Water Research 36 (2002) 2053–2061

Combined biological and ozone treatment of log yard run-off Michael G. Zenaitis, Harinder Sandhu, Sheldon J.B. Duff* UBC Pulp and Paper Centre and Department of Chemical and Biological Engineering, The University of British Columbia, 2216 Main Mall, Vancouver, BC, Canada V6T 1Z4 Received 1 January 2001; accepted 1 August 2001

Abstract Batch biological treatment of log yard run-off reduced biochemical oxygen demand (BOD), chemical oxygen demand (COD) and tannin and lignin (TL) concentration by 99%, 80%, and 90%, respectively. Acute (Microtox) toxicity was decreased over treatment, from an initial EC50 of 1.83% to a value of 50.4% after 48 h of treatment. Kinetics of biodegradation were determined using respirometry and fitted using the Monod and Tessier model. For the Monod model the maximum substrate uptake rate, and Ks values determined were 0.0038 mg BOD/mgVSS min, and 1.4 mg/L, respectively. The efficacy of ozone as a pre- and post- biological treatment stage was also assessed. During ozone pretreatment, TL concentration and acute toxicity were rapidly reduced by 70% and 71%, respectively. Pre-ozonation reduced BOD and COD concentration by o10%, however a larger fraction of residual COD was non biodegradable after ozonation. Biologically treated effluent was subjected to ozonation to determine whether further improvements in effluent quality could be achieved. A reduction in COD and TL concentration was observed during ozonation, however no further improvement in toxicity was observed. Ozonation increased BOD by 38%, due to conversion of COD to BOD. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Logyard run-off; BOD; COD; Toxicity; Biological treatment; Ozone

1. Introduction Log sort yards include those associated with sawmills and others such as dry land sorts (DLS). The primary function of these facilities is to receive cut logs, sort them by species, size and quality, and to facilitate transport of the logs to the appropriate processor. These facilities can range in size from less than a hectare to over 100 ha, and process wood volumes ranging from a few thousand cubic meters to well over a million cubic meters annually. Large quantities of woody debris, from 3% to 6% by volume of the processed wood, are generated at log sort yards [1]. Water is introduced into log yards through a variety of means, including: rainfall, snow melt, carry over with *Corresponding author. Tel.: +1-604-822-485; fax: +1-604822-6003. E-mail address: sduff@chml.ubc.ca (S.J.B. Duff).

logs transported in water, equipment cleaning, and sprinkling of log decks and/or yard surface to prevent fire, dust or deterioration of wood. Contact between this water and wood and woody debris (such as bark and hog fuel), other solid wastes and equipment can produce a run-off or leachate contaminated with a range of contaminants [2–6]. The volume and characteristics of the run-off from a particular site are dictated by a number of factors, including: species and volume of wood processed, climatic considerations (rainfall/snowfall amounts, intensity), characteristics of the site (log yard surface cover, grade, permeability of the soil), and practices (sprinkling of wood, equipment cleaning practices, run-off control/treatment measures). The type of wood processed at a sort yard can exert a two-fold influence on run-off quality. Firstly, wood extractives, a primary cause of run-off toxicity, can vary dramatically in character and concentration among wood species [4]. Secondly, the ease with which

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extractives are leached from the wood is an important determinant of run-off concentration and toxicity [3,7,8– 10]. In an attempt to capture many of the constituents of concern, a candidate parameter list for monitoring has been proposed: resin acids, fatty acids, phenols, pH, dissolved oxygen (DO), oil and grease (O & G), chemical oxygen demand (COD), biochemical oxygen demand (BOD), tannins and lignins (TL), and total suspended solids (TSS) [6]. Bioassay testing should accompany the chemical analysis because bioassays integrate the toxic effects of various constituents and are therefore considered a more reliable indication of leachate impact than are the chemical analyses alone [4]. Considerable effort has been put into the development and implementation of Best Management Practices (BMPs) for log yard run-off [1–5,7,8,11,12,14]. Despite implementation of these practices, some sites may still produce a run-off which requires treatment prior to reintroduction into the receiving environment. A number of treatment technologies have been suggested [4], including: biological treatment (aeration lagoons, activated-sludge systems and artificial wetlands) and physical/chemical methods (aeration, carbon adsorption, chemical oxidation (e.g. using ozone, calcium hypochlorite, hydrogen peroxide, or potassium permanganate), chelation, coagulation, ion exchange, neutralization, precipitation and reverse osmosis). Borga et al. [15] have shown that the levels of contaminants of concern in recycled sprinkler water is stabilised by biological treatment. However, little laboratory- or pilot-scale work has been carried out to evaluate the effectiveness of biological treatment alone or in combination with other treatment technologies. This study examined the effectiveness of biological treatment alone, and biological treatment preceeded by, and followed by ozonation for the treatment of log yard run-off.

