Sewerage System Definition

A sewerage system is a network of pipes, pumping stations, and treatment facilities designed to collect and transport wastewater from homes, businesses, and industries. It also manages stormwater runoff from rain and melting snow. There are primarily three types of sewerage systems: the combined system, the separate system, and the partially separate system. Each system has distinct characteristics based on what types of water they are designed to carry.

Combined Sewerage System Components

The question asks about the characteristics of a combined system of sewerage system. As the name suggests, a combined sewerage system is designed to carry a combination of different types of water. Specifically, it collects and transports both domestic/industrial wastewater and stormwater (rainwater) in the same pipe or conduit.

• Sewage: This refers to wastewater from residential, commercial, and institutional buildings, which includes human waste, kitchen waste, and other household discharges. Industrial waste, if non-hazardous and treatable, can also be part of the sewage.
• Rain Water (Stormwater): This is the runoff generated from precipitation (rain, snowmelt) that flows over surfaces like roofs, roads, and other paved areas, eventually entering the sewer system through street inlets and drains.

Therefore, a combined sewerage system handles both the dry weather flow (sewage and industrial waste) and the wet weather flow (rainwater) through a single network of pipes.

Analyzing the Options for Combined Sewerage

Let's examine each option provided in the context of a combined sewerage system:

• Option 1: Sewage and rain water

  This option accurately describes what a combined sewerage system is designed to carry. It includes both the regular wastewater (sewage, which also encompasses typical industrial waste) and the stormwater (rainwater). This is the defining characteristic of a combined system.

• Option 2: Dry weather flow and rain water

  Dry weather flow primarily refers to sewage and industrial wastewater that flows through the system during periods without precipitation. While this option mentions "dry weather flow" and "rain water," which are indeed components, "sewage" is a more direct and common term used to represent dry weather flow in such contexts. The distinction is subtle, but "sewage and rain water" is the most direct and universally understood combination for a combined system.

• Option 3: Sewage and industrial waste

  While industrial waste is often part of sewage, this option only describes the composition of wastewater and does not include rainwater. A system carrying only sewage and industrial waste (without rainwater) would typically be part of a separate sewerage system dedicated to sanitary waste.

• Option 4: Industrial waste and rain water

  This option excludes domestic sewage, which is a major component of wastewater. A system carrying only industrial waste and rainwater is not what is typically defined as a combined sewerage system; such systems usually handle all forms of wastewater and stormwater.

Conclusion on Combined Sewerage System

Based on the definition and common understanding in environmental engineering, a combined sewerage system is one that collects and transports both sanitary sewage (which includes domestic and approved industrial wastewater) and stormwater runoff (rainwater) within the same set of pipes. Therefore, the option stating "Sewage and rain water" correctly identifies the components carried by such a system.