**3. Results and discussion**

The temperature variation for 1 week was measured during February, 2015 in the posttreatment unit with the aid of ThermoManager sensors in Ouagadougou, Burkina Faso. The sensors recorded temperature data every five mins during the week. **Figure 3** shows the temperature pattern in the post-treatment unit. The maximum and minimum temperatures recorded from the bottom were 51.0 and 10.5°C. The middle recorded 50.0 and 9.5°C for maximum and minimum temperatures while the top recorded maximum of 78.5°C and a minimum of 6.5°C. Obviously, the lower temperatures were recorded in the night and high temperature during the day.

The estimated changes in concentration of *Ascaris* for the scenarios S1–4 are shown in **Figure 4**. The concentrations declined from the initial value of 336 eggs/g dry-compost. S1 with high temperature gave high decline rate of the concentration due to high inactivation rate coefficient. Each scenario showed high and low reduction rates, because high temperature at day time and low temperature at night respectively. All scenarios for *Ascaris* obtained reduction of eggs in 295 h and the differences of the temperature resulted in the differences in concentrations. The changes in concentration of norovirus with elapsed of time under all scenarios

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are shown in **Figure 5**. The concentration declined from the initial of 6.72 × 10<sup>8</sup>

**Figure 5.** Change in norovirus concentration for post-treatment.

**Figure 6.** Change in *Salmonella* concentration.

**Figure 3.** Temperature distribution assumed in the risk estimation.

**Figure 4.** Change in *Ascaris* eggs concentration for the post-treatment.

of eggs in 295 h and the differences of the temperature resulted in the differences in concentrations. The changes in concentration of norovirus with elapsed of time under all scenarios are shown in **Figure 5**. The concentration declined from the initial of 6.72 × 10<sup>8</sup> copies/g-dry

**Figure 5.** Change in norovirus concentration for post-treatment.

temperature gave high decline rate of the concentration due to high inactivation rate coefficient. Each scenario showed high and low reduction rates, because high temperature at day time and low temperature at night respectively. All scenarios for *Ascaris* obtained reduction

**Figure 4.** Change in *Ascaris* eggs concentration for the post-treatment.

**Figure 3.** Temperature distribution assumed in the risk estimation.

112 Agricultural Waste and Residues

**Figure 6.** Change in *Salmonella* concentration.

compost. Higher temperature condition also gives higher decline rate. The reduction rate of norovirus concentration had difference among four scenarios like the *Ascaris* case. The concentration varied due to the varied temperature especially at night. As expected, the day time recorded higher temperatures and lower temperatures were recorded at night. All the scenarios achieved safe level at 845 h.

unit. This is to ensure that the unit is not too deep to reduce the efficiency of the unit. The unit is considered as a batch reactor (BR) where concentration of the compost would change with time. The expected concentration can be obtained by adjusting the reaction time. The temperature distributions in S1 recorded a shorter time than the other scenarios. The treatment time can be reduced if the heating process of the unit is improved. During the day, there is a sufficient increase in temperature, but it suddenly decreases towards the evening and at the nights. This phenomenon causes sufficient inactivation by the balance of the high inactivation rate at high temperature and the low inactivation at low temperature. To reduce treatment time, one needs to improve the post-treatment unit increasing the maximum temperature and

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The required times to reach the safe level for norovirus for the scenarios S1–4 were 264, 362.5, 554 and 845 h respectively. And also the required times for *Salmonella* were respectively 90.5, 143, 356.5 and 969.5 h respectively. Comparing *Ascaris*, norovirus and *Salmonella*, *Salmonella* requires more time at lower temperatures than *Ascaris* and norovirus to reach safe level of 10−4 per person per year (pppy) [16]. This is probably due to the fact that lower temperature are favourable conditions for bacteria. Therefore, *Salmonella* is more important indicator for the design of the unit, even though *Ascaris* eggs have possibility to survive several months in a

Risk assessments for post-treatment of compost have received very little documentation. Seidu et al. [17] reported increased levels of *Ascaris* and rotavirus infection for farmers due to accidental ingestion of contaminated soils. The estimated median risk values for farmers were 0.99 and 7.2 × 10−2 pppy for Ascariasis and rotavirus. The study indicated that the elevated hazard posed by the soils on the farm could be attributed to the persistence of *Ascaris*

keeping temperature during the night.

