MODELO MUNDELL-FLEMING CON TIPO DE CAMBIO FIJO

As the Boyer mill treats water from the Derwent River, known as “clearwater”, for use in the paper making process, metal levels in the Derwent represented baseline trace metal concentrations. Clearwater influent samples were collected daily by the Boyer staff, and refrigerated before

29 | P a g e transport to Launceston for AAS analysis. As the changes in the operation of the mill did not affect the quality of the clearwater influent samples the mean trace metal concentrations of both sampling periods were simply combined and averaged (Table 2.3). The trace metals were close to the limit of detection for flame AAS analysis, excepting calcium and magnesium where the clearwater

contributed approximately 30% of the total concentration detected in the SETP.

Table 2.3: Concentration of selected trace metals in the Boyer pulp and paper mill treated

clearwater influent averaged over 21st Sep 2009 to 9th Oct 2009 and 11th Jan 2010 to 5th Feb 2010.

Ca (mg/L) Co (mg/L) Cu (mg/L) Fe (mg/L) Mg (mg/L) Mo (mg/L) Zn (mg/L) Inlet Clearwater 5.5 ± 1.2 0.002 ± 0.001 0.008 ± 0.006 0.02 ± 0.035 1.6 ± 0.475 < 0.001 ± 0.0008 0.016 ± 0.01

Two sample periods were then selected for further testing to determine metal levels in the mill wastewater and the effects of the plant changes brought about by the commissioning of TMP 3. The samples to be collected included the primary and secondary clarifier samples and the SETP samples. The two sampling periods were selected to include periods before and after the plant changes, from 21st Sep 2009 to 9th Oct 2009 and 11th Jan 2010 to 5th Feb 2010 (Appendix A).

In total there are 16 wastewater sampling sites at the NSB mill, to allow any pollutant to be traced back to a particular source. For this study the sample sites within the WWTP are the most important, especially those in the SETP. The SETP comprises of four sample sites: activated sludge reactor (ASR), biofilm reactor (BFR), return activated sludge (RAS) and waste activated sludge (WAS). The samples were collected by NSB staff and refrigerated until analysis by flame AAS. After metal analysis a one- way ANOVA statistical analysis comparing the mean metal concentrations at each of these four sample sites before and after the TMP 3 commissioning was undertaken.

The mean metal concentrations from the before and after the TMP3 commissioning and the respective P-values for the statistical analysis from the WWTP samples are given in Table 2.4 (a summary table of all sample sites is given in Appendix C). There were significant differences between before and after the TMP3 commissioning in ten instances, two for copper, three for iron, three for magnesium and two for zinc . Increases in the iron and zinc concentrations in hardwood species have been reported compared to softwood species [93]. The mean concentrations of iron and zinc were higher in the SETP samples before the TMP3 commissioning where hardwood was a portion of the

30 | P a g e feed stock. However, the differences in the iron and zinc mean concentrations in the primary and secondary clarifier were higher in the post TMP3 commission (Table 2.4). In all the sample sites the mean magnesium concentration was higher in the post-TMP3 commission sample. Of those, the increase in mean concentration in three sample sites was statistically significant. Magnesium is an important trace metal for all trees and has been found to be at concentration of between 0.1 ppth and 1.8 ppth dry weight in both soft and hard woods of North America [89, 93].

Table 2.4: Mean concentrations (mg/L) of metals detected in the WWTP from the samples collected before and after the TMP 3 commissioning. P-values for the analysis of mean trace metal

concentration of the before and after TMP 3 samples (one-way ANOVA; 95% confidence interval). P- values in red indicate a significant difference.

