Step by Step - Track the Progress of our Project!


August 14, 2013


A second biogas reactor for the Pestalozzi Children's center ...

The construction of the second biogas reactor and the cleaning of the constructed wetland are under way


Evermore pupils are attending the Pestalozzi school in Lusaka, Zambia. With an additional 120 students since the original project commissioning, more wastewater than can be processed by the Decentralized Wastewater Treatment System (DEWATS) is being produced. The massive increase of influent water is not only being produced due to the increasing number of pupils attending the school but also due to lower-quality plumbing and toilet fixtures, which need to be regularly maintained or replaced by better quality fixtures.

The overload of influent water has caused high flow rates and irregular water currents inside the Anaerobic Baffled Reactor (ABR). The resulting turbulent environment in the ABR hinders the decomposition of the organic waste material and has led to a blockage in the constructed wetland, which in turn has deteriorated the quality of the effluent water. In order to provide for wastewater treatment at its best, it is crucial to reduce the amount of influent water. In this regard the Pestalozzi Zambia Children´s Trust has recently completed a big project in which all showers and sinks have been maintained with new, better quality fittings. In order to provide full operational capability of the downstream constructed wetland it is being cleaned of built up organic material first and is now planted anew with additional banana plants and reed and canna flowers for productive reuse of the treated wastewater effluent. Furthermore the school kitchen is in need of a greater quantity of biogas for cooking due to the growing number of pupils. Therefore the construction of a second 40 m3 biogas reactor began on the 1st July.

During the project in Lusaka we gained various lessons learnt. We are very happy about the 120 additional pupils at the Pestalozzi school, but as such an increase has arisen unexpected it has created problems of the operational capacity of the system. The constructed systems need to be maintained regularly. The most important instrument of the system is the people who maintain it. First of all, a collective awareness for the added value of the system for their every-day life needs to be generated. A general awareness of their responsibilities in using the system needs to be created. In general it is very important to sensitize people to plan for having enough time for the maintenance of the system. Not only do they have to be sensitized about the use and operation of the system, but also the consciousness about the benefits for their every-day life needs to be supported. Especially in the case of the DEWATS plant in Lusaka it is furthermore important to encourage the school management to use the treated wastewater effluent for productive purposes.

1. The pit for the second biogas reactor is being drawn out ...
2. The dome is almost finished ...
3. The inside of the dome is being fettled with wax hermetically.
4. Both Biogas reactors are being connected with each other.

Changes of habits take time and the reasons people are hesitant to use the treated wastewater effluent now need to be validated. Further steps need to be set up through sensitive methods as well as in cooperation with the people in order to improve the use of valuable water resources. The school is now using the treated effluent, as it is more than what the pupils need to water their gardens, in a simple gravity irrigation scheme which automatically diverts the effluent to a fruit orchard. The school decided this way to be safer in the long term, as it will avoid the need for direct handling of the treated wastewater.


Reward we devote to our project partners BORDA, the Water and Sanitation Association of Zambia (WASAZA) and the Pestalozzi Zambian Children´s Trust. We especially thank Christopher Kellner for his technical advice and Jeannette Laramee for her project coordination.

September 01, 2009


Congratulations - the first cup of tea brewed on a biogas stove!

The Biogas Plant at Pestalozzi School Lusaka, Zambia is up and running!


The Biogas Plant at Pestalozzi School Lusaka, Zambia is now producing Biogas and the first attempt at getting the stove working was a sucess! We would like to thank Peter Lungu and Chris Kellner, who were both deeply involved in the contruction process of the "Decentralised Wastewater Treatment System". In the last couple of days they have managed to install gas pipes and adjust the stove. As you can see in the picture they enjoyed the fruits of their work in the form of tea brewed on a biogas stove!

The gas streams - the stove is burning cleanly
Chris adjusting the stove
Peter Lungu (l.) and Chris Kellner (r.)

August 25, 2009


Filled with gravel, planted and hopefully taking root soon...

The final pieces of work for the planted gravel filter are now completed. Now it's down to the plants, which need to take root deeply enough to allow us to connect the planted gravel filter to the other modules of the decentralised wastewater treatment system.


We would like to thank Jeanette Laramee and Pestalozzi World for the great pictures, which show the plantation of the gravel bed with marsh plants such as reeds and rushes.




Pic 2 - Now the Seedlings need to root
Pic 1 - Plantation of the Bed with Seedlings



As the wastewater flows horizontally through the beds it is cleaned through a variety of means: firstly, the stones and gravel act as a filter removing particles in mechanical way; secondly microorganisms get to work degrading the organic matter; and thirdly, the wastewater becomes oxygenated.

After passing through the beds the cleaned water flows downhill into a collecting tank (Pic 2). The treated water will later be used for the irrigation of the school's garden.

July 21, 2009


Baffled Tank Reactor Finished - Planted Gravel Filter Under Construction

Now that the biogas-digester has been burried underground and the Baffled Tank Reactor has been covered in concrete, only one piece of the jigsaw remains: the Planted Gravel Filter.


