Methods of Wastewater Treatment. Among the traditional wastewater purification technologies, one of the most common is aerotank treatment.
Those are, as a rule, rectangular reactors with many chambers, which contain high concentrations of aerobic microbes in suspended floccules (biological sludge) and are equipped with a system of continuous aeration and recirculation of sludge. Aerotanks with prolonged aeration promote the development of bacteria which can effectively remove organics, as well as oxidize ammonia nitrogen to nitrates.
For complete removal of nitrogen from wastewater after nitrification, anaerobic denitrification is required by installing additional vessels or creating special chambers in existing ones.
Phosphorus can be removed by chemical sedimentation or microbial assimilation.
Single reactor systems are also widely used in the world: sequencing batch reactors and membrane bioreactors, as well as oxidation ditches.
The other type of devices are systems with immobile biomass (biofilm). These include trickling filters and rotating biological contactors.
Methods of Wastewater Treatment. Trickling filters are usually cylindrical vessels filled with natural or artificial materials with high mean surface area, on which aerobic and anaerobic bacterial proliferate, and which is in contact with wastewater. Rotating biological contactors consists of several disks up to 3 meters in diameter, installed vertically on a horizontal shaft and submerged (35-40%) into wastewater.
The biological purification of wastewater can also be performed in conditions close to natural. One of the simple methods that can be used for secondary treatment of wastewater is the biological pond. Stabilization ponds are usually artificial rectangular ponds (without higher plant life), connected in a three level cascade: anaerobic pond (2 – 5 meters deep), optional anaerobic pond (1-2.5 meters deep), and an aerobic pondа (0.5-1.5 meters deep). These systems are constructed in at least two parallel lines. Minimum temperature for operation is 8°С.
Stabilization ponds can also be equipped with aeration devices (mechanical aerators usually), which improve the efficiency of purification and makes it possible to use the ponds in lower temperatures.
Another technology of the same nature is the ponds with horizontal subsurface flow of wastewater. They consist of a reservoir covered by watertight material, a layer of filtration material (gravel, sand etc), higher plant life and waste water that moves mostly horizontally below the filter layer.