Chemical Oxygen Demand removal rate comparative analysis using three different biogas digesters

Kevin Nnanye Nwaigwe, Chibuike Ononogbo, Emmanuel E Anyanwu, Christopher C Enweremadu


The Chemical Oxygen Demand (COD) end value of effluent discharged from a bioreactor into the environment is a critical indicator of its capacity to pollute the environment. A comparative parametric analysis of COD removal rate using three different biogas digesters is presented.  The three bioreactors are Upflow Anaerobic Sludge Blanket (UASB), Upflow Bioreactor with Central Substrate Dispenser (UBCSD), and Continuous Stirred-Tank Reactor (CSTR). In order to select the most fitting bioreactor type among the three considered, experimentation was carried out using organic municipal waste (OMW) as substrate. A 10-day hydraulic retention time (HRT) was used, while cattle rumen microbes were used to improve digestion rate. UBCSD showed the highest level of percentage COD removal of 95.2%, followed by the CSTR with a value of 80.8%; while the UASB offered the lowest level of percentage COD removal of 79.0%.  This outcome indicates that effluent from the UBCSD digested substrate is more suitable and safer for use as organic fertilizer in agricultural practices. It similarly implies that a bioreactor with enhanced mixing capacity is safer for digestion.


Chemical Oxygen Demand; biogas digesters; parametric analysis; hydraulic retention time.

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