Environ. Sci. Technol. 1003, 27, 547-557
(37) Dodd, J. A.; Ondov, J. M.; Tuncel, G.; Dzubay, T. G.; Stevens, R. K. Environ. Sei. Technol. 1991,25, 890-903. (38) Evans, M.; Vithanaduage, I.; Williams, A. J . Inst. Energy 1981, 179-186. (39) Lahaye, J. Carbon 1992,30,309-314. (40) Ogren, J. A.; Charlson, R. S. Tellus 1984, 36B, 262-271. (41) Smith, D. M.; Akhter, M. S.; Jassim, J. A.; Sergides, C. A.; Welch, W. F.; Chughtai, A. R. Aerosol Sci. Technol. 1989, 10, 311-325.
Received for review June 29,1992. Revised manuscript received
November 5,1992. Accepted November 10,1992, This work was supported in part by NSF Grant ATM-9007796, and also by Grant CIR-D519 from Arizona State University. Microscopy was done at the Facility for High-Resolution Electron Microscopy in the Center for Solid State Science and in the Materials Science Electron Microscope Laboratory, both at ASU. The Facility for High-Resolution Microscopy was established with support from the National Science Foundation (Grant DMR-86-11609) and also ASU. The Materials Science Electron Microscopy Laboratory was established with aid from a grant from the United States Department of Education.
Effect of Biological Treatment on Halogenated Organics in Bleached Kraft Pulp Mill Effluents Studied by Molecular Weight Distribution Analysis Jounl K. Jokela,
st
Mlnna Lahe,$ Mats Ek,s and Mirja Salklnoja-Salonent
Department of Applied Chemistry and Microbiology, University of Helsinki, Viikki, SF-007 10 Helsinki, Finland, Department of Biochemistry, University of Turku, SF-20500 Turku, Finland, and IVL, Swedish Environmental Research Institute, Box 21060, S-10031 Stockholm, Sweden
The removal potential of different biological treatments of organohalogen compounds in kraft pulping and bleaching effluents was studied by nonaqueous size-exclusion chromatography and grouping the compounds by solubility and adsorption characteristics. Organohalogen compounds of waste waters from five pulp mills with different processes exhibited similar molecular weight distributions, ranging from 100 to 4000. The anaerobic/ aerobic lagoon system removed 58-6690 of the organochlorine compounds from the water phase and the fullscale activated sludge plants removed 19-55%. Both biotreatments removed all size classes of organochlorine molecules and slightly changed the relative size distribution of the compounds remaining in the water phase toward the larger molecular weights. The organic chlorine compounds were divided into three categories on the basis of extractability to organic solvent and adsorption to activated carbon, one of the categories being recalcitrant to the biotreatments studied.
Introduction The wood pulping and bleaching industry discharges large quantities of mainly lignin-related chlorinated compounds to the receiving waters. These effluents have a negative impact on plant and animal communities in receiving areas (1). Two different possibilities to handle this problem are to make internal changes to the pulping and bleaching processes to lower the level of the discharged compounds or to improve the waste water treatment technologies. The adsorbable organic halogen (AOX) discharge from pulp mills in Finland decreased from 2.7 kg of AOX/ ton of pulp in 1989 to 1.7 kg/ton in 1991 (average of soft- and hardwoods) (2). This favorable development is to an important part based on the operation of biological treatment plants that are now operative at 13 of the 15 mills (3). Also, process changes have already resulted in substantially
* Correspondence: Department of Applied Chemistry and Microbiology, University of Helsinki, Faculty of Agriculture and Forestry, Viikki, SF-00710 Helsinki, Finland. University of Helsinki. *University of Turku. Swedish Environmental Research Institute. 0013-936X193/0927-0547$04.00/0
decreased formation of chlorinated organic compounds (4). The biological treatment methods for industrial waste waters most widely used are activated sludge and aerated lagoon processes. These methods effectively remove oxygen-consuming substances and suspended solids. An important group of compounds in pulping and bleaching waste waters are the chlorinated compounds, some of which are known to be toxic, mutagenic, and even carcinogenic (5,6). However, the concentrations of these compounds in bleached kraft pulp mill effluent (BKME) are so low that the waste waters are not acutely toxic. The removal of several individual organochlorine compounds during biological waste water treatment has been described (7-13),but understanding