K52137 - Characterisation of on-site sanitation materials and products

K5/2137 - Characterisation of on-site sanitation materials and products

VIP latrines and pour-flush toilets


Funded by: Water Research Commission

April 2012 – March 2015


Project description



This project consists of two parts; namely (1) an investigation into the treatment of VIP sludge using LaDePa technology, and (2) characterisation of sludge from pour flush toilets.

Processing of VIP latrine slude


When eThekwini Municipality was established in 1999, over 60 000 ventilated improved pit (VIP) latrines were inherited from the incorporated local entities. Some of the pits were found to be unlined and hence they were not able to be safely emptied, in other areas the households were connected to an extended sewer. Thus in 2009, the municipality set out to empty over 35 000 VIP latrines, which were already full. One of the challenges from this operation was the disposal of the sludge in an environmentally safe way. The initial idea was to dispose of the sludge in wastewater treatment plants but the first trials caused overloading and dysfunction of the treatment plant and so the municipality had to seek for alternative solutions. This led to the concept of the Latrine Dehydration and Pasteurization (LaDePa) machine, manufactured by Particle Separation System (PSS). This machine is used to process the emptied sludge into dry and pasteurized pellets, which can be used as a soil conditioner, or which could be combusted as a fuel. In the developed technology, the pellets pasteurization and drying occur by combining convective and infrared radiation heating.

A LaDePa machine small-scale prototype has been installed in the Pollution Research Group (PRG) laboratory, situated at the University of KwaZulu-Natal, Durban.  Its objective is to understand better the involved phenomenology in LaDePa process and optimize the operation of the full-scale machine.

The aim of this work is to characterize LaDePa process using the laboratory-scale machine. This will ultimately lead to the determination of the optimum operating conditions for drying and pasteurization.   This research lie on two main aspects. The first one corresponds to the study of the drying behaviour of the faecal sludge in the LaDePa, which was done by measuring the moisture, volatile matter and ash content at different heating intensities and residence times. The second aspect is the biological, chemical and physical characteristics of the processed pellets. Indeed, the state of the Ascaris egg in the processed pellets will be performed in order to determine the extent of deactivation. The chemical analysis of the major nutrients, namely nitrogen, phosphorus and potassium, will be done in order to evaluate the pellets for agriculture proposes. The calorific value, thermal conductivity and heat capacity will be determined in order to evaluate the use of the pellets as a biofuel.

In a more general context, this work can be of great interest for the scientific community from the sanitation sector, as no works in literature exist about faecal sludge drying and its applications.

In order to ensure simplicity of understanding the research process and outcomes, the studies of both pour flush and LaDePa are summarized in two separate main chapters in this report.

Characterisation of Pour Flush Toilets


The pour-flush system is used extensively throughout South East Asia, where the system is designed with a squatting pan and the users are “washers”. It was considered that this type of on-site sanitation systems might be beneficial and well accepted in South Africa from user perspective as this is one step closer to the conventional flush toilet. The system was adapted to the South African context and culture by Partners in Development (PID). Hence a sitting pedestal was designed which accommodated for the use of toilet paper rather than water for anal cleansing.

In the context of South Africa, the pour-flush system is viewed as an upgrade from the Ventilated Improved Pit latrine (VIP), which is the standard for basic sanitation in the country. For this reason, the performance and the user acceptance of the system are of interest. On the other hand, it is important to understand the characteristics of the sludge produced and stored in the leach pit to help understand the environmental impact of the system, mechanisms for emptying the pits once they are full and potential for reuse of the sludge, and how they compare to the VIP use and sludge characteristics.

PID successfully ran a pilot scheme involving the installation of approximately 25 pour-flush latrines in the greater Edendale area (Slangspruit, France and Azalea) outside of Pietermaritzburg in the province of KwaZulu-Natal, South Africa. The pour-flush systems installed in this area by PID were used for the basis of this research project. Sludge was sampled from selected pits repeatedly over a period of 11 months. The sludge was analysed chemically, physically and biologically to provide a base understanding of the sludge characteristics and possible mechanisms occurring in the pit. The filling rates of the pits were also monitored, as this is important information for planning future pit-emptying schemes and pit design.

It was found that the pour-flush and VIP sludge had minor differences in terms of the chemical composition. However, physically, the pour-flush sludge is more homogeneous with lessof non-faecal material in the leach pits than in the VIP pits. This means filling rates are slower as there is less non-degradable material in the sludge. Also, mechanical pit emptying is easier (provided the sludge is wet enough) without the presence of non-faecal material, which is often the cause for blockage or damage of pit emptying equipment.

It was thought that the concentration of ammonia in the sludge would be high enough to create a self-sanitising environment within the leach pit. However it was determined early on that the concentration of ammonia in the sludge was too low to have a sanitising affect.

Publications and Reports

Journal Papers




Conference Papers and Presentations



Reports and other


  • Final report to the Water Research Commission