MASTER'S THESIS - SuSanA

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4 Presentation of technologies for rural areas 4.3.4.4 Up-flow anaerobic sludge blanket reactor (UASB) The UASB reactor (see Figure 4.16) is a reactor with suspended anaerobic sludge in the lower part and a gas-liquid-solid separation in the top. Wastewater enters the lined tank at the bottom through a distribution system and flows upwards. Organic compounds get degraded by microorganisms in the sludge layer. Biogas is produced in this process that can be collected and used to win energy. Gas bubbles flow up and mix the water and sludge (Wehrle et al. 2007). To prevent that microorganisms get flushed out of the reactor they have to get agglomerated. Therefore, granule-forming organisms are preferably agglomerated (Tilley et al. 2008). The outflowing wastewater enters a settling compartment where sludge can settle down and will be brought back into the digestion compartment. Figure 4.16: UASB reactor (Tilley et al. 2008) Advantage of the UASB is that the process produces effluent with higher quality than a septic tank (BOD removal around 85 % (Wehrle et al. 2007)), only little land is required and no odours and no flies occur. But an UASB reactor is only appropriate if the area has a constant water and electricity supply. Other disadvantages of this reactor are the difficult construction and maintenance, especially the control of hydraulic and organic loads. And the last main concern is that the UASB is an established technology for industrial wastewater, but the application for domestic wastewater is very new (Tilley et al. 2008). Therefore it is not clear if it is at all an appropriate solution for urban wastewater (in rural areas). For all the mentioned reasons (constant electricity supply requirement , difficult operation, no or little experience for urban wastewater, etc.), the technology is not appropriate for the rural areas of Albania. 4.3.4.5 Activated sludge The activated sludge technology consists of several chambers for aeration and settling. The process makes use of mostly aerobic microorganisms to degrade the biological matter in the wastewater. Frequent oxygen supply is necessary to keep aerobic conditions and to keep biomass suspended (Tilley et al. 2008). The flow scheme of the process is shown in Figure 4.17 (p. 40). 39
4 Presentation of technologies for rural areas Figure 4.17: Flow scheme of the activated sludge process (Wehrle et al. 2007) The activated sludge process needs a primary treatment and is combined with tertiary treatment. Advanteges are the high BOD and pathogen removal (up to 99 %), the resistance against shock-loading and the big flow-range at what the plant can be operated. But the process needs very well trained stuff and a constant electricity supply. The process is more appropriate for larger wastewater flows from 10,000 up to 1,000,000 PE (Tilley et al. 2008). Therefore, the technology is not suitable for a GIZ project in rural areas of Albania. 4.3.5 Sludge treatment 4.3.5.1 Sedimentation or thickening pond Sedimentation or thickening ponds (see Figure 4.18) are simple ponds where sludge can settle down for thickening and dewatering purpose. The total solids (TS) content can be increased up to 14 %. The pond also allows stabilisation of the sludge due to anaerobic processes. The pond has a liquid outlet. Sludge has to be removed monthly and treated regularly. Mechanical sludge removal is possible with frond end loader or special equipment. Sludge thickening in a pond should be combined with on-site drying or composting process for desinfection (Tilley et al. 2008). Figure 4.18: Sedimentation or thickening pond (Tilley et al. 2008) To construct a sedimentation pond, large space is needed far away from settlement as odours and flies will occur. This can be a limiting factor if land is expensive or not available due to geographical conditions. In general, it is a low-cost option without energy requirements for hot and temperate climates without too much rain as rain is not good for the process. Expertise knowledge for design is necessary and proper maintenance is important (Tilley et al. 2008). 40
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MASTER'S THESIS UIM/2011/7
Page 3 and 4: 1 Problem Statement / Background At
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Page 7 and 8: List of Abbreviations ADA ADF ALL A
Page 9 and 10: UNECE VF WB WFD WHO WRA WSP WSS WSS
Page 11 and 12: Table of content Preface...........
Page 13 and 14: 5.3 Other constructed wetland plant
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7 Presentation of the institutional
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8 Development of a guideline for th
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List of sources (EG 1991): (Engelma
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Selbständigkeitserklärung Hiermit
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3.1.4 Dam partly surrounding the fi
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4.3.6 4.3.7 4.3.8 PE-pressure pipe
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