MASTER'S THESIS - SuSanA

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4 Presentation of technologies for rural areas treatment plants have to handle only municipal wastewater without the surface run-off, the can be designed smaller. • Solid free sewer (SFS): Transport of pre-treated wastewater due to the use of a pre-treatment tank between household and sewer network allows the construction of sewer networks with smaller diameters. The advantage is, next to the smaller diameters, that pipes can be laid at shallow depths and that they follow the topography. Therefore, the SFS is cheaper than the conventional sewer. Other term in use is small bore sewer (SBS). Wastewater treatment: • Constructed wetlands (CW): Constructed wetlands are man-made “natural” wastewater treatment systems, working on the basis of physical and biological processes. A more detailed description is given in chapter 5.1 Constructed wetlands in general (p. 51). • Anaerobic baffled reactor (ABR): The ABR is an improved septic tank that contains a series of baffles to increase the contact time what leads to increased treatment performance. ABR can be installed in every type of climate, but lower temperatures will lower the efficiency. Needs a long start-up. The tank is installed underground, what makes it inappropriate for areas with high groundwater table (Tilley et al. 2008). • French vertical-flow constructed wetland (French VFCW): The French VFCW is a special type of constructed wetlands that does not need any pre-treatment. • Trickling filter (TF): A trickling filter is a fixed-bed biological filter where wastewater is sprayed (trickled) on. The filter material offers surface on which microorganisms are growing in a so called biofilm. Pre-treatment is necessary to prevent clogging of the filter. Effluent needs to get clarified as well in settling tanks or ponds as biomass can get flushed out of the filter. Skilled operator and constant energy supply are necessary. The TF can be adapted to cold climate (Tilley et al. 2008). • Rotating biological contactors (RBC): A rotating biological contactor is a fixed-bed reactor with several discs rotating on a horizontal shaft. RBCs are used for secondary treatment after sedimentation (physical pre-treatment). As reactor is rotating, microorganisms on the discs are alternately exposed to wasteater and air, what causes sequenced aerob and anaerob conditions. With this technology, a high removal of biodegradable organic pollutants on a small area is possible, but continuous energy supply is necessary (Heeb and Wafler 2011,b). • Waste stabilisation ponds (WSP): Waste stabilisation ponds are man-made ponds that are lined to the underground. Ponds can be aerobic, facultative and anaerobic. They are most effective if ponds are linked in a series of three ore more ponds and water is lead through in the following order anaerobic – facultative – aerobic pond. The anaerobic pond is important for the removal of solids and BOD, the facultative pond for further BOD removal and the aerobic pond, also polishing pond, for the pathogen removal. WSPs have their highest capacity in warm and sunny climates, but it is also possible to construct them for colder climates (Tilley et al. 2008). In some literature, the term lagoon is used for it. Wastewater disposal: • Leach fields: Leach fields (also drain fields or drainage fileds) are a wastewater disposal system, connected after a septic tank. The water is drained into the ground by perforated pipes that are laid into the ground. Pipes are normally surrounded by gravel to increase the percolation area (WB 2012). In Germany, disposal of wastewater without biological treatment is not allowed. 29
4 Presentation of technologies for rural areas • Forrest irrigation: Pre-treted wastewater is lead into ditches between trees by gravity due to flooding of the ditches. Microorganisms in the soil take part of the treatment process. According to (Tilley et al. 2008), irrigation can be divided into drip irrigation and surface water irrigation. Forrest irrigation belongs to the second group and can be used in winter times as well. Sludge treatment: • Dry beds: Sludge is applied on the drying bed in thin layers to decrease of sludge volume. No stabilistation takes place. Can be used together with (co-)composting. Sludge removal has to be done every 10 – 15 days. Other term is unplanted sludge drying bed (see sub-chapter 4.3.5.2 Unplanted drying bed, p. 41). • Reed beds: Similar to unplanted drying beds, but sludge can be applied on the old sludge layers. Dewatering and stabilisation take place. Sludge needs to get removed only every few years. Other term is planted sludge drying bed (see sub-chapter 4.3.5.3 Planted drying bed, p. 41). • (Co-)Composting: Controlled aerobic degradation of organic substances that can reduce pathogens. Combination of sludge and biodegradable solid waste is useful for the process as solid waste will give structure and therefore allows air to enter the compost piles. Composting should be done with distance to homes because of odours and flies. For further information about the presented technologies please refer to the mentioned report and the presentation. According to (Gjinali 2011,b), efforts on dry toilets are not wanted by GIZ Albania, as every household has somehow water in the house. Therefore, this type of sanitation was not considered in the presentation. A research article about small and medium size wastewater treatment plants in Macedonia describes four plants that are working very well in rural areas of Macedonia (Ertl et al. 2010). Three out of the four were included in the consultants presentation. The four plants are: • Activated sludge system for 5,000 PE • Aerated lagoons for 4,000 PE (the same as aerated ponds, technology is included in the presentation of Martin Wafler) • Trickling filter system for 3,000 PE (technology is included in the presentation of Martin Wafler) • Constructed wetland for 250 PE (technology is included in the presentation of Martin Wafler) As Macedonia is a neighbouring Balkan country of Albania and the conditions are very similar (climate, geography, people's mentality, income, etc.), the experience should be used for future projects in Albania. Therefore, the technologies aerated lagoons, trickling filter and constructed wetlands can be considered for further assessment in the Albanian context. Activated sludge systems were not presented by Martin Wafler and will be described briefly in the following chapter together with other small and medium size technologies for rural areas. What has been remarked in that report is that only constructed wetlands were installed for a small community (250 PE), while the other technologies were used for much bigger villages (3,000 – 5,000 PE). Some of the options presented by Martin Wafler seem to be not very appropriate, for example because of constant energy supply demand, too high complexity or expertise knowledge requirement for operation. To give a bigger range of possibilities to select from, the following sub-chapter 4.3 will give an overview over additional low-cost options that can be used in rural areas. 30
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