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1、Available at journal homepage: of Kraft pulp ECF bleaching effluents by catalytic hydrotreatmentL. Calvo?, M.A. Gilarranz, J.A. Casas, A.F. Mohedano, J.J. Rodr guezSeccio n de Ingenier a Qu mica, Facultad de Ciencias, Universidad Auto noma de Madrid, Cantoblanco, 28049 Madrid, Spaina r t i c l e i
2、n f oArticle history:Received 24 July 2006Received in revised form13 November 2006Accepted 13 November 2006Keywords:Bleaching effluentsHydrotreatmentPd/AC catalystsEcotoxicityAOXa b s t r a c tTwo different effluents from the D1and E1stages of the ECF bleaching of Eucalyptus globuluskraft pulp were
3、treated by catalytic hydrogenation in a trickle bed reactor using commercialand homemade Pd/AC catalysts. The reactor was fed with the bleaching effluent and aH2/N2gas stream. The variables studied were space-time (1.45gcatmin/mL), gas to liquidflow ratio (2861000vol.), gas feed concentration (H2:N2
4、, 1:11:7.3vol.), temperature(251001C) and pressure (111bar). Hydrotreatment performance was evaluated in termsof ecotoxicity, adsorbable organic halogen (AOX), chemical oxygen demand (COD),biological oxygen demand (BOD5) and colour removal. In all the runs, the ecotoxicity ofthe effluents decreased
5、as a result of the treatment, achieving reductions that ranged from70% to 98%. Simultaneously to the reduction of toxicity, the hydrotreatment led to adecrease of the colour of the effluents, being the decrease significantly higher in the case ofE1effluent. The AOX content was reduced by 85% and 23%
6、 for E1and D1effluents,respectively. In the case of D1effl uent the removal of ecotoxicity was significantly higherthan that of AOX, which indicates that much of the toxicity of the effluent must beassociated to non-chlorinated organics. In spite of the important reduction of ecotoxicity,the biodegr
7、adability of the effluents only increased slightly. The homemade catalysts,prepared from activated carbons with a high external or non-microporous surface area andmesopore volume and a convenient surface chemistry showed a higher efficiency than thecommercial one.fax: +34914973516.E-mail address: lu
8、isa.calvouam.es (L. Calvo).WAT E R R E S E A R C H41 (2007) 915 923smallnichemarketaround5%ofthe worldbleached chemicalpulpproduction,beingmainlysoldand usedinGermany(Pryke,2003).Ontheopposite,ECF bleaching has become the world standard for chemical pulp bleaching accounting for more than 75% of all
9、 chemi- cally produced pulp and has displaced gradually chlorine bleaching. This trend is expected to continue at least at medium term. The D0E1D1E2D2sequence can be considered as representa- tive of conventional ECF bleaching (Pinto et al., 2005), where D stands for chlorine dioxide oxidation stage
10、 at acidic condi- tions and E for an alkaline extraction with aqueous sodium hydroxide. Chlorine dioxide causes lignin cleavage and the oxidation of lignin fragments giving rise to hydrophilic carboxylic groups. These combined actions increase the overallsolubility oflignin(Sjo stro m,1993).Duringth
11、e reaction between chlorine dioxide and lignin some chlorine is formed, which is responsible for part of the bleaching and much of the generation of chlorinated organics. As a common practise the E2effluent is reused in the E1stage and the D2effluentissenttotheD1stage. Themajority ofthe chlorinated
12、organics formed are thus contained in theeffluent from the E1and D1stages. As a result, these effluents have strong colour and chemical oxygen demand (COD) (Ali andSreekrishnan,2001),likewisetheycontain variable amounts of chlorinated organics (Torrades et al., 2003).The ECF bleaching effluents are
13、considered less environ-mentally friendly than the TCF effluents since they contain chlorinated organics, although it has been shown that there are no important differences of toxicity between them, being the natural constituents of wood probably responsible for some of the toxicity of these bleachi
14、ngeffluents(Vertaetal.,1996).Toassessthehazardsassociated to ECF bleaching effluents it must also be taken into account that chlorinated organics are acute or even chronic toxins and that they can induce genetic defects and cancer in exposed organisms (Ali and Sreekrishnan, 2001). Chlorinatedorganic
15、salsoshowaninhibitoryeffectto microbes in conventional biological treatments (Vidal et al., 1997), which in addition to the low biodegradability of ligninfragments leads to a low efficiency of conventional biological processes (Xie et al., 2005; Ali and Sreekrishnan, 2001; Peralta- Zamora et al., 20
16、04). Thus, in biological systems the typicalremoval efficiencies of COD and adsorbable organic halogens (AOX) show values of 3570% and 2555%, respectively (Tezel et al., 2001). Due to the limitations of biological treatments, a variety of physicalandchemicalprocesseshavebeenproposed forthetreatmentofbleachingeffluents,includingcoagulation, precipitation, ultrafiltration, reverse osmosis, ion exchange, freezing, e