The run-off for the ozone/biological treatment was obtained from the same sawmill in March 2001. Sample pH was 5.8. Initial BOD, COD, and TL concentrations were 1250, 8050, and 1550 mg/L, respectively. Acute toxicity (EC50) of the sample as measured by Microtox was 7.6%. Seed for the biological/ozone treatability studies and for BOD tests was obtained from the recycle line of the full-scale UNOXs activated sludge treatment system at Western Pulp’s 750 adtpd kraft pulp mill near Squamish BC. At the time of sampling the treatment system was operating at an 8 h HRT and with a mean cell retention time (MCRT) of 10 days. The recycle activated sludge (RAS) was stored at 41C until use.

2. Materials and methods

Table 1 Summary of experimental conditions for batch treatability study

2.1. Log yard run-off and biological seed Log yard run-off for the batch biological and biological/ozone treatment was collected as a grab sample during a rain event in June 2000 from a sort yard at a sawmill on Vancouver Island, BC. The mill processes approximately 500 000 m3/yr of wood, primarily Douglas fir and Western hemlock. As received, the run-off was dark brown in colour, had a pH of 5.9 and an initial acute toxicity (Microtox) EC50 of 1.86% (v/v). The initial BOD, COD, tannin and lignin concentration were 1540, 4890 and 1410 mg/L, respectively. The runoff was collected in 20 L Nalgene carboys and stored at 41C until use. Prior to biological treatment, suspended solids were removed by centrifugation (5000 g, 20 min).

2.2. Batch aerobic biological treatment Batch biological treatability studies were carried out under operating conditions typical of full-scale treatment systems (Table 1). The experimental program was carried out in a 15 L (8 L working volume) cylindrical jacketed Plexiglas reactor. Reactor temperature was maintained at 351C by circulating water from a constant temperature bath (VWR Scientific, Model 1131) through the annular Plexiglas jacket encasing the reactor. Samples were collected from the sampling port at the bottom of the reactor. The reactor was aerated through a sintered glass stone at a rate of approximately 1 volume/volume reactor
min using building air and the concentration of DO was monitored to maintain the DO level above 5 mg/L. Samples were centrifuged at 2000 rpm (B650 g) and the supernatant was acidified to pH 2 or less with concentrated H2SO4. The resulting samples were stored at 41C with minimal headspace prior to analysis.

Raw wastewater volume (L) Seed volume (L) Seed concentration (mg SS/L) Initial MLSS (mg/L) Run time (h) Temperature (1C) pH BOD nutrient solutions added (mL nutrient/L wastewater) Phosphate buffer MgSO4 CaCl2 FeCl3 BOD : N : P

8 2.4 10 580 2800 48 35 7

1.1 1.1 1.1 1.1 100 : 5 : 1

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2.3. Determination of kinetic parameters for biological degradation Microbial substrate uptake kinetics were determined in duplicate using a respirometric method developed by Cech et al. [16]. The respirometer (Fig. 1, Canadian Scientific Glassblowing Company Ltd., Richmond BC) consisted of a jacketed 180 mL glass vessel equipped with ports for DO measurement, aeration and sample injection. Vessel temperature was maintained at 351C by circulating water from a constant temperature bath (VWR Scientific, Model 1131) through the annular

Fig. 1. Schematic of respirometer.

