Question

If you analyzed waste water directly after primary treatment, what would you notice? A. Harmful bacteria and other biological agents have been killed or removed B. The water is potable C. Much of the dissolved solids have been removed D. Many suspended solids have been removed E. The water is mostly sludge

Short answer

D. Many suspended solids have been removed

Step-by-step solution

- Understand the Primary Treatment Process

Primary treatment in wastewater treatment primarily involves the physical removal of suspended solids via settling.

- Identify What Remains After Primary Treatment

After primary treatment, some smaller suspended solids and dissolved substances still remain. This stage does not typically remove harmful bacteria or make the water potable.

- Evaluate Each Option

A. Harmful bacteria and other biological agents are not removed during primary treatment.B. The water is not potable after primary treatment.C. Primary treatment does not remove much of the dissolved solids.D. This is correct; many suspended solids are removed in primary treatment.E. The water is not mostly sludge after primary treatment.

- Select the Correct Answer

From the evaluation, the correct option is D. Many suspended solids have been removed.

Key concepts

Suspended Solids Removal

Primary wastewater treatment is a crucial first step in cleaning wastewater. This initial phase is designed to remove suspended solids through a process known as physical settling. When wastewater enters a treatment facility, it contains various suspended particles that need to be eliminated.
The treatment system typically involves large settling tanks or clarifiers where the wastewater is held for a period. As the water stays still, gravity helps heavier solids to settle at the bottom of these tanks, effectively separating them from the water.

Eventually, these settled solids, sometimes referred to as sludge, can be treated further or disposed of properly. By the end of the primary treatment, many large solids have been removed, leading to clearer water ready for the next treatment stage.

Wastewater Treatment Stages

Wastewater treatment is typically divided into several stages, each designed to progressively clean the water more thoroughly:

• Primary Treatment: This stage focuses on the physical removal of suspended solids through settling processes. Large debris and heavier particles are removed here.
• Secondary Treatment: At this stage, biological processes, often involving microorganisms, are used to treat the water. Here, dissolved and suspended organic matter is broken down.
• Tertiary Treatment: This is the final polishing phase, where remaining impurities are removed. Processes like filtration, chemical treatment, and disinfection (to kill harmful bacteria) are used.

Each of these stages builds upon the previous one, ensuring that the wastewater becomes increasingly cleaner and closer to potable standards.

Physical Settling Process

The physical settling process is key in the primary treatment phase. Here’s how it works:

• Influx of Wastewater: Wastewater enters the settling tanks at a controlled rate.
• Quiescent Conditions: The tanks provide a calm environment, allowing particles to naturally settle due to gravity.
• Accumulation of Sludge: The settled particles form a layer of sludge at the bottom, while the lighter water rises to the top.
• Removal of Clarified Water: The clear water on top is then removed for further treatment.

It's important to remember that, while this process is effective for removing larger particles, it does not address dissolved substances or bacteria. This underscores the need for subsequent stages of wastewater treatment.