**Figure 8.** Norovirus annual infection risk with post-treatment.

soil system [17].

The change in concentration of *Salmonella* with elapse time under all scenarios are shown in **Figure 6**. The concentration declined from the initial of 6.72 × 10<sup>7</sup> CFU/g dry-compost. Higher temperature condition also gave higher decline rate. The reduction rate of *Salmonella* concentration had difference among four scenarios like the *Ascaris* and norovirus case. All scenarios achieved safe level at 969.5 h.

The 95-percentile annual risk of *Ascaris,* norovirus and *Salmonella* infections for the all scenarios are shown in **Figures 7**–**9**. The risk of the pathogens are almost 1 at the initial for all scenarios. This means the people who use the compost would be heavily polluted by the pathogens. They would be infected if the composting reactor fails to reduce the pathogen concentration and also if they do not apply the post-treatment. Schönning et al. [15] also reported a 95-percentile risk of rotavirus and *Ascaris* for 0 months' storage in a worst case as 1. The results show the risks for the *Ascaris* for S1 and the low temperatures as S2–4 reduced concentrations and reached a safe level at 97.5, 138, 190 and 295 h respectively.

The volume of the composting reactor is 100 L. Taking account of the temperature distribution with depth of the unit, the top and bottom temperature would achieve a safe level before the middle because that is the lowest temperature zone in the post-treatment unit. It should be noted that about 25% of the volume of the composting reactor was used for the design of the

**Figure 7.** Ascaris annual infection risk associated with post-treatment.

unit. This is to ensure that the unit is not too deep to reduce the efficiency of the unit. The unit is considered as a batch reactor (BR) where concentration of the compost would change with time. The expected concentration can be obtained by adjusting the reaction time. The temperature distributions in S1 recorded a shorter time than the other scenarios. The treatment time can be reduced if the heating process of the unit is improved. During the day, there is a sufficient increase in temperature, but it suddenly decreases towards the evening and at the nights. This phenomenon causes sufficient inactivation by the balance of the high inactivation rate at high temperature and the low inactivation at low temperature. To reduce treatment time, one needs to improve the post-treatment unit increasing the maximum temperature and keeping temperature during the night.

compost. Higher temperature condition also gives higher decline rate. The reduction rate of norovirus concentration had difference among four scenarios like the *Ascaris* case. The concentration varied due to the varied temperature especially at night. As expected, the day time recorded higher temperatures and lower temperatures were recorded at night. All the

The change in concentration of *Salmonella* with elapse time under all scenarios are shown in **Figure 6**. The concentration declined from the initial of 6.72 × 10<sup>7</sup> CFU/g dry-compost. Higher temperature condition also gave higher decline rate. The reduction rate of *Salmonella* concentration had difference among four scenarios like the *Ascaris* and norovirus case. All scenarios

The 95-percentile annual risk of *Ascaris,* norovirus and *Salmonella* infections for the all scenarios are shown in **Figures 7**–**9**. The risk of the pathogens are almost 1 at the initial for all scenarios. This means the people who use the compost would be heavily polluted by the pathogens. They would be infected if the composting reactor fails to reduce the pathogen concentration and also if they do not apply the post-treatment. Schönning et al. [15] also reported a 95-percentile risk of rotavirus and *Ascaris* for 0 months' storage in a worst case as 1. The results show the risks for the *Ascaris* for S1 and the low temperatures as S2–4 reduced concen-

The volume of the composting reactor is 100 L. Taking account of the temperature distribution with depth of the unit, the top and bottom temperature would achieve a safe level before the middle because that is the lowest temperature zone in the post-treatment unit. It should be noted that about 25% of the volume of the composting reactor was used for the design of the

trations and reached a safe level at 97.5, 138, 190 and 295 h respectively.

**Figure 7.** Ascaris annual infection risk associated with post-treatment.

scenarios achieved safe level at 845 h.

achieved safe level at 969.5 h.

