**2.1. Post-treatment unit**

People would collect the compost from the rural model of composting toilet with urine diversion (**Figure 1**) in the pilot families and used it in their gardens as fertiliser. Application of the post-treatment would be achieved by spreading the compost evenly in the steel box as shown in **Figure 2**, and leaving it under the sunshine. The steel box was fabricated with a length of 60 cm, a width of 40 cm, and a depth of 10 cm. The total volume of the box is 24 L. The steel box has steel septa which facilitate deep penetration of heat to compost. The steel box is painted black in colour to aid in the absorption of heat. The steel box does not have a solar concentrator [4, 5]. The temperature distribution of the compost in the box was measured at 3 positions which were 1, 5, and 10 cm from the surface.

middle and bottom at 1, 5 and 10 cm depth from the top surface, respectively. A basic scenario was set at actual temperature in the steel box (S1) as a post-treatment for the assessment. For investigating the effect of temperature, 3 temperature levels, such as −5°C lower temperature as S2, −10°C lower temperature as S3 and −15°C lower temperature as S4 derived from the temperature measured in the steel box, were considered in this simulation, because the temperature varied by weather conditions. For the calculation of concentration in the compost, the inactivation rates coefficient from the previous measurement were used [6]. The details of

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**Figure 2.** A proposed compost solar sanitisation installation that could reduce the heat loss [4].

the ingestion model are as follows:

**Figure 1.** Arrangement of the composting toilet.

#### *2.1.1. Scenarios for reuse of compost*

During the utilisation of the compost, people may accidentally ingest compost with the pathogens orally. The people exposed to the pathogens would have diseases with a probability estimated by risk assessment. The temperature distribution was considered at 3 positions as top, Post-Treatment and Microbial Risk Assessment of Compost for Food Production http://dx.doi.org/10.5772/intechopen.78216 109

**Figure 1.** Arrangement of the composting toilet.

compost after withdrawal from the rural model of composting toilet after 3 months of operation. Therefore, post-treatment of the collected compost is required to minimise the health risk when recycling the faeces as fertiliser on farmland. For the inactivation of pathogens, several methods of treatments are proposed, including heating, drying, chemical treatments, treatment by worms, long storage times, etc. In low income countries some people cannot pay materials for post-treatment, however, they have abundant solar energy. Therefore; this study proposes a solar disinfection unit to inactivate the pathogens. The operation condition to inactivate pathogens should be designed based on the risk assessment by setting a safe

Norovirus, *Ascaris* eggs and *Salmonella* were selected as reference pathogens in this study. Noroviruses are a major cause of human gastroenteritis, and they are frequently associated with food, water contamination [1] and accidental ingestion. *Ascaris* infections are very common in developing countries. One fertile egg can cause infection of Ascariasis to humans. The carrier state of *Salmonella typhi* is defined as persistent shedding in faeces for greater than 12 months [2]. These enteric infections can be transmitted through the compost from faeces to the human body with pathogenic species. Quantitative microbial risk assessment (QMRA) has been widely used to establish the health risks associated with wastewater reuse in both developed and developing regions under different scenarios. The QMRA-Monte Carlo techniques (QMRA-MC) based on the work of Haas et al. [3] was used to estimate risk in this study.

The objectives of this study are to perform risk assessment for the design of the post-treatment unit by using the QMRA-MC and to determine the treatment time to reach the safe level of

People would collect the compost from the rural model of composting toilet with urine diversion (**Figure 1**) in the pilot families and used it in their gardens as fertiliser. Application of the post-treatment would be achieved by spreading the compost evenly in the steel box as shown in **Figure 2**, and leaving it under the sunshine. The steel box was fabricated with a length of 60 cm, a width of 40 cm, and a depth of 10 cm. The total volume of the box is 24 L. The steel box has steel septa which facilitate deep penetration of heat to compost. The steel box is painted black in colour to aid in the absorption of heat. The steel box does not have a solar concentrator [4, 5]. The temperature distribution of the compost in the box was measured at 3

During the utilisation of the compost, people may accidentally ingest compost with the pathogens orally. The people exposed to the pathogens would have diseases with a probability estimated by risk assessment. The temperature distribution was considered at 3 positions as top,

level of pathogens concentration in the compost after post-treatment.

pathogens in the compost.

108 Agricultural Waste and Residues

**2.1. Post-treatment unit**

**2. Material and methods**

*2.1.1. Scenarios for reuse of compost*

positions which were 1, 5, and 10 cm from the surface.

**Figure 2.** A proposed compost solar sanitisation installation that could reduce the heat loss [4].

middle and bottom at 1, 5 and 10 cm depth from the top surface, respectively. A basic scenario was set at actual temperature in the steel box (S1) as a post-treatment for the assessment. For investigating the effect of temperature, 3 temperature levels, such as −5°C lower temperature as S2, −10°C lower temperature as S3 and −15°C lower temperature as S4 derived from the temperature measured in the steel box, were considered in this simulation, because the temperature varied by weather conditions. For the calculation of concentration in the compost, the inactivation rates coefficient from the previous measurement were used [6]. The details of the ingestion model are as follows:

• To consider the worst case, 50,000 eggs/g in wet faeces is excreted from a heavily infested person [7]. The value of the initial concentration of *Ascaris* eggs was 336 eggs/g-dry compost. This number was estimated by multiplying the number of eggs excreted per gram (50,000 eggs/g) by the 100 g of compost dividing by the bulk density of the compost.

where *PI*

their statistical analyses [14].

The annual probability of infection, *PI*(*A*)

*PI*(*A*)

are 17,700 and 0.23475 respectively.

*2.1.4. Exposure assessment*

*2.1.5. Risk characterisation*

estimated as the infection risk.

**3. Results and discussion**

temperature during the day.

(*d*) is the probability of infection in an individual (infection/event), *d* is the ingested

Post-Treatment and Microbial Risk Assessment of Compost for Food Production

(*d*) (pppy), is given by:

(*d*) ] *<sup>n</sup>* (2)

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(*d*) = 1 − [1 − *PI*

Where *n* is number of events per year to the single *Ascaris* dose (−) [14]. For norovirus, the dose response data set of Teunis et al. [1] was used in place of the β-Poisson equation [14]. The β-Poisson equation was used to assess the dose response of salmonellosis. The *N*50 and *α* used

The human exposure assumed to take place is an event when farmers work on compost. Practically, one egg is enough to cause an infection. Norovirus has an extremely low infec-

The Monte Carlo technique has been used to evaluate the infection risk. The random number is applied for estimation of variables with distributions for simulation of Eqs. (1) and (2). The simulation was repeated 10,000 times [14]. Then, 95 percentile of the probability was

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

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

tious dose [9] and salmonellosis is a public health concern in Burkina Faso [2].

number of *Ascaris* eggs on one occasion (eggs/event), *N*50 is the mean infective dose number of *Ascaris* eggs (eggs), *I* means considerable spice for calculation of probability (−) and *α* is an infectivity constant of *Ascaris* (−). They found the values of *N*50 and *α* to be 859 and 0.104, respectively. Since they were working with epidemiological data on *Ascaris* prevalence rather than conducting human *Ascaris* dose-challenge studies, the value found for *N*50 is not a measure of the actual median *Ascaris* infective dose, but rather an empirical value arising from

