Biological treatment is the most widely used and effective method for managing the biodegradable substances present in wastewater, leveraging naturally occurring microorganisms to accelerate natural degradation under controlled engineering conditions. This white paper provides a detailed comparative analysis of the two fundamental approaches to biological treatment—aerobic and anaerobic systems—to serve as a decision-making tool for engineers evaluating technologies for specific industrial waste streams. The primary objective of biological treatment is the removal and stabilization of degradable organic substances, which can exist in suspended, colloidal, and dissolved forms. Wastewater characteristics are typically quantified using key metrics such as Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), Total Organic Carbon (TOC), and Volatile Suspended Solids (VSS). The effectiveness of both aerobic and anaerobic systems is ultimately governed by the fundamental metabolic principles of the microorganisms they employ.