Effect of Calcium Carbonate and Calcium Sulfate on E.coli survival in fine sand mixtures

Results showed that electrical conductivity (EC), acidity (pH) and other chemical properties of cow manure had no adverse effect on bacterial growth (Fig.l, r ²= 0.92), which indicate its suitability for bacterial activity and survival. As time passes, bacterial density were increased in cow manure extract (Figure 1). Electrical conductivity of sand-CaSO ₄ mixtures were more than sand-CaCO ₃ mixtures, while the pH of sand-CaCO ₃ was more than that of sand-CaSO ₄ mixture. Electrical conductivities of tested samples were from 0.184 to 1.34 dS m ^-1, which shows that this factor has no inhibition effect on bacterial growth. Variance analyses of the DATA indicated that the effects of compound concentration, exposure time and their levels were statistically significant (p<0.05, r ²=98%). DATA means comparison showed that CaCO ₃ had more (positive or negative) effects on bacterial growth. The effect of proportion of mean concentration in 20% level on bacterial growth was 40%, 60% and 80% times more. When CaCO ₃ levels were increased, E. coli concentrations were decreased. Minimum density of E. coli was observed in 80% level. However, no significant difference was witnessed between 40%, 60% and 80% levels. Variance analyses showed that the effect of exposure time was significant (p<0.05) in sand medium treated with CaCO ₃. Maximum density of E.coli was observed at 15 hours after incubation that was more related to 20% level. Bacterial density after 15 h incubation was 1.8, 2 and 4.7 times more than 10, 5 and 2.5 hours of incubation. There was a significant difference between 15 hours incubation and 5 and 10 hours. No significant difference between 5 and 10 hours of incubation was observed. Interactions of level versus time showed that the inhibitory effect of CaCO ₃ may be present at 40% and 60% levels. DATA means comparison of bacterial growth on sand-CaSO ₄ medium demonstrated that there were significant differences between CaSO ₄ levels (p<0.05). Mean density of grown bacteria were as follows: 60%>80%>40%>20% which means 160.13×10 ³>147.51× 10 ³> 91.18× 10 ³> 68.56× 10 ³, respectively. The effect of CaSO ₄ was more distinguishable than CaCO ₃. As CaSO ₄ levels increased no adverse effect was observed on bacterial growth. The proportion of E. coli density in 20%, 40%, 60% and 80% vs. 60% level were 2.3: 1.8: 1: 1.1, respectively. The effect of exposure time was significant in sand-CaSO ₄ medium like Sand-CaCO ₃ medium (p<0.05). Maximum and minimum density for grown E. coli was observed in 80% and 20%, respectively. Results illustrated that CaCO ₃ and CaSO ₄ had no inhibitory effect on E. coli growth at 20% level (Figure 2), but when CaCO ₃ level increased bacterial densities were decreased. This trend was observed in 40%, 60% and 80% levels, and maximum correlation coefficient was witnessed in 60% level (Figures 3, 4 and 5). On the other hand as CaSO ₄ levels increased bacterial density was increased. It seems that E. coli use CaS04, especially SO ₄ anion in its structure body, while high concentrations of CO ₃ anion have inhibitory effect on E. coli growth. Another noteworthy point is that the density of E. coli were increased and decreased exponentially in 60% and 80% of sand-CaSO ₄ and sand-CaCO ₃ mixtures, respectively; while this trend was linear at 20% and 40% levels (Figures 4 and 5). Finally, this study indicated that if CaCO ₃ compound is used in the waste discharge system, E. coli cells would be flirted, on the other hand this compound is plenty in geological area of Iran, which can decrease filtration costs.