On many occasions, better results can be obtained by changing composting conditions, e.g. by changing the pH. The addition of NaOH or Mg(OH)2 may result in a significant reduction in hydrogen sulfide emissions by transforming it to the ionized form. The addition of sodium hydroxide, due to the better solubility of this substance in water as compared to the solubility of magnesium hydroxide, results in a faster change of the pH. The addition of magnesium hydroxide, on the other hand, improves the value of composted sludge as the fertilizer (Krach et al., 2008).