm), scoria (7 mm aggregate), and coir | 40% v/v | Maximum 12% improvement annually | |
[76] | Pilot-scale | Crushed, recycled brick, compost, peat, and crushed bark | NA | Maximum 10% improvement | |
[77] | Field-scale | NA | 2.5, 5, and 10% w/w | 36.6 | 41.5, 39, and 37.8 |
[62] | Software modeling | Loam and expanded clay | 3 cm and 5 cm depths of biochar | 55.05–65.29 | 66.9 and 69.15 |
[78] | Pilot-scale | Heat-expanded clay | 15% v/v | 36% improvement | |
[79] | Pilot-scale | Crushed clay, peat, and green compost | Pelleted wood (10 and 15 cm deep substrates) | 25 and 30 | 33 and 45.5 |
Pumice, lapillus, peat, and green compost | Flake wood (10 and 15 cm deep substrates) | 38 and 45.5 | 41.5 and 47 |
Reference | Approach | Substrate | Biochar Setup | Pollutant | Concentration without Biochar (mg/L) | Concentration with Biochar (mg/L) | Load without Biochar (mg) | Load with Biochar (mg) |
---|---|---|---|---|---|---|---|---|
[58] | Pilot-scale | Recycled brick, expanded clay, spongilite, and peat | Wood/sewage sludge/food waste biochar | TN | 2.20 ± 1.20 | 13.8 ± 21.2/4.23 ± 3.20/7.87 ± 9.03 | NA | NA |
TP | 0.38 ± 0.35 | 0.33 ± 0.32/1.57 ± 2.23/0.42 ± 0.35 | ||||||
[64] | Field-scale | Recycled, crushed brick, compost, crushed bark, and sphagnum moss | Surface biochar | TP and TN | NA | NA | Sedum: 40 and 580; meadow: 45 and 700 (m−2) | Sedum: 35 and 550; meadow: 41 and 560 (m−2) |
Buried biochar | NA | NA | Sedum: 29 and 350; meadow: 28 and 400 (m−2) | |||||
[71] | Pilot-scale | Gravel, sand, silt, clay, pumice, Fiber Life compost, and paper fiber | NA | Organic carbon (sedum and ryegrass) | 78.8 and 73.6 | 25.7 and 21.6 | 1436–1521 and 1024–1236 | 425–488 and 395–439 |
Inorganic carbon (sedum and ryegrass) | 13.3 and 18.6 | 12.7 and 17.2 | 233–288 and 257–322 | 223–242 and 335–345 | ||||
TP (sedum and ryegrass) | 10.3 and 17.4 | 8.3 and 8.4 | 199–216 and 238–352 | 119–183 and 151–182 | ||||
TN (sedum and ryegrass) | NA and 79.2 | NA and 10.1 | NA | NA | ||||
[72] | Pilot-scale | Peat, vermiculite, perlite, and sawdust | NA | TP | 0.15 | 0.21 | 0.002 ± 0.001 (m−2) | 0.003 ± 0.001 (m−2) |
TN | 16.14 | 9.85 | 0.205 ± 0.089 (m−2) | 0.096 ± 0.042 (m−2) | ||||
Zn | 0.03 | 0.02 | NA | NA | ||||
Fe | 0.13 | 0.1 | 0.001 ± 0.001 (m−2) | 0.001 ± 0.001 (m−2) | ||||
[74] | Pilot-scale | Peat, vermiculite, perlite, and sawdust | NA | TP (substrate 5, 10, 15, and 20 cm) | 0.28, 0.19, 0.25, and 0.38 | 0.32, 0.24, 0.35, and 0.43 | 0.003 ± 0.009, 0.002 ± 0.003, 0.004 ± 0.008, and 0.005 ± 0.008 (m−2) | 0.005 ± 0.009, 0.004 ± 0.009, 0.007 ± 0.015, and 0.006 ± 0.008 (m−2) |
TN (substrate 5, 10, 15, and 20 cm) | 22, 28, 29, and 17 | 10.5, 8, 12, and 12 | 0.277 ± 0.359, 0.370 ± 0.437, 0.375 ± 0.468, and 0.310 ± 0.433 (m−2) | 0.114 ± 0.166, 0.087 ± 0.110, 0.169 ± 0.262, and 0.171 ± 0.229 (m−2) | ||||
K (substrate 5, 10, 15, and 20 cm) | 5, 6.5, 11, and 14 | 3.75, 4, 9, and 6 | 0.046 ± 0.045, 0.064 ± 0.079, 0.135 ± 0.143, and 0.177 ± 0.163 (m−2) | 0.033 ± 0.034, 0.039 ± 0.046, 0.083 ± 0.087, and 0.064 ± 0.066 (m−2) | ||||
Ca (substrate 5, 10, 15, and 20 cm) | 120, 95, 90, and 60 | 65, 48, 50, and 45 | 0.842 ± 0.864, 0.898 ± 1.117, 0.958 ± 0.962, and 0.696 ± 0.600 (m−2) | 0.479 ± 0.497, 0.432 ± 0.506, 0.448 ± 0.459, and 0.487 ± 0.489 (m−2) | ||||
Fe (substrate 5, 10, 15, and 20 cm) | 0.07, 0.08, 0.16, and 0.15 | 0.05, 0.06, 0.11, and 0.13 | 0.792 ± 0.948, 1.241 ± 2.192, 2.365 ± 2.889, and 2.388 ± 3.135 (m−2) | 0.715 ± 1.053, 0.915 ± 1.643, 1.644 ± 2.774, and 1.324 ± 2.033 (m−2) | ||||
