Desludging frequency of septic tanks based on assessment of sludge accumulation and generation rates in septic tanks and treatment plants

Septic tanks require periodic desludging and further treatment at the Septic Sludge Treatment Plant (SSTP). However, the relationship between desludging frequency (DF), which is influenced by the sludge accumulation rate (SAR) in the sludge accumulation rate (SAR) inside different types of septic tanks, and the sludge generation rate (SGR) at the SSTP remains unclear. This work presents a systematic analytical approach for predicting and validating DF by simultaneously investigating the SAR and SGR from septic tanks and the SSTP, respectively. Seventy-eight (78) septic tanks, i.e., fiberglass (FG, 10), plastic (PL, 44), and reinforced concrete (RC, 24), were evaluated for their SAR based on serving population equivalent (PE) and sludge depth profiles over the years. No significant difference in SAR was found across these tanks, with an average SAR of 0.043 m 3 PE -1 yr -1 . To verify this, the SGR was found to range from 1.251 to 1.933 metric tons d -1 for the coarse ( cs ), fine ( fs ), and rotary drum screenings ( rds ) at the SSTP, resulting in a similar average SAR (0.044 m 3 PE -1 yr -1 ). Consequently, a standardized DF of every three years is recommended for 6-PE septic tanks. This work provides insight into SAR (septic tanks) and SGR (SSTP), offering a more realistic estimate of DF to enhance their design and operational guidelines. • No significant SAR differences across different types of tanks. • A SAR of 0.043 m 3 PE -1 y -1 was obtained via septic tank investigation. • SGRs from SSTP validated SAR at 0.044 m 3 PE -1 y -1 . • Recommended desludging frequency of 3 years for 6-PE tanks.