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

Degree Name

Masters of Science in Environmental Engineering

Date of Award


Online Submission Date


First Advisor

Edward Smith

Committee Member 1

Sameh Abdel Gawad

Committee Member 2

Abdallah Bazaraa

Committee Member 3

Maher Y.A. Younan

Document Type



160 leaves :

Library of Congress Subject Heading 1


Library of Congress Subject Heading 2

Factory and trade waste.


The author retains all rights with regard to copyright. The author certifies that written permission from the owner(s) of third-party copyrighted matter included in the thesis, dissertation, paper, or record of study has been obtained. The author further certifies that IRB approval has been obtained for this thesis, or that IRB approval is not necessary for this thesis. Insofar as this thesis, dissertation, paper, or record of study is an educational record as defined in the Family Educational Rights and Privacy Act (FERPA) (20 USC 1232g), the author has granted consent to disclosure of it to anyone who requests a copy.

Call Number

Thesis 2002/51



Included in

Engineering Commons