| Organic acids inhibit microbial activities in the initial phase of composting, and different organic acids vary considerably in their inhibitory effects. The inhibition of microbial activities adversely affect the degradation rate of compost and thereby the efficiency of composting. As very few experimental studies were reported in investigating the effects of organic acids in composting, this study examined the inhibitory effects of acetic, butyric, lactic and propionic acids on the microbial growth under different experimental conditions.;In addition, the populations of total mesophilic and thermophilic microorganisms increased between 8.00 and 65.0 % in the acidified samples following treatment with several alkalis (calcium hydroxide, potassium phosphate, sodium acetate and sodium carbonate). Supplemental findings showed that treatment with sodium acetate enhanced microbial activity and increased degradation rate of compost during composting The improvement in this composting process was probably related to the occurrence of a main stream of an acetic acid resulted in less inhibitory effects on microorganisms, compared to the occurrence of several types of organic acids in compost.;This study revealed that the inhibitory effects of organic acids were more severe when the pH decreased during the early phase of composting, but were effectively ameliorated by application of an alkali. Overall, in similar acidic microenvironments, thermophilic microorganisms tolerated organic acids better than did mesophilic microorganisms. Microbial or environmental factors might contribute to the differences in the inhibitory effects of the organic acids. Finally, the method of extracting and treating small compost samples allowed the experimental and statistical comparisons of response data, the additional findings of microbial or environmental factors and the development of a regression model for predicting microbial population, which would be useful in assessing and understanding organic acids in composting microbiology research.;Full (24:16 runs plus four quality controls) and fractional ( 24-1IV : 8 runs plus two quality controls) factorial designs were conducted on the days when the pH started to decrease and when it subsequently increased, respectively, during the early phase of food-waste composting. Food waste was composted in a laboratory-scale reactor under aerated and microbial self-generated heat conditions. Large numbers of small samples were extracted from the reactor and treated with the acids, and the numbers of microbial populations were analyzed. The results show that butyric acid or lactic acid alone, and butyric, lactic, and propionic acids in combination significantly inhibited total thermophilic microorganisms (alpha = 0.05) on the day when the pH started to decrease. Only 52.0 to 66.0% of the average microbial population would exist at high acid concentration (0.5 mmol/g wet sample) in the compost. No significant inhibitory effects on total mesophilic microorganisms were found. On the day when the pH was increasing, no significant inhibitory effects on thermophilic or mesophilic microorganisms were observed (alpha = 0.05). |
