Principles and Practice of Engineering (PE) Civil: Water Resources and Environmental (WRE) Practice Exam

During anaerobic decomposition, the primary process that occurs is methanogenesis. This process is a form of anaerobic respiration carried out by microorganisms, particularly methanogenic archaea. In environments devoid of oxygen, these microorganisms convert organic matter into methane (CH4) and carbon dioxide (CO2). This is crucial in settings such as landfills, wetlands, and the digestive tracts of certain animals (like ruminants), where organic material breaks down in the absence of oxygen.

Methanogenesis is integral to the carbon cycle and has implications for energy production in anaerobic digesters, where it can be harnessed for biogas production. This process differs fundamentally from aerobic processes that rely on the presence of oxygen and involve different biochemical pathways.

The other processes listed do not primarily occur under anaerobic conditions. Oxygenation involves the addition of oxygen to a system, which contradicts the anaerobic context. Nitrification refers to the microbial conversion of ammonia to nitrate and is an aerobic process that requires oxygen. Dephosphatation typically involves the removal of phosphorus from wastewater and may occur in various conditions, but is not specific to anaerobic decomposition. Thus, methanogenesis is definitively the correct response, as it directly reflects the anaerobic