Examination of pit sludge management and physico-chemical characterisation. The case study of Ntopwa, Blantyre, Malawi

Abstract

Urbanisation in most major cities around the world often results in overpopulation and inadequacy of public sanitation facilities and infrastructure. Similarly, in most developing countries inclusive Malawi, almost all unplanned urban settlements are not connected to a municipal sanitation facility and residents utilize onsite sanitation facilities with both traditional pit latrines and improved pit latrines (VIP) being the most commonest and popular types. While pit latrines and VIP’s have and continue to be the simplest and hygienically acceptable onsite facility, they present two major problems: a) filling up and risk of contaminating the surrounding environment; and b) Once a pit latrine is full, it has proven to be a great challenge to manage full pit latrines especially in unplanned settlements where there is space limitation for emptying equipment to properly navigate to targeted pits to empty it and for disposal of the emptied material. Regardless of these challenges, residents often times abandon the filled pit and develop a new pit for use. It is against this background that motivated this study to understand the Physico-Chemical characteristics of the pit latrine contents in filled up pit latrines and VIPs. At the onset of the study, a survey was conducted to understand user practices of the pit latrines with an emphasis of understanding how many users use an individual pit, what kind of domestic waste users dump in the pits and any special chemicals or additives use for cleaning the latrines, odor reduction and pest control. While the study had expected to find a relationship between user practices of the pit latrine and the different Physico-chemical characteristics of the sludge, no attempt was made to see if there would be any relationship between the actual results of the laboratory analysis of the sampled pit latrines and the user practices since the survey had reviewed that most pit latrines were shared among several families and had different practices on how they make use of the latrine. Ten pit latrines in Ntopwa Township, an informal peri-urban settlement were selected for sampling after inspecting them to have a satisfactory amount of sludge that enabled for multiple point height sampling (at the surface, 0.5 meters, 1.0 meters and 1.5 meters) within the pit latrine were randomly selected for sludge sampling for laboratory analysis for various Physico-Chemical characterisation. The Physico-Chemical characterisation included pH, moisture content, Chemical Oxygen Demand (COD), Ammonia, Total Solids (TS), Total Volatile Solids (TVS), Fixed Solids (FS), Total Kjeldahl Nitrogen (TNK), Phosphorus (P), potassium (K). vi The survey revealed that the majority of the residents (61.5%) had access to an onsite sanitation facility with a minimal percentage practicing open defecation. The average number of users per pit latrine was more than five with two or more families utilizing a single pit latrine. The majority (55.2%) of users were also aware of the relationship between pit latrine management and water quality with some making a direct link to groundwater contamination and disease outbreaks. The Physico-chemical characterisation results for COD and TVS from the ten pit latrines showed that in unlined pit latrine, sludge from the bottom layers still needs further additional degradation for it to be fully stabilized and to ascertain its biological safety. It was also observed that there were variation in trend for the different parameters from pit latrine to pit latrine (p<0.001). Only COD values from different depths were significantly different (p=0.01). While macro-nutrient (NPK) were detected at the different depths, there is a need to ascertain its biological safety since the study had shown that there is a need for further degradation and stabilization of the sludge as this is an indication of low microbial load due to natural die-off.