Kraft Mill Effluent Research Articles

Secondary and tertiary stress responses to BKME exposure in the St. Maurice River fish populations

In the St-Maurice River, Canada, white suckers (Catostomus commersoni) collected at two stationslocated downstream of a bleached kraft mill effluent(BKME) outfall exhibited increased muscle lipidconcentrations relative to upstream reference fish.White suckers collected in a physicochemicallycomparable but uncontaminated river, also demonstratedan increasing trend of lipid accumulation withdistance downstream. The similar general trends inboth rivers may result from a river continuum in whichincreasing loads of nutrients with distance downstreamincrease the energy available to fish.

The Occurrence and Bioavailability of Retene and Resin Acids in Sediments of a Lake Receiving BKME (Bleached Kraft Mill Effluent)

Retene (7-isopropyl-1-methylphenantrene) is an alkyl substituted PAH derived primarily from bacterial aromatization of abietic type resin acids. Retene has been shown to induce cytochrome P450 1A in rainbow trout whereas e.g. dehydroabietic acid does not induce it. We analysed resin acids and retene in sediments from seven sites receiving pulp and paper mill effluents from 4 mills, and from two reference sites. All mills have employed treatment of waste waters by activated sludge. The highest concentration of retene measured in sediment was 1600 μg/g d.w. (11 700 μg/g organic carbon, OC) while the highest concentration of resin acids was 1500 μg/g d.w. (9 300 μg/g OC). Downstream from the point (12 km) of bleached kraft mill effluent discharge, the concentration of retene at the depth of 5-10 cm in sediment was still 16 μg/g d.w. (650 μg/g OC) and the concentration of resin acids 139 μg/g d.w. (1700 μg/g OC). Background concentration for retene on the upstream reference site was below 0.1 μg/g d.w and for resin acids below 70 μg/g d.w. Substantial concentrations of retene (54 μg/g d.w.) and resin acids (1470 μg/g d.w.) were also detected in sedimenting particles collected at the sediment sampling sites. When the concentrations and sedimentation rates before and after the installation of activated sludge systems were compared, the effect of improved waste water treatment on total amount of sedimenting resin acids and retene (μg/m2/day) is clear. To assess the bioavailability of retene we analysed its concentration in the bile of feral fish caught 1-2 km downstream of pulp and paper mill. Data on roach shows that retene in sediments can be bioavailable to fish feeding on benthic food chain.

Quantitation of the Population Size and Metabolic Activity of a Resin Acid Degrading Bacterium in Activated Sludge Using Slot-Blot Hybridization to Measure the rRNA:rDNA Ratio.

The 16S rRNA:rDNA ratio is a useful parameter for measuring metabolic activity of a selected member of a complex microbial community, as in pulp effluent activated sludge systems. The RNA:DNA ratio of Sphingomonas sp. DhA-33, previously isolated from a sequencing batch reactor treating pulp mill effluent, is positively correlated with its growth rate (µ) under steady-state conditions. DhA-33 was grown in a chemostat with growth rates ranging from 0.04 to 0.15 cell divisions per hour. DhA-33 was also able to degrade dehydroabietic acid in bleached kraft mill effluent (BKME) plus mineral medium in batch culture. Slot-blot hybridization with radioactively labeled species-specific oligonucleotide probes for 16S rRNA and 16S rDNA was used to measure rRNA, rDNA, and the RNA:DNA ratio of this strain when in a mixed sludge community. An increase in DhA-33 rDNA indicated growth of DhA-33 within the community. The RNA:DNA ratio of DhA-33 increased sharply during exponential growth and declined as cells entered stationary phase. The RNA:DNA ratio decreased earlier and faster in DhA- 33/sludge co-cultures than in DhA-33 pure cultures, presumably due to an earlier depletion of nutrients. The species-specific quantification of the RNA:DNA ratio makes it possible to estimate the metabolic activity of selected members of a microbial community in situ.

Isolation and characterization of thermophilic bacteria capable of degrading dehydroabietic acid.

