Ammonia inactivation of Ascaris ova in ecological compost by using urine and ash

Abstract

Viable ova of Ascaris lumbricoides, an indicator organism for pathogens, are frequently found in feces-derived compost produced from ecological toilets, demonstrating that threshold levels of time, temperature, pH, and moisture content for pathogen inactivation are not routinely met. Previous studies have determined that NH(3) has ovicidal properties for pathogens, including Ascaris ova. This research attempted to achieve Ascaris inactivation via NH(3) under environmental conditions commonly found in ecological toilets and using materials universally available in an ecological sanitation setting, including compost (feces and sawdust), urine, and ash. Compost mixed with stored urine and ash produced the most rapid inactivation, with significant inactivation observed after 2 weeks and with a time to 99% ovum inactivation (T(99)) of 8 weeks. Compost mixed with fresh urine and ash achieved a T(99) of 15 weeks, after a 4-week lag phase. Both matrices had relatively high total-ammonia concentrations and pH values of >9.24 (pK(a) of ammonia). In compost mixed with ash only, and in compost mixed with fresh urine only, inactivation was observed after an 11-week lag phase. These matrices contained NH(3) concentrations of 164 to 173 and 102 to 277 mg/liter, respectively, when inactivation occurred, which was below the previously hypothesized threshold for inactivation (280 mg/liter), suggesting that a lower threshold NH(3) concentration may be possible with a longer contact time. Other significant results include the hydrolysis of urea to ammonia between pH values of 10.4 and 11.6, above the literature threshold pH of 10.

Fig 1

Ascaris suum viability in six ecological compost matrices during 16 weeks of experimental observation. Each data point represents the average value from triplicate measurements. The matrices consist of compost and the following additional materials: matrix 1, DI water (■); matrix 2, DI water and ash (□); matrix 3, stored urine (▲); matrix 4, stored urine and ash (△); matrix 5, fresh urine (●); matrix 6, fresh urine and ash (○). Open symbols and dashed lines represent matrices with ash. The pooled standard deviations of the triplicate measurements are 2.1 for matrix 1, 3.7 for matrix 2, 3.3 for matrix 3, 2.2 for matrix 4, 14.2 for matrix 5. and 6.6 for matrix 6.

Fig 2

Ammonia gas (NH₃) concentrations in six ecological compost matrices during 16 weeks of experimental observation. Each data point represents the average value from triplicate measurements. The matrices consist of compost and the following additional materials: matrix 1, DI water (■); matrix 2, DI water and ash (□); matrix 3, stored urine (▲); matrix 4, stored urine and ash (△); matrix 5, fresh urine (●); matrix 6, fresh urine and ash (○). Open symbols and dashed lines represent matrices with ash. The pooled standard deviations of the triplicate measurements are 0.1 for matrix 1, 14.3 for matrix 2, 19.0 for matrix 3, 201.2 for matrix 4, 224.6 for matrix 5, and 77.5 for matrix 6.

Fig 3

pH values in six ecological compost matrices during 16 weeks of experimental observation. Each data point represents the average value from triplicate measurements. The matrices consist of compost and the following additional materials: matrix 1, DI water (■); matrix 2, DI water and ash (□); matrix 3, stored urine (▲); matrix 4, stored urine and ash (△); matrix 5, fresh urine (●); matrix 6, fresh urine and ash (○). Open symbols and dashed lines represent matrices with ash. The pooled standard deviations of the triplicate measurements are 0.0 for matrix 1, 0.0 for matrix 2, 0.1 for matrix 3, 0.0 for matrix 4, 0.1 for matrix 5, and 0.0 for matrix 6.

Fig 4

Total-ammonia concentrations in six ecological compost matrices during 16 weeks of experimental observation. Each data point is the average value from triplicate measurements. The matrices consist of compost and the following additional materials: matrix 1,= DI water (■); matrix 2, DI water and ash (□); matrix 3, stored urine (▲); matrix 4, stored urine and ash (△); matrix 5, fresh urine (●); matrix 6, fresh urine and ash (○). Open symbols and dashed lines represent matrices with ash. The pooled standard deviations of the triplicate measurements are 3.2 for matrix 1, 14.3 for matrix 2, 291.6 for matrix 3, 201.7 for matrix 4, 714.5 for matrix 5, and 78.1 for matrix 6.