Co-composting of fecal matter in Mongolia using two different technologies

Inadequate sanitation is a global challenge that affects people's daily lives and standards of living, most especially in developing countries across the globe. At the end of 2011, about 2.5 billion (10⁹), i.e. approximately 40% of the world population, was still lacking basic sanitation and had no access to improved sanitation facilities (WHO/UNICEF Joint Monitoring Programme (JMP) for Water Supply and Sanitation 2013). The lack of inadequate water supply and basic sanitation is the most vital issue concerning sustainable development, most especially in developing countries (Sigel et al. 2012).

This research was conducted in Ulaanbaatar (UB), the capital city of Mongolia, which is known to be the coldest capital city in the world. Mongolia is the most sparsely populated country in the world with a population of 2.74 million inhabitants (National Statistic Office of Mongolia 2010). The majority of the people living in Ger areas (60% of UB's population) are served with poorly constructed simple pit latrines as means of excreta disposal (Sigel et al. 2012). The usage of simple pit latrine leads to surface and groundwater contamination, which has caused a severe health hazard, most especially Hepatitis A, among the people of the area (Basandorj & Altanzagas 2007). The epidemic of Hepatitis A has covered up to 92% of the total related Hepatitis diseases in Mongolia, which is seven times more than the international average (World Bank 2004).

The composting process as a sustainable sanitation approach has been widely used in managing and treating human excreta, especially in developing countries, due to its accessibility, low environmental pollution, low cost of operation and maintenance as well as significant pathogens reduction (Esrey et al. 2001). It is a controlled biological process that involves aerobic microorganisms in breaking down and converting organic material into a biologically stable product called ‘compost’ (Said-Pullicino et al. 2007). Co-composting of excreta with organic matter (OM) used as bulking agents has been carried out by different researchers. However, little research has been conducted on the effect of technologies and different recipes used in fecal composting for sustainability.

The aim of this research work was to sustainably solve the sanitation problems faced by the people in Ger areas, by determining the feasibility of co-composting fecal matter with different recipes via composting facility (CF) and greenhouse (GH) technology.

The composting activities took place at a particular site that is located at the outskirts of UB. Two facilities, CF and GH, were constructed on the site by Action Contre la Faim (ACF) Mongolia. Figure 1(a) and 1(b) shows the schematic diagrams of the CF, with the arrangement of four bins that represent the first four trials as shown in Figure 1(b), while the fifth trial was later conducted in the GH facility.

The fecal matter used in these trials was collected in a container beneath the toilet's superstructure and manually emptied at 3-month intervals. The co-composting materials (feedstock) used as carbon sources were wood chips, sawdust, straw and food waste. Preliminary activities such as sorting, shredding (1–5 cm) and separations were conducted before mixing with fecal matter. The C/N ratio of each trial was approximately 30:1.

The following analytical parameters for effective composting were conducted in Mongolia State University of Agriculture. Moisture content (MC), total solid and total carbon (TC) were determined before mixing as shown in Table 1 in accordance with American Public Health Association standard methods (Greenberg et al. 1992). pH (1:10 w/v compost:water extract) was measured with a hand-held pH meter (HANNA HI9125N, Italy), while total nitrogen (TN) was analyzed by the Kjeldahl method (Novozamsky et al. 1983). The process stability on CO₂/O₂ was monitored by biogas analyzer (Geotech-Biogas 5000, UK) to check the aeration level in the piles.

Trials (1–4) were conducted in the CF, while Trial 5 was conducted in the GH. The physicochemical properties of the recipes in the five trials are given in Table 2.

Four 660 L of waste bins were used as reactors as shown in Figure 1(b). Each bin was fully covered with 150 mm thick Styrofoam to minimize the heat lost. On top of each bin, a ventilation pipe of 10 cm diameter discharges the toxic gases and odor out of the room. The perforated boards for carrier plates were placed 10 cm from the base of the reactors to support the composting bed and ensure uniform aeration. The compost pile temperatures were monitored hourly with data loggers that were placed diagonally inside the bins to determine the temperature at the top, core and bottom of the piles.

Ventilation systems across the piles were intermittently supplied and maintained (30 minutes off and 30 minutes on with the help of a stop clock) at 0.5 L kg/minutes (dm) from the bottom of each reactor. Turning was manual with pitchfork on a weekly basis to allow every part of the pile to be exposed to heat for pathogens destruction.

The objective of the second type of trial was to define the feasibility of the composting process using GH technology. Passive aeration was adopted to distribute ambient air evenly across the pile, which diffuses through the bored blocks and slanted planks that were placed against the wall. The composting pile was stacked to a volume of about 1.2 m³, which was 80% of the inner volume of the slot. For this trial, a data logger was placed horizontally at the center of the pile and the average temperatures were recorded. The turning was conducted fortnightly, not only to reduce the stress of the labor but also to minimize ammonia volatilization.

Temperature variations against composting time are shown in Figure 2(a)–2(e). The ambient temperature ranged from 18–24 °C, which shows no significant influence on the process. As composting began, the thermophilic phase (>50 °C) was reached within 3 days for Trial 1, 2 and 3, as shown in Figure 2(a)–2(c), respectively. This could be understood to be a result of the co-substrates used in the first three trials, i.e. woodchips or straw, which provided spaces within the piles for evenly distributed aeration. The rapid increase in temperature also indicated that the available OM and nitrogenous compound decomposed gradually and were utilized by microorganisms. Only Trial 4 reached the stage (>50 °C) after a week of composting as shown in Figure 2(d).