Using a semi-continuous enrichment method, we isolated two thermophilic bacterial strains, which could completely degrade abietane resin acids, including dehydroabietic acid (DhA). Strain DhA-73, isolated from a laboratory-scale bioreactor treating bleached kraft mill effluent at 55 degrees C, grew on DhA as sole carbon source; while DhA-71, isolated from municipal compost, required dilute tryptic soy broth for growth on DhA. DhA-71 grew on DhA from 30 degrees C to 60 degrees C with maximum growth at 50 degrees C; while, DhA-73 grew on DhA from 37 degrees C to 60 degrees C with maximum growth at 55 degrees C. At 55 degrees C, the doubling times for DhA-71 and DhA-73 were 3.3 and 3.7 h, respectively. DhA-71 and DhA-73 had growth yields of 0.26 and 0.19 g of protein per g of DhA, respectively. During growth on DhA, both strains converted DhA to CO2, biomass, and dissolved organic carbon. Analyses of the 16S-rDNA sequences of these two strains suggest that they belong to two new genera in the Rubrivivax subgroup of the beta subclass of the Proteobacteria. Strains DhA-71 and DhA-73 are the first two bacteria isolated and characterized that are capable of biodegradation of resin acids at high temperatures. This study provided direct evidence for biodegradation of resin acids and feasibility for biotreatment of pulp mill effluent at elevated temperatures.

Altered Challenge Response in Whitefish Subchronically Exposed in Areas Polluted by Bleached Kraft Mill Effluents

Exposure to impaired water quality, as in bleached kraft mill effluents (BKMEs), has recently been demonstrated to impair the ability of fish to elicit an acute stress response. Acute stress caused by catching is, in most field studies, an unavoidable incident that may markedly affect physiological functions. Consistently, dissimilar stress responses to catching procedures in exposed and reference animals may lead to altered results. In this study, juvenile whitefish (Coregonus levaretus) were caged for 30 days in two reference areas and three areas affected by different BKMEs, and the immediate effects of low-level handling on physiological functions in four periods within an hour of the start of the disturbance were clarified. Both primary and secondary stress responses were evident and consistent in fish caged in the two reference areas. Instead, despite the strong cortisol response in fish caged in polluted areas, the secondary stress response was weak or altered with respect to all other measured parameters excluding blood glucose in two of the three polluted areas. Thus, exposed fish may, when compared with reference fish, give different results depending on the exact period from the onset of the catching disturbance to sampling, and therefore, the results may be masked or totally inverted. Because the impacts of acute stress on physiological parameters are immediate and, in exposed areas after low-level handling, dissimilar in nature, this study points to the necessity for time-dependent standardization in field studies whenever sampling is delayed.

The occurrence and bioavailability of retene and resin acids in sediments of a lake receiving BKME (bleached kraft mill effluent)

Retene (7-isopropyl-1-methylphenantrene) is an alkyl substituted PAH derived primarily from bacterial aromatization of abietic type resin acids. Retene has been shown to induce cytochrome P450 1A in rainbow trout whereas e.g. dehydroabietic acid does not induce it. We analysed resin acids and retene in sediments from seven sites receiving pulp and paper mill effluents from 4 mills, and from two reference sites. All mills have employed treatment of waste waters by activated sludge. The highest concentration of retene measured in sediment was 1600 μg/g d.w. (11 700 μg/g organic carbon, OC) while the highest concentration of resin acids was 1500 μg/g d.w. (9 300 μg/g OC). Downstream from the point (12 km) of bleached kraft mill effluent discharge, the concentration of retene at the depth of 5-10 cm in sediment was still 16 μg/g d.w. (650 μg/g OC) and the concentration of resin acids 139 μg/g d.w. (1700 μg/g OC). Background concentration for retene on the upstream reference site was below 0.1 μg/g d.w and for resin acids below 70 μg/g d.w. Substantial concentrations of retene (54 μg/g d.w.) and resin acids (1470 μg/g d.w.) were also detected in sedimenting particles collected at the sediment sampling sites. When the concentrations and sedimentation rates before and after the installation of activated sludge systems were compared, the effect of improved waste water treatment on total amount of sedimenting resin acids and retene (μg/m 2 /day) is clear. To assess the bioavailability of retene we analysed its concentration in the bile of feral fish caught 1-2 km downstream of pulp and paper mill. Data on roach shows that retene in sediments can be bioavailable to fish feeding on benthic food chain.

