Fecal Sludge Management (FSM) and Digital Transformation (DX)

We are conducting empirical studies on septic tank performance and fecal sludge emptying and treatment in Asian and African cities (Vietnam, Myanmar and Uganda so far). In our previous study in Mandalay, Myanmar, about three-fourths of fecal sludge emptying was done as an informal business, and much of the emptied fecal sludge was illegally dumped, but contrary to expectations, people paid more for informal emptying services than for formal services. However, contrary to the expectation, people paid more for informal pumping than for formal pumping. It was found that people did not prefer informal pumping services because they were cheaper, but because they required prompt emptying service delivery by an informal business as an emergency response is needed when the toilet malfunctioned.

These suggest that unmonitored and unmaintained septic tanks and the resulting sudden demand for emptying is the root problem of informal emptying and succeeding dumping in Mandalay. Our research group aims to establish a system to prevent sudden malfunctioning of septic tanks, avoid informal emptying and dumping, and enable effective operation of septic tanks through easy registration and monitoring of septic tanks using IoT sensors and smartphone-based App, which have been dramatically reduced in price in recent years. Currently, with the support of the Bill & Melinda Gates Foundation, we are developing a device to realize the above, and with the support of UNICEF, we are building a new business model for septic tank management to put this system into practice.

Septic Tank Management and Strategic Sewerage Development

Many cities in low- and middle-income countries have plans for sewerage development, but the development of such systems requires huge investments and technical capabilities. On the other hand, these cities also have some onsite sanitation facilities, but their management conditions are often poor. Improving these facilities, even before the sewerage system is constructed, may contribute to the improvement of urban sanitation. In our research, we will study the possibility of improving the operation of existing urban sanitation facilities in urban areas of low- and middle-income countries as a measure to improve urban sanitation in a provisional and immediate manner to complement sewerage development.

For example, in Hanoi, Vietnam, 89.6% of septic tanks have never been emptied, resulting in poor performance of pollutant removal. It was estimated that proper emptying and improved performance could significantly reduce pollutants, by 72.8% in terms of COD compared to the current condition. In other words, the improvement of septic tank function by regular emptying may realize a provisional and rapid improvement of urban sanitation. The results of this study have led to their use in several policy documents.

Further, even developing sewerage, many sewerage adapted from developed countries fails in operation since wastewater characteristics in low- and middle-income countries are often much different from such countries; the characteristics will change dramatically due to the rapid city development. Our study in Hue, Vietnam showed that sewage of a target drainage area was weaker than the typical weak-strength sewage and that sewage exfiltration ratios of a sewer network reached 65.6%. In the study site, only 23% of the water supplied reached the sewer outlet in a dry season, while 123% flowed in a rainy season. These results demonstrate that exfiltration and infiltration due to a poor sewer network greatly affected the wastewater quantity and quality. Currently, we are seeking a strategic designing procedure of sewerage for Asian and African countries.

Greenhouse gas (GHG) emission from urban sanitation systems

Septic systems are potentially a significant source of greenhouse gases (GHGs). The present study investigated GHGs from the blackwater septic systems that are widely used especially in low- and middle-income countries. Ten blackwater septic tanks in Hanoi, Vietnam, were investigated using the floating chamber method. The average methane and carbon dioxide emission rates measured at the first compartment (65% of total capacity) of the septic tanks were 11.92 and 20.24 g/cap/day, respectively, whereas nitrous oxide emission was negligible. Methane emission rate was significantly correlated with septage oxidation–reduction potential (ORP) (R = −0.67, p = 0.034), chemical oxygen demand mass (R = 0.78, p = 0.007), and biochemical oxygen demand mass (R = 0.78, p = 0.008), whereas it was not significantly correlated with water temperature (R = 0.26, p = 0.47) and dissolved oxygen (R = −0.59, p = 0.075) within the limited range: 30.6–31.7 °C and 0.03–0.34 mg-O2/L. The methane emission rates from septic tanks accumulating septage for >5 years were significantly higher than those at 0–5 years (p = 0.016). These results suggest that lower ORP and higher biodegradable carbon mass, in association with longer septage storage periods are key conditions for methane emissions. To the best of our knowledge, this is the first study to characterize GHG emissions from septic systems. (Environ. Sci. Technol. 2021, 55, 2, 1209–1217)

Currently, we are expanding the boundary of GHG emission estimations to study the GHG emission characteristics across the entire sanitation service chain from toilet/on-site sanitation facilities to emptying/transportation to treatment to disposal/resource recovery. Also, we study how GHG emissions will be affected by future development scenarios of urban wastewater systems in areas where septic tanks are currently widely used.