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jacket encasing the respirometer. Mixing was provided by the DO probe (YSI Inc., Model 5905) as well as a magnetic stir plate and stir bar. An aquarium pump (Rolf C. Hagen Inc., Optima Model) provided the necessary aeration. For respirometry, RAS obtained from the Western Pulp mill was diluted to a concentration of 700–800 mg/L mixed liquor suspended solids (MLSS); the exact concentration was measured at the end of the test and used in subsequent calculations. This diluted mixed liquor was added to the respirometer and aerated for 30 min in order to degrade any substrate present. After this aeration period, aeration was stopped and the DO probe was inserted into the respirometer. Prior to sample addition, the probe was given time to stabilize, and the endogenous respiration rate was measured for at least 2 min. A known amount of substrate, adjusted to pH 7 with concentrated NaOH, was added through an injection port using Becton-Dickinson syringes and the change in oxygen uptake rate (DOUR), as reflected by changes in the concentration of DO, was monitored. Upon injection, the OUR immediately increased and then slowly returned to the initial endogenous rate. In order to ensure that the complete OUR profile (Fig. 2) was captured, data were collected for 2–3 min after sample injection. At the end of the test, data collection was terminated, and the DO probe was removed from the respirometer. Before another sample was injected, the mixed liquor was aerated until the DO value reached 6–8 mg/L. The data from the DO meter (YSI Inc., Model 59) were imported into a spreadsheet-using Collect/W (Labtronics Inc., Guelph, Canada), a software program that gathers data from the DO meter’s RS-232 port. The DO, percent saturation, and temperature were recorded every second. Using a macro, the DOUR and mass of oxygen consumed (OC) were determined for each substrate injection. The DOUR values were divided by the MLSS concentration in the respirometer in order to obtain specific DOUR (SOUR). The DOUR or SOUR values were divided by the OC per mass of substrate (BOD) metabolized (i.e. OC/S) to obtain substrate uptake rates (SUR) or specific SUR, respectively.

Fig. 2. Sample of data from respirometric determination of biodegradation kinetics.

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Depending on the experimental data, the microbial growth or specific substrate uptake rate can be described using Monod, Tessier or other kinetics. Monod and Tessier kinetics can be expressed in terms of substrate uptake rate as follows: qmax S ; S þ Ks

Monod:

q¼

Tessier:

q ¼ qmax ð1  ekS Þ;

ð1Þ ð2Þ

where q is the substrate uptake rate, qmax is the maximum substrate uptake rate, S is the substrate (BOD) concentration, Ks and k are constants. Kinetic parameters qmax ; Ks ; and k were estimated through nonlinear regression. 2.4. Sequential biological treatment/ozonation Biologically treated effluent was collected from the batch reactor after 48 h and treated with ozone. Ozonation was carried out in a 3 L (2.5 L working volume) jacketed glass vessel equipped with ports for ozone inlet and outlet. Mixing was provided by a magnetic stir plate and stir bar. The outlet from the reactor was connected to an ozone gas analyser (OzoMetert, Model HA-100GTP, Hankin Atlas Ozone Systems). Prior to sample addition, the ozone gas analyzer was turned on and allowed to stabilise, and flowrate of oxygen going in was adjusted to 1 L/min. The sample was then added to the reactor. The ozone generator (Grace Davison Chemical, Model LG-2-L1) was then turned on, and flow rate of oxygen was readjusted to 1 L/min. This flowrate corresponded to an ozone gassing rate of 0.013 vvm. The concentration of ozone in the exit gas stream was imported into a spreadsheet every 15 seconds using the Collect/W software. 2.5. Sequential ozonation/biological treatment The run-off sample was centrifuged at 2000 rpm (B650 g) for 20 min. Part of the sample was set aside in order to compare biological treatment of ozonated and unozonated samples. Two 2.5 L samples were then treated with ozone as described above, one for 10 min, the other for 30 min. Prior to biological treatment, nitrogen and phosphorus were added in the form of NH4Cl and NaH2PO4 in order to ensure a BOD : N : P ratio of 100 : 5 : 1. RAS was added to obtain a MLSS concentration of 2500 mg/L and 100 mL aliquots of the mixed liquor were dispensed into duplicate 250 mL Erlenmeyer flasks and incubated in a shaker at 351C and 150 rpm. After 2, 4, 8, 12, 24, and 33 h of biological treatment, duplicate samples were removed from each flask and centrifuged at 2000 rpm (B650 g). The resulting supernatant was acidified to pH 2 or less with

