In South Korea, 94 wt.% of cattle manure (CM) is composted, which generates greenhouse gases and air pollutants, affecting climate, air quality, and causing water and soil pollution. Anaerobic digestion (AD), which converts organic matter into biogas and digestate, offers an alternative to composting. However, CM in Korea has lower biodegradability due to compost-oriented management practices, hindering its application to AD. Thermo-alkali pretreatment (TA) can enhance biodegradability of CM, possibly making AD a viable alternative. TA applies heat and alkali, combining the advantages of thermal hydrolysis process (THP) and alkali pretreatment (AP).

  This study assesses and elucidates the effect of TA on chemical properties, and evaluates net energy and economic benefits. CM underwent pretreatment at various temperatures (25, 50, 70, and 90 °C) and NaOH dosages (0, 4, 8, and 12 wt.% on total solids (TS)). Methane potential and chemical properties were measured before and after pretreatment. Principal component analysis (PCA) and hierarchical regression were used for statistical analysis.

  CM treated at 90 °C and 12 wt.% NaOH on TS showed the highest methane potential (139 mL/g-VS), a 51 vol.% increase compared to untreated CM. TA outperformed thermal hydrolysis pretreatment (THP) by 37 vol.% in methane potential and alkali pretreatment (AP) by 21 vol.%.

  Multiple linear regression (MLR) exhibited the highest correlation (R2 = 0.95) between methane potential and pretreatment conditions. PCA revealed that methane potential was closely related to lignin decomposition ratio, COD, carbohydrate, and protein solubilization ratio. Single linear regressions (SLR) of above ratio to methane potential showed fair correlations of R2 of 0.80, 0.85, 0.84, and 0.82, respectively.

  Lignin exhibited the highest correlation with methane potential among other lignocellulose components. MLR showed best fit (R2 = i 0.88) with pretreatment conditions, same as methane potential supporting the fairly strong relationship between them.

  The fair correlation between COD solubilization ratio and methane potential suggested that methane primarily originated from soluble organic matter, with no or weak anaerobic digestion inhibition. MLR was the best fit for COD solubilization ratio (R2 = 0.90) with pretreatment conditions. The strong correlation between COD solubilization ratio and carbohydrate (R2 = 0.95) or protein (R2 = 0.90) solubilization ratios indicated their predominant presence in COD of CM. High correlation (R2 = 0.89) of carbohydrate and protein solubilization ratio to methane potential by MLR with interaction terms (MLRI) supported the influence of soluble carbohydrate and protein composition on microbial communities of AD.

  Inclusion of lignin as an independent parameter did not enhance correlation of COD, carbohydrate, and protein with methane potential, suggesting lignin had less impact than other properties on methane potential.

  TA yielded 51 % more net energy benefit compared to untreated CM. Also, TA outperformed other treatments showed up to 41 and 17 % increase of net energy benefit compared to THP and AP, respectively. Net energy benefit sensitivity to heat recovery efficiency rose with increasing pretreatment temperature.

  Net economic benefit did not significantly increase after TA, but still provided 34 % more net economic benefit than AP. However, the net economic benefit of TA was lower than that of THP declining 65 % for every 4 wt.% increase of NaOH dosage on TS. This suggests that TA is more economically efficient than AP but less so than THP. A sensitivity analysis revealed that NaOH dosage had the greatest impact on net economic benefit, followed by electricity efficiency and price, heat efficiency and price, and heat recovery efficiency.