Effects of sawdust addition on bio-drying efficiency and bacterial community of food waste

As we all know, the bio-drying of food waste has problems such as high moisture content and low internal porosity, and these conditions can be improved by adding auxiliary materials. In particular, the appropriate amount of auxiliary materials can help promote the degradation of organic matter and the formation of humus during bio-drying process, so as to improve the efficiency of bio-drying. As one of the auxiliary materials with abundant carbon source and low cost, sawdust has been widely used in the research of various waste resource utilization in recent years, but the mechanism of how the ratio of food waste and sawdust regulates the succession of microbial communities and thus improves the efficiency of bio-drying is not clear. Based on this, in our study, three treatments with a wet-weight ratio of food waste and sawdust were set up, including 5:1 (T1), 7:1 (T2) and 10:1 (T3). And we carried out experiments in a 55 L bio-drying reactor in order to explore their effects on key physicochemical indexes and bacterial community structure during bio-drying, such as temperature, moisture content (MC), volatile solids content (VS), electric conductivity (EC), seed germination index (GI), total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), carbon-nitrogen ratio (C/N), and so on. The results showed that compared with the other two treatments, the duration of the high temperature period of T2 lasted the longest, extending by 50.00% and 100.00%, respectively. And at the end of bio-drying, the removal of moisture content was the lowest, the degradation rate of organic matter was the highest, the water removal rate was 37.14%, and the degradation rate of volatile solids was 15.88%. The seed germination index of T2 reached more than 80% earlier 3 and 6 days than T1 and T3 treatments, and the total nutrient content increased by 28.32% at the end of bio-drying, among which the total phosphorus content increased the most significantly, increasing by 121.62%, which was about 1.92 and 1.90 times that of the other treatments, indicating that the material and additive ratio of T2 treatment was more conducive to promoting the maturity of the pile and increasing the nutrient content. Furthermore, the relative abundance of beneficial compost genus such as Bacillus, Ureibacillus and Thermobifida in T2 was higher, and the Chao1 and Shannon indexes were larger than that of others. Correlation analysis showed that the relative abundance of Ureibacillus, Symbiobacterium, Tepidimicrobium and Bacillus were significantly positively correlated with temperature of pile (P<0.05), the relative abundance of Thermobifida, Pusillimonas, Vulgatibacter, Mycobacterium were positively correlated with seed germination index (P<0.05), and negatively correlated with volatile solids content, moisture content and total nitrogen content (P<0.05). When the wet-weight ratio of food waste and sawdust was 7:1, the results of water removal and organic matter degradation were the best, and bacterial community richness was the highest, especially the relative abundance of beneficial bacteria in the compost. Therefore, it is beneficial for the targeted screening and cultivation of functional microorganisms, and improves the bio-drying efficiency of food waste.