#### Guest Column | November 30, 2016

By Daniel Theobald, "Wastewater Dan"

Water Online’s “Math Solutions” series, presented by wastewater consultant and trainer Dan Theobald (“Wastewater Dan”), instructs operators on hydraulic loading calculations.

Hydraulic loading is defined in a wastewater treatment process unit as the volume of wastewater applied to the surface of the process unit per time period. It is often expressed in gallons per day per square foot (gpd/ft2).

Hydraulic loading design criteria are often expressed as maximum days to optimize water clarity resulting from actual square feet surface area per incoming flow rate.

Water clarity is often improved by either increasing surface area or decreasing incoming  flow rate.

This tool for operators, represented through video tutorials, offers mathematical templates to master the hydraulic loading gallons per day per square foot by evaluating the incoming flow and surface area.

The tool also provides definitions, explanations, and alternative applications for the calculations beyond the specific examples presented. In addition to operators, it may also serve educators, engineers, regulators, and others.

A representative hydraulic loading math word problem followed by exact step-by-step solutions is presented  below.

Determine the number of the four (4) large, idle clarifiers ‘out of service’ that are needed to put ‘in service’ in the wastewater treatment plant. Assume flow of 2,000 gpm from 7:00 a.m. to 5:00 p.m. and 511.9048 gpm from 5:00 p.m. to 7:00 a.m. Seven (7) small clarifiers in service have a diameter of 213.2968387 feet and the four large clarifiers in service have a diameter of 282.166324 feet; the design-required gpd per square foot must not exceed 2.75.

Flow Calculation Solutions:

Flow – Daytime (10 hours):

Flow – Nighttime (14 hours):

Flow – gpd (24 hours):

Surface Area Calculation Solutions:

Surface area – One small clarifier:

Surface area – One large clarifier:

Surface area – All clarifiers in service:

Gallons per day per square foot (gpd/ft2):

Combined required surface area (ft2):

Number of idle large clarifiers to put in service:

Playlist of 35-plus ‘conversions’ wastewater math calculations

Playlist of 20-plus ‘volume’ wastewater math calculations

Playlist of all 160-plus Math Solutions

This is the Hydraulic Loading Calculations presentation in my series of “Math Solutions.” If you have specific wastewater math queries, please submit a question