Zn (substrate 5, 10, 15, and 20 cm) | 0.05, 0.04, 0.08, and 0.13 | 0.025, 0.023, 0.05, and 0.03 | 0.305 ± 0.334, 0.231 ± 0.241, 0.594 ± 0.604, and 0.439 ± 0.497 (m−2) | 0.145 ± 0.135, 0.101 ± 0.116, 0.231 ± 0.225, and 0.191 ± 0.171 (m-2) | ||||
[77] | Field-scale | NA | 2.5, 5, and 15%, w/w | Organic carbon | NA | NA | 355 (m−2) | 310, 400, and 325 (m−2) |
Nitrate | 1.7 (m−2) | 2, 1.5, and 3 (m−2) | ||||||
Phosphate | 33 (m−2) | 25.5, 24, and 20 (m−2) | ||||||
[88] | Pilot-scale | Crushed, recycledbrick, compost, peat, and crushed bark | NA | TP (planted and pre-grown) | NA | NA | 130 and 125 (m−2year−1) | 50 and 55 (m−2year−1) |
TN (planted and pre-grown) | NA | NA | 3500 and 1200 (m−2year−1) | 1100 and 600 (m−2year−1) | ||||
[89] | Pilot-scale | Porous aggregates, composted organic matter, and fine sand | Granulated 1–2 mm | P, TN, K, Ca, and Mg (first flush/second flush) | 1.1, 23, 200, 170, and 60/0.65, 7.5, 85, 88, and 31 | 0.9, 27.5, 260, 220, and 76/0.7, 7, 65, 84, and 29 | 0.0038, 0.085, 0.75, 0.65, and 0.23/0.0015, 0.018, 0.23, 0.22, and 0.075 (m−2) | 0.0029, 0.085, 0.8, 0.65, and 0.24/0.0013, 0.012, 0.12, 0.15, and 0.05 (m−2) |
Granulated 2.8–4 mm | 0.8, 27, 240, 190, and 73/0.75, 7.5, 67, 85, and 30 | 0.0035, 0.1, 0.9, 0.7, and 0.27/0.0014, 0.015, 0.14, 0.17, and 0.06 (m−2) | ||||||
Unprocessed 1–2 mm | 0.85, 25, 280, 185, and 70/0.65, 6, 110, 78, and 30 | 0.0021, 0.06, 0.7, 0.4, and 0.16/0.0011, 0.009, 0.18, 0.13, and 0.05 (m−2) | ||||||
Unprocessed 2.8–4 mm | 0.7, 16, 160, 140, and 45/0.6, 4, 65, 70, and 25 | 0.0027, 0.05, 0.7, 0.4, and 0.16/0.0013, 0.008, 0.14, 0.14, and 0.055 (m−2) | ||||||
[90] | Pilot-scale | Pumice or expanded clay, and compost | NA | TP (lowest and highest) | 0.05 and 1.47 | 0.18 and 2.09 | NA | NA |
[91] | Pilot-scale | NA | NA | TN | 3.27 | 2.16 | NA | NA |
[92] | Pilot-scale | Topsoil, wood chip, waterworks sludge, and pumice | NA | TN (rain intensity: 5,10, and 15 mm/h) | 7.5, 9.5, and 11.2 | 6.2, 7.5, and 10.8 | NA | NA |
[93] | Pilot-scale | Light expanded clay aggregate, coir chips, and mulch | 7.5% mixed— medium biochar | TN and TP | 3.7 to 31 and 0.35 to 0.67 | 4.8 to 48 and 0.81 to1.29 | NA | NA |
15% mixed— medium biochar | 7.1 to 47 and 0.56 to 1.66 | |||||||
7.5% buried— medium biochar | 2.2 to 21 and 0.74 to 1.27 | |||||||
7.5% mixed— fine biochar | 6.1 to 51 and 0.53 to 0.94 | |||||||
7.5% surface— fine biochar | 9.5 to 58 and 0.98 to 2.41 | |||||||
[94] | Pilot-scale | Local soil, perlite, and vermiculite | Rice husk/Maize straw (10∼20% v/v) | TN | 103.68 | 26.21~52.77/10.12~3.97 | NA | NA |
TP | 0.27 | 0.22~0.57/0.58~1.07 | ||||||
Organic carbon | 94.47 | 101.76~59.41/52.45~26.73 | ||||||
[95] | Pilot-scale | Sewage sludge biochar (10% and 20% v/v) | TN (at the beginning/the end) | 4.1–11.9/0.9–1.0 | 27.2–32.8/0.5–0.7 and 13.4–47.3/0.5–0.6 | NA | NA | |
TP | 0.04 to 1.63 | 0.18 to 2.00 and 0.03–1.71 |
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Nguyen, C.N.; Chau, H.-W.; Kumar, A.; Chakraborty, A.; Muttil, N. Biochar Amendment in Green Roof Substrate: A Comprehensive Review of the Benefits, Performance, and Challenges. Appl. Sci. 2024, 14, 7421. https://doi.org/10.3390/app14167421
Nguyen CN, Chau H-W, Kumar A, Chakraborty A, Muttil N. Biochar Amendment in Green Roof Substrate: A Comprehensive Review of the Benefits, Performance, and Challenges. Applied Sciences. 2024; 14(16):7421. https://doi.org/10.3390/app14167421
Chicago/Turabian StyleNguyen, Cuong Ngoc, Hing-Wah Chau, Apurv Kumar, Ayon Chakraborty, and Nitin Muttil. 2024. "Biochar Amendment in Green Roof Substrate: A Comprehensive Review of the Benefits, Performance, and Challenges" Applied Sciences 14, no. 16: 7421. https://doi.org/10.3390/app14167421