of the removal process is poor. The results reported for bioremoval of organic halogen compounds, measured as AOX, during waste water treatment in the wood pulping industry varied between 25 and 65% (14,15), indicating that these compounds are relatively resistant to biological treatment. Also, the fact that AOX has accumulated downstream of pulp mills (16) indicates incomplete degradation of organochlorine compounds under environmental conditions. It is commonly thought that the major reason for the recalcitrance is the large molecular size of the organic halogen compounds, termed chlorolignins, said to account for up to 80% of the AOX (15,17).It is also thought that chlorinated organic matter is more recalcitrant to biodegradation than are nonchlorinated compounds. We recently showed that the apparent large size of chlorolignin is more related to the tendency to form intermolecular associationsthan actual covalent bonds (18). When diluted to concentrations that are likely to occur in recipient water, 65% of the AOX behaved as molecules of' sizes ranging from MW 100 to 1000 (18). It is therefore important to evaluate the effects of treatment systems on this molecular size range with particular emphasis on the aquatic phase which is discharged into the environment. The biodegradability and uptake of xenobiotic compounds by microbial biomass very likely depend on their absorption and solubility properties. The least polar compounds will migrate from the water phase into sludge, also independent of active uptake by biomass. Therefore study of the adsorption and solvent solubility properties of waste water organochlorines may give important clues
0 1993 Amerlcan Chemical Society
Environ. Sci. Technol., Vol. 27, No. 3, 1993 547
to understanding biodegradability. In this study we measured the changes of molecular weight distribution (MWD), solubility, and adsorptivity of the organochlorine compounds found in the aqueous phase of the BKME during the course of biotreatment. Our report shows that the recalcitrant organochlorine compounds do not represent any specific size class, that no enrichment of highly chlorinated matter to the water phase occurred as a result of biotreatment, and that organic chlorine compounds could be separated into categories having different recalcitrance toward biotreatment by a simple extraction protocol. Experimental Methods Sampling. Waste waters from mills A, C, and D were sampled during 1991 and bleaching effluents from mill E during 1990. Waste water from mill A was sampled before and after the equalization basin (25000 m3) and also after activated sludge treatment, before discharge into the receiving basin (recipient). Volumes of the aeration and postclarification basins of the full-scale activated sludge plant were 25 000 m3 each. An aerobic/anaerobic pilot-scale treatment plant for bleached kraft pulp and paper mill effluents was run at mill B in 1988/1989. Samples were taken at this plant from the influent and the effluent during 1989. The hydraulic retention time was 2 d during the first sampling period (Pl) and 4 d during the second period (P2). The aeration basin (five compartments of 5 m3, total volume 25 m3) was divided into three sections aerated differently: full aeration (first section, 10 m3),anoxic (second section, 5 m3), full aeration during sampling period P1 and low aeration (0.5-0.8 mg of O,/L) during sampling period P2 (third section, 10 m3). During the second period, another aeration basin (25 m3) was connected in series after the first aeration basin and was used for postaeration and clarification. Mill C had anaerobic/aerobic lagoon treatment after clarification. Municipal waste water was also treated in this plant, joining the system after the first sampling point and accounting for 0.5% of the total BOD in the waste water. Waste water was sampled before and after the anaerobic lagoon used for equalization (150000 m3) and also after aerobic lagoon treatment (400000 m3)at the exit to the recipient. The total volume of the treatment basins of the full-scale activated sludge plant of mill D was 9OOOO m3and the flow 97 500 m3/d. Waste water was sampled after neutralizing and nitrogen addition stages and then after secondary clarification before discharge. Bleaching effluent streams from mill E were biotreated both in pilot and in laboratory reactors. The pilot reactors (Pl, 3.8 m3; P3,4.4 m3) were fed with ultrafilter permeate of the EOP stage spent liquor, mixed with spent liquors from the (D+C), D,, and Ez stages (E, alkali; 0, oxygen; P, peroxide; D, chlorine dioxide; C, chlorine). The laboratory reactors L1 and L2 were fed with spent EOP plus (D+C) stage liquors. Ultrafiltration was performed by a full-scale test plant consisting of four ultrafiltration modules having polyether sulfcne membranes with a nominal molecular weight cutoff of 25000 and a total membrane area of 50 m2. Flow schemes of the pilot reactors and ultrafiltration test plant and their modes of operation are described elsewhere (19). The pilot and laboratory reactors were sampled before and after anaerobic and aerobic treatment (Pl, L1) or aerobic treatment only (P3, L2). Samples were stored at +4 "C (short period) or frozen. 