Assessment of Alkali Modified Coal Fly Ash As a Potential Pit Latrine Additive for Elimination of Pathogens Using Synthetic Faeces As Proxy

Abstract

In this study, alkali modified coal fly ash (MFA) and unmodified coal fly ash (unMFA) were applied, as pit latrine additives to eliminate faecal coliforms from synthetic faeces (SF), which were used as a proxy for real pit latrine waste. The X-ray diffractogram spectrum showed that mullite and quartz were converted into hydroxysilicate. Two separate studies were run over a period of seven weeks. The first study had the treatment combinations of SF: MFA, SF: unMFA, SF: MFA: synthetic greywater (SGW), SF: unMFA: SGW, SF: MFA: synthetic urine (SU), SF: unMFA: SU and SF (as a control) while the second study consisted of the combinations of SF: MFA, SF: unMFA, SF: MFA: lime (6g), SF: unMFA: lime (12g), SF: MFA: lime (24g), SF: unMFA: lime (50g) respectively. The pH in both studies ranged between 7.07 and 12.38. The average initial concentrations of faecal coliforms from each of the experimental treatments ranged from 9.96 x 106 to 1.06 x107 ± 2 x106 cfu/g of dry weight on the first day of the experiment. However, they were removed completely after 7 days with no regrowth for a period of 7 weeks indicating removal of faecal coliforms to level below the detection limits of the enumeration technique used. On the first study on the fourth week, faecal coliforms reappeared in the pit latrine treatment SF: MFA: SU (5.60 x 105 ± 8.66 x 105 cfu/g dry weight) followed by SF: MFA (1.78 x 105 ± 2.89 x 105 cfu/g dry weight) but thereafter could not be detected (detection limit was 545 cfu/ g dry weight of SF) for the remainder of the study. The concentration of chemical oxygen demand (COD), ammonium, phosphate ranged between 6.35 x102 ± 1.26x102 – 22.11 x102, 0.116±0.091 – 21.38 x102 ± 1.77x102 and 1.35x102 ±0.348 – 31.18x102 ±0.348 mg/g of dry weight respectively while nitrate concentration was zero. In conclusion, both studies showed that MFA and unMFA can be used as pit latrine additives for the removal of pathogenic microorganisms, however, the contents of the pit latrine might have an influence on how fast and effective the additive might be as shown in the first study where SU or SGW were introduced.