Which methods are considered forms of secondary treatment for wastewater?

The methods considered forms of secondary treatment for wastewater include trickling filters and the activated sludge process. Secondary treatment is designed to remove dissolved and suspended organic matter from wastewater through biological processes.

Trickling filters involve a bed of media where microorganisms grow and feed on organic matter as the wastewater trickles over it. This process effectively reduces the concentration of pollutants in the water. The activated sludge process, on the other hand, involves aerating wastewater in the presence of microorganisms, which consume organic pollutants during their growth. Both processes rely on biological activity to break down waste, highlighting their classification as secondary treatment methods.

The other methods listed do not fall into the category of secondary treatment. Bar screens and sedimentation are part of primary treatment, which focuses on removing larger solids before biological treatment. Chemical coagulation is a method typically used in pre-treatment or primary treatment to remove suspended solids and some dissolved substances, often through the addition of chemicals to promote aggregation. Rapid infiltration and irrigation are more related to land treatment methods, focusing on the application of wastewater to soil for treatment and nutrient absorption, rather than intervening directly in the wastewater’s biological treatment.