The data were subjected to a rigorous statistical analysis. For all the four types of bacteria, the average for the seven days, the standard deviation and percentage change relative to the control were calculated. To test for significance, Student’s t-test was resorted to. Table 2 contains all the calculated values, along with the t values.
Part of this data is presented in a graphical form in Figs 2, 3 and 4. These refer respectively to the growth of Staphylococci, Bacillus and Corynebacteria. The full data with all tables and charts are available8. Only a representative sample is given here for purposes of illustration. The statistical analysis was done for the full data and all conclusions have been substantiated by the full data.
Figure 2 shows the rate of growth of Staphylococci during the span of 7 days. It is seen that in all cases, except FGP2 and FGO, there is a rapid growth on the first day itself. The growth slows down and becomes steady, the rate of growth becoming constant. The control shows the largest growth, with PWR, PWP and FGP1 showing lower values. The actual count of the microorganism is shown against the experimental points for the sake of convenience. It is also seen that there is no growth at all in the case of FGP2 and FGO.
The same trend is also observed in the case of Bacillus (Fig. 3). In this case also, the rate of growth on the first day is very steep, tapering off into a steady growth for all cases except FGP2 and FGO. There is not much variation among control, PWR, PWP and FGP1. Here again, there is hardly any growth in the case of FGP2 and FGO.
In Corynebacteria, the data follow the same trend as in the two earlier cases (Fig. 4). The rate of growth on the first day is quite steep for all cases except FGP2 and FGO, gradually tapering off to a steady increase. The variation in the individual values is of the same order as in the case of Staphylococci. Again, the data show that the growth is nil for the case of FGP2 and FGO.
One striking feature of this data is that the three microorganisms studied are dormant and do not show any growth in the case of fiberglass pyramids with a square and an octagonal base. This does not necessarily mean that the microorganisms have been destroyed. Only their growth is inhibited. Once the samples are withdrawn from the pyramids they are subject to decay exactly as the control exposed to the atmosphere.
These results were supplemented with visual observations, which have been summarized in
Table 1. The visual observations referred to the color, smell and the appearance of the samples observed everyday. However, only the observations for the first and the seventh days are given in the table for the sake of brevity. The pH values are also included in the table for the sake of completeness. Full particulars of all the data and observations are available8.
Table 2 contains the summary of the bacterial characteristics for all pyramidal structures and the control for all the seven days of the experiment. It also gives the average values and the standard deviations as calculated from the raw data, which were also subjected to Student’s t-test for significance.