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Municipal sewage sludge (SS) and food waste are two typical organic solid wastes generated by urban metabolism, and their low-carbon resource recycling is an important part of the construction of "Zero-Waste Cities". In recent years, the pyrolysis and carbonization of sludge have gradually gained attention and application in China. Anaerobic digestion of food waste for energy recovery as biogas has become the mainstream technology, but the utilization of the large amount of biogas residue produced along with it has become a hot topic. Currently, there are limited demonstration projects on the synergetic valorization of sludge and food waste anaerobic residue across the country. This study conducted lab- and pilot-scale research on the co-pyrolysis of SS and food waste digestate (DS) from the perspective of reducing investment and operating costs through their synergetic conversion. A demonstration project on the collaborative pyrolysis of dewatered SS and DS with a daily treatment capacity of 20 tons on a dry basis was established, and a long-term stable operation analysis was carried out. The lab results showed that the yield of biochar increased from 62.71 wt.% to 73.14 wt.% with the SS to DS ratio from 1∶0 to 1∶3 under the pyrolysis temperature of 600 ℃. Correspondingly, the yields of pyrolysis oil and gas decreased. The potassium and phosphorus are mainly enriched in the biochar after co-pyrolysis, and the heavy metals were well immobilized in biochar with the proportions of the residual and oxidized forms over 80%. Compared with the pure SS biochar, the O—H stretching vibration peak in the co-pyrolysis biochar was significantly weakened, but the C=O absorption peak was enhanced. The pilot-scale demonstration results indicated that the yields of biochar from SS, SD, and SS+SD were in the range of 25~30 wt.% with the pyrolysis temperature of 400~500 ℃. The higher heating value of biochar was between 4500 kJ·kg-1 and 5500 kJ·kg-1 with the volatile matter and fixed carbon of 13~15 wt.% and < 10%. The biochar applied in soils can realize the carbon sequestration due to its stable carbon which can be kept in the soil for a long time without being decomposed to release CO2. Compared with sludge incineration, pyrolyzing 1 ton of sludge is equivalent to reducing the direct CO2 emissions by 0.024 tons. Moreover, the forms of heavy metals in the biochar were preferred to be stable solidification, which was consistent with their trends from the lab.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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