Effects of high organic loading on mixed photosynthetic wastewater treatment

It has been shown that the presence of high sludge concentrations in a well mixed photosynthetic reactor does not necessarily impose a light limitation on the system. The growth of algae is enhanced as a result of the additional nutrients present in the sludge while the pH of the system is subject to far less variation than in the HRAP. This is important because of the inhibition of algae growth by ammonia at high pH. DO is a good indicator of the state of the system, since oxygen concentrations are high at a high pH where carbon limitation may be evident. The biodegradation of sludge is usually anaerobic and results in significant carbon losses to the atmosphere in the form of CH₄ and CO₂. Hospital sludge was found to be amenable to biological degradation after an initial lag phase and supported significant growth of algae. In photosynthetic systems with high organic loading, the mixed reactor has increased algae yield while the quality of product water has not suffered.