Pic 1, 2 and 3 show the installation of the pipes, through which the wastewater flows from chamber to chamber. Pic 2 shows the overflow system, which operates by allowing water to overflow from one chamber to the next through a down-pipe. The water runs through the pipes to the ground of each consecutive chamber, where it ascends through a layer of active biomass, or settled sludge. The sludge is fixed by a second, perforated floor, shown in the picture. The area above each perforated floor is then filled with stones as a filtering material; this decreases the risk that the active biomass will be washed out. The increased contact time with active bacteria, which grow on the filter material, results in the improved treatment of the wastewater.



3. Exact leveling
5. Inflow, biogas outlet and outflow of the Biogas Digester / In the background: the poured slab
6. Waxing job
7. Membrane and pebbles of the Planted-Gravel-Filter
1. Installation of the overflow pipes
2. Down pipes and perforated bottom
4. Pouring the slab of the anaerobic Baffled Reactor

To guarantee that the system can be maintained easily if it is clogged, all installed pipes remain open at the top (Pic 2). The exact levelling of the whole complex, and specifically of the overflows, is absolutely essential because the system is based on a simple hydraulic gradient (Pic 3). There is no need for a pump or anything similar. A minimal gradient guarantees natural hydraulics and discounts the need for any energy input.


Pic 4 shows the pouring of the Baffled Reactor’s top slab. As you can see, every chamber is installed with a hatch to allow future repairs such as desludging. The Biogas Digester is now complete except for the galvanised pipe which will transport the gas to the kitchen.  The digester has now been waxed, so we are just waiting for it to be hermetically sealed (Pic 6).


The construction of the final component of the "Decentralised Wastewater Treatment System" the Planted-Gravel-Filter (PGF) has begun (Pic 7). It has been lined with an HDPE membrane and is filled with pebbles. The PGF is a large gravel and sand-filled channel, which is planted with aquatic vegetation. As wastewater flows horizontally through the bed, the filter material removes particles, the microorganisms degrade the organic material, and the wastewater becomes oxygenated.


Once more we would like to thank the Zambia-team for the excellent photos and documentation.

June 09, 2009


The Biogas Digester in Zambia is Nearly Complete

The last construction phase – plastering work – of the Biogas Digester is complete, The construction of the Baffled-Tank-Reactor has just begun.



Pic 1 and 2 illustrate the plastering work on the outside surface of the dome and on the inlet of the unit. In Pic 2 you can see the inlet (left side) and outlet (right side) of the Biogas Digester. Differing elevations of the inlets and outlets guarantee correct flow of the wastewater. The next step is to install on the top of the dome the valve that will release the gas. When in operation, bacteria in the fermentation tank will feed on the biomass and will produce the biogas. As you can see, the plant will be buried underground. The reason for this is not only a question of aesthetics. The earth covering the reactor's surface increases the external pressure on the plant and enhances its capacity to withstand the internal pressure created by the biogas accumulating inside the reactor.



Pic 3 - The Baffled Tank Reactor Under Construction
Pic 4 - Overview of the Whole Complex
Pic 1 - Plaster Work on the Branch of the Digester
Pic 2 - Near Completion

In parallel, the second module of the treatment system – the Baffled-Tank-Reactor – is also under construction (Pic 3). The Baffled-Tank-Reactor is used to clean the wastewater, which comes out of the fermentation tank. It consists of a series of baffles. As the wastewater passes through each chamber the heavy sludge sinks to the bottom while the cleaner and lighter water bypasses the baffle to the next chamber. Thus, from chamber to chamber, the water gets progressively cleaner. The quality of clarification depends on how many baffles the reactor consists of and how long the wastewater stays in contact with the active biomass (sludge), which catalyzes the ongoing fermentation process. The time the wastewater needs to run through the whole system depends on its speed (flow velocity) which in turn depends on how much wasterwater flows into the tank and again on the size and number of baffles. The ongoing anerobic fermentation process in the Baffled-Tank-Reactor is an additional source of biogas and increases the system’s effectiveness.


Once again, we would like to thank Jeanette Laramee for the excellent documentation of the project.


May 05, 2009


Biogas Digester - The Construction Works at the beginning

We're making progress! The excavation work began 2 weeks ago, and the biogas digester at the Pestalozzi School in Lusaka is now near completion.


First of all, we would like to thank Jeannette Laramee for the great pictures. The photographs show each construction step of the biogas digester: In the first and second picture you can see the "compass-technique" which guarantees the exact spherical shape of the dome. To ensure this, bars are fixed in the centre point of the construction area with the radius length of the dome. The bars serve as a standard gauge for the masonry work. On the side of the dome you can see the inflow and outflow structures. With the aid of bricks (picture 3) the top edge of the wall is weighted in an outward direction to avoid the dome from collapsing during construction. Picture 4 shows the digester close to completion.


Pic 3 - Stabilizing the construction with bricks
Pic 1 - Using the "compass-technique"
Pic 2 - Combined efforts
Pic 4 - Construction nearly accomplished

April 20, 2009


Biogas Digging

The 900 students at Pestalozzi Children´s Village in Lusaka will soon have biogas stoves in their school kitchen. The system will be fuelled by the new wastewater treatment system currently being installed. The digging for the construction of the new biogas digester began in early April and should be completed by May 2009.

The project is a cooperation between Pestalozzi World, the Water and Sanitation Association of Zambia and GTO.


Ground-breaking ceremony in Lusaka