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.

Disaster Risk Management, Ventilated Improved Pit Latrines, and Sanitation Challenges in South Africa

“…Similar observations were made for the metals such as lead, nickel, and cadmium. These findings indicate that mixing fly ash into the VIP faecal sludge would, over the treatment periods suggested by Madikizela et al [94], lead to a limited mobility of heavy metals from fly ash into the surrounding faecal sludge or that soil/groundwater could be limited. This indicates that the fly ash treatment could pose a viable option to treat the VIP faecal sludge.…”

“…In 2019, Collings et al reported on the application of the untreated fly ash in the elimination of 92% of the initial concentration of faecal coliforms from the synthetic faecal material under the ambient conditions and within 3 weeks of incubation at ambient temperatures [93]. Modification of the coal fly with sodium hydroxide resulted in the production of an additive that has been shown to decrease the concentration of faecal coliforms below 545 colony-forming units per gram of synthetic faecal sludge [94]. The period of stabilisation ranged from 2 to 6 weeks based on the pit additive used.…”

“…The period of stabilisation ranged from 2 to 6 weeks based on the pit additive used. Six weeks was achieved as a stabilisation period for an additive of 120 g of fly ash into 200 g of synthetic faeces material, while the period stabilisation was shortened to 2 weeks, if 50 g of lime was added to the fly ash [94]. The use of such additives would be possible to apply even if the moisture content of the pit sludge reaches 80%, as the coal-fly ash has been shown to sterilize the greywater in a modified mulch tower-type reactor [95].…”

“…Pretreatment of the coal-fly ash with alkali under elevated temperatures could make the surfaces of the fly ash particle more prone to function as sorption uptake sites and sites of precipitation [94,103]. Therefore, to investigate the chemical composition of the coal-fly ash from South Africa before and after alkaline hydrothermal treatment, the coalfly ash of Madikizela et al was examined [94]. More Information can be found in the Supplementary information.…”

“…This would require personal protective equipment, which is equivalent to working with the microbiological laboratory with biosafety level 2 (see page 24 in reference [112]). The mixing of the modified fly ash into the bulk of the VIP faecal sludge would have to be accomplished for adequate treatment [93,94].…”