DECLARATION 2 PUBLICATIONS
3. RESULTS
3.1 Factors contributing to microbiological quality of crops
3.1.2 Soil microbiology and chemistry
At the start of the trial, six samples of the Berea red soil used for the trial were analysed and at intervals throughout the trial, further samples of the soil from each of the irrigation treatments were analysed for alkalinity, free ammonia, Ascaris ova, COD, conductivity, E. coli, Enterococcus, Staphylococcus and total coliforms to detect any changes. The results are presented in Table 3.1, with all the microbiological readings presented as log10 values.
Table 3.1: Results from Physico-chemical and microbial analyses performed on soil samples from unwatered plants and plants irrigated with greywater, hydroponic solution or tap-water respectively. Mean, maximum, minimum and Standard deviations are provided for all parameters. No statistical significance was found between parameters measured and treatments (p≤0.05) except in the case of Enterococcus where the level in greywater irrigated soil was statistically higher than for the other treatments (p≤0.05).
Irrigation water type Alkalinity COD Conductivity Ammonia (free)
Ascaris lumbricoides
E coli Enterococcus Staphylococcus Total coliforms
Total Viable
mg/g dry
mg/g dry
mS/
m mg/
g dry
Ova/
g dry
Ova/g
dry Log10 cfu/g dry Unwatered
(n=4) Mean 139 117.6 5.52 0.00 0 0
Min 52 86 5 0
Max 241 184 5.8 0 2.3 3.7 5.4
Std
Dev 100.2 40.3 0.31 0
Greywater irrigated (n=9)
Mean 86 273.7 6.82 0.75 0 2.45 3.1 5.2
Min 86 78 5.3 0.5 0 0 0 0
Max 86 406 9.4 1.3 1 0 0 2.99 10.6 5.8
Std
Dev 0 89.99 1.46 0.28 0 2.5 3.2 5.2
Hydroponic solution irrigated (n=10)
Mean 86 365.4 6.47 0.95 0 1.3 3.9 5.2
Min 86 214 4.9 0 0 0 0
Max 86 492 8.5 1 0 0 1.9 4.7 5.5
Std
Dev 0 83.70 1.24 0 1.4 4.2 5.1
Tap water irrigated (n=11)
Mean 86 722.6 6.12 0.87 0.00 0 0 1.3 3.6 5.1
Min 86 138 5.1 0.5 0 0 0 0
Max 86 1553 7.6 1.8 0 2 4.5 5.5
Std
Dev 0 579.3 0.68 0.40 0 1.4 3.9 5.1
No E. coli or viable Ascaris ova were detected in the soil from any of the treatments.
Staphylococcus and total coliforms did not show significant differences among treatments (p≤0.05), but the level of Enterococcus in the greywater-irrigated soil was statistically greater than that for the other two treatments (p≤0.05).
3.1.3 Greywater
At the start of the project, microbiological analyses were conducted on samples of greywater (n=32), tap water (n=20) and the hydroponic solution (n=18). The averaged results are presented in Table 3.2. No Ascaris ova, Salmonella, Shigella or somatic coliphage were detected in any of the water samples and E. coli, Enterococcus and Staphylococcus were only detected in the greywater and were present at a statistically higher level than for hydroponic solution or tap water (p≤0.001). Total coliforms were significantly higher in the greywater than in either of the other two water types used for irrigation (p≤0.001). In line with normal practice at eThekwini laboratory, a log conversion of actual bacteriological counts was used in microbiological analysis. In all cases where no microorganism was detected, the minimum detection level of 1 colony forming unit (cfu) per unit volume or mass was used. This allowed a log value of zero to be used in further computations.
Nine samples of each of the water types were subjected to chemical analysis and the data are presented in Table 3.2. The conductivity of the greywater was significantly lower (p≤0.05) than that of the hydroponic solution, indicating that the level of salts in the hydroponic solution was higher than in the greywater. The level of ammonia in the greywater was not significantly different (p≤0.05) from that in the hydroponic solution and both were significantly higher than that in the tap water (p≤0.05) where the level was extremely low. The chemical oxygen demand (COD) of the greywater was high and approximately 30% was readily biodegradable as can be seen from the results for the biological oxygen demand (BOD) and chemical oxygen demand (COD) presented in Table 3.3. This could have been as a result of kitchen and bathroom washings or organic contamination from cleansing products in use by the households.
Table 3.2: Results from physico-chemical and microbial analyses performed on greywater, hydroponic solution or tap-water respectively. Mean, maximum, minimum and standard deviations are provided for all parameters. E. coli, Enterococcus and Staphylococcus were only detected in the greywater and were present at a statistically higher level than for hydroponic solution or tap water (p≤0.001). Total coliforms were significantly higher in the greywater than in either of the other two water types used for irrigation (p≤0.001). The conductivity of the greywater was significantly lower (p≤0.05) than that of the hydroponic solution. The level of ammonia in the greywater was not significantly different (p≤0.05) from that in the hydroponic solution and both were significantly higher than that in the tap water (p≤0.05). The significance of the difference between the Chemical Oxygen (COD) demand in greywater and the other two water treatments could not be tested as no COD was detected in the latter.
Alkalinity (n=9) Ammonia (NH3) (n=9) Chemical oxygen demand (n=9) Conductivity (n=9) Ascaris lumbricoides (n=32,20,18 respectively) E. coli (n=32,20,18 respectively) Enterococcus (n=26, 20, 18 respectively) Staphylococcus (n=26, 20,18 respectively) Total coliforms (n=32,20,18 respectively) Somatic coliphage (n=32,20,18 respectively)
Total Viable
mg/L mg/L mg/L mS/m Ova / g Log10 (cfu/100 mL) Greywater
Mean 179.03 19.76 584.30 69.82 0 0 4.76 0.41 1.16 6.74 0
Max 706 157 1120 230 0 0 9.00 5.34 7.53 11.11 0
Min 0 0.5 39 13 0 0 0 0 0 0 0
Std
Dev 161.2 37.08 342.76 56.16 2.95 1.23 2.07 2.12 -
Hydroponic solution
Mean 29 32.5 0 223 0 0 0 0 0.04 0.84 0
Max 29 33 0 223 0 0 0 0 0.84 4.08 0
Min 29 32 0 223 0 0 0 0 0 0 0
Std
Dev - 0.70 - - - 0.19 1.12 -
Tap water
Mean 66 <0.5 0 30 0 0 0 0 0 0.55 0
Max 66 <0.5 0 30 0 0 0 0 0 1.81 0
Min 66 <0.5 0 30 0 0 0 0 0 0 0
Std
Dev - - - 0.59 -
Table 3.3: Statistical values for the measurement of biological oxygen demand (BOD) and chemical oxygen demand (COD) in greywater. Approximately 30% of the oxygen
demand could be attributed to Biological Oxygen Demand (BOD) which could be as a result of washings from the kitchen and bathroom or organic contamination from cleansing products in use by the households. Levels for both BOD and COD were significantly higher than for either hydroponic solution or tap water when tested at the p=0.05 level
BOD mg/L COD mg/L
Mean 180.625 Mean 584.303
Standard Deviation 84.65371 Standard Deviation 342.7572
Minimum 40 Minimum 39
Maximum 320 Maximum 1120