concentrated H2SO4 and stored at 41C with minimal headspace prior to analysis. 2.6. Sample analyses 2.6.1. Biochemical oxygen demand Soluble BOD was measured according to Standard Method 5210 B, 5-day BOD test [17]. The pH of the preserved samples was adjusted to seven using concentrated NaOH prior to analysis. RAS obtained from Western Pulp was used to seed the BOD tests. 2.6.2. Chemical oxygen demand Soluble COD was measured according to Standard Method 5220 B, closed reflux, colorimetric method [17]. The pH of the preserved samples was not adjusted before testing. In accordance with Standard Method 5220 B [17], all samples were analyzed in triplicate, and their absorbance measured at 600 nm. A new calibration curve was prepared whenever new COD chemicals were prepared, using seven standards of known COD concentration, ranging from 20 to 900 mg/L. 2.6.3. Tannins and lignins (TL) Tannins and lignins were measured according to Standard Method 5550 B [17]. The pH of the preserved samples was not adjusted before testing. All samples were analyzed in triplicate and their absorbance was measured at 700 nm. 2.6.4. Acute toxicity Acute toxicity of effluent samples adjusted to pH 7 was determined using a Microtoxt 500 analyzer, since this test has been previously shown to be suitable for wood process wastewater [18]. The test measures biological activity as indicated by light output from Vibrio fischeri, a bioluminescent bacterium. Toxicity is expressed as an EC50 value, the concentration of the sample that will cause a 50% reduction in light emission. Simultaneous analyses were run for three samples, according to standard procedures (Azur Environmental, Carlsbad, CA). The toxicity data were analyzed using Microtoxt computer software. In order to calculate the percent toxicity removal, EC50 values were converted to toxicity units (TU). TU ¼ 100=EC50 : The conversion of EC50 values to TU results in a higher weighting of the lower EC50 values. 2.6.5. Mixed liquor suspended solids Mixed liquor suspended solids were measured according to Standard Method 2540 D [17] with the exception that samples were analysed in triplicate instead of duplicate. Solids analysis was always performed immediately after sampling.

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decreased over treatment, from an initial EC50 of 1.83% to a value of 50.4% after 48 h, for a 96% reduction in toxicity (as calculated based on TU).

3. Results and discussion 3.1. Batch biological treatment of run-off Biological treatment of the log yard run-off was effective in reducing the concentration of most parameters of concern. Batch biological treatment of log yard run-off reduced BOD, COD and TL concentration by 99%, 80%, and 90%, respectively (Fig. 3). Final values of BOD, COD and TL were 32, 1046 and 132 mg/L, respectively. Acute (Microtox) toxicity was

3.2. Biodegradation kinetics The respirometry data were fitted using both Monod and Tessier kinetics (Fig. 4). The maximum specific substrate uptake rate (qmax ) and the Ks value were found to be 0.0038 mg BOD/mg VSS min and 1.4 mg/L, respectively. Values for the Tessier constants qmax and

6000

60

5000

50

4000

40

BOD COD 3000 TL (mg/L)

30

2000

20

1000

10

0

Microtox EC50 (%v/v)

0 0

10

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30

40

50

60

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Fig. 3. Removal of BOD (~), COD (m), TL (  ) and acute toxicity (’) during batch biological treatment of logyard run-off.

0.004 0.0035 0.003 0.0025 q 0.002 (1/min) 0.0015 0.001 0.0005 0 0

2

4

6

8

10

BOD (mg/L)

Fig. 4. Substrate uptake rate data as fitted by Monod (F) and Tessier (FF) models.

12

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the k were 0.0033 mg BOD/mg VSS min and 0.48 mg/L, respectively. The Monod constants obtained for run-off were comparable to qmax (0.0032 values mg BOD/mg VSS min) and Ks (1.4 mg/L) previously determined for bleached kraft pulp mill effluent (BKME) using this technique [19]. Biological treatment of BKME prior to discharge is mandated by Canadian federal regulations. During respirometry, oxygen uptake rate kinetics are dominated by the most readily biodegradable fraction of a multicomponent substrate. Therefore, while logyard run-off can be described as a readily biodegradable material based on its kinetic constants, it should be noted that, for multicomponent wastewaters, kinetics can vary greatly over the course of treatment due to the different kinetics of the various wastewater fractions. During respirometry, the value of OC/S can be considered to be the portion of the oxygen uptake that went directly into substrate oxidation. Based on this, 1-OC/S can be used as an estimate of the growth yield, or the fraction of substrate not directly oxidized. In this study, the growth yield constant was approximately 0.77 mg VSS/mg S.

