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One alternative for treating wastewater is the use of biological systems. Thus it is possible to decrease the organic content of water, as well as remove pathogens and parasites. The biological water treatment can be achieved through aerobic and anaerobic processes.
Here are some:
Sludge ponds:
In this case, mechanisms are used entering air into the tanks. On contact with air, the organisms react to generate flocs, settles them in passing the so-called clarification tanks. To treat wastewater through the biological system, you need: an aeration tank and a clarification by the sludge being passed repeatedly.

The main objective of activated sludge system is the oxidation of biodegradable matter in the aeration tank, and flocculation, which enables the separation of biomass from treated effluent. Removal can be achieved up to 90% of the organic load. However, there are some drawbacks: it requires expensive facilities and investment in electromechanical equipment with a high energy cost. It also produces a significant amount of sludge that later require further treatment by anaerobic reactors and / or landfill disposal installed correctly.