The Kraft process is typically used for pulping non-wood raw materials, I ike rice straw, in order to dissolve the non cellulose organic fraction, essentially lignin, and leave behind the fibrous residual as pulp for paper production. Rice straw, however, also contains a high percentage of silica that dissolves in the process. The wastewater derived from vacuum filtration of the pulp solution is referred to as black liquor, owing to its dark color and complex makeup with high BOD, caustic, silica, and TDS. The high silica concentration in the black liquor prohibits conventional chemical recovery due to scaling of the boiler unit. Energy recovery through burning the organic matter in the liquor is also prohibited leading to additional economic problems. Moreover, the facility is left with high BOD wastewater having the potential of polluting receiving water bodies. Thus, selective removal of silica immediately after fiber separation but prior to chemical recovery is crucial to the sustainability of the industry, especially in developing countries. Therefore, the objectives of this research are to assess the environmental impact of black liquor on receiving water bodies and to understand the impact of lignin on silica speciation in black liquor. The hypothesis is that lignin compounds form aqueous complexes with silica, thereby increasing its solubility and inhibiting its removal by conventional precipitation. A water quality model was devised to accomplish the first objective, and an experimental program, using lignin model compounds as representatives for lignin, was proposed to test the stated hypothesis. The results of BOD simulations have shown that Egyptian non-wood pulp and paper industry has a significant contribution to the degradation of the water quality of Abu Quir Bay, and that there is urgency for adequate treatment of its wastewater. Findings associated with the experimental work have established the formation of Silica-Ferulic Acid, Silica-Vanillic Acid, and Silica-4-Methoxycinnamic Acid complexes, but no evidence was detected for the formation of Silica-Yeratryl Alcohol complex. The results suggest that complex formation is a general reaction provided that lignin is found in acid form. The lignin in the black liquor consists of more complex compounds than those used in the study. While these compounds are very difficult if not impossible to study by available methods, it is also likely that they have an even greater tendency to form silica complexes, confirming the research hypothesis that silica-lignin complexation is leading to enhancing silica solubility and inhibiting its precipitation. Lignin removal prior to de-silication is one of several proposed alternatives for effective management of black liquor discharges.
School of Sciences and Engineering
Masters of Science in Environmental Engineering
Date of Award
Online Submission Date
Committee Member 1
Sameh Abdel Gawad
Committee Member 2
Committee Member 3
Maher Y.A. Younan
160 leaves :
Library of Congress Subject Heading 1
Library of Congress Subject Heading 2
Factory and trade waste.
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(2002).Impact of lignin from non-wood pulping processes on Kraft wastewater treatment and receiving water quality [Thesis, the American University in Cairo]. AUC Knowledge Fountain.
Nour, Mohamed Hamdy. Impact of lignin from non-wood pulping processes on Kraft wastewater treatment and receiving water quality. 2002. American University in Cairo, Thesis. AUC Knowledge Fountain.
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