548
Environ. Sci. Technol., Vol. 27, No. 3, 1993
Fractionation of the Waste Water. A tetrahydrofuran (THF) extract was prepared by freeze-drying a BKME sample and then extracting the residue with THF as described earlier (18). BKME samples were not acidified prior to freeze-drying. The organic halogen compounds contained in the BKME were divided into the three following groups: carbon adsorbable organic halogen nonextractable into THF (AOX,,), carbon adsorbable organic halogen extractable into THF (AOX,), and carbon nonadsorbable organic halogen extractable into THF (NOX,). Equations 1-3 show that this grouping builds upon the measurements of the AOX of the BKME (AOXBKME), the AOX of the THF extract (AOXTHF), and the total halogen measurement from the THF extract (EXTHF; EX, extractable halogen), AOX,, = AOXBKME - AOXTHF
(1)
AOX, = AOXTHF
(2)
NOX, = EXTHF - AOXTHF
(3)
Analytical Procedures. Total organic carbon (TOC) was analyzed by the TOC-5000 total organic carbon analyzer (Shimadzu). Chemical oxygen demand (CODc,) was measured according to standard SFS-5504 (20),which is consistent with the corresponding Danish, Norwegian and Swedish standards. Halogen was measured by using the Euroglas halogen analyzer ECS 1000 (Euroglas BV, Delft, The Netherlands). Active carbon adsorbable organic halogen (AOX) was analyzed according to standard SCAN-W 9:89 (21). Solvent (THF) extractable halogen was quantitated after an aliquot of the extract was evaporated in a porcelain cup under a flow of Nz. The contents was then combusted in the oven (1000 "C) of the Euroglas equipment, and the hydrogen halide formed was microcoulometrically titrated according to the manufacturer's manual. To measure the AOX content of the THF extract, THF was evaporated in a flow of Nz, the residue was dissolved into water, and AOX was measured from this water solution. THF extracts were used for the analysis of MWDs by high-performance size-exclusion chromatography (HPSEC). Analysis of molecular weight distribution was performed as described earlier (18) using polystyrene standards of narrow MWD and three lignin model compounds for calibration. Statistical Analysis. A total of 34 MWDs of the chlorinated compounds of the waste waters were analyzed statistically by principal component analysis (PCA). For this purpose, original MWD data were transformed so that 143 uniformly distributed chlorine concentrations (mg/L) between 63 and 44000 could be used as variables. In order to compare the relative proportions of the chlorinated compounds of different chromatograms, each MWD was area-normalized. MWD data were centered before computing the PCA vectors. PCA was performed by data analysis software for MATLAB using a PC computer. More details of the software are reported elsewhere (22). Results Waste water and treatment plant operation of five bleached kraft pulp mills (designated as A-E) were studied. Table I summarizes the essential process features, characteristics of treatment facilities, and waste waters. Table I1 presents the data on the absolute and relative (%) reduction of organic carbon and adsorbable organic halogen, respectively, during the treatment of waste water. It shows
Q
i3
f
ss
R
2 08
R
B
08
4
R
a
E
"a
RE 2
0
Envlron. Scl. Technol., Vol. 27, No. 3, 1093 540
:k ,,,.. ,/ , ..... , ! ! ................-\:
3
0
10
100
1000 loo00 Molecular weight (g/ml)
h
r
@
1,w
2s
E
1,w
3
1 3
In
4 1,M 0,74
z 0
E"
654-
3-
p/
c'
,.i
2-
1 10
100
1000
10000
Molecular welght (g/mol)
:.,
- 0
~
10
100
1000
:#I-
10000
Molecular weight(g/ml)
------- after equalization basin prior to treatment 1I -
.................. After activated sludge, to the recipient
Fkure 1. Changes of molecular welsht dlstrlbutlons of UV-absorbing materlal (UV) and organic halogen compounds (GI) of BKME during full-scale activated sludge treatment on mills A and D: AS, activated sludge.
