Anaerobic Wastewater Treatment: Methanogenesis Kinetics, UASB Reactor Hydraulics, and Granular Sludge
Anaerobic wastewater treatment utilizes complex consortia of anaerobic micro-organisms to stabilize organic matter in the complete absence of molecular oxygen. Unlike aerobic processes that require intensive energy for mechanical aeration, anaerobic digestion converts complex organic pollutants primarily into biogas, consisting mainly of methane ($\text{CH}_4$, 60%–70%) and carbon dioxide ($\text{CO}_2$, 30%–40%), while producing significantly lower excess biological sludge. The biological conversion occurs via four sequential biochemical stages: Hydrolysis, Acidogenesis, Acetogenesis, and Methanogenesis. Methanogenesis is the rate-limiting step governed by strict anaerobes (methanogens). Stoichiometrically, the theoretical ultimate methane yield per unit of COD destroyed under standard conditions ($0^\circ\text{C}$ and $1\text{ atm}$) is derived as: $$V_{\text{CH}_4} = 0.35 \cdot \left(\text{COD}_{\text{removed}} - 1.42 \cdot P_x\right)$$ Where $V_{\text{CH}_4}$ is the daily vo...