Typically, the only limiting nutrient in solution is phosphate, which is conveniently
added in concentrations ranging from about 1 to 5 mg/l using concentrated phosphoric
acid. As shown in the equations, there is a need to add oxygen, which is accomplished
through either natural or artificial aeration of the solutions. The minimum dissolved
oxygen needed is on the order of 2.0 mg/l. In addition to these environmental factors, the
presence of toxic and/or inhibitory substances reduces the effective rate of degradation to
below its optimal level.