Pressure sewers

The flow in sanitary sewers may be controlled by gravity (gravity sewers) or pressure (pressure sewers). In a partially filled gravity sewer, transfer of oxygen across the air-water interface (reaeration) is possible, and aerobic heterotrophic processes may proceed. On the contrary, pressurized systems are full flowing and do not allow for reaeration. In these sewer types, anaerobic processes will, therefore, generally dominate. 

The residence time in the sewer network affects the degree of transformation that may occur. The residence time depends on the size of the catchment and specific sewer characteristics, such as slope and length. The residence time is often relatively high in a pressure sewer, principally during nighttime hours. 

Aerobic + Oxygen Partly filled gravity sewer Aerated pressure sewer... 

Anoxic - Oxygen + Nitrate Pressure sewer with addition of nitrate... 

Typically anaerobic conditions in pressure mains exist after a short initial aerobic phase, depending on the DO concentration of the incoming wastewater. The factors of importance for the sulfide production in a pressure sewer are dealt with in Section 6.2.3 and include wastewater and system characteristics. 

TABLE 6.1. Empirical Equations to Predict the Areal Sulfide Production Rate, fa, in Pressure Sewers in Units of gS nr2 tr1. 

Tanaka, N. and T. Hvitved-Jacobsen (2001), Sulfide production and wastewater quality — investigations in a pilot plant pressure sewer, Water Science and Technology, 43(5), 129-136. 

Tanaka, N., T. Hvitved-Jacobsen, T. Ochi, and N. Sato (2000b), Aerobic-anaerobic microbial wastewater transformations and reaeration in an air-injected pressure sewer, Water Env. Res., 72(6), 665-674. 

FIGURE 7.2. Outline of a pilot plant sewer. Studies can be performed under gravity sewer and pressure sewer conditions. 

From a process point of view, it is typical to distinguish between wastewater collection in pressurized systems and gravity sewer networks. The reason is that anaerobic conditions typically prevail in pressure sewers, whereas in gravity sewers, conditions are established for aerobic processes. Different empirical models for pressure mains and gravity sewers have, therefore, been developed. 

There are several drainage mechanisms are employed at petroleum and related facilities - surface runoff or grading, spill containment (diking), gravity sewers (oily water and sanitary) and pressurized sewer mains, and lift station collection sumps. 

Oily water gravity and pressure sewer systems Ship, rail or truck loading facilities Storage Tanks for flammable liquids... 

B. Drainage System Upgrade Install above-grade, pressurized sewers, segregating stormwater and process water systems. 

Raw material pressure sewer duct foam/skin... 

Oily water gravity and pressure sewer systems... 

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