Answer:

Anaerobic treatment processes are used in wastewater treatment to remove organic matter in the absence of oxygen. Among the options given, the process that works on pure anaerobiosis is the septic tank.

1. Septic Tank:
A septic tank is a simple and commonly used anaerobic treatment system for domestic wastewater. It consists of a watertight underground tank that receives raw wastewater from households or small communities. The treatment process occurs in three stages:

- Settling: The wastewater enters the septic tank where the solids settle at the bottom forming sludge, while the lighter materials like grease and oils float to the top forming scum.

- Digestion: The settled solids undergo anaerobic digestion by microorganisms present in the tank. These microorganisms break down the organic matter, converting it into simpler substances such as methane and carbon dioxide.

- Effluent Discharge: The remaining liquid, known as effluent, flows out of the tank and enters the drain field or leach field, where it is further treated and disposed of into the soil.

Other Options:

- Grit Chamber: A grit chamber is a physical treatment process used to remove sand, gravel, and other heavy particles from wastewater. It is not an anaerobic treatment process but rather a pre-treatment step to protect downstream equipment.

- Activated Sludge Process: The activated sludge process is an aerobic treatment process that utilizes oxygen to break down organic matter in wastewater. It involves the growth of microorganisms in a suspension (activated sludge) that consumes and oxidizes the organic pollutants.

- Trickling Filter: A trickling filter is another aerobic treatment process where wastewater is distributed over a bed of rocks or other porous media. Microorganisms attached to the media break down the organic matter as the wastewater trickles through, using oxygen to carry out the oxidation reactions.

In summary, the septic tank is the only option among the given choices that operates solely on anaerobiosis.