degradation of compounds of less concern, for example high molecular weight COD. For this reason, it was desirable to examine the efficacy of ozone as a polishing treatment on biologically treated effluent. After 30 min of ozone treatment, COD and TL concentration were reduced by 22% and 68%, respectively (Fig. 5). BOD concentration increased by 38% after 30 min of ozonation. This increase in BOD was due to the conversion of a portion of the high molecular weight COD to lower molecular weight compounds capable of exerting a BOD. Ozonation did not improve acute (Microtox) toxicity over that achieved with biological treatment. In making this conclusion it should be noted that there is a large amount of variability in Microtox measurements made on samples with low toxicity. It is possible that residual toxicity is due to compounds not affected by ozone treatment (for example metals). Further work is required to determine the cause of this residual toxicity and whether it is detectable using other toxicity assays such as trout and Daphnia. 3.4. Sequential ozonation/biological treatment

3.3. Sequential biological treatment/ozonation The potential of ozone for water and wastewater treatment has received increasing attention in recent years [20]. Ozone has a number of advantages over conventional technologies, including potential for mineralisation of wastewater constituents of concern, rapid reaction rates, and applicability to intermittent flows. However, ozone application to wastewater has been limited due to excessive ozone consumption for the

In an effort to determine whether pre-ozonation of logyard run-off would have a beneficial effect on subsequent biological treatment, samples were ozonated for 10 or 30 min and then inoculated with activated sludge. Ozonation had a small effect on run-off COD and BOD with the COD and BOD reduced by 10% and 3%, respectively, after 30 min ozonation. For the first 8 h of biological treatment, BOD decreased more rapidly in ozonated samples, however, approximately the same

1200

100 90

1000

80 70

800

60

BOD COD 600 TL (mg/L)

50 40

400

Microtox EC50 (%v/v)

30 20

200

10 0

0 0

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35

Time (min)

Fig. 5. Removal of BOD (~), COD (m), TL (  ) and acute toxicity (’) during ozonation of biologically treated logyard run-off.

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Approximately 15 h of biological treatment were required in order to achieve the 70% reduction in TL obtained by 30 min of ozonation. However, by the end of the biological treatment period the same final TL concentration remained in both unozonated and ozonated samples. As was observed with TL, acute toxicity was rapidly reduced during ozonation (71% removal after 30 min), however the final EC50 after biological treatment was approximately 50% regardless of whether the sample was pre-ozonated or not (Fig. 9).

overall removal of BOD was observed at the end of the biotreatment (Fig. 6). It is interesting to note that, over the course of the biotreatment, the COD of the ozonated samples was reduced by only 1400 mg/L as compared to 2150 mg/L for the unozonated sample (Fig. 7). This may be due to a shift in the molecular weight distribution and/or the generation of recalcitrant material after ozonation. Tannin and lignin levels were reduced much more quickly by ozonation than biological treatment (Fig. 8).

800 700 600 500 BOD 400 (mg/L) 300 200 100 0 0

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Fig. 6. Removal of BOD during biological treatment of ozonated logyard run-off. (E) No ozonation, (’) 10 min ozonation, (m) 30 min ozonation.

3000

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2000 COD 1500 (mg/L) 1000

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0 0

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Fig. 7. Removal of COD during biological treatment of ozonated logyard run-off. (E) No ozonation, (’) 10 min ozonation, (m) 30 min ozonation.

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M.G. Zenaitis et al. / Water Research 36 (2002) 2053–2061 800 700 600 500 TL 400 (mg/L) 300 200 100 0 0

5

10

15

20

25

30

35

Biological treatment time (h)

Fig. 8. Removal of tannins and lignins during biological treatment of ozonated logyard run-off. (E) No ozonation, (’) 10 min ozonation, (m) 30 min ozonation.

70 60 50 Microtox 40 EC50 (% v/v) 30 20 10 0 0

5

10

15

20

25

30

35

Biological treatment time (h)

Fig. 9. Removal of Microtox toxicity during biological treatment of ozonated logyard run-off. (E) No ozonation, (’) 10 min ozonation, (m) 30 min ozonation.

