MASTER'S THESIS - SuSanA

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5 Learning from already implemented CWs (in Albania and the Balkan region) Photos of the pilot constructed wetland plant at the SOS Children’s village Tirana, including some detailed descriptions, can be found online on the following homepage: http://www.flickr.com/photos/gtzecosan/sets/72157623262182867/ For further information please refer to the <strong>SuSanA</strong> document “Case study of sustainable sanitation projects – Wastewater treatment using constructed wetlands Tirana, Albania” (Gjinali et al. 2011). 5.2.3 Necessary operation and maintenance work (O&M) According to Jens Nowak (Nowak n.y.,b), the necessary time for O&M of the pilot plant in Tirana is assumed to be around two hours per week. The following Table 5.4 lists the necessary O&M tasks together with the information about how often they should be done. At the moment, the work is done by the SOS children’s village technician, who got trained by Joachim Niklas (designer of the plant) and Jens Nowak, both German engineers. Table 5.4: O&M works for the pilot plant at SOS children's village, compiled from (Nowak n.y.,b) How often Task 1x/day • Control the pump 2x/week • Drain off the sludge from the Imhoff tank • Open the valve of the sludge pipe in the sludge drying bed until sludge-free water is flowing out • If sludge pipe is clogged regularly, release of sludge every day 1x/week • Control of distribution pipes in the vertical filter • If necessary cleaning the holes in the distribution pipe • Change distribution of WW to the other vertical filter bed • Make a note in the operator’s handbook • Control water level in the horizontal filter • If necessary change position of knee-fitting pipe in the shaft between horizontal filter and effluent storage tank 1x/month • Measure sludge level in second settling chamber • Note it in the operator’s handbook • If sludge reaches level of one third of the chamber, it has to be removed • Removal of sludge on the complete ground of the chamber • Removal of old leaves on the filter beds, if necessary 1x/year • Removal of undesired plantation on filter beds, if necessary 61
5 Learning from already implemented CWs (in Albania and the Balkan region) 5.2.4 Financial aspects of construction and O&M The costs for the plant were around 60,000 €. This can be divided into 50,000 € for construction and material, 5,000 € for supervision and training and 3,000 € for documentation and public relations (Gjinali et al. 2011). The cost estimation, that was given by the construction company Gener2 counted only around 40,000 € for the construction works and the material. Analysing the cost estimation, the construction works counted for around 30 % and the material for around 70 %. As O&M is done by the SOS children’s village technician, no extra costs arise. The bill of quantities with the cost estimation prepared by the construction company Gener2 is attached in Appendix A. 5.2.5 Problems of the pilot plant and recommendation for reconstruction in 2010 In September 2010, the German engineer Jens Nowak visited the pilot plant in the SOS children’s village and proved the well-functioning of the plant. In his report to the GIZ “Reconstruction of Constructed Wetland SOS children’s village Tirana” (Nowak 2010,b), he describes the state of the plant in 2010 and the problems that occurred at that time. The document includes also recommendations for reconstruction. The main findings are presented in the following section. Some of the concrete shafts have holes and are located in a way that rainwater can infiltrate into the sewer system while heavy rainfall. This can cause hydraulic overload and washing-out of sludge from the pretreatment to the filter, what causes clogging of the filter bed and the distribution pipes. Another reason for clogging could have been the large amount of grease in the influent to the vertical filter. The old septic tank with three chambers was reconstructed as one Imhoff tank and one pumping chamber, not using the third chamber. This was changed during the re-construction in 2010, to use the third chamber as additional settling chamber because sludge separation in the Imhoff tank was assumed to be insufficient due to the design. The Imhoff tank was built too shallow, only 2.8 m deep, and with an insufficient slope of the funnel, which should be at least 1:1.7. The influent pipe could not be equipped with a knee-fitting as it is usual, as the top of it would have been above the water level. The distance between the water level in the Imhoff tank and the sludge pipe, that should normally be more than 1 m, counted only 0.2 m. The sludge pipe going from the bottom of the Imhoff tank to the sludge drying bed was built with a pipe DN 100 only, instead of at least DN 200. Additionally, the pipe had no valve at the outlet like it was planned. Therefore, the sludge pipe was replaced by a pipe DN 160 (as DN 200 was not available) and a free accessible valve at the end of pipe was recommended. The pipe was built with T-fitting in DN 160. Because the pre-treatment was not working satisfying and therefore solid matter was in the water that was pumped to the vertical filters, the valves for feeding the vertical beds were clogged and could not be closed completely. This led to a permanent feed flow of wastewater to both vertical filter beds. Additionally, distribution pipes and the holes in the pipes were partly clogged and only the front part of the vertical filter beds was fed with wastewater. Cleaning of both valves for wastewater discharge to the vertical filter beds took place in 2010 in order to be able to close them again. As some plant roots were growing in some of the shafts, it was recommended to remove them from time to time to avoid the risk of destroying the concrete. To increase the pressure in the distribution pipes in each vertical filter, one distribution pipe was removed and closed. The discharge holes were on top of the distribution pipe and high fountains up to 2 m caused aerosol and smell. For improvement of the plant, they had to be turned so that the holes were on the side and not at the top. Also extra discharge holes with the diameter of 8 mm had to be added on the other site with a distance between the holes of at least 1 m to guarantee an even distribution of the wastewater on the vertical filter bed. 62
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