Principles and Practice of Engineering (PE) Civil: Breadth Practice Exam 2025 - Free PE Civil Breadth Practice Questions and Study Guide

Secondary wastewater treatment is primarily focused on the biological processes that aim to remove biodegradable organics and suspended solids from wastewater. This stage of treatment utilizes microorganisms, such as bacteria, to oxidize organic matter present in the wastewater. As these microorganisms metabolize the organics, they help convert them into simpler, less harmful substances, which are then further broken down or settled out of the water.

This process not only significantly reduces the levels of biodegradable organic pollutants but also helps to reduce the overall biochemical oxygen demand (BOD) of the effluent, making it safer for discharge into the environment. The effectiveness of secondary treatment can be influenced by various factors, such as the aeration method used, the retention time, and the type of microorganisms present.

The other options relate to different aspects of wastewater treatment that do not specifically characterize secondary treatment. For example, removing heavy metals and other nutrients pertains more to tertiary treatment, while polishing effluent after primary treatment involves additional methods to clarify and disinfect. Chemical treatments typically focus on inorganic compounds rather than the biological breakdown central to secondary treatment processes.