In a practical operation, very little evidence exists that pH should be artificially adjusted. Generally, the pH begins to drop during initial stages of composting. This results from the activity of acid-forming bacteria which break down complex carbohydrate material (polysaccharides and cellulose) to organic acid fermentation intermediates under anaerobic conditions. These materials give off strong odors! The microorganisms that produce the acids also can utilize them as food after higher oxygen concentrations are established. This typically occurs within a few days after the most readily biodegradable substances have been destroyed. The net effect is that the pH begins to rise after a few days. The rise continues until a level of 7.5 to 9.0 is reached, and the mass becomes alkaline. Attempts to control pH with sulfur compounds are often difficult to justify because of the cost involved. It is more important to manage aeration so that fermentation and odor formation is reduced.
Water management critically affects composting. When excess water is allowed to accumulate at the base of compost piles, anaerobic conditions are the result followed by odors and leachate formation. Inadequate water retards the process. Grass in dry yardwaste mixtures, for example, is preserved as musty (moldy) hay. This factor is most often overlooked by operators of composting systems.