Speaker: Mamadou Camara NDIAYE
In sub-Saharan Africa, majority of the urban population rely on on-site sanitation system. However, there still is a considerable gap-knowlegdde on faecal sludge physical-chemical-microbiological characteristics to design proper FSTP. Therefore, the need on precise and reliable data on sludge characteristics is still relevant for engineer to optimize time and financial resources. The key to tapping this topic lies in proper multicentric characterisation conducted in 10 sub-Saharan urban cities to make sludge constituents. High sludge variabilities shown allow authors to conclude that there is no need to make sludge characteristic campaign for further Faecal Sludge Treatment Plant design in sub-Saharan countries.
Study area is constituted by countries listed in Table 1. At least 15 emptying truck have been sampled for each city. All samples were collected directly from trucks. Samples were collected by Bassan et al. al., 2013, method: 4 samples of 1 L collected at the beginning, in the middle and at the end of the discharge. 1 L of composite was made by mixing all samples collected per truck.
Analyzed parameters included pH, BOD, DCO, TSS, TS, TVS, NH4+, NO3-, NTK, TN, TP, Faecal coliforms, helminths eggs. Standards characterization methods used are given in Table 2. For each country, analysis was carried out in specialized laboratories. Descriptive statistic methods were used to analyze the data.
Average concentration of TS is 13806 ± 6704 mg/L. This result is similar to that founded by Bassan et al. 2013 (11820 ± 9781 mg / L) on samples originated in Ouagadougou. Average of TVS is 68% ± 14% and faecal sludge contained in the septic tanks seems to have the same content as indicated by SANDEC studies conducted in the 1990.
TSS average is 14237±4584 mg/L and similar to Koottatep et al., 1997 results operated in 150 suldge samples from septic tanks in Bangkok. Average for Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are respectivly 3525±2636 mg/L and 12462±9422 mg/L. In Burkina Faso and Benin, faecal sludge shows to be not readily biodegradable, while in Senegal, Ivory coast, Guinea and Cameroon, faecal sludge should be in favor of an organic treatment. Ammonium average obtained is 780±585 mg/L. For public toilets infrastructure, ammonium concentration are 2.5 to 6.4 higher than the obtained results (Strauss and Montangero, 2004). Nitrate concentration is an average of 97±15 mg/L. Based on studies conducted in Thailand on private septic tanks, sludge nitrate value varies between 0.2 and 21 mg/L.(Koottatep et al., 2005). For total nitrogen (NT) and Kjeldahl nitrogen (NTK) average concentration value obtained are respectively 503±448 mg/L and 802±347 mg/L. Coliforms bacteria average concentration is estimated at 2.54E+08±3,73E+08 i.e 384 to 4033 times more faecal coliforms than in domestics wastewater. Helminth eggs concentration varies between 17.2 and 9000 Eggs/L, i.e. 10 times higher than sludge from public toilets (Heinss et al., 1998). The heterogeneity of results could be explained by potential laboratory measurement errors, intrinsic sludge heterogeneity (age of the sludge, storage conditions, soil qualities, temperature) and applied pumping methods (truck with or without sludge pump).
This study on Faecal sludge physical, chemical and microbiological characteristic provide essential data on sludge nature and complexity. Large dispersion values around average data show that there is no significant difference between all counties results on physical, chemical and microbiological parameters. While it is always preferable to carry out local faecal sludge quality analysis, implementation of sampling and analysis campaigns is excessively time and fund consuming. Project budgets does not often allow to carry out sludge characterization campaign under good conditions leading to generate reliable and representative data. Hereby, EDE has shared his 15 years experiences on country faecal sludge characterization results among sub-Saharan urban capitals. Data shown can be used by sanitation engineers for proper design of further new faecal sludge treatment plants in all sub-Saharan African countries.
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