4. Conclusions Batch biological treatment of log yard run-off reduced BOD, COD and tannin and lignin concentration by 99%, 80%, and 90%, respectively. Acute (Microtox) toxicity was decreased over treatment, from an initial EC50 of 1.83% to a value of 50.4% after 48 h. Respirometric evaluation confirmed that the kinetics of biodegradation were comparable to BKME. The use of ozonation as a polishing treatment for the biologically treated run-off reduced COD and TL by

22% and 68%, respectively. Ozonation did not result in further improvements in toxicity, and increased the BOD by 38%. As a pre-processing step, ozone rapidly decreased TL and acute toxicity, but did not improve performance of downstream biological treatment. This study indicates that biological treatment of log yard run-off can be an effective means to reduce the concentration of contaminants of concern in log yard run-off. However, implementation of biological treatment would be challenging at many log sort yards due to a number of factors, including: intermittent nature

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of the run-off flows, remoteness and harsh ambient environmental conditions of the sort yard sites, and lack of available power and skilled operating personnel.

Acknowledgements The authors gratefully acknowledge the funding support of Grad Ilic and the BC Hydro Water and Wastewater Centre and the BC Science Council. We are also grateful to the participating companies that supplied run-off and biological seed and to the UBC Dept. of Civil Engineering for the loan of the ozone generator. Thanks are also due to Julie Orban who helped to conduct the literature review. Finally, we would like to acknowledge contribution made by three anonymous referees, whose comments served to improve the paper.

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[7] Schuytema GS, Shankland RD. Effects of log handling and storage on water quality. US Environmental Protection Agency, EPS-600/2-76-262, 1976. [8] Pease BC. Effects of log dumping, rafting on the marine environment of southeast Alaska. Fisheries Research InstituteFUSDA Forest Service GeneralFUniversity of Washington, Seattle. Technical Report. Pub #: PNW-22. Seattle, WA, USA. 1974, 58pp. [9] Borga P, Elowson T, Liukko K. Environmental loads from water-sprinkled softwood timber. 1. Characteristics of an open and a recycling watering system. Environ Toxicol Chem 1996;15(6):856–67. [10] Taylor BT, Goudey JS, Carmichael NB. Toxicity of aspen wood leachate to aquatic life: laboratory studies. Environ Toxicol Chem 1996;15(2):150–9. [11] Alberta Forest Products Association (AFPA). Evaluation and control of environmental effects from logyard sites in Alberta. Edmonton, AB, 1999. [12] Department of Environment (DOE), Fraser River Action Plan (FRAP). Guidelines on storage, use & disposal of wood residue for the protection of fish & fish habitat in British Columbia. DOE/DFO Report 95-18. 1996, 28pp. [13] Washington State Department of Ecology (WDOE). The Washington State, Department of Ecology, 2000. home page: http://www.ecy.wa.gov [14] Toews DAA, Brownlee MJ. A handbook for fish habitat protection on forest lands in British Columbia. Department of Fisheries and Oceans. Vancouver, BC. 1981, 173pp. [15] Borga P, Elowson T, Liukko K. Environmental loads from water-sprinkled softwood timber. 2. Influence of tree species and water characteristics on wastewater discharges. Environ Toxicol Chem 1996;15(9):1445–54. [16] Cech JS, Chuboda J, Grau P. Determination of kinetic constants of activated sludge microorganisms. Water Sci Technol 1985;17:259–72. Technol 1985;17:259–72. [17] APHA. In: Clesceri L, Greenberg A, Eaton A, editors. Standard methods for the examination of water and wastewater, 20th ed. American Public Health Association, 1998. [18] Firth BK, Blackman CJ. Comparison of Microtox testing with rainbow trout (acute) and Ceriodaphnia (chronic) bioassays in mill wastewaters. Tappi J 1990;73(12):169–74. [19] Helle SS. A respirometric investigation of the activated sludge treatment of BKME during steady state and transient operating conditions. Ph.D. Thesis, UBC Department of Chemical and Biological Engineering, 1999. [20] Rice RG. Applications of ozone for industrial wastewater treatmentFa review. Ozone Sci Eng 1997;18:477–515.