Effect of sewage sludge and mineral fertilization on ethanol production from Jerusalem artichoke and optimization of the bioconversion process

This study examined the effects of fertilization type, biomass pretreatment, and process supplementation on ethanol yield and fermentation efficiency from Jerusalem artichoke biomass sewage sludge (S₁₀₀, S₁₆₀) or mineral fertilizer (M₁₀₀, M₁₆₀) at nitrogen doses of 100 and 160 kg N ha^-1 using the simultaneous saccharification and fermentation (SSF) method. Biomass composition varied with fertilization type and dose. Sewage sludge fertilization increased cellulose content by 14% compared to the unfertilized control, while mineral fertilization had a negligible effect. Lignin content also increased, with the highest levels observed in M₁₆₀ (6.19% DM) and S₁₀₀ (6.14% DM), representing 20-25% more than in the control (5.05% DM). The SSF process was highly effective in converting pretreated biomass into ethanol. The highest ethanol concentration (1.87% v/v) and productivity (0.39 cm³ A₁₀₀ dm^-3 h^-1) were achieved with the S₁₆₀ treatment, indicating that nutrient-rich sewage sludge improved substrate digestibility and yeast performance. Shortening the SSF duration from 96 to 48 h further increased productivity, with only a slight decrease in fermentation efficiency. Omitting the rinsing step after alkaline pretreatment increased ethanol concentration by 23% (95% CI 15.4-30.1%) but slightly reduced fermentation efficiency (6.11%; 95% CI 3.48-8.74%), except for S₁₆₀, where the effect was negligible. Supplementing the fermentation medium with mineral salts or additional substrate further increased ethanol yield, with mineral salt addition being more effective, especially for fertilized biomass. These results demonstrate the influence of fertilization on lignocellulosic composition and its relationship to ethanol yield. Optimizing SSF operational conditions, combined with nutrient recycling through sewage sludge, can improve the efficiency and sustainability of second-generation bioethanol production.