Year of Publication

2012

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Agriculture; Engineering

Department

Biosystems and Agricultural Engineering

First Advisor

Dr. Michael D. Montross

Abstract

Algae can be used to treat wastewater and manure while producing a feedstock for renewable energy. Algae require nutrients to achieve their maximum growth and manure could provide those nutrients, thereby reducing the cost of algae production and the impact of manure treatment. Algae concentration during cultivation is a critical variable that is difficult to measure due to the high concentration of suspended solids present in manure. This dissertation addresses methods to measure algae concentration in the presence of manure solids.

Quantifying the algae concentration gravimetrically or by optical density was unreliable due to manure solids interfering with the measurement. Cell counting to determine algae concentration was accurate but time consuming, subjective, required dilution of concentrated samples and only small sample volumes could be measured. Chlorophyll extraction was a consistent method to determine algae concentration in manure based media, but the model had to be adjusted to account for solids interference. The proposed equation predicted chlorophyll concentration from Chlorella vulgaris in dairy manure better than the reference equation. Different algae strains (Chlorella vulgaris, Cylindrocystis sp, and Scenedesmus sp.) and manure sources (dairy, beef, swine, and sheep) were used to validate the proposed equation and all combinations had a linear relationship between actual and predicted chlorophyll concentration, but not all comparisons followed a 1:1 reference line. Even with chlorophyll extraction the manure solids interfered with the chlorophyll measurement and calibrations had to be developed based on manure type.

A method based on spectral deconvolution was used to quantify algae concentration in the presence of manure without chlorophyll extraction. Various manure-algae mixtures were scanned with a spectrophotometer. Algae concentration was accurately determined with the four manure sources. Measuring algae concentration required absorbance spectra from 600 to 700 nm and manure solids concentration between 280 and 350 nm. Spectral deconvolution was able to differentiate algae concentration and manure solids concentration with a Pearson coefficient of 95.3% and 99.8% respectively. This method proved to be an accurate and efficient method for estimating algae and manure solids content in unprocessed samples. A critical factor was utilizing appropriate reference spectra.

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