114 Agricultural Waste and Residues

The required times to reach the safe level for norovirus for the scenarios S1–4 were 264, 362.5, 554 and 845 h respectively. And also the required times for *Salmonella* were respectively 90.5, 143, 356.5 and 969.5 h respectively. Comparing *Ascaris*, norovirus and *Salmonella*, *Salmonella* requires more time at lower temperatures than *Ascaris* and norovirus to reach safe level of 10−4 per person per year (pppy) [16]. This is probably due to the fact that lower temperature are favourable conditions for bacteria. Therefore, *Salmonella* is more important indicator for the design of the unit, even though *Ascaris* eggs have possibility to survive several months in a soil system [17].

Risk assessments for post-treatment of compost have received very little documentation. Seidu et al. [17] reported increased levels of *Ascaris* and rotavirus infection for farmers due to accidental ingestion of contaminated soils. The estimated median risk values for farmers were 0.99 and 7.2 × 10−2 pppy for Ascariasis and rotavirus. The study indicated that the elevated hazard posed by the soils on the farm could be attributed to the persistence of *Ascaris*

**Figure 8.** Norovirus annual infection risk with post-treatment.

78°C (maximum temperature during the day) − 6.5°C (min temperature during the night) and approximately time of 295 h to achieve the safe level of 10−4 pppy. For norovirus, posttreatment requires temperature from 78 to 6.5° and approximately time of 845 h for all the scenarios to achieve a safe level. *Salmonella* requires temperature range from 78 to 6.5°C and time of 969.5 h, for all scenarios to reach a safe level. The evaluation of the performance of post-treatment unit for risk assessment of the targeted pathogens has been achieved with the

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This study was carried out with the grant project of Science and Technology Research Partnership for Sustainable Development (SATREPS) supported by JST (Japan Science and

[1] Teunis PF, Moe CL, Liu P. Norwalk virus: How infectious is it? Journal of Medical

[2] Berger S. Echinococcosis: Global Status. GIDEON Informatics Inc.; 2015. Available from: https://books.google.bf/books?id=c2QBwAAQBAJ&pg=PA49&lpg=PA49&dq=Prevalen

[3] Haas CN, Rose JB, Gerba CP. Quantitative Microbial Risk Assessment. New York: John

[4] Andreev S, Samoil V. Solar thermal sanitisation of human faeces—An affordable solution for ensuring sustainability of EcoSan initiative. 2009. http://www2.gtz.de/Dokumente/oe44/ecosan/en-solar-thermal-sanitisation-of-human-faeces.pdf [Accessed: 18

[5] Darimani HS, Ito R, Sou M, Funamizu N, Yacouba H, Maiga AH. Design of posttreatment unit for compost from a composting toilet with microbial risk assessment.

ce+of+salmonella+in+Burkina+Faso&source [Accessed: 12 June, 2014]

Technology agency) and JICA (Japan International Cooperation Agency).

1 School of Engineering, Wa Polytechnic, Wa, Upper West Region, Ghana 2 Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan

\* and Ryusei Ito2

\*Address all correspondence to: hamidnid2012@gmail.com

developed mathematical model.

**Funding**

**Author details**

**References**

Hamidatu S. Darimani<sup>1</sup>

Virology. 2008;**80**:1468-1476

Wiley and Sons; 1999

February, 2014]

**Figure 9.** *Salmonella* annual infection risk associated with post-treatment.

in the soils. This implies that compost must be treated properly before reuse as fertiliser so as not to pose even greater risk in the soils. However, in semi-arid regions where the compost is expected to be used, inactivation of *Ascaris* occurs in soils rapidly [9] which indicates that post-treatment in these regions could be feasible. The results of this study indicate that high temperature with prolonged treatment time could reduce the hazard considerably. Mara et al. [14] reported risk of fieldworkers' involuntary ingestion of 100 mg of waste-water contaminated soils. The median of norovirus infection risk for an ingestion of 100–1000 mg, 10–100 mg, 1–10 mg of contaminated soil were 0.98, 0.32, and 3.7 × 10−2 pppy respectively. The study also reported the median *Ascaris* infection risk for ingestion of 100–1000 mg, 10–100 mg, and 1–10 mg of contaminated soils as 0.14, 1.5 × 10−2, and 1.5 × 10−3 pppy respectively. In this study, the risk associated with the exposure of *Salmonella* at lower temperature was estimated to be the highest, thus, this level of pathogen reduction will provide sufficient protection against *Ascaris* and norovirus infections.