Adsorption of phenolic compounds and color from bleached Kraft mill effluent using allophanic compounds

Synthetic and natural allophanic compounds were used to evaluate the phenolic compounds and color removal capacity from a biological treated softwood bleached Kraft mill effluent. Kinetics studies and solid/solution relationship using synthetic allophanic compounds were studied and compared with powder activated carbon adsorption. On the other hand, the pH effect (4 to 9) on allophanic compounds adsorption was studied. The adsorption capacity of three allophanic soil profiles (10–20, 20–40 and 40–60 cm) activated by washing the soil with H 2SO 4, 0.1 M, and by calcination at 550°C was also evaluated. Kinetics studies showed that the adsorption half-time was 2 min in both activated carbon and synthetic allophanic compounds and more than 90 and 70% removal occurred in the first 5 min, respectively. The adsorption of color and phenolic compounds increased with decreasing solid/solution ratio in both activated carbon and synthetic allophanic compounds. pH plays an important role in adsorption phenomena. Phenolic compounds and color removal increased with the decreasing of suspension-effluent pH, obtaining the optimum at pH 5.0 with 87 and 96% removal, respectively. Phenolic compounds and color removal were near 90 and 75% when 20–40 cm acidified and calcinated soil profile was used, respectively. The organic matter content in the 10–20 cm soil profile and the low content of the fine colloidal fraction in the 40–60 cm profile reduced the removal capacity of the allophanic soil.

Factors Affecting Oxygen Transfer in Lab-Scale Activated Sludge Reactors Treating Bleached Kraft Mill Effluent

Abstract In aerobic biological wastewater treatment processes, oxygen must be transferred from the gas phase to the liquid phase to support oxidation of dissolved organics and endogenous metabolism by the bacteria. Power required to supply this oxygen in suspended growth systems can represent a significant fraction of the operating costs of such processes. In this study, the interfacial mass transfer coefficient KLa for water was found to be reduced by up to 28% (average 13%) by the addition of antifoaming agent. KLa values were reduced by up to 43% (average 26%) by the dissolved organics in primary treated bleached kraft mill effluent. There was no significant difference between the KLa for water and biologically treated bleached kraft mill effluent.

Using microbial fatty acids to quantify, characterize and compare biofilm and suspended microbial populations in wastewater treatment systems

Spectra of microbial fatty acid methyl esters were used to assess the influence of pH on the biofilm and suspended biomass populations within bench scale moving bed bioreactors treating bleached kraft mill effluent. The fatty acid spectral data were reduced by logcontrast canonical component analysis. The first canonical component differentiated biofilm from suspended populations and the second two appeared to indicate an influence of pH on microbial ecology. Thus, the biofilm and suspended microbial communities were distinct, as were the populations acclimated at pH 6 and pH 8. Experimental data for total organic carbon removal suggested that the more recalcitrant fraction of the influent was consumed by the slower growing, high SRT biofilm fraction of the biomass. Since the biofilm ecology was sensitive to pH within typical pH operating limits of full-scale systems, tighter pH control might improve treatment reliability in the event of process transients.

Molecular analysis of bacterial isolates and total community DNA from kraft pulp mill effluent treatment systems

Chloroaliphatics are major components of bleached kraft mill effluents. Gene probes and oligonucleotide primers were developed to monitor kraft pulp mill effluent treatment systems for the presence of key genes (dehalogenases) responsible for the dehalogenation of chloroaliphatic organics. The primers were used for polymerase chain reaction (PCR) analysis of genomic DNA extracted from dehalogenating bacterial isolates and from total community DNA extracted from water and sediments of mill effluent treatment system. PCR amplification with oligonucleotide primers designed from dhlB, encoding the haloacid dehalogenase from Xanthobacter autotrophicus, revealed the presence of dehalogenase genes in both aerated lagoons and stabilization basins. Similarly, positive results were obtained with mmoX primers designed from the soluble methane monooxygenase gene of Methylococcus capsulatus Bath. The haloacetate dehalogenase encoding gene (dehH2) from Moraxella sp. was typically not detected in mill effluent treatment systems unless the biomass was selectively enriched. DNA sequence analysis of several PCR fragaments revealed significant similarity to known dehalogenase amd methane monooxygenase genes. The results indicated a broad distribution of known dehalogenation genes and bacteria with chloroorganic-degrading potential in the mill effluent treatment systems.

Does annual variation in growth and sexual maturation of white sucker (Catostomus commersoni) confound comparisons between pulp mill contaminated and reference rivers?

