During the processing of organic fertilizers, the raw materials must undergo a fermentation process in which fermenting microorganisms play a crucial role. These microorganisms thrive best in neutral to slightly alkaline environments, which facilitates their reproduction, decomposition activities, and survival. Therefore, regulating the pH value is essential to ensure optimal fermentation performance. This article explains the importance of pH control during organic fertilizer processing:
Bacteria and actinomycetes prefer neutral to slightly alkaline environments, whereas fungi favor acidic conditions. When organic wastes such as manure are fermented, the bacteria and fungi break down the organic matter and release organic acids. As fermentation progresses, these acids accumulate, causing the pH of the compost to drop. This acidic environment is conducive to fungal growth and the degradation of lignin and cellulose in the compost. As the fermenting bacteria further degrade the organic acids, the pH gradually rises. Under these optimal pH conditions, actinomycetes and fungi multiply rapidly, accelerating the decomposition and maturation of the compost.
A pH that is too low is typically caused by excessive moisture or overly fine particle sizes. Under these conditions, the fermentation of organic wastes like manure easily becomes anaerobic. In an anaerobic state, the accumulation of organic acids can cause the pH to drop below 4.5, severely inhibiting microbial activity and forcing the fermenting bacteria into dormancy or causing them to die. In such cases, a compost turner must be used to aerate the pile. Turning the pile improves ventilation and restores adequate oxygen levels, which helps bring the pH back to the normal range.
Conversely, if the pH is too high, the activity of many fermenting microorganisms decreases, slowing down decomposition and reproduction. If the pH exceeds 11.5, large numbers of fermenting bacteria will die, leading to protein denaturation and enzyme inactivation within the compost. This disrupts the fermentation cycle and compromises the quality of the final organic fertilizer.
However, the pH of most common fermentation feedstocks does not require adjustment. Materials that typically do not need pH regulation include livestock manure, sewage treatment plant sludge, straw, peat, and mushroom residue. The normal pH range for composting fermentation is between 5 and 9. If the pH of the manure exceeds 9 during fermentation, it should be adjusted by adding ferric chloride, alum, strong acids, or recycled compost. If the pH falls below 4, it can usually be corrected by adding lime or peat ash. Properly adjusting the pH during manure fermentation optimizes the fermentation environment, promotes microbial growth and decomposition, shortens the fermentation cycle, and enhances both the quality and yield of the final organic fertilizer.