that full-scale biotreatment removed 50% of TOC and 53% of AOX on average. The removal of CODc, and AOX
from the water phase by the pilot-scale biotreatments averaged 56% and 5370, respectively. These results indicate that the removability of organic halogens (AOX) in BKME was at least as good as the overall removability of organic compounds (TOC, CODc,) in the five different treatment units. Aerobic treatment removed TOC more efficiently than sole anaerobic treatment, averaging 49% (mills A, D, and E) and 19% (mills C and E), respectively, but AOX removal was equal, 50% and 49%, respectively. Combined anaerobic/aerobic removals for TOC and AOX (mills C and E) averaged 52% and 6 1 % , respectively. Thus, combining anaerobic and aerobic treatments clearly improved total AOX removal. Since the biotreatment removed only approximately 50% of the AOX and TOC, we next investigated the question of whether the recalcitrant fraction differed from the removed fraction in molecular size. Molecular size 550
Envlron. Scl. Technol., Voi. 27, No. 3, 1993
distribution analysis of BKME was carried out by nonaqueous HPSEC. Results of MWDs measured as UV/ visible-absorbing (225-445 nm) and halogen-containing molecules are shown in Figures 1-3. The UV/visibleabsorbing and halogen-containingmaterial was in all cases located between 100 and 10000, irrespective of wood species, bleaching sequence, and waste water treatment protocols. Ninety percent (84-97 %) of the chlorinated compounds in untreated waste waters studied and 87% (77-97%) in biotreated waste waters were smaller than 1000. Significant removal of BKME components was observed in all size classes of molecules, from 100 to 3000. It is actually surprising that the MWDs of organic halogens of BKMEs having undergone different biotreatment were so similar. Removal of organic halogen compounds at different stages of the biotreatment, determined as MWDs of the tetrahydrofuran-soluble halogen (Figures 1-3), correlated by a factor of 0.88 (see Figure 4) with the overall
-
0
-.__ 10
1000
100
lo000
Molecular weloht lo/moll
I\
CI
Molecular weight (glmol)
-Prior to treatment
-.-.-.-. After equalization basin + anaerobic lagoon
Figurr 2. Changes of molecular weight dlstrlbutlons of UV-absorblng material (UV) and organlc halogen compounds (Ci) of BKME during full-scale anaeroblc aerobic lagoon treatment (mlll C) and plbt-scale aerobic/anaeroblc treatment (mill B): P, pllot scale, AL, anaerobic -I-aeroblc lagoon.
+
AOX removal efficienciespresented in Table 11. The level of removal was over 10% units higher when calculated from MWD results. Correlation between the removal of the UV/visible-absorbing compounds and that of the organic carbon compounds measured as TOC (Table 11) was less clearcut. The level of removal was over 10% units lower when calculated from UV/visible absorption results. This may indicate that biotreatment increased the light absorptivity of the organic compounds. This increment in the specific absorptivity may originate from the oxidation of the waste water compounds. Aerobic treatment of the mill E bleach plant effluent increased the absolute amount of organic halogen compounds having molecular weights over 500 (Figure 3). This was seen in the case of the pilot reactor (P3) and also in the case of the laboratory reactor (L2),thus independent of the ultrafiltration pretreatment of the bleaching liquor. This polymerization phenomenon was not seen in the waste waters of the other mills, where total mill effluent
was being treated. The photometric quantitation, though uncertain as pointed out above, also indicated polymerization of the bleach plant effluent at mill E. The data in this investigation are not enough to conclude whether the different waste waters caused polymerization in one case and not in the others. When replicate THF extracts were prepared from four sets of BKME samples from mill A (AS1-3) and mill C (AL2),the average coefficient of variation (CV) for chlorine content was
