MASTER'S THESIS - SuSanA

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4 Presentation of technologies for rural areas 4.3.2.3 Imhoff tank The Imhoff tank is an improvement of the septic tank, that allows sedimentation and sludge stabilisation. The tank has two compartments, that are flown through horizontally. The upper compartment serves for the settling of solids, in the lower compartment the anaerobical stabilisation of the settled solids takes place. The process produces low amounts of biogas, that leave the reactor through vent channels in order not to disturb the settling process (Stauffer 2012). Funnel-shaped walls help to collect settled solids at the bottom. Desludging of the Imhoff tank is possible through water pressure by using a desludging pipe with an outlet below the water level of the tank. Figure 4.8: Imhoff tank (Stauffer 2012) Figure 4.9: Imhoff tank (Nowak 2010,a) The effluent from the Imhoff tank requires secondary treatment. Imhoff tanks are used preferably when further treatment takes place near residential houses, in open ponds or vertical flow constructed wetlands (Sasse 1998). Imhoff tanks need regular sludge removal to keep effluent quality high. Sludge needs further treatment and disposal. Imhoff tanks are a low-cost option suitable for small communities or house clusters. As they can be installed underground, they do not require much land. To avoid groundworks, the Imhoff tank can be installed on the ground, but needs to be insulated in colder climates. O&M is simple costs therefore low (Spuhler 2012). 4.3.3 Transport Transport of wastewater can be realised by sewer system or sucking and transport vehicle and is presented briefly in sub-chapter 4.1.1 Components of a sanitation system (p.25). Vacuum systems are excluded from that work as this technology is too sophisticated for the Albanian context. 4.3.4 (Pre-) Treatment Treatment of wastewater can be distinguished into pre-treatment, primary, secondary and tertiary treatment. Pre-treatment and primary treatment refer to physical treatment processes while secondary treatment refers to biological treatment processes, where degradable biological matter is used by microorganisms. Pre-treatment can be combined with the primary and secondary treatment in one plant, but most technologies need a separated pre-tretment primary treatment facility where solids can settle down. Tertiary treatment is a final treatment step to improve the effluent quality if necessary. 35
4 Presentation of technologies for rural areas 4.3.4.1 Ponds Ponds are in some literature also referred as to lagoons and can be distiguished into • Settling ponds for pre-tretment and • Waste stabilisation ponds (WSP), aerated ponds, aquaculture ponds and floating plant (macrophyte) ponds for wastewater treatment. Settling ponds are used for pre-treatment where the settlement of solid particles and their anaerobic digestion takes place. These ponds should have a specific surface area of at least 1.5 m²/PE (Heise and Nowak 2007). As odours can appear they should be located somewhat away from the settlement. Waste stabilisation ponds (WSP) can be low-cost options for domestic wastewater treatment considering construction and operation and can remove pathogenes very effectively. WSP are artificial water bodies filled with wastewater, that can even be used for settlement and removal of solid particles if there is no pretreatment installed before (Heise and Nowak 2007). They work with the „natural processes of biodegradation, desinfection by sunlight, and particle settling under gravity“ (Choukr-Allah 2011). Improvement of the treatment is possible if several ponds are used in a row. The anaerobic and aerobic treatment in the ponds can reach a BOD removal up to 75 % (Tilley et al. 2008). WSPs are shown in Figure 4.10. Figure 4.10: Waste stabilisation ponds (WSP) (Tilley et al. 2008) Stabilisation ponds are an anaerobic treatment facility that can cope with very high loading rates, but also have a large area demand. Therefore, they are only feasible when the price of the land is low. Some of the advantages of WSPs are the high pathogen reduction, that they can be built with local material, have low operation costs and no electricity demand. Disadvantages are the possible odours that can develop, the large area requirement that can be very expensive, and the need of secondary treatment or appropriate discharge of effluent and sludge (Tilley et al. 2008). 36
Page 1 and 2: MASTER'S THESIS UIM/2011/7
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Selbständigkeitserklärung Hiermit
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