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| Aspect | Conventional aboveground WTPs | Underground WTPs |
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| Environmental and landscaping effects | The upper parts of the WTP structures can be used for “greenification” and landscaping, but they tend to be quite scattered. Furthermore, much of their equipment is exposed. Consequently, the environmental and landscaping effects of aboveground WTPs are mediocre at best. | Other than the processing rooms and their ancillary facilities that must be constructed at the surface, the only other features of an underground WTP that lie on the surface are the equipment hatch, escape hatch, ventilation ports, and odor discharge port. Therefore, large swathes of surface area are still available for greenification, which allows underground WTPs to have excellent environmental and landscaping effects. |
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| Social benefits | Integrating aboveground WTPs into natural landscapes and using these sites for other purposes are difficult. As urbanization progresses in China, regional development has been restricted to some extent by wastewater-treatment facilities that were constructed in the past. | Underground WTPs have, to an extent, changed the perception of the general public on WTPs, and they are useful for increasing environmental awareness. Underground WTPs are viable as “in-city treatment plants.” |
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| Economic benefits | Aboveground WTPs are inefficient in terms of land use, and they exert a negative effect on the usability and market prices of their surrounding lands. | Underground WTPs are more flexible in terms of where they can be built, and they can be constructed near their serviced areas to reduce delivery and maintenance costs. Because the structures of underground WTPs are tightly clustered, they use less land and thus incur lower land-purchase costs. Furthermore, the land above and around an underground WTP still retains a high level of usability and value. |
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| Construction costs | Low | High |
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| Operational costs | Low | High |
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| O&M | Inspection, repair, maintenance, and equipment hoisting in aboveground WTPs are relatively straightforward. | O&M conditions are far less ideal in underground WTPs, and high levels of ventilation and illumination are required. Using large machinery for equipment maintenance in underground WTPs is not possible. Hoisting large pieces of equipment requires hoisting holes, and the process depends on the layout of the underground space. Communication between aboveground and underground spaces can be difficult. |
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| Working environment | Aboveground WTPs have an amenable working environment because they are usually on the surface or inside a processing room where ventilation and illumination issues can be trivially resolved. | Because the working environment is underground, artificial illumination and comprehensive mechanical air supply and exhaust systems are required to maintain these environments, which effectively increase the operational costs. |
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| Noise and deodorization | Environmental requirements can be met by sealing parts of the WTP or by collecting odorous gases. However, any malfunction in the deodorization system will have a significant effect on the WTP surroundings. | Because the wastewater-treatment facilities are tightly clustered in an underground WTP, the exhaust ports for deodorization are also clustered. Sealing and collecting odorous gases from the treatment facilities are relatively straightforward, and odorous gases are unlikely to spread to the WTP surroundings in the event of a malfunction in the deodorization system. Because the vast majority of the WTP equipment is located underground, restricting noise emissions is relatively straightforward. |
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| Fire control and safety | Most of the processing rooms only require outdoor and indoor fire-hydrant systems. Workers inside a processing room can easily escape. In addition, flooding is unlikely to occur. | Underground WTPs are required by law to have many fire compartments and a large number of fire escapes that directly lead to the surface. In addition to the fire-hydrant systems, automatic fire-extinguishing systems must be installed. Care must be taken to prevent flooding. |
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