In wastewater treatment, biological processes are employed mainly to remove…

Concept

Biological wastewater treatment uses living microorganisms to convert biodegradable dissolved and finely dispersed organic matter into biomass and stable end products.

Physical operations such as screening, sedimentation, and filtration mainly remove settleable or suspended solids, while disinfection targets microorganisms in the treated effluent.

Application

1. Classify the listed constituents by their role: bacteria and fungi are microorganisms; suspended solids are particulate matter; colloids are finely dispersed matter; soluble organics are dissolved biodegradable matter.

2. Biological flocs adsorb colloidal organics, and microorganisms assimilate and oxidize soluble organics.

Contrast

• The grouping of bacteria, suspended solids, and fungi mixes treatment organisms with solids that are chiefly separated physically.

• The grouping of suspended solids with colloidal matter includes a physically clarified fraction and omits the dissolved organic load.

• The grouping of fungi, colloidal matter, and soluble organic compounds treats a decomposer organism as material to be removed.

Cross-check

Secondary treatment reduces biochemical oxygen demand chiefly by converting biodegradable colloidal and dissolved organic matter, which independently confirms the classification.

Result

Therefore, the constituents mainly removed by the biological stage are colloidal matter and soluble organic compounds.