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Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Bassi, Amarjeet.

2nd Supervisor

DeGroot Christopher.

Co-Supervisor

Abstract

Microalgal cultivation process had been extensively studied in the past for its potential for pollutant removal and high value product production. In this study, a biofilm photobioreactor was proposed to decrease operation cost and enhance biomass yield, based on the utilization of chitin. Main goal of this study is to utilize chitin as a cheap nitrogen source for algal growth and to enhance microalgal immobilization process in a biofilm adhesion system. This study can be generally divided into 3 stages, from laboratory to pilot scale. Stage 1 investigated the biological activities (i.e. cell growth, nitrogen release and phosphorus removal) as well as environmental impact when utilizing 3 different types of chitin: . In the stage 2, a poly (vinyl alcohol)/chitin blend hydrogel was proposed to enhance hydrogel property and biofilm adhesion. Finally in the third stage, an umbrella biofilm photobioreactor was investigated for: (1) computational fluid dynamics modeling for topology changes, (2) application of poly (vinyl alcohol)/chitin blend hydrogel for both nutrient uptake and biofilm growth in an open system.

In stage 1, algae Chlorella vulgaris CPCC 90 utilized 3 different variants of chitin as nitrogen source: chitin. Experiments were conducted in 500 ml Erlenmeyer flasks with nitrogen deficient cell media. Overall, by utilizing chitin, maximum cell number was 3.3*107, 1.3*107, and 1.9*107 cells ml-1, respectively, over a 13-day cultivation process. Other than that, no nitrogen release was observed which implied rapid and efficient nitrogen uptake. Compared to chitin, chitin was shown to have the most algal biomass yield. In stage 2, The addition of chitin enhanced hydrogel surface roughness, and resulted with a maximum storage modulus of 0.047MPa. As for biofilm growth, an average of 0.4mm biofilm thickness was observed. It was found that blending chitin particles with hydrogel is beneficial for biofilm attachment and growth. For the last stage, in USPBR, biofilm was observed on hydrogel surface, a maximum biofilm thickness of 0.3 mm and a maximum algal concentration 0.4 g biomassL-1 were achieved. Furthermore, pH value of the system was stable around 7, which is optimal for algal growth, and a 45% removal rate of phosphate was observed. The study led to a novel approach that combined chitin, hydrogel, and biofilm photobioreactor for low-cost algal cultivation and harvesting process.

Summary for Lay Audience

Microalgae are a single cell life form that can use sunlight to survive and reproduce. During the process, carbon dioxide and other pollutant in wastewater can be removed. Then, harvested microalgae can be used for high value product extraction. However, currently microalgae cultivation process is still limited by high energy and operation cost input. In this study, the usage of chitin (a natural substance found in many life forms) was investigated, a chemical can be utilized by microalgae to grow, and poly (vinyl alcohol) hydrogel, a material that allows microalgae to attach to, to decrease cost and energy limitations. This is study can be divided into 3 stages. In stage 1, algae were cultivated on 3 types of chitins that have different molecule arrangement, and particle size. It was showed that chitin extracted from crab shell result with highest microalgal growth. In stage 2, chitin and hydrogel were combined to create a system to allow microalgae cell to attach to and grow on. It was showed that after blending chitin with poly (vinyl alcohol) