Which element in sewage treatment is primarily responsible for breaking down organic matter?

The primary role of bacteria in sewage treatment is to decompose organic matter. In the sewage treatment process, bacteria specifically break down complex organic materials, such as food waste and human waste, into simpler substances. This biological process is termed anaerobic or aerobic digestion, depending on whether oxygen is present. During this breakdown, bacteria convert organic materials into environmentally safer compounds, thereby reducing the harmful effects of sewage.

Bacteria are essential in various stages of sewage treatment, particularly in secondary treatment processes, where they help in achieving significant reductions in biochemical oxygen demand (BOD) and total suspended solids (TSS). By digesting organic matter, bacteria facilitate the transformation of sewage into a less harmful effluent that can either be treated further before being released into the environment or reused in some capacity.

Other elements such as chlorine are used for disinfection purposes, not for breaking down organic matter, while phosphate and nitrogen are nutrients that can be part of the sewage but do not play a direct role in the decomposition process.