Suitability of fecal sludge from composting toilets as feedstock for carbonization

Composting toilets provide a promising decentralized alternative to sewer based sanitation systems. However, the valorization of fecal sludge from composting toilets (CFS) by conventional technologies is limited. In this study, we evaluated carbonization as an alternative valorization route for CFS, providing a time-efficient, decentral applicable and hygienically safe treatment option. CFS was carbonized using either pyrolysis (at 500 °C for 1 h) or hydrothermal carbonization (HTC, at 200 °C for 4 h). CFS exhibits promising feedstock characteristics, such as high total solids (TS, 21 ± 9%) and low ash content (9 ± 2%TS). HTC of CFS exhibits high char yields (75 ± 7%) while pyrolysis char from CFS exhibits elevated higher heating values (25 ± 2 MJ kg−1) and low ash content (24 ± 5%TS) compared to chars produced from fecal sludge (FS) from other sources. Further calculations showed that FS with low TS amended with sawdust can be used as inexpensive feedstock to achieve energy self-sufficient pyrolysis operation.

Characterization of Mineral Macronutrients Kinetics During Faeces-Based Composting Process in Composting Toilets

Given the environmental concerns and public health risks that could arise, the use of composting toilets by-products requires compliance with quality standards beforehand. However, such quality assessment is often lacking for those by-products in rapidly urbanizing sub-Saharan cities. This study examines the kinetics of major mineral nutrients [i.e., nitrogen (N), phosphorus (P), and potassium (K), which are among the key indicators of a compost’s stability] during a composting process of fecal matters from composting toilets. The monitoring was carried out at Abobo-Sagbé, Abidjan, Côte d’Ivoire over a 4.5-month period. Feces-based compost data collected on 6 different dates (i.e., on the 28th , 48th , 62nd , 76th , 90th , and 133nd day from the start of the composting process) were analyzed, and screened for their contents in total N, total P and K. Results showed a rapid decrease of the content of all three elements during the first 29 days, followed by a sharp increase, especially for P and K, and then a quite stable variation during the last 2 months of the monitoring. Variations of C/N ratio during the study were similar to those reported previously. Although the proportions of P and K were satisfactory at the end of the monitoring period, the final C/N ratio was relatively high compared to suitable ratios characterizing mature composts, suggesting therefore additional time may be required before any use of the compost as fertilizer in agriculture.

Ecological Sanitation in Tropical Environments: Quantifying the Inactivation Rates of Microbiological Parameters During a Feces-Based Composting Process

Dry composting toilets are increasingly being used as practical sanitation systems in areas with inadequate sewage disposal and inefficient (or inexistent) hydraulic network. In Côte d’Ivoire, the by-products from such systems are progressively used in peri-urban agriculture as organic fertilizer, most of the times regardless of any hygienic quality assessment; constituting thereby a major health risk. The main objective of this study was to assess the inactivation rates of key microbiological parameters [i.e., total coliforms (TC), fecal coliforms (FC), fecal streptococci (FS) and Ascaris lumbricoides (AL)] during the composting process of fecal matters from dry composting toilets. Feces from dry composting toilets pits located at Abobo- Sabgé, Abidjan, Côte d’Ivoire, were collected every two weeks from February to June 2017 and their microbiological contents, along with two physico-chemical characteristics (moisture content and pH) were analyzed. Results revealed noticeable concentration decreases for all the microbiological parameters, except AL. The concentrations dropped from 7.72 to 3.93, 7.61 to 2.70, and 7.10 to 3.11 (log FCU/g) for TC, FC and FS, respectively, during the monitoring period. Regarding AL, there was an increase during the first 29 days, then a decrease in their concentrations over the last 3 months. Furthermore, the study revealed that all fecal bacteria followed a first-order kinetic with the inactivation rates being 0.31, 0.24, and 0.21 d-1 for FC, TC and FS, respectively. The amount of fecal bacteria in the composts suggests that an additional time is required for maturation before any uses of such material as fertilizer.

SDG Indicator 6.2.1: Proportion of population using safely managed sanitation services including a hand-washing facility with soap and water (2015)

Population using an improved sanitation facility at the household level that is not shared with other households and where excreta is safely disposed of in situ or treated off site, including a handwashing facility with soap and water in the household. Improved sanitation facilities include flush or pour flush toilets to sewerage systems, septic tanks or pit latrines, improved pit latrines (pit latrines with a slab or ventilated pit latrines) and composting toilets. A handwashing facility is a device to contain, transport or regulate the flow of water to facilitate handwashing. Hygiene Sanitation SDGs Use/Reuse