RCHES-RWANDA is a company in Rwanda that deals with treatment of water, soil and air, the company conducts research and offers technical assistance for interested people and industries in Chemistry and related fields. One of the treatment offered by this company is the biological treatment. The biological treatment is good because it avoids the excessive use of chemicals. Bacteria are given oxygen and use waste water organics as food, they use this food to grow and produce CO2 and removes nutrients. In activated sludge, the active bacteria (sludge) are in suspension and settled in a sedimentation tank and part of the sludge is recycled.