Neutral initial pH enhances the formation of humic acid by inhibiting the growth of Lactobacillus in food waste composting

Composting was the main way to treat food waste and achieve its resource utilization, but the fermentation of food waste could easily produce acid, which affects the microbial community of composting. As of now, the impact of this process on humification was still unclear. This study investigated the effects of initial pH on humic acid formation during food waste (FW) composting, as well as the microbial regulatory mechanisms under pH conditions of 5.0, 6.0 and 7.0. Our study investigated that adjusting the initial pH to 6.6, especially in 7.0, promoted total organic carbon degradation and compost maturation, as indicated by germination index and decreased electrical conductivity. However, higher pH levels also increased total nitrogen loss. Adjusting the pH to 6.0 or 7.0 facilitated the conversion of reducing sugars, amino acids and polyphenols into humic acid and promoted the formation of complex HA components. Our results also indicated that pH regulation inhibited Lactobacillus growth, reshaped bacterial composition, influenced amino acid and polyphenol dynamics, and ultimately enhanced humic acid formation in initial pH of 6.0, especially in initial pH 7.0. From a cost perspective, it was recommended to adjust the initial pH of food waste to 6.0 for composting. • Increasing pH to 6.0 or 7.0 promotes humic acid formation and maturation in food waste composting. • Increasing pH to 6.0 or 7.0 promotes the conversion of precursors into humic acid. • Higher pH could promote the formation of HA-C, but inhibit the formation of HA-N. • Increasing pH inhibits Lactobacillus and alter the bacterial community.