Metcalf & Eddy 5e Liu correlation
Estimates biogas / methane / pipeline-RNG yield from a WWTP, food-waste, or codigestion digester via mass-balance VS-destruction model
VS_destruction% = 13.7·ln(HRT) + 18.9 (mesophilic Liu, M&E 5e Ch 14)
combined with substrate-specific methane yield (M&E Table 14-7, WEF MOP-8). Includes 40 CFR 503 Subpart D Class A (PFRP) / Class B (PSRP) pathogen-reduction assessment.
Feed Stream
m³/d
%
Thickened primary+WAS typical 4–6%; WAS only 0.8–2.5%; food waste 8–25%.
%
Fresh primary sludge 75–80%; WAS 70–75%; food waste 80–90%.
kg/m³
Digester & Substrate
°C
days
m³/kg VSdest
M&E Table 14-7 / WEF MOP-8 substrate-specific; Buswell ceiling ~0.42 for pure sludge.
%
Leave blank to auto-compute via Liu correlation; override for site-specific data.
Biogas & Biosolids
%
Sludge biogas typical 60–70%.
%
%
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Engineering Basis
VS destruction (Liu correlation): M&E 5e Ch 14 — VS_dest% = 13.7·ln(HRT) + 18.9 for mesophilic, +26.9 for thermophilic. Capped 70%.
Substrate-specific CH₄ yield: M&E Table 14-7 + WEF MOP-8 — 0.30 (WAS) to 1.10 (FOG) m³ CH₄/kg VS destroyed.
40 CFR 503 Class B PSRP Alt 1 §503.32(b): HRT ≥ 15 d at 35–55°C OR ≥ 60 d at 20°C.
40 CFR 503 Class A PFRP Alt 1 §503.32(a): t (h) = 50,070,000 / 10^(0.14·T) at T ≥ 50°C — at 55°C ≈ 22 d.