Which substances can be added to a digester to neutralize a sour condition?

The correct choice involves substances that effectively address sour conditions in a digester, which is a common issue stemming from the production of volatile fatty acids and a subsequent drop in pH levels. Lime (calcium hydroxide) is a strongly alkaline substance that can raise the pH and neutralize acidity, making it beneficial for restoring balance in a digester environment. Soda ash (sodium carbonate) functions in a similar capacity by providing alkalinity and assisting in pH adjustment. Sodium bicarbonate (baking soda) can also help in neutralizing acidic conditions due to its buffering capacity.

This combination of compounds is particularly suitable for stabilizing pH in anaerobic digestion processes where maintaining an optimal environment is crucial for microbial activity and digestion efficiency. Each of these substances contributes to reducing acidity and promoting a more favorable chemical environment for the breakdown of organic materials.

The other options do not provide the same effect of neutralizing sour conditions effectively. For instance, sodium chloride primarily acts as a salt and does not significantly impact pH. Hydrochloric acid is an acid, which would further lower the pH rather than neutralize it. Calcium carbonate, while it can provide some alkalinity, alone may not be as effective as the combination in the correct choice