Effect of Successive Shock Events on the Performance of a Packaged Decentralized Wastewater Treatment System (PDWWTS) over 1000-Day Operation

Abstract Integration of multiple units in packaged decentralized wastewater systems (PDWWTS) makes PDWWTS vulnerable to cascading failures, where disturbances in upstream units propagate downstream. An integrated, two-compartment, methanogenic–partial nitrification–anammox (ME-ANA) system was subjected to four temperature (19–39 °C) and hydraulic (10–48 h) shock events (SEs) over 1021 days to study how the two compartments (C1 and C2) responded to SEs and whether compartmentalization impacted integrated performance. C1 exhibited greater resistance, with lower mean relative disruption in performance (RDP, 3.7 d) and removal efficiency (RE) decline (3–25%) than C2 (RDP, 8.8 d; RE decline, 24–52%). C1 also cushions temperature shocks in C2, delaying disturbance and accelerating recovery. With time, overall recovery improved from 28 to 3 days, RDP declined (≤0.5 d), and performance improved (COD: 91.4 ± 2.8%; ammonium: 70.1 ± 6.9%). Compartmentalization helped microbial populations to differentiate from heterotrophy in C1 to autotrophy in C2 despite statistically similar communities (methanogenic taxa─C1:31.4%; C2:38.9%; nitrogen-removing taxa─C1:5.03%; C2:12.6%). Autotrophic populations exhibited greater resilience to SEs than heterotrophic populations. This study highlights the evolving resilience of an integrated system exposed to successive SEs, effectively making it suitable for decentralized application with limited supervision.