# Math Solutions: Controlling Secondary Treatment

By Daniel Theobald, "Wastewater Dan"

Water Online’s “Math Solutions” series, presented by wastewater consultant and trainer Dan Theobald (“Wastewater Dan”), instructs operators on specific math solutions for operator certification exam preparation.

Wastewater sidestreams, per the U.S. EPA (EPA Publication 832R85102), constitute the flows generated within a wastewater treatment plant that are in addition to the plant influent — including supernatants, backwash waters, rinse waters, plant drainage water, etc. They can be recycled either to the head end of the WWTP or into secondary treatment units, and feature characteristics that are highly variable depending on the plant's treatment process and operation practices. Wastewater Dan presents math solutions to help operators successfully calculate sidestreams and control the secondary treatment process, as well as solve related math problems when posed on certification exams.

The following is a hypothetical question/wastewater scenario presented with a three-step instructional method to controlling secondary treatment:

The influent flow to a secondary treatment plant has a primary effluent of 4,791,667 gallons/hour (GPH) with 123 mg/L suspended solids and a sidestream of .97 MGD with 1,458 parts per million (PPM) suspended solids. What percentage is the sidestream suspended solids to the influent load of the secondary treatment plant?

Calculate primary effluent solids (lbs.):

Calculate sidestream solids (lbs.):

Calculate percentage of sidestream solids to total influent:

This is the Simulating Jar Test Results presentation in my series of “Math Solutions.” If you have specific wastewater math queries, please submit a question.