A previous study on the effect of pulp and paper effluents on white sucker (Catostomus commersoni), conducted in 1991 and 1992, in both effluent-exposed and reference rivers showed that fish grew faster at downstream sites than at upstream sites. However, in contrast with fish from a reference river, fish exposed to effluent showed no decrease in age or size at first maturity or increase in gonad size or fecundity in response to greater growth. The objective of the present study, conducted in 1993, was to test if differences in measures of growth and sexual maturation between fish populations in exposed and reference rivers would vary from year to year and whether such variation would affect conclusions concerning the effects of pulp mill effluents. Although size at age, fecundity, and age at first maturity varied between the two studies, patterns of demographic responses to pulp mill effluents, relative to reference populations, remained the same, i.e., conclusions about effects of pulp mill effluents did not change despite variation in demographic variables between years and sites. This study reaffirmed the view that only by including the fish populations in a reference river could effects due to bleached kraft mill effluent be separated from effects due to nutrient gradients.

Environmental Assessment of Benthic Impacts Associated with Pulp Mill Discharges. II. Distribution of Sediment EOX in Relation to Environmental Factors

Between 1991 and 1992, comprehensive toxicological, chemical, and benthic community structure surveys were conducted at Jackfish Bay, Lake Superior, Ontario, to assess sediment quality below a bleached kraft mill effluent (BKME) outfall. In this report, we describe the spatial distribution and concentration of extractable organic chlorines (EOX) in sediments below the outfall in relation to effluent discharge patterns, sediment deposition, and bioaccumulation potential. Triplicate sediment samples were collected by Ekman grab from 29 and 44 stations in 1991 and 1992, respectively, and from 15 stations in three reference areas not exposed to the effluent. For each sample, organic carbon content, dry weight, and sediment-associated EOX were determined. In addition, sediment traps were used to determine sediment deposition along two tangents transecting the effluent plume and at a reference station located approximately 4,200 m from the outfall. The spatial distribution of sediment EOX consisted of two distinct concentration gradients, each linked to effluent discharge patterns from Blackbird Creek and dominant circulatory patterns in Jackfish Bay: a north-south gradient, extending along the west shore of Jackfish Bay, and a east-west gradient. Sediment EOX ranged from 7,000 mg/kg organic carbon (oc) (2,050 mg/kg dry solids (ds)) in depositional sediments of Moberley Bay to nondetectable at some stations in eastern and outer Jackfish Bay. Reference (background) concentrations ranged from nondetectable to 3,000 mg/kg oc (1-15 mg/kg ds). The attenuation of EOX was significantly correlated with the rate of sediment deposition (r2 = 0.57; p </= 0.001). Although the concentration of sediment EOX was strongly correlated with toxicity to some invertebrates (Sibley et al. [1997] Arch Environ Contam Toxicol 32:274-284), bioaccumulation factors were typically <2 based on analysis of oligochaete tissues. The results of this study demonstrate that the spatial distribution of sediment-associated contaminants adjacent to pulp mill effluent outfalls are determined primarily by hydrodynamic and depositional characteristics of the receiving waters and that EOX can be used to accurately delineate areas of contamination.

Effects of ECF-Bleached Kraft Mill Effluent on Reproductive Steroids and Liver MFO Activity in Populations of Perch and Roach

Samples of perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) populations were collected in Lake Saimaa in September-October, after the onset of vitellogenesis and deposition of yolk in the eggs. The study area received elemental chlorine-free (ECF)-bleached kraft mill effluent (BKME). The pulp and paper mill studied used chlorine dioxide for bleaching and its effluents were treated in a modern activated sludge plant. The amounts of chlorophenolics in the bile of perch and roach at the mill site, 1 km from the discharge point, were two to four times higher than in fish from the upstream reference site. In the roach population near the mill liver the 7-ethoxyresorufin 0-deethylase (EROD) activity was four times that measured in the reference areas. However, the EROD activity in the perch remained unchanged. The liver 7-pentoxyresorufin 0-dealkylase (PROD) activity was induced to twice the amount only in male roach near the mill, whereas the relative liver size (LSI) was increased in female and male roach and female perch. The plasma concentrations of oestradiol-17β were decreased in female perch and female roach, but increased in male roach at the mill site. Near the mill, vitellogenin gene expression was also reduced in female perch. In addition, the plasma testosterone concentrations were reduced in female and male perch near the mill. No differences were noted in the plasma immunoglobulin concentrations in roach and in the relative gonad size (GSI) in the perch and roach populations. The condition factor was significantly lower only in female roach near the mill.

