Performance of Full-Scale UASB Reactors Treating Low or Medium Strength Municipal Wastewater

Upflow Anaerobic Sludge Blanket (UASB) reactors treating low or medium strength municipal wastewater were monitored under field conditions in India. The study aimed to evaluate the efficiency of the UASB process (in terms of organics, solids and nutrients removal) and to highlight the causes and remedies for odour nuisances. The UASB reactors represent a robust and efficient technology for sewage pre-treatment (COD removal: 51%; BOD: 56%; TSS: 54%), capable to generate renewable energy (biogas yield: 0.20–0.40 m³ kg⁻¹ COD removed) under the conditions prevailing in India. The UASB performed significantly better when low strength wastewater (COD ~300 mg L⁻¹) was treated, giving a final effluent COD of around 120 mg L⁻¹, similar to aerobic treatment systems. In the case of medium strength municipal wastewater with high sulphate content (COD: 600 mg L⁻¹; SO₄: 175 mg L⁻¹), a 10-fold increase of the effluent sulphide concentrations was recorded (from 3 to 34 mg L⁻¹), compared to low strength sewage processing (from 1.5 to 7.0 mg L⁻¹). As such, major odour nuisances (release of H₂S) may originate from the anaerobic effluent itself, as well as from spontaneous biogas losses.