September 01, 2009
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
August 25, 2009
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
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 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
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
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.
