Abstract
On-site sanitation facilities, mostly pit latrines are the main points of human excreta disposal in peri-urban low-income settlements in Kenya. Collection, treatment and final disposal of pit latrine faecal sludge, pose a significant management problem and present public health risks. The choice of appropriate faecal sludge treatment technology depends on precise region based data on the sludge characteristics that are often unavailable. The study analysed physiochemical characteristics of faecal sludge sampled at different depths of pit latrines. Twenty-four samples were collected from six pit latrines along the depth strata at 1-m intervals from the surface to 3 m depth. Samples were analysed for chemical oxygen demand (COD), biochemical oxygen demand (BOD), ammonia, total nitrogen and total phosphorus. The mean COD: BOD ratio was 1:5 with a concentration of 112800 and 24600 mg/L, respectively. Concentrations for all parameters were variable and higher in comparison with properties reported in literature. Upper layers had higher concentrations than lower depths. The concentrations of the sludge were 10-100 higher than acceptable limits for in-fluent sludge into municipal wastewater treatment plants. These results show that disposal of pit latrine faecal sludge into the wastewater treatment plants without co-treatment overload the system since treatment plants in use currently have not been designed to handle pit latrine sludge. The properties of faecal sludge analysed indicate that the wastewater treatment plants may not be capable of treating faecal sludge unless co treatment mechanisms are applied. Therefore, influent faecal sludge must be maintained within allowable concentrations; otherwise, the effluents may lead to significant environmental pollution impacts. Key words: On-site sanitation, depth strata, faecal sludge disposal, low-income settlements.
Highlights
The results show variation of faecal sludge properties within and across pit latrines
Documented characteristics of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), NH3 and total phosphorus (TP) indicate higher concentrations as compared to those reported in literature necessitating region based analysis to inform development of appropriate faecal sludge (FS) treatment technologies
The COD concentration that infer on the extent of degradation showed a reduction in concentration by 22% from surface to 3 m depth but with no significant differences between surface concentration and lower depths
Summary
Despite significant steps and achievements towards meeting the Millennium Development Goals (MDGs) on sanitation, approximately 2.5 billion people did not have access to improved sanitation services as at 2015. Sanitation gaps exist regarding services offered to urban poor and rural communities in developing countries. According to the 2015 Joint Monitoring Program (JMP) progress report, in sub-Saharan Africa, only 30% of the current population have access to improved sanitation facilities. The region has the greatest share of people practicing open defecation and recorded an increase in open defecation cases, whereas all other regions of the world recorded a decrease since 1990 (WHO/UNICEF, 2015)
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