Description of water and sewage treatment systems

A description of a typical potable water supply, process water supply and small- and large-scale sewage treatment systems follows. Additional information on water and sewage treatment equipment and systems is presented in paragraph 9-3, General water and sewage treatment equipment description and operation.

1. Facility potable water and process water supply. The water supply to a facility normally meets potable (drinking) water standards. The water supply is separated from facility potable water with a back-flow preventer and from the facility process water with a second back flow preventer.
   1. A typical water system is shown in figure 9-1, Schematic of a typical potable and process water system. The system consists of the water supply, isolation valves, strainer, back flow preventers, drain, pressure regulators and gages.\

1. 1. Water treatment is needed for process water used in chilled water, heating water and steam and cooling tower systems. The type of treatment depends on the quality of the water supply and the types of equipment in service. The typical systems presented elsewhere in the course material include a chilled water system and a heating water system. Process water is used for fill and makeup water on both of these systems.
   2. Process water for closed loop chilled and heating water systems needs to be treated to control corrosion, scale formation, growth of biological agents and pH. In the closed cooling water system, treatment of the water for dissolved oxygen (O2) to prevent corrosion is needed during filling or when opened for maintenance. Scale is usually not a problem in chilled water systems. In the closed heating water system, monitoring is needed for corrosion from dissolved O2 and scale formation from precipitation of minerals in the water. A typical process water treatment system is presented in figure 9-2, Process water treatment schematic. Process water treatment consists of a pot feeder, feeder fill point, isolation valves and chemicals.

1. Sewage treatment systems. Sanitary sewage is any liquid waste containing animal matter, vegetable matter and/or certain chemicals in suspension or solution. It excludes storm, surface and ground water. Sewage treatment removes impurities so that the remaining water can be safely returned to the natural water cycle.
   1. Sewage treatment for small facilities in remote or rural areas involves a septic tank and drain field. Refer to figure 9-3 for a cross section of a septic tank.
   2. Sewage treatment for larger facilities and facility complexes can consist of source, preliminary, primary, secondary and advanced treatment operations.
   3. Treatment at the source of wastewater to render it safe for sanitary sewage treatment can vary greatly depending on the chemical, manufacturing, or operational processes which produce the waste water. In the sewage treatment facility, preliminary treatment is provided to protect downstream equipment and minimize operational problems. Preliminary treatment includes neutralization, screening, grit removal and temperature adjustment. Primary treatment at times requires chemical addition but mainly involves physical treatment of the waste to remove settleable and floatable materials. In primary treatment, settling tanks are used for solids removal.
   4. Secondary wastewater treatment relies on naturally occurring microorganisms acting to break down organic material and purify the liquid. Secondary treatment brings air and therefore O2 in contact with sewage to encourage micro-organisms to grow, thereby removing substantial quantities of dissolved organics and colloidal materials. This results in purified water. The process or combination of processes used in advanced sewage treatment systems are dictated by effluent quality standards which exceed established secondary treatment standards.
   5. The typical sanitary sewage waste treatment system selected for discussion in this manual is the trickling filter process shown in figure 9-4, Sewage trickling filter process. The system consists of a preliminary treatment system, primary sedimentation tank, high rate trickling filter, secondary sedimentation tank, disinfection unit, sludge thickener, sludge dewatering tank and sludge digestion unit.
2. Water and sewage treatment systems. More information on design, maintenance and testing of water and sewage treatment systems is found in the Management of Industrial Pollutants by Anaerobic Processes by Alan W. Obayashi and Joseph