Date of Award

2015

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Biological and Irrigation Engineering

First Advisor

Ronald C. Sims

Abstract

The Logan Lagoons, Logan City’s Wastewater Treatment Facility ensures 15 million gallons of wastewater are cleaned and filtered each day. With the implementation of new and stricter wastewater effluent standards, the city of Logan now has to guarantee the phosphorous concentration in the effluent is also reduced. Algal biomass produced and harvested from the lagoons has been proven to affect the way nitrogen and phosphorous are removed, while having the potential to be converted to biofuels. Therefore, implementing a secondary type clarifier in the Logan Lagoons would produce treated water with a reduced phosphorous concentration, and algae feedstock for biofuel production.

While several factors influence clarifier design, the settling characteristics of flocculent algae in wastewater were the main focus of this project. Sedimentation columns were used to calculate surface overflow rate, detention time and algae percent settling. The addition of chemicals and variation of zeta potential, to promote flocculation and higher algae percent settling, were also studied.

Preliminary results revealed a large fraction of the algae can be settled by means of sedimentation prior to chemical dosing. A suspended settling efficiency of 40%-60% with a detention time of 2-2.8 hours was attained and a surface overflow rate between 51-69 ft/day was calculated. Furthermore, a pH of 8-11 influenced a neutral zeta potential, increasing algae percent settling and phosphorous removal even further. A brief discussion about other factors that affect algae percent settling and future tests for a complete scale-up procedure are also included in this report.

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