Table 2: Comparison of aerobic and anaerobic treatment methods.

ParameterAerobic treatmentAnaerobicReferences

ProcessDegradation of organic matter occurs in the presence of oxygenDegradation of organic matter occurs in the absence of oxygen[83]

By-productsThe process generates carbon dioxide, water, and excess biomassThe process generates carbon dioxide, methane, and excess biomass[44, 84]

ApplicabilityHighest removal efficiency for wastewater having low to medium organic content (COD < 1000 ppm) that is complex to biodegrade, for example, municipal sewage and refinery wastewaterHighest removal efficiency for wastewater having medium to high organic content (COD > 1000 ppm) and easy biodegradability, for example, food and beverage industry’s wastewater rich in organic content. But also applicable to low strength wastewater (COD > 300 and <1000 mg/L)[25, 85]

Reaction kinetic Decay rate = 0.06 d−1Decay rate = 0.03 d−1[44, 83, 84]

Sludge yield coefficient (kgVSS/Kg COD)0.35–0.45 (relatively high) Biomass yield is fairly constant irrespective of the type of substrate metabolized0.05–0.15 (relatively low) biomass yield is not constant and varies with the type of substrate metabolized[86]

PosttreatmentDirect discharge, followed by filtration/disinfectionGenerally done by aerobic methods[21, 83, 87, 88]

Foot print1.0 to 2.4 kgCO2/kgCOD removed (depending on the wastewater strength)0.5 to 1.0 KgCO2/kgCOD removed (depending on the wastewater strength)[44, 45, 85, 89]

Capital cost12–40 US$/inhab.40–65 US$/inhab.[49, 9092]

Typical technologiesActivated sludge, trickling filters, extended aeration, oxidation ditch, downflow hanging sponge (DHS), Membrane Bioreactor (MBR), Moving Bed Bioreactor (MBBR)UASB, continuously stirred tank reactor/digester/Upflow Anaerobic Filters, ultrahigh rate fluidized bed reactors, hybrid high rate reactors, two-stage UASB reactor[15, 24, 60, 67]