Recovery of nitrogen and phosphorus fertilizer from pig farm biogas slurry and incinerated chicken manure fly ash
2021
Zeng, Weishen | Wang, Dehan | Wu, Zhaoyun | He, Lintong | Luo, Zifeng | Yang, Jie
There is insufficient land to use the large amount of nitrogen-rich biogas slurry, a potential agricultural nonpoint source pollutant, produced by anaerobic digestion of pig manure on large-scale pig farms in South China, and biochemical treatments of this product are often insufficient for meeting discharge standards. In addition, a large amount of phosphorus-rich fly ash (FA), which has poor phosphorus bioavailability and cannot be directly used in agriculture, is produced by chicken manure incineration. Therefore, there is an urgent need to find a way to treat this solid waste. This study explores the possibility of synergistic management and comprehensive utilization of these two wastes. The results indicated that the leaching effect of sulfuric acid was better than that of hydrochloric acid, citric acid and oxalic acid in phosphorus extraction from FA. When the amount of sulfuric acid used was 0.75 mol/L, L/S was 10, and the leaching time was 120 min, 87.33% of the phosphorus in FA was extracted; when the wastewater pH was 9.5 and the molar ratio of Mg:N:P was 1:1:2, 95.43% of ammonia nitrogen was recovered from the pig farm biogas slurry. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicated that the main component of the resulting NP fertilizer was struvite, and pot experiments showed that this NP fertilizer was more effective than superphosphate (SP) for plant growth. The residual wastewater met discharge standards after SBR treatment. The present research shows that two different agricultural wastes from one farm, N-rich biogas slurry and P-rich FA, can be treated together to yield recycled NP fertilizers and that the residual wastewater meets the standards for discharge. This study provides an innovative method for the comprehensive treatment and resource utilization of waste in modern and large-scale farms.
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