Sustainable Environmental Protection Using Modified Pit-Latrines

Pit-latrines are on-site excreta disposal facilities widely used as anaerobic accumulation system for stabilizing human wastes like excreta, both in rural and urban settlements of developing countries. Flooding of pit-latrines is often a common phenomenon, especially in situations of high water table (HWT) conditions and during the rainy season, causinga healthjeopardy to residents. The pits are not water-tight, the (ground)watercan freely flow in and out of the pit, especially in HWT areas. This results in groundwater (GW) pollution and even surface water pollution in the neighbourhood and pits that are filling up far too quickly. With a growing concern of public health, GW pollution and the reuse of nutrients from human waste, there is a serious need to study and improve the pit latrines, especially those in HWT areas. Specifically, the scope of this thesis was to study the socio-cultural aspects of excreta disposal inDar-es-SalaamCity, to improve the understanding of the biological stabilization processes in anaerobic accumulation systems and to come upwith properoperational guidelines for emptying practices.

A literature research and the results of a survey on excreta handling amongst 207 households in 9 of the 52 wards ofDar es Salaam(Dsm.) presented in this thesis shows that 50% of the filling up of pits in Dsm. city is the result of HWT. Moreoveralmost 16,131 kgCOD/day from pit-latrinesreach GW sources (Haskoning and M-Konsult, 1989). In this study an improvement of the pit-latrine was proposed using a plastic tank as pit. A 3000-liter experimental improved pit-latrine without urine separation (IMPLWUS) was constructed and monitored at a 10-person household in Mlalakuwa settlement inDsm.,Tanzania. The influent to the reactor merely consisted of urine and faeces in the ratio of 1.3:1. The results obtained revealed that, after 380 days of use as a daily pit-latrine, the reactor content was not yet stabilized. 8000 mg/l dissolved COD (but only 100mg COD/l volatile fatty acids) were still present. Part of this dissolved COD was shown to be biodegradable signifying the need for further stabilization of the reactor content. It was hypothesized that the slow conversion of dissolved COD was due to the fact that the reactor was started with sludge that was not adapted to the resulting high ammonia concentration of 3000 mg N/l, i.e. the system in fact was still under start-up, and in subsequent runs of the reactor the conversion of dissolved COD would be much faster.

 

For further evaluation of the conversion processesproceedingin the improved pit-latrine a simple mathematical model was used. The model results for the course of the concentration of the different COD components in the accumulating sludge in improved pit latrines receiving black water or night soil reactors, revealed that under tropical conditions 97% sludge stabilization is achievable within 1 year of reactor use. If 99% or more stability is desired, an accumulation period of 2.5 years is required or closing the reactor without adding any new materials for at least two weeks before desludging is necessary.When assuming Monod kinetics withk _m = 1 gCOD×gCOD ^-1×d ^-1 (Batstone et al,. 2003)it was calculated that for a latrine receiving black water as influent the specific methanogenic activity of the sludge after reactor closure will be about 0.12 g COD/g VSS/day. At a sludge concentration of 30 g VSS/l the volume to be left in the reactor as seed sludge for the subsequent runs is about 250 litres.

Finally a short survey was done of existing composting latrines of the type of Ecosan toilets installed in Dar-es-Salaam. The survey revealed that high pH values occur (up to 10.4) in Ecosan toilets due to addition of charcoal ashes. High pH assist in the reduction of E-Coli and Ascaris eggs, but on the other hand could not allow biological degradation of waste. The separated urine in Ecosan toilets showed on average E-coli counts of 1525 no./100 ml. indicating that urine was not adequately separated. In the light of sustainable development and in view of cost and economy, simple sanitary systems like Ecosan and IMPLWUS is the correct approach in Dar-es-Salaam and other tropical regions of developing countries. Sludge drying beds can be used for further stabilization of emptied sludge since they are cheaper than mechanized ones. Correct separation of urine in Ecosan toilets is necessary with the assistance of user health education. Comparing the Ecosan toilets to the improved pit-latrines it has to be concluded that both systems are promising alternatives to the conventional pit-latrine systems. However, both systems are still at their developing stage and require further work to provide a genuine sustainable solution for the disposal of human excreta in Dar-es-Salaam. The wealthy developed countries need to work with the developing countries in implementation of public sanitation aspects in low cost manner instead of advocating the expensive systems that will fail anyway.