What are the four steps of mechanical treatment in wastewater processing?

The correct answer identifies the appropriate sequence of processes involved in the mechanical treatment of wastewater. Mechanical treatment typically encompasses the initial stages of wastewater processing aimed at removing larger solids and particulate matter.

The first step, referred to as preliminary treatment, involves the removal of large debris through screens, which helps to protect subsequent processing equipment. Following this, primary treatment focuses on the sedimentation of suspended solids, allowing heavier particles to settle out of the wastewater.

The secondary treatment phase includes biological processes that further reduce organic matter and nutrients, although the term "secondary" in the provided answer indicates a mechanical context rather than biological. Finally, tertiary treatment represents advanced processes to remove remaining contaminants and improve water quality before it is released or undergoes further treatment.

Understanding these four stages provides insight into the overall goal of wastewater treatment, which is to purify water to meet regulatory standards and protect environmental and public health.