Pretreatment of wastepaper and pulp mill sludge by aqueous ammonia and hydrogen peroxide

Pretreatment of two different softwood-based lignocellulosic wastes (newsprint and Kraft pulp mill sludge) was investigated. Pretreatment was done by aqueous ammonia and hydrogen peroxide (H2O2), two delignifying reagents that are environmentally benign. Three different treatment schemes were employed: aqueous ammonia alone (ammonia recycled percolation [ARP]), mixed stream of aqueous ammonia and H2O2, and successive treatment with H2O2 and aqueous ammonia. In all cases there was a substantial degree of delignification ranging from 30 to 50%. About half of the hemicellulose sugars were dissolved into the process effluent. Retention of cellulose after pretreatment varied from 85 to 100% for newspaper feedstock and from 77 to 85% for the pulp mill sludge. After treatment with aqueous ammonia alone (ARP), the digestibility of newspaper and the pulp mill sludge was improved only by 5% (from 40 to 45% for the former and from 68 to 73% for the latter), despite a substantial degree of delignification occurring after the ARP process. The lignin content thus did not correlate with the digestibility for these substrates. Simultaneous treatment with H2O2 and aqueous ammonia did not bring about any significant improvement in the digestibility over that of the ARP. A successive treatment by H2O2 and ARP showed the most promise because it improved the digestibility of the newspaper from 41 to 75%, a level comparable to that of alpha-cellulose.