Due to seasonal changes within the pond waters, the BOD loading is ideally varied to suit them. The treated wastewater fed to the ponds contains fine solids and soluble organic compounds. The bacteria and algae live in a symbiotic relationship i.e. they support each other. The algae produce oxygen and consume the product of the bacterial action. The carbon dioxide is utilised by the algae in the presence of sunlight in a photosynthetic process and the oxygen produced is available for use by the bacteria.
Anaerobic activity is more vigorous in the summer.
In the summer rapid bottom decomposition requires greater amounts of oxygen which fortunately coincides with a rapid increase in algal activity. Algal species commonly found include chlorella, scenedesmus and ankistrodesmus to name a few. It is often read over a 5-day period, thus called BOD5. These are primarily compounds of Nitrogen and Phosphorus which, if present in excessive amounts, could promote algal blooms and seaweed growth in the receiving waters. Pathogen indicators Pathogens can be transmitted via the waste stream.