System Boundary Separation of Anaerobic Digestion for Improved Direct Methane Emission Estimation in WWTP; [하수처리시설 내 혐기성 소화 공정의 시스템 경계 분리를 통한 메탄 직접 배출량 산정법 개선]

초록

This study evaluated the structural consistency of direct methane (CH4) emission estimation in wastewater treatment plants (WWTPs) by defining the anaerobic digester as separate from the overall system boundary and examining the effect. Under current Korean guidelines, the entire WWTP is treated as a single system boundary, and CH4 emissions are estimated based on overall organic matter removal and the amount of CH4 recovered from anaerobic digestion. However, this approach does not explicitly distinguish CH4 generation, recovery, and residual emissions occurring within the anaerobic digester from those of the overall facility. To address this gap, a process-based organic matter mass balance was developed using an influent load normalized to 100 ton BOD, with the potential organic load entering the anaerobic digester estimated at 42.1 ton BOD. Using the current guideline, direct CH4 emissions were calculated as 0.86 ton CH4 without anaerobic digestion and 1.17 ton CH4 with anaerobic digestion, indicating that reported emissions can increase even when CH4 is recovered. When the waste activated sludge feeding ratio to the anaerobic digester was reduced from 100% to 50% and 0%, the actual digester influent load decreased from 42.1 to 36.0 and 30.0 ton BOD, and recovered CH4 decreased from 15.36 to 13.15 and 10.94 ton CH4, respectively. In contrast, direct emissions estimated using the current method increased from 1.17 to 2.49 and 3.80 ton CH4, demonstrating a reversal between actual CH4 generation potential and reported emissions. However, when the anaerobic digester was defined as a separate system boundary from the overall WWTP, total direct CH4 emissions consistently decreased from 1.67 to 1.55 and 1.43 ton CH4, demonstrating an improvement in the consistency of direct CH4 emission estimation and better reflecting variations in digester influent load. © 2026, Korea Society of Waste Management. All rights reserved.

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