Article pubs.acs.org/IECR
A Combined Coagulation/Flocculation and Membrane Filtration Process for the Treatment of Paint Industry Wastewaters Dimitris P. Zagklis, Petros G. Koutsoukos, and Christakis A. Paraskeva* Institute of Chemical Engineering Sciences, Foundation for Research and Technology, Hellas (FORTH/ICE-HT), Stadiou Street, Platani, Patras, GR 26504, Greece, and Department of Chemical Engineering, University of Patras, GR 26504, Rion, Patras, Greece ABSTRACT: Coagulation/flocculation process is considered as a nonexpensive and effective method to reduce organic and inorganic content of industrial wastewaters. In the present study series of polyelectrolytes were tested to optimize the existing procedure with new chemical reagents that resulted in removal percentages up to 93%. Organic load expressed in terms of chemical oxygen demand, particle size distribution, pH, and ζ potential of suspended particles were among the parameters that were investigated for the best coagulation/flocculation of particles suspended in paint industrial wastewaters. The target was to find the optimum concentration values of polyelectrolytes that neutralize the ζ potential and shrink the particle size distribution. The remaining organic compounds were further treated with a combined ultrafiltration/reverse osmosis system that almost eliminated the organic content, and the final permeate stream is suitable for reuse in the premises of the industry.
1. INTRODUCTION Industrial wastewaters can cause serious environmental damage if disposed untreated to water banks, a fact that makes their effective treatment imperative. This kind of waste contains a large variety of compounds, with adverse effects to the environment and to human health, some well-known and others still under investigation.1 If the wastewater produced by a factory has great variation from sanitary wastewaters then it must be pretreated before it is disposed to the sewage system.2 As large quantities of water are needed in most of the industrial processes, the most viable solution for the occurring wastes is their recycling,3 which can be achieved through several treatment processes. Paint industry produces wastewaters with significant organic content, unfit for direct disposal. The occurring waste consists mostly of washing waters from polymerization and mixing tanks,4 containing the final products diluted. A possible treatment method is coagulation/flocculation with the use of polyelectrolytes, which is widely used for the treatment of industrial wastewaters.4−6 Different applications of coagulation/flocculation for the treatment of industrial wastewaters are summarized in Table 1, accompanied by their treatment efficiency and cost. As it is shown, coagulation/ flocculation combines moderate to high treatment efficiency and relatively low treatment cost. By administering the appropriate dosage of coagulants and polyelectrolytes in the right conditions (pH) the contained chemical oxygen demand (COD) and total solids (TS) can be reduced significantly. Aboulhassan et al.4 have achieved a COD reduction of 91% with the use of FeCl3 combined with high molecular weight polyelectrolytes (flocculants). Other coagulants like FeSO4, Al2(SO)4, and poly(aluminum) chloride have been used in combination with high molecular weight polymers, yielding a COD reduction of 96%.5 Eremektar et al.6 have also used FeCl3 and FeSO4 as well as sodium bentonite and alum, leading to 52% of COD removal. After coagulation/flocculation has removed most of the contained COD and TS, any remaining organic content can be removed with the use of membrane filtration. Membrane filtration has © 2012 American Chemical Society
Table 1. Treatment Efficiency for Different Wastewaters with Coagulation/Flocculation wastewater tannery
paint
paint
brine paint
coagulant/ flocculant
dosage mg/L
alum alum−(C-496) alum−(A-100) Fe Fe−PO Fe−SU Fe−PR Fe−PO−SU Fe−PO−PR sodium bentonite alum FeCl3 FeSO4 Volclay KWK Pangel C 150 FeSO4 Al2(SO4)3 PACl
418 100−5 160−5 650 650−160 650−2.4 650−5 650−80−1.2 650−80−2.5 100 100 50 100
2000 2500 4000
COD % reduction
cost €/m3
53.3 36.2 48.3 82.55 88.46 88.37 84.42 90.35 90.80 33
0.14 0.05 0.06 0.45 0.88 0.46 1.70 0.67 1.29 0.04
52 40 53 49 56 30−80 70−95 98
ref 7
4
6
0.04 0.03 0.04 8 5
been successfully implemented in the industry,3,9−13 enabling the reuse of large quantities of water, minimizing the expenses of wastewater disposal, and it has also been used by the authors for the treatment of olive mill waste waters with significant results.14,15 Lau et al.11 in their review paper present a large number of papers referring to the successful use of nanofiltration membranes in the textile industry, where they Received: Revised: Accepted: Published: 15456
August 4, 2012 November 4, 2012 November 8, 2012 November 8, 2012 dx.doi.org/10.1021/ie302086j | Ind. Eng. Chem. Res. 2012, 51, 15456−15462
Industrial & Engineering Chemistry Research
Article
CAS 30551−89−4, supplied by Polysciences, Inc.; poly(diallyldimethylammonium chloride) (PDADMAC) average Mw
