Table 3.
Common pretreatment methods of rice straw for biogas production in China
| Province | Feedstock | Pretreatment method | Biogas yield | References | ||
|---|---|---|---|---|---|---|
| Physical | Chemical | Biological | ||||
| Jiangsu | Rice straw | Pretreatment of rice straw with the steam explosion at a temperature range of 200 to 220 °C in 10 °C increments | X | X |
The maximum rate of biogas reached 328.7 mL/g total solids (51% increase) |
Zhou et al. 2016 |
| Sichuan | Rice straw | Pretreatment of rice straw at (90, 150, 180, and 210 °C, respectively) for 15 min | X | X | The maximum yield of biogas was 306.6 mL/g total solids | Wang et al. 2018 |
| Hunan | Rice straw | A pre-aeration treatment of rice straw for 0, 2, 4, 6, and 8 days under 25, 35, and 45 °C, respectively | X | X | The highest biomethane yield (355.3±18.7 mL/g volatile solids) was achieved at 35 °C for 2 days | Zhou et al. 2017 |
| Jiangxi | Rice straw + pig manure | A combined pretreatment of rice straw using ultrasonic at 53 kilohertz and 350 watts for 30 min, microwave at 800 watts for 5 min, coupled with alkali treatment at 37 ℃ for 24 h | * | X | The biogas yield was increased in the case of ultrasonic and alkaline combined pretreatment by 39.41% and in the case of microwave, alkaline, and ultrasonic combined by 46.07% | Xiang et al. 2021 |
| Nanjing | Rice straw | X | Chemical pretreatment of rice straw using calcium hydroxide, hydrogen peroxide, and ammonia–water at different times | X | Pretreatment with calcium hydroxide for 72 h had the highest biogas yield of 413.5 mL/g volatile solids, which is 45.2% higher than the control | Du et al. 2019b |
| Hubei | Rice straw | X | Pretreatment of sodium hydroxide solution (2%, volume/volume), with a biomass-to-solution ratio: of 10% (weight/volume) at 60 ℃ for 48 h, followed by anaerobic digestion coupled with fermentation and enzymatic hydrolysis | X | The maximum biogas yield was achieved via the anaerobic digestion of the fermentation broth resulting from rice straw fermentation without distillation (249.9 L/kg volatile solids), with a biomethane content of 79.3% | Elsayed et al. 2018 |
| Shanghai | Rice straw + swine manure | * | Rice straw was pretreated in the following scenarios alkaline, microwave, and alkaline-microwave, then co-digested with pig manure | X | The pretreatment increased biogas yield by 25%, which could reach 355–357 L/kg total solids | Qian et al. 2019 |
| Jiangsu | Rice straw | * | Hydrothermal and alkaline thermal pretreatments of rice straw using calcium hydroxide | X | The highest biogas reached 411.1 mL/g volatile solids, with an increase of 24.04% compared to the control | Du et al. 2019a |
| Henan | Rice straw | X | X | Pretreatment of rice straw using five microbial reagents, including cow manure, sheep dung, liquid consortium, straw-decomposing consortia, and biogas slurry | The highest biogas production was obtained under the sheep dung treatment (311.7 mL/g volatile solids), with an enhancement of 88.7% | Amin et al. 2021 |
| Jiangxi | Rice straw + pig manure | X | X | Biological pretreatment of rice straw and pig manure by cellulolytic microbial consortium | The maximum methane yield could reach 0.64 L methane/day, 62.4% higher than the control | Shen et al. 2018 |
| Tianjin | Rice straw | X | * | Combined pretreatment of biological and chemical methods using calcium oxide and liquid fraction of digestate | The combined pretreatment resulted in a methane yield of 274.65 mL/g volatile solids, indicating a 57.56% increase compared to the control | Guan et al. 2018 |
| Zhejiang | Rice straw | * | X | Combined pretreatment of fungal (Pleurotus ostreatus fungus) by incubation for 10, 20, and 30 days at 28 ℃, and milling (less than 2 mm) followed by solid-state anaerobic digestion | Fungal pretreatment for 30 days, followed by milling before anaerobic digestion, resulted in 30.4% lignin removal, and the maximum methane output was 258 L/kg volatile solids | Mustafa et al. 2017 |
As mentioned earlier in Table 2, many of the main challenges and obstacles to using rice straw as a feedstock for biogas production are due to some characteristic issues. Therefore, rice straw can be pretreated via different methods, commonly physical, chemical, and biological methods. These treatments can enhance the straw digestibility to maintain the stability of the anaerobic digestion process while enhancing the biogas yield
*: indicates the method is combined with other pretreatment methods
X: indicates the pretreatment method is not used