II.5 Estructura de la solución
II.5.2 Cambio innovador
The results from both analyses of the two sets of samples were analysed using a Two Sample T-Test Assuming Equal Variation, using both RStudio Version 0.98.1103 – © 2009-2014 (RStudio, Inc, 2015), and Microsoft Excel (Microsoft, 2015).
5.3 Results
5.3.1 Particle Size Distribution
The results of the particle size and heavy metal concentrations are shown in Table 5.1 below. In order to compare the particle size distribution of the samples, the d50 value was used, as in previous chapters. This is the median particle size (i.e. 50 % of particles are smaller in diameter than d50), and is used in order to characterise the sample. For the ‘wash-off’, an average was calculated for each run, i.e. the 30 minute ‘Sample’ corresponding to the wet- vac sample.
Table 5.1: d50 Values from ‘Wet vac’ and ‘Wash-off Sampling Methods
The t-test showed that there was no significant difference in the mean of the two sample sets (p = 0.7110). An unpaired T-test was applied, as despite sample locations being adjacent to each other, it was not possible to collect runoff from the area that had been wet-vacuumed, as this removed the sediment.
5.3.2 Heavy Metals
The results from the heavy metal analysis are shown in Table 5.2 below. As per
Chapter 5, the data provided is the concentration (mg/kg or µg/kg), not the
mass. This is because it is accepted that due to slight variance in the sampling, it is more effective to compare characteristics (concentrations) rather than absolute amounts.
All of the metals analysed showed no significant difference between ‘Wet Vac’ and ‘Wash-off’ sampling methods (p = 0.3126, 0.1160, 0.0545, 0.6572, 0.2908 and 0.0709 respectively).
Sample
Wet Vac
Washoff
1
44.8764.71
2
71.4384.67
3
87.86111.76
4
89.1092.38
5
102.09108.23
6
99.1193.18
7
117.46134.01
8
137.68136.54
9
65.9885.60
Mean
90.62 101.23SD
26.28 22.30d50
(µm)
Table 5.2: Metal Conc. from 'Wet Vac' and 'Wash-off' Sampling Methods
5.4 Discussion
The statistical analysis showed that none of the parameters tested were significantly different whether the sample had been collected via the ‘wet vac’ method, or as runoff. Zinc was deemed to be ‘Not quite significantly different’, with p = 0.0545). This is most likely due to the greater variance (S.D. = 333.10) compared to other metal concentrations (S.D. = 21.52 – 268.03).
Sample Wet Vac Washoff Wet Vac Washoff Wet Vac Washoff 1 84.23 286.98 26.75 9.18 85.43 24.44 2 89.69 272.35 34.63 24.46 120.92 118.10 3 129.80 83.80 42.60 13.26 152.00 57.00 4 81.32 31.67 24.78 7.36 65.73 35.82 5 125.37 96.50 26.99 32.17 88.38 108.47 6 140.72 102.34 29.54 17.78 115.37 69.10 7 102.58 26.09 35.46 6.43 123.62 23.84 8 101.12 140.87 36.84 43.22 85.70 107.48 9 76.32 199.82 34.97 51.81 75.52 80.71 Mean 103.46 137.82 32.51 22.85 101.41 69.44 SD 22.00 90.58 5.50 15.48 26.34 34.73
Sample Wet Vac Washoff Wet Vac Washoff Wet Vac Washoff 1 222.75 127.21 548.50 207.60 49.10 13.40 2 579.18 1194.26 693.49 761.32 54.85 51.17 3 689.60 603.42 955.00 163.08 83.40 24.21 4 332.07 157.56 326.87 2.05 38.36 14.45 5 260.95 775.31 319.54 348.73 52.79 56.23 6 480.04 442.53 459.68 401.81 51.50 32.08 7 500.90 100.38 0.20 231.96 44.28 7.79 8 351.02 470.52 771.13 767.81 54.27 63.51 9 296.90 367.21 629.97 544.09 50.35 65.11 Mean 412.60 470.93 522.71 380.94 53.21 36.44 SD 148.89 333.10 268.03 250.71 11.76 21.52 Zn (mg/kg) Cd (mg/kg) Cr (mg/kg) Cu (mg/kg) Ni (mg/kg) Pb (mg/kg)
With these results, it could be suggested that the ‘Wet Vac’ method is not only effective as a sampling method in investigation of surface build up, but also that it is representative of the wash-off process.
