Effectiveness of coagulation and acid precipitation processes for the pre-treatment of diluted black liquor.
The effectiveness of coagulation (using aluminium-based chemicals and ferrous sulfate) and acid precipitation (using H(2)SO(4)) processes for the pre-treatment of diluted black liquor obtained from a pulp and paper mill is reported. Commercial alum was found to be the most economical among all the aluminium and ferrous salts used as a coagulant. A maximum removal of chemical oxygen demand (COD) (ca. 63%) and colour reduction (ca. 90%) from the wastewater (COD = 7000 mg l(-1)) at pH 5.0 was obtained with alum. During the acid precipitation process, at pH < 5.0, significant COD reductions (up to 64%) were observed. Solid residue obtained from the alum treatment at a temperature of 95 degrees C showed much better (3 times) settling rate than that for the residue obtained after treatment with the same coagulant at a temperature of 25 degrees C. The settling curves had three parts, namely, hindered, transition and compression zones. Tory plots were used to determine the critical height of suspension-supernatant interface that is used in the design of a clarifier-thickener unit. High heating values and large biomass fraction of the solid residues can encourage the fuel users to use this waste derived sludge as a potential renewable energy source.
Garg
Anurag
A
Chemical Engineering Department, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India. a.garg@iitb.ac.in
Mishra
I M
IM
Chand
S
S
D000143:Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste; D010209:Paper; D013696:Temperature; D013783:Textile Industry; D014873:Water Pollutants / Q000302:isolation & purification
D000143:Acids; D007220:Industrial Waste; D014873:Water Pollutants