Jar testing was carried out for four different toxins, washing powder, zinc sulphate, sodium dodecyl sulphate and bleach (Figure 8-1). Samples were taken for the first 60 minutes after dosing, at ten minute intervals, as this was when the most perturbation had been observed previously in the dosing trials (Chapters 6 and 7) and to ensure that the jar tests provided a biological system with a similar response to that seen in the porous pots and MBR. None of the toxins dosed contributed directly to the parameters measured.
The biomass used for the SDS, bleach and zinc sulphate jar tests had similar pre dosing CSTs of 100 seconds whereas the biomass used for the washing powder trial had an unusually low CST of 50 seconds, however, no explanation
156 was found for this as the origin of the biomass was the same and no changes had been made to the operational parameters of the MBR.
Three different responses were observed for the four toxins with respect to the CST measurements taken (Figure 8-1). The response to the sodium dodecyl sulphate (SDS) and zinc sulphate dosing was minimal with only small variations of less than 20%, from the pre dosing levels. This was expected as neither of these toxins had had any effect on CST in the previous MBR dosing trials. The washing powder dose produced an immediate 20 second increase which then remained stable over the remaining 60 minutes monitoring period. In contrast, the bleach dose produced a more delayed and steady increase in CST of approximately 5 seconds for each ten minute interval until a peak of 130 seconds was observed at the 40 minute sample, an overall increase of 20 seconds from pre dosing levels. This effect had not been observed in the MBR dosing trials, but is likely to be influenced by the oxidation action of the bleach on any organic content in the mixed liquor.
All of the jar tests had a similar SMP turbidity before dosing of approximately 2 NTU. As previously, the bleach, sodium dodecyl sulphate and zinc sulphate doses had little effect on the SMP turbidity. The washing powder dose, however, caused an immediate increase of turbidity from 2.2±0.02 NTU before dosing to 10.5±0.09 NTU ten minutes after. The peak turbidity was at 20 minutes after dosing at 14.8±0.03 NTU, thereafter the level settled to around 10 NTU (10.9±0.1 NTU, 9.5±0.1 NTU and 10.4±0.1 NTU at 30, 40 and 50 minutes respectively). This effect is the same as that experienced in the porous pot and MBR trials where the washing powder dose produced an instantaneous increase in SMP turbidity, however, as the jar test is a closed system the reduction in SMP turbidity after 20 minutes must have been due to a reflocculation of some of the colloidal element within the biomass matrix.
All the pre dosing samples had similar SMP protein levels of 10 to 12 mg.l-1. Again the bleach, sodium dodecyl sulphate and zinc sulphate doses had little
157 effect on the SMP proteins measured. The washing powder, however, caused an immediate increase from 13.0±0.2 mg.l-1 before dosing, to 44.8±0.3 mg.l-1 after 10 minutes stirring time. This increase continued until a peak, after 50 minutes stirring, of 58.5±0.2 mg.l-1.
The four toxins dosed produced a varied response in terms of SMP carbohydrates. The biomass used for both the zinc sulphate and the SDS had a high level of SMP carbohydrates of 17±0.3 and 16±0.4 mg.l-1 pre dosing, respectively, whereas the biomass for the washing powder and bleach jar tests had pre dosing levels of 3.7±0.3 and 8.2±0.5 mg.l-1.The washing powder dose showed only a slight increase over the first twenty minutes from the pre dose level of 3.7±0.3 mg.l-1 to 4.4±0.4 mg.l-1, however, the SMP carbohydrates increased steadily over the remaining forty minutes monitored, to a peak of 12.1±0.1 mg.l-1 at 50 minutes. The bleach dosing produced a more erratic response in the SMP carbohydrates with levels being around 8 mg.l-1, apart from at 30 minutes where there was an increase to 12.6±0.3 mg.l-1.
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Figure 8-1 – (a) CST (b) SMP Turbidity (c) SMP proteins and (d) SMP carbohydrates for biomass dosed with washing powder (■), bleach (▲), SDS (x) and zinc sulphate (●) (t at -5 minutes = biomass only before toxin testing).
159 A summary of the effects observed in the first hour of the porous pot, MBR trials and the jar tests is given below (Table 8-1). The washing powder produced the most pronounced effects over the parameters measured with changes observed across the three systems used. For example, an increase of at least 7 NTU in SMP turbidity was observed across the three dosing trials. The other three toxins produced more varied responses with changes in parameters seen in some dosing trials but not others (Table 8-1).
In general, the effects observed in the jar tests reflected those in the other dosing trials, with the results following the MBR trials more closely than the porous pot trials. This is understandable as the biomass used for the jar testing was MBR biomass. An explanation of the effects observed have been described and explained in the previous trials chapters, the same being true for the jar tests. There were some exceptions, however, for example, in the first hour after the washing powder dose the CST increased by 40 seconds in the porous pot trial and by 100 seconds in the MBR trial, whereas for the jar testing the increase was only 30 seconds over the hour monitored.
Table 8-1 – Summary of the effects observed in the first hour after dosing for the porous pot and MBR trials.
Parameter Toxin dosed Porous pot trial MBR trial Jar testing
CST WP1 60 to 106 156 to 255 47 to 72
1WP = washing powder, 2SDS = sodium dodecyl sulphate.
160 Although the jar testing set up did not mirror the conditions or environment of the two dosing trials exactly, it would provide an opportunity to observe trends in the behaviour of the release of foulants and in the mitigation effects of the coagulants added.