Civil Engineering ETDs

Publication Date

Spring 4-6-2017


Algae have been identified as a source of renewable, clean energy, with much research being devoted to identifying high energy yield algae, energy extraction methods, and reactor design with mono-cultures of algae, but little research has been done on reactor design and operational conditions with mixed cultures of algae to improve productivity and solids separation. The objective of this study was to determine if the settling characteristics of mixed algal cultures can be enriched or improved through manipulation of reactor design characteristics by incorporating cyclic settling or floating phases into operation, timing of light/dark cycles, and/or control of the solids and hydraulic residence time. Photobioreactors constructed of cast acrylic were operated as sequencing batch reactors. Each reactor was run with identical feed, light/dark cycle, and working volume. Biomass measurements were taken regularly to measure growth and productivity. Density measurements were taken to observe operation conditions effects on solids separation. The sludge volume index (SVI) was used to assess the degree of solids separation in each reactor. Selection for algal biomass with good settling or flotation characteristics was assessed in experiment 1. In experiment 2 the effects of the light/dark cycle on settling and density were investigated. In experiment 3 the solids separation time, hydraulic retention time, and solids retention time were explored in regards to solids separation and biomass productivity. Experiment 4, the final experiment, investigated the effects of low and high carbon environments on solids separation, SVI, and biomass productivity. Results from these studies suggest that the light/dark cycle does not influence density or solids separation, low carbon environments are not an underlying mechanism for solids separation, and that good settling systems are more dependent on the species of algae, morphology and size of the settling flocs. Results from this study could be applied for practical purposes in solids separation.


Algal biofuels, solids separation, algal density, biomass productivity

Document Type




Degree Name

Civil Engineering

Level of Degree


Department Name

Civil Engineering

First Committee Member (Chair)

Andrew J. Schuler

Second Committee Member

Rebecca Bixby

Third Committee Member

Jose M. Cerrato