Sequencing Batch Reactor
A sequencing batch reactor goes through a cycle of 5 steps: Filling, reacting, settling, decanting and idling. During the filling stage, the feed water is directed into the tank which contains pre-existing sludge from previous cycles and is mixed mechanically to resuspend the sludge blanket into the wastewater.
At the reacting stage, air is provided which promotes the function of aerobic bacteria that consume the waste as nutrition, producing carbon dioxide, nitrates and nitrites. At this stage, alum can be added to precipitate out soluble phosphoric compounds.
Next, the aeration is stopped and the sludge is allowed to settle, promoting anoxic conditions. Here the nitrites and nitrates are converted into nitrogen oxides or nitrogen gas.
After settling, the supernatant is removed and can be used for irrigation or discharge. The sludge that remains is reused for the next cycle. Portions of the sludge are removed regularly to avoid over-accumulation.
To maximise efficiency of this batch process, two tanks are recommended such that each can be in different cycles of the process.