(mg/L) Pri In Pri Eff Sec In Sec Eff BFR RAS WAS ASR

Ca Before 21.4 22.1 19.9 20.7 20.2 21.7 24.4 20.1 After 19.1 20.1 18.3 18.5 18.2 18.4 18.9 18.7 P-Value 0.49 0.54 0.57 0.44 0.46 0.23 0.06 0.59 Co Before 0.004 0.004 0.004 0.004 0.003 0.004 0.004 0.004 After 0.003 0.003 0.003 0.004 0.004 0.003 0.003 0.004 P-Value 0.12 0.19 0.16 0.40 0.69 0.34 0.13 0.60 Cu Before 0.05 0.03 0.03 0.03 0.02 0.03 0.03 0.04 After 0.03 0.02 0.02 0.03 0.03 0.03 0.03 0.03 P-Value 0.01 0.22 0.03 0.44 0.87 0.62 0.88 0.21 Fe Before 0.27 0.31 0.22 0.28 0.27 0.54 0.87 0.27 After 0.36 0.27 0.16 0.20 0.25 0.26 0.53 0.18 P-Value 0.01 0.35 0.22 0.11 0.58 0.00 0.00 0.08 Mg Before 5.0 4.9 4.7 4.7 4.3 4.8 5.4 4.5 After 5.5 5.5 5.7 5.9 5.1 5.4 5.7 5.3 P-Value 0.32 0.16 0.05 0.01 0.06 0.17 0.56 0.05 Mo Before 0.004 0.003 0.002 0.002 0.002 0.002 0.001 0.002 After 0.003 0.003 0.002 0.002 0.002 0.002 0.001 0.002 P-Value 0.20 0.99 0.55 0.90 0.98 0.84 0.72 0.84 Zn Before 0.16 0.17 0.21 0.11 0.20 0.33 0.26 0.22 After 0.19 0.15 0.24 0.19 0.24 0.23 0.25 0.25 P-Value 0.11 0.11 0.07 0.00 0.18 0.00 0.68 0.20

31 | P a g e Calcium is another important trace metal that is required by trees for growth [89, 93]. There was no significant difference in the mean concentrations of calcium in the before and after the change over from mixed feedstock to solely Pinus radiata. Similarly with the mean cobalt and molybdenum detected there was no significant difference between the two means from before and after the mill feed stock change. The mean concentration of cobalt and molybdenum in the WWTP sample sites ranged between 0.003 – 0.004 mg/L and 0.001 – 0.004 mg/L respectively.

As the concentrations of metals in the initial grab sample and the inter-laboratory samples were different (Table 2.1 and Table 2.2), it was not unexpected to have some differences between the samples collected prior to and following commissioning of TMP 3. However, if there were major changes in the trace metal concentrations from the change of feed stock, then it would be expected that these would be seen in all the WWTP samples, which was not the case. The individual mean metal concentration at each sample site can be found in Appendix C.

As there were only four statistically significant differences found between the mean metal concentrations detected within the SETP (that is, from the BFR, RAS, WAS and ASR sample points) from the samples collected before the TMP 3 commissioning and those following the TMP 3 commissioning (Table 2.4), the data from each SETP sample sites were compared. From this comparison there were no significant differences in the mean concentrations of metals from the SETP sample points and the four SETP sites were combined to determine the long term mean trace metal concentrations (Table 2.5).

The long term mean metal concentrations were seen to differ from the levels detected in the initial grab sample (Table 2.1), notably for calcium, copper, iron and zinc. The mean calcium concentration was found to be higher than the grab sample while the mean concentrations of copper, iron and zinc were all at most 50% of the concentration in the initial grab sample.

As can be seen in Table 2.5 the concentrations of calcium, magnesium and zinc were found to be either above or within the estimated microbial trace metal requirements. The analyses of zinc indicated that the grab sample result was not typical and the concentration was generally within the estimated requirements with the mean zinc concentration of 0.25 mg/L. The concentration of zinc in the initial primary clarifier grab sample was 1.35 mg/L, significantly higher than the accepted

requirement. It could not be determined if the high zinc level in the sample was from sample contamination or process inputs. However, if the concentration of zinc in the SETP was prolonged over consecutive days above 1.0 mg/L it most likely would have had a toxic effect on the SETP biota [50, 94].

32 | P a g e The mean concentrations of cobalt, copper, iron and molybdenum were below the accepted microbial requirements. The reported cobalt concentration for optimal microbial growth in

municipal activated sludge has been between 0.02 – 0.05 mg/L [49], while the maximum estimated nutrient requirements from Table 2.5 has been calculated to be up to 0.5 mg/L. The mean

concentration of cobalt in the SETP was found to be approximately 0.003 mg/L, significantly lower than the estimated requirements given in the literature (see Table 2.5).