Interrenal dysfunction in fish from contaminated sites: In vivo and in vitro assessment

AbstractCortisol, synthesized in the interrenal cells of teleost head kidney, has a major role in the physiologic response to physical and chemical stressors. Plasma levels of cortisol increase in physiologically competent fish acutely exposed to stressors such as cadmium or mercury. The effects of chronic low level exposures are less well understood. We have diagnosed an endocrine impairment characterized by a reduced capacity to elevate plasma cortisol levels in response to an acute standardized capture stress in yellow perch (Perca flavescens) and in northern pike (Esox lucius) sampled at sites contaminated by mixtures of pollutants (heavy metals, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls), by heavy metals, or by bleached kraft mill effluent. Our studies with fish, as well as with amphibians at contaminated sites, demonstrated that low level chronic exposures impair secretion of corticosteroids. We have developed new tests for assessment of the functional integrity of teleost and amphibian interrenal tissue by using an adrenocorticotropic hormone (ACTH) challenge, in vivo and in vitro. The reduced ability to respond to ACTH indicates that the normal neuroendocrine response to stressors may be disrupted and that the ability to cope with biotic and abiotic stressors in the environment may be significantly reduced in the impaired animals.

Using microbial fatty acids to quantify, characterize and compare biofilm and suspended microbial populations in wastewater treatment systems

Spectra of microbial fatty acid methyl esters were used to assess the influence of pH on the biofilm and suspended biomass populations within bench scale moving bed bioreactors treating bleached kraft mill effluent. The fatty acid spectral data were reduced by logcontrast canonical component analysis. The first canonical component differentiated biofilm from suspended populations and the second two appeared to indicate an influence of pH on microbial ecology. Thus, the biofilm and suspended microbial communities were distinct, as were the populations acclimated at pH 6 and pH 8. Experimental data for total organic carbon removal suggested that the more recalcitrant fraction of the influent was consumed by the slower growing, high SRT biofilm fraction of the biomass. Since the biofilm ecology was sensitive to pH within typical pH operating limits of full-scale systems, tighter pH control might improve treatment reliability in the event of process transients.

Immunoreactivity of Roach,Rutilus rutilus,Following Laboratory Exposure to Bleached Pulp and Paper Mill Effluents

In order to study immunomodulation, controlled laboratory experiments were carried out with roach (Rutilus rutilus) exposed to bleached kraft mill effluent (BKME) or spent bleach liquor (SBL) from two pulp and paper mills using elementary chlorine and chlorine dioxide for bleaching. The total number of immunoglobulin-secreting cells (ISC) and the number of specific antibody-secreting cells (ASC) were determined by ELISPOT assay. Exposure to BKME resulted in decreased numbers of ISC in the spleen. To study the capability of response against foreign antigens the fish were immunized with bovine γ-globulin. Exposure to BKME or SBL reduced antigen-specific ASC response in fish. Moreover, the suppression of ASC response did not require exposure prior to immunization. Depuration of fish in clean water reveals that the immunosuppression caused by BKME is reversible. The ASC response in the BKME-pretreated fish returned to the same or even a higher level compared to untreated immunized fish and, in addition, the number of ISC increased greatly. The results of this study verify an earlier finding on poor antibody response due to exposure in a lake contaminated with BKME. Exposure to SBL alone suppresses antibody-mediated immunity, suggesting that compounds formed in bleaching are at least partly responsible for immunotoxic effects.

The effects of tetrachloroguaiacol on the growth, survival, and development of the fathead minnow, Pimephales promelas.

Fathead minnow (Pimephales promelas) larvae were exposed for 7 days to tetrachloroguaiacol (TeCG), within 24 h of hatching, at concentrations of 0, 25, 50, 100, 200, 400 microg/L. No significant difference in growth or larval survival was found among treatments. Embryos, within 24 h of fertilization, were also exposed to TeCG at concentrations of 0 and 100 microg/L for 10 days. No significant difference was found between the control and treatment groups for larval survival, body length, body width, or for yolk size of the eleutheroembryos. However, a significant difference was found in the hatching success of the eggs (p = 0.05). Since fathead minnows have been known to spawn in areas close to sites that discharge bleached kraft mill effluent (BKME) which contains TeCG, into receiving waters, naturally occurring populations will likely be affected by the toxicant.

