Design value of surface loading for horizontal flow circular sedimentation

The design value of surface loading for horizontal flow circular sedimentation is given as 30-40m3/m2/d (option A). This value represents the maximum flow rate of water per unit area that can be applied to the sedimentation tank without compromising its efficiency. Let's understand this in detail.

Horizontal flow circular sedimentation
Horizontal flow circular sedimentation is a common method used for the separation of solids from liquids in wastewater treatment plants. In this process, wastewater is introduced into a circular tank and allowed to flow horizontally through the tank. The suspended solids in the wastewater settle down under the influence of gravity, forming a sludge layer at the bottom of the tank. The clarified water is collected at the top and discharged for further treatment.

Surface loading
Surface loading refers to the rate at which wastewater is applied to the surface area of the sedimentation tank. It is typically expressed in terms of volume per unit area per day (m3/m2/d). The surface loading rate determines the hydraulic and solids loading on the sedimentation tank, which in turn affects its performance.

Design value
The design value of surface loading for horizontal flow circular sedimentation is determined based on various factors such as the settling characteristics of the suspended solids, the desired effluent quality, and the size of the sedimentation tank. The aim is to find a balance between maximizing the treatment capacity of the tank and ensuring efficient sedimentation.

Explanation of the answer
Option A, 30-40m3/m2/d, is the correct answer because it falls within the typical range for the design value of surface loading in horizontal flow circular sedimentation. This range is commonly used in practice and has been found to provide effective and efficient sedimentation.

By applying a surface loading rate within this range, the sedimentation tank can effectively remove suspended solids from the wastewater, producing a clarified effluent. If the surface loading rate is too low, the tank may be underutilized, resulting in a larger tank size and increased capital and operating costs. On the other hand, if the surface loading rate is too high, the tank may become overloaded, leading to poor sedimentation and reduced effluent quality.

Therefore, the design value of surface loading for horizontal flow circular sedimentation is crucial in achieving optimal performance and ensuring the desired effluent quality. The range of 30-40m3/m2/d provides a practical and reliable guideline for designing sedimentation tanks in wastewater treatment plants.