The rapid increase in temperature corresponds to the observation made by Haug (1993) that the thermophilic phase (>45 °C) must be reached within hours or days in a well monitored composting process. The maximum temperatures reached in Figure 2(a)–2(d) were 60.6, 63.0, 60.1 and 64.2 °C, respectively. Also, the periods of temperatures that were maintained above 55 °C were 11, 15, 10 and 16 days as shown in Figure 2(a)–2(d), respectively. Furthermore, in the case of Trial 4, which took 1 week to reach the thermophilic phase, the delay was probably caused as a result of there being no larger particles to create more space for adequate aeration, and also, the fact that the sawdust used was from pine trees that contain high acidity level and lignin content, which are not easily digestible by the microorganisms. After the active phase of the process, microbial activities decreased as a result of the decrease in OM and thereby led to a decrease in temperatures to ambient on 36th day.

Turning ensures pathogens die off throughout the entire mass of compost. For every weekly turning, there was a slight increase in the temperatures across all the piles. If only the center of the piles reach thermophilic phase, turning becomes imperative to ensure all parts of the piles are well sanitized. In accordance with most international standards on compost guidelines, all of the four trials met the sanitation requirements, such as the Canada standard (55 °C for 3 days, In-vessel; 3 days, aerated static pile; 15 days, Windrow) (CCME 2005), United States standard (55 °C for 5 days, In-vessel; 15 days, Windrow) (U.S. Environmental Protection Agency 1993) and WHO (50 °C ≥ 1 week) (WHO 2006).

In this trial, sensors were placed horizontally at the center of the pile and temperatures were logged as shown in Figure 2(e). The ambient temperature inside the GH dropped from 39 to 4 °C as there was a corresponding drop of outside temperature from 15 to −20 °C, respectively, at the end of the trial. At the fourth day of the composting process, the temperature reached 70 °C; this high temperature could either be influenced by the ambient temperature of the GH or the easily digestible carbon source that was added, i.e. food waste. Also, such a high temperature within a few days could be a result of monitored pH and moisture content; arrangement of the pile's structure for adequate aeration and available nutrients during the process. The temperatures above 55 and 65 °C were maintained for 2 weeks and 8 days, respectively, which satisfies all the sanitation requirements including the German standard. After 2 weeks of composting with declining temperature, the pile was turned to ensure other parts were exposed to high temperature. After turning, the temperature rose back to 65 °C and gradually fell as the outside temperature dropped below 0 °C. The sufficient high temperatures obtained in this trial were in line with observations made by Germer et al. (2010) that mixing of food waste into feces provides easily digestible carbon to the microbes and thus maintained a high temperature for a longer period of time.

pH is one of the chemical parameters that affects the composting process (Haug 1993), i.e. it affects the growth response of microbial activities. The microbial decomposition began after the piles were formed, and a gradual increase in temperature was observed. At the initial stage of the process, pH dropped from 6.8 ± 0.5 to 5.0 across all the trials, as shown in Figure 2(f). This was due to the bio-oxidative action of the microorganisms, i.e. formation of volatile fatty acids and carbonic acid, which could lower the pH of the piles, thereby increasing the growth of fungi and degradation of lignocelluloses substance.

When the acidification phase was over and the intermediate metabolites were mineralized, i.e. degradation of organic acid compounds, pH tended to increase with increasing temperature during the thermophilic phase, which led to ammonia volatilization. In all the trials, the measured pH values across the piles ranged from 5.0 to 9.2. High ammonia volatilization was observed in all the trials, which could be a result of the high concentration of nitrogen contained in Mongolians' urine, weekly turning of the piles, or mineralization of organic nitrogen. However, as observed by Haug (1993), for optimum decomposition and mineralization by microbial activities, pH should be within the range of 5.5–8.5. Therefore, since on the last day of the process the pH values ranged from 6.9 to 7.7, this showed that all the pH values at the end of the experiments were within the suggested optimum range.

On a yearly basis, more than 200 million tons of human excreta are indiscriminately discharged into the environment without proper collection and treatment (UNDP 2008). According to research findings, if these tons of fecal matter are properly collected, 22% of the global phosphorus demand could be derived from fecal matter (Mihelcic et al. 2011), while 33% of the nitrogen could be recovered (WHO 2006).

Fecal compost is applied as an organic amendment to improve the physical, chemical and biological properties of the soil. The perception of fecal matter application is gradually changing, especially in developing countries such as China and some other Asian countries (Mackie Jensen et al. 2008). However, applying fecal compost on soil to boost food production is still unacceptable among some residents of the studied areas (ACF document not published). This is not because some people do not realize the potential in fecal compost but because having a quality assurance on the final products (i.e. free from pathogens) is a major concern. Consequently, this has narrowed the acceptance and willingness-to-pay for the compost, and hence it hinders its marketability.

These trials focused on how to solve peri-urban sanitation problems holistically in a sustainable way. To maintain high temperature, there is need for an easily digestible carbon source like food waste which can maintain the thermophilic phase of the process for a longer period. The GH was used not only to replace the CF based on economic aspects but also to harness the natural heat generated inside the structure, and to extend the period of the composting cycle (twice) within a year. The temperature increased up to 70 °C in GH as a result of the technology used, the easily digestible carbon that was added, and the arrangement of the slot for proper aeration across the pile.

There is a need for strong social marketing in order to break the barrier of sociocultural beliefs and taboos that are associated with fecal compost and urine application. People need to change their perceptions toward fecal matter; it should be viewed as a valuable resource, not as waste to be discarded.

These research findings were conducted under a PhD research project that was fully financed and supported by Action Contre la Faim (ACF) France, in collaboration with the University of Science and Technology Beijing (USTB), China.