A soak-and-press method for the alkali treatment of fibrous crop residues. Laboratory studies on aspects of the procedure

Abstract

Four experiments were conducted to establish criteria for a soak-and-press method of treating fibrous crop residues with alkali. Experiment 1 showed that the in vitro organic matter digestability of barley straw was maximised after 18–24 h of soaking in a sodium hydroxide solution, using 12 or 18 g NaOH per 100 g straw dry matter. In experiment 2, barley straw and sugarcane bagasse were soaked in solutions of sodium hydroxide for 24 h and then mechanical pressure was applied at levels up to 64 kg cm −2 so as to remove liquid and thereby decrease the sodium content and the alkalinity of the treated materials. Rice straw was soaked similarly and subsequent pressures up to 8 kg cm −2 were used. In all three materials, a pressure of 1 kg cm −2 appeared to be appropriate. Experiment 3 showed that a given amount of sodium hydroxide dissolved in twenty times as much water as the mass of barley straw, rather than ten or fifteen times as much water, resulted in a tendency towards less organic matter loss in soaking and pressing and a lower ash content of the treated material. In Experiment 4 the effects of re-using the alkali soaking solution were examined. The system appeared to stabilise after about six batches of barley straw or rice straw were soaked and pressed. Whereas barley straw soaked in a fresh solution of sodium hydroxide lost 14% of its organic matter, when a solution had been used to soak six batches the organic loss had declined to around 4% and did not change for the following fifteen