Final answer:
Anaerobic secondary wastewater treatment produces methane gas during the anaerobic decomposition of sludge, which can be used as fuel for the plant.
Step-by-step explanation:
Production of Gaseous Fuel in Wastewater Treatment
The process that produces a gaseous product that can be used as fuel to provide heat or power for a wastewater treatment plant is the anaerobic secondary wastewater treatment. This process involves the anaerobic decomposition of organic sludge, which produces methane gas. Methane is a clean-burning fuel that can be utilized for generating energy within the treatment plant. In comparison, aerobic processes rely on oxygen and do not produce a fuel byproduct. Primary treatment primarily involves separation of solids from liquids and does not result in fuel production.
During sludge digestion, which is a separate process from wastewater treatment, the sludge scrapped from the settling tank during the primary treatment is treated. In an environment devoid of oxygen (anaerobic), bacteria break down the organic matter in the sludge, resulting in the production of methane, which can be captured and used as fuel. This gaseous biomass is an important byproduct as it represents a renewable energy source for the plant's operations or for external use.