Furthermore, with the ‘Wash-off’ values taken over a range of rainfall intensities (19 mm/h – 54 mm/h), it can be suggested that the ‘Wet Vac’ method is representative over a range of rainfall events. However, with the results of
Chapter 5 determining that there is no significant difference between the
intensities in question, this is not surprising.
It could be argued that the methods show no significant difference due to the large variation for each parameter. However, it is apparent that variation occurs in both groups. This is not unusual, with similar levels of variation occurring in results from Chapter 5 and this study. When all of the many potential factors influencing pollutants/variety of sources are considered, it is not unexpected.
5.5 Conclusion
The results of the assessment show that there was no significant difference between the physical (PSD) and chemical (heavy metal concentration) characteristics of samples obtained by the ‘wet-vac’ method, and those obtained from sampling runoff. Therefore, it can be concluded that the ‘wet-vac’ method is a viable method of collection a sample representative of runoff.
6 Biodegradation of PAH in Channel Drain Sediment
This paper is prepared in the format for submission to The Science of the Total Environment Journal, or alternatively a conference proceeding.
This paper relates to the final phase of the Conceptual Model, ‘Treatment’. The previous papers have identified the potential sources of pollutants, the real- world characteristics of accumulated sediment, and the subsequent transport into the channel drain. It is in this chapter that potential treatment of these pollutants is identified, and investigated.
Source Accumulation Transport
Treatment
The objective of this paper is to: ‘Identify potential evidence for the biodegradation of PAH in channel drain sediment.’
6.1 Introduction
Polycyclic Aromatic Hydrocarbons (PAH) are identified as one of the major sources of urban pollution, and as such are classified as Priority Pollutants by the EU (EU, 2000). They are deposited from a wide range of sources, including tyres, vehicle emissions, brakes, highway materials and road materials (Thorpe and Harrison, 2008; Mostafa et al., 2009; Dong and Lee, 2009; Bjorkland, 2011). The effects of PAH on the environment have the potential to be devastating.
Degradation of PAH may occur by a number of processes: adsorption, volatilisation, photolysis and chemical degradation. However, biodegradation, the breakdown of compounds by microrganisms, has been identified as the main process by which PAH degrades (Haritash and Kaushick, 2009).
The process of biodegradation has been identified as a possible form of treatment in SUDS. Several studies (Pratt et al., 1999; Newman et al., 2004, 2005) have studied the effects of biodegradation in pervious pavements, generally finding that reduction of PAH concentration occurred. This was
developed further by Puehmeier (2005, 2013), who used a floating mat with an oil degrading biofilm in infiltration systems to further increase biodegradation. Although similar treatment has not been considered in channel drains, there may be the potential for it to occur. It has been observed (Lundy et al., 2014) that channel drains retain sediment, and it is within this that biodegradation may occur.
A study by SNIFFER (2008) conducted an experiment in which soil from roadside SUDS was spiked with PAH, and the degradation observed over 60 days. The results generally showed a reduction in concentration over the incubation time period, suggesting that there is the potential for biodegradation of PAH in these conditions. The effect of treatments including variations in pH, temperature, moisture content and PAH concentration were observed, as these are known to affect biodegradation (Leahy and Colwell, 1990).
The sediment in channel drains comes from similar sources to that used in (SNIFFER, 2008), and as such, it may provide a similar medium for treatment. Therefore, the objective of this study is to quantify the microbial degradation of PAH in channel drain sediment. The methodology is based on that of SNIFFER (2008) study, albeit using sediment extracted from channel drains. In doing this, the results can be compared, and more generally channel drains compared to established forms of SUDS, with the possibility of suggesting channel drains are as effective as accepted SUDS at treatment of sediment.