Table 8.
Utilisation of biochar to alleviate stressors in anaerobic digestion systems
| Biochar | Pyrolysis conditions | Feedstocks | Biochar dosage | Inhibitor | Fermentation pattern | References |
|---|---|---|---|---|---|---|
| Wheat straw | 550 °C | Food waste and sludge | 10 g L−1 | Volatile fatty acids (> 4000 mg L−1) | Propionate reduced to 1460 mg L−1; specific methane yields improved to 24% | Kaur et al. (2020) |
| Sewage sludge | 350 °C | Fruit waste and activated sludge | 0.5, 1, 1.5, and 2 g L−1 | Volatile fatty acids (2587 mg L−1) | Total volatile fatty acids volume were reduced to 387, 1196, 1465, and 1594 mg L−1 for biochar additions, respectively | Ambaye et al. (2020a) |
| Sewage sludge | Volatile fatty acids (2943 mg L−1) | Total volatile fatty acids volume reduced to 1196, 1821, 646, and 1142 mg L−1 for biochar additions, respectively | Ambaye et al. (2020a) | |||
| Sawdust waste | 500 °C for 1.5 h | Food waste and sludge | 20 g L−1 | Volatile fatty acids (57,900 mg COD L−1) |
– Butyrate decreased up to 70% – Methane content boosted over 70% |
Wang et al. (2021d) |
| Vermicompost | 500 °C for 2.0 h | Chicken manure and kitchen waste | 24 g L−1 | Volatile fatty acids (> 12,000 mg L−1) | Total volatile fatty acids reduced from 10,798 to 3957 mg L−1 | Wang et al. (2017b) |
| Wood chips | 800 °C | Food waste | 5 g L−1 | Volatile fatty acids (> 3000 mg L−1) | Methane outcome boosted by 18% | Lim et al. (2020) |
| Rice husk | 550 °C for 2 h | Corn stover and chicken manure | 10 g L−1 | Total ammonia nitrogen (> 6300 mg L−1) | Methane generation aspect enhanced by 28–96% | Yu et al. (2021b) |
| Macadamia nutshells | 350 °C for 2 h | Food waste | 33.3 g L−1 | Ammonia nitrogen (1500 mg L−1) | Chemical oxygen demand removed up to 90%, compared with 8% without biochar | Su et al. (2019) |
| Fruitwood | 800–900 °C | Glucose solution | 10 g L−1 | Ammonia (7 g-N L−1) | Peak methane generation rate prompted by 47.1% | Lü et al. (2016) |
| Pine pellets | Gasification 600–710 °C | Primary sludge | 2.49 and 4.97 g per gTS sludge | Ammonia nitrogen (400–450) |
– Increased methane yield by 3.9–9.5% – Increased ammonia nitrogen quantity by 67% for anaerobic system without biochar compared with by −7.2 to 4.7% with biochar |
Shen et al. (2016) |
| Corn stover | Gasification 850 °C | Primary sludge + waste activated sludge | 0.25, 0.375, 0.5, and 1 g per d | – | Enhanced methane content by 13.7–25.3% | Shen et al. (2017) |
| Wheat bran pellets | Pyrolysis 800 °C | Wheat bran pellets | 25 g L−1 | Ammonia nitrogen (200–250) |
– Increased total volatile fatty acids removal and reduced lag phase – No adsorption of ammonia by biochar |
Viggi et al. (2017) |
| Wheat straw | Pyrolysis 350, 450, and 550 °C | Chicken manure | 5% w/w | Total ammonia nitrogen (4.48 g L−1) | Total ammonia nitrogen reduced by 25% than the control | Pan et al. (2019) |
The biochar produced at various pyrolysis temperatures, particularly those between 500 and 900 °C, can alleviate several inhibitors that have a detrimental effect on the anaerobic digestion process. Specifically, volatile fatty acids, ammonia nitrogen, and total nitrogen levels may decrease following biochar addition, indicating that biochar plays a role in alleviating anaerobic digestion inhibitors and improves overall digestion performance