Table 2.5: Mean concentration of selected trace metals (mg/L) in SETP from Boyer.

Metal (mg/L) Ca Co Cu Fe Mg Mo Zn

Mean Concentration of

Combined SETP Samples 19.9 ± 7.8 0.003 ± 0.001 0.03 ± 0.03 0.38 ± 0.29 5.1 ± 1.3 0.002 ± 0.002 0.25 ± 0.09 P-Value Between SETP

Sample Sites 0.994 0.794 0.717 0.232 0.741 0.105 0.801 Accepted Microbial Trace

Element Requirements[8, 71, 76] 3 - 5 0.02 – 0.50 0.1 – 1.0 1 - 4 3 - 10 0.02 – 0.05 0.01 – 1.0 SETP Metal removal* 4% 3% 35% 33% 0% 24% 20% Concentration of Metals in

Sludge (mg/kg) 1.35 x 10

-4 _{7.89 x 10}-7 _{2.74 x 10}-5 _{6.18 x 10}-4 _{3.52 x 10}-3 _{1.21 x 10}-5 _{2.48 x 10}-5

Sludge digest St Dev 5.99 x 10-4 1.99 x 10-7 1.52 x 10-6 1.03 x 10-4 3.88 x 10-4 1.02 x 10-5 1.60 x 10-5

*The removal of metals calculated from the primary clarifier effluent and the secondary clarifier influent.

The removal of metals in the SETP was determined by subtracting the secondary clarifier influent metal concentration from the primary clarifier effluent concentration. Estimating the concentration of individual metals removed in the SETP was important in understanding how they react with the sludge and in estimating the bioavailable concentration for each metal. As expected, due to the solubility of calcium and magnesium there were only limited amounts removed in the SETP process. Additionally only minimal amounts of cobalt were removed in the SETP, something observed in previous studies [49]. On the other hand between 20 and 35% of the copper, iron, molybdenum and zinc in the primary clarifier were removed in the SETP. The fate of metals in activated sludge will be discussed in Chapter 5.

There was only a single sludge sample collection period between the 21st Sep and 9th Oct 2009 where samples were collected daily prior to the commissioning of the TMP 3. The concentration of metals in the sludge was low compared to the guidelines for the land application of biosolids [95], ranging between 7.9 x 10-7 mg/kg Co to 3.5 x 10-3 mg/kg Mg (Table 2.5). The acceptable metal levels given in the Tasmanian Biosolids Reuse Guidelines are copper and zinc, 100 mg/kg and 200 mg/kg,

respectively [95] while the acceptable levels of cobalt and molybdenum have been reported to be 40 mg/kg and 5 mg/kg, respectively in the Land Application of Municipal Sewage Sludge Guidelines [96].

33 | P a g e Metals with the higher concentration in solution generally had a greater concentration in the sludge. Although, the concentration of iron was 6.18 x 10-4 mg/kg and the concentration of calcium was 1.35 x 10-4 mg/kg where the concentration of iron in the aqueous phase was significantly lower than that of calcium, at 0.38 mg/L and 19.9 mg/L, respectively. The greater level of iron in the sludge

compared to calcium reflects the solubility of the two metals at pH 7. The removal of iron, copper and zinc from the SETP was also an indication of the affinity of those metal ions to bind to solid surfaces in the sludge or complex with the organic ligands and precipitate out of solution [97, 98]. Chapter 5 gives detailed discussion on the fate of metals in activated sludge.

A single spike of 1.20 mg/L molybdenum was also detected in the PM2 effluent, on Monday 28th Sep 2009. This decreased over 3 days to the base line concentration of 0.002 mg/L. In two separate studies Burgess et al. have found the addition of 0.5 mg/L molybdenum to be beneficial to activated sludge in one experiment [8] and in another they reported that molybdenum had a toxic effect [9]. The spike in the PM2 effluent had a limited effect on the molybdenum concentration in the primary clarifier influent increasing from a mean 0.002mg/L to 0.007 mg/L on the day.