The fate of resin acids-2. The fate of resin acids and resin acid derived neutral compounds in anaerobic sediments

A sediment, sampled from a hydroelectric lake receiving a bleached kraft mill effluent discharge, was incubated anaerobically for 264 days. Both recipient and sterilised control sediments were periodically sampled and analysed to monitor the changes in resin acid composition with time. Over 264 days of incubation, the concentration of total resin derived compounds decreased by 50%. The total resin acid concentration was reduced by 50% whereas the concentration of resin derived neutrals decreased by 54%. Relative to an incubated sterile control sediment, the pimaranic acid concentration remained constant, 8-pimarenic and 8-isopimarenic acid concentrations slightly increased and pimaric, isopimaric, abietanic and secodehydroabietic acid concentrations decreased. Dehydroabietic acid was transformed to tetrahydroretene simultaneously with the transformation of labelled dehydroabietic acid to a variety of labelled products. Throughout the incubation period, the concentration of fichtelite remained constant. The concentration of retene slightly increased until the final 50 days of incubation, during which time dehydroabietin and tetrahydroretene concentrations decreased. This is the first study reporting the degradation of a variety of resin acids and derived neutrals in an anaerobic sediment.

Effect of H 2O 2 on characteristics and biological treatment of TCF bleached pulp mill effluent

Totally chlorine-free (TCF) bleaching technologies can result in high concentrations of residual hydrogen peroxide in combined mill effluent. This study was undertaken to determine the effect of hydrogen peroxide on effluent characteristics (biochemical oxygen demand (BOD), toxicity), biological sludge characteristics (oxygen uptake rate (OUR), catalase activity) and the efficiency with which laboratory-scale activated sludge reactors treat TCF bleached kraft mill (BKM) effluents. The presence of over 20 mg/L hydrogen peroxide in TCF-BKM effluent was found to decrease the BOD by up to 25%. The complete decomposition of hydrogen peroxide concentrations of up to 1000 mg/L was not found to have an effect upon the effluent toxicity, as measured by Microtox R. Increasing concentrations (5–1000 mg/L influent) of peroxide were continually added to a reactor treating combined TCF-bleached kraft mill effluent. Treatment efficiency, as measured by removal of BOD, chemical oxygen demand (COD) and toxicity, was found to be unaffected by hydrogen peroxide concentrations of up to 1000 mg/L influent. Several methods of gauging reactor acclimatization to hydrogen peroxide were performed throughout the study. Activated sludge mixed liquor samples from the continuous reactor were shocked with varying concentrations of hydrogen peroxide. Oxygen uptake rate of activated sludge samples, especially when unacclimated, was found to decrease dramatically when subjected to shock loads of increasing concentrations of peroxide. Activated sludge which had been acclimated to hydrogen peroxide in the reactor feed was more resistant to H 2O 2 shock loading. Catalase-equivalent induction in activated sludge was also monitored as a means of gauging reactor acclimatization to the presence of hydrogen peroxide. Catalase-equivalent activity was found to increase with increasing H 2O 2 feed concentration, and appeared to reach a maximum level of 1.3–1.5 (min g biomass) −1. It was concluded that activated sludge is able to treat TCF bleached kraft mill effluent which contained H 2O 2, and that the microorganisms present in the sludge were able to adapt to receiving such an effluent.

The effect of pre-hydrolysis of D-stage filtrate on the biotreatability of chlorinated organic compounds in bleached kraft mill effluents

The influence of pre-hydrolysis of D-stage filtrate on the biotreatability of bleached kraft mill effluent was investigated at the bench scale using four continuous aerated “lagoons” operated in parallel. In comparison to non-hydrolyzed effluent, pre-hydrolysis of D-stage filtrate at pH 11 and 60°C for an hour reduced the AOX inlet to the treatment system by 40% and the outlet AOX discharge after biological treatment by 13%. Overall, pre-hydrolysis followed by biological treatment resulted in a 63% AOX removal, which was significantly higher, at the 95% confidence level, than the 58% removal achieved by biological treatment alone. COD and BOD 5 removals for both feeds were 45 and 99%, respectively, and were not significantly affected by the pretreatment. Studies on the pre-hydrolysis effect on known non-biodegradable organochlorine model compounds showed that pre-hydrolysis was effective in improving the biodegradability of a monomeric model, but not the dimeric model compound.