Application of a Sludge Blanket Reactor for Effluent Treatment: A Laboratory Study

Abstract

Energy is required in all societies worldwide. This led to a dependency of fossil fuel. During uncertain times fossil fuel supply become highly politically and used as an influencing source. This requires establishing a more environmentally friendly processes to decrease dependency. To produce biogas from municipal, agricultural and industrial waste a laboratory benchtop up-flow sludge blanket reactor with a operating volume of 2850 ml was designed build, started up, and operated using prepared municipal wastewater and separated liquid cow manure at a hydraulic retention time of 1 day, 3 days and 6 days after an 120 h adjustment time prior to testing.
 While using wastewater as influent, the laboratory benchtop up-flow sludge blanket reactor system was not able to reduce the chemical oxygen demand content significantly. Especially at a high volumetric flow rate for the 1-day hydraulic retention time. The produced gas amount decreased from 0.59 ±0.07 (ml/h)/L at a hydraulic retention rate of 6 days to 0.042 ±0.04 (ml/h)/L. The fluctuating influent chemical oxygen demand of 25 ±1 mg/L to 74 ±15 mg/L resulted in a stable effluent concentration of 39 ml/L and 45 ±11 mg/L respectively.
 The laboratory benchtop up-flow sludge blanket reactor system with separated liquid cow manure showed a higher chemical oxygen demand degradation capability but resulted in higher chemical oxygen demand in the effluent. The influent chemical oxygen demand of 308 ±42 mg/L was broken downs to 59 ±1 mg/L at a hydraulic retention time of 6 days and to 114 ±5 mg/L for 1 day retention time. The biogas production result in a stable gas production rate of 0.27 ±0.02 (ml/h)/L through all three hydraulic retention times. For both the wastewater and separated liquid cow manure operation the biogas without carbon dioxide was between 55 and 65%.
 The results show that the laboratory benchtop up-flow sludge blanket reactor system can reduce high chemical oxygen demand in wastewater and separated liquid cow manure. However, a minimum feed level having a minimal chemical oxygen demand above 36 mg/L is needed, otherwise, the active bacterial mass contributes to the effluent level as seen for the influent level below 36 mg/L and 25 mg/L which resulted in a minimum effluent level of 39 mg/L for a hydraulic retention time of 3-days and 6-days.