Reduction of the environmental footprint of thermo‐alkali pretreatment by reusing black liquor during anaerobic digestion of lignocellulosic biomasses

Abstract

In this study, the effect of thermo‐alkaline pretreatment and recycling of the liquid fraction (black liquor) for successive pretreatment steps on chemical composition and methane yields from horse manure was investigated. At first, horse manure was subjected to alkaline pretreatment at 70 °C for 1 h (8.6 g NaOH/100 g total solids). Pretreated biomass was then separated into solid and liquid fractions (black liquor). In the subsequent stages, black liquor was mixed with 20% (v/v) of fresh NaOH and was reused to pretreat subsequent batches of horse manure (cycles 1–4). Chemical analyses showed that thermo‐alkaline pretreatment was effective in the delignification and solubilization of organic matter and thereby increased the holocellulose (cellulose and hemicelluloses) content in the solid fraction of horse manure. On comparison with untreated horse manure methane yields (225 ± 1 L CH4 kg−1 VSadded), thermo‐alkaline pretreatment improved the methane yields of horse manure by 39% (313 ± 16 L CH4 kg−1 VSadded). However, the effectiveness of black liquor recycling on methane production decreased (from 39 to 12%) with an increase in the number of recycling steps (from 1 to 4). Nevertheless, recycling of black liquor reduced the consumption of NaOH (40%) and water use (60%). Thus, thermo‐alkaline pretreatment with liquor recycling was found to be an effective pretreatment with an economic gain of 2.4 to 10.4 compared to pretreatment without recycling. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Anaerobic Digestion of Wastewater Sludge and Alkaline-Pretreated Wheat Straw at Semi-Continuous Pilot Scale: Performances and Energy Assessment

“…Improved biodegradability can further decrease the HRT or size of the reactor required to treat the same quantity of feedstock. Similar results have been reported during the alkaline pretreatment of lignocellulosic biomass [3,15]. For instance, an increase in the hydrolysis constants by 86% and 12% was reported for alkaline pretreatment of horse manure [3] and sunflower stalks [15].…”

“…Similar results have been reported during the alkaline pretreatment of lignocellulosic biomass [3,15]. For instance, an increase in the hydrolysis constants by 86% and 12% was reported for alkaline pretreatment of horse manure [3] and sunflower stalks [15].…”

“…[1,2]. The perspective of a low-cost process that turns organic wastes into biogas (composed primarily of methane and carbon dioxide), a source of renewable energy and profit, has certainly increased the interest around this technology [3]. Biogas can be further used for heat production, biofuels, or injected into the natural gas grid.…”

“…Pretreatments are generally classified as physical, thermochemical, biological, or a combination of them [2]. Many studies have been reported in the literature about the impact of lignocellulosic biomass pretreatment and in particular thermochemical pretreatment has been shown to improve the production of biogas [3,11]. Indeed, thermoacid pretreatments are used to solubilize carbohydrates, and alkaline pretreatment are known to be more effective in delignification and partial solubilization of hemicelluloses [3,11].…”

“…Many studies have been reported in the literature about the impact of lignocellulosic biomass pretreatment and in particular thermochemical pretreatment has been shown to improve the production of biogas [3,11]. Indeed, thermoacid pretreatments are used to solubilize carbohydrates, and alkaline pretreatment are known to be more effective in delignification and partial solubilization of hemicelluloses [3,11]. For instance, reported a methane enhancement of 48% and 67%, respectively, with 1% and 10% NaOH (w/w TS) pretreatment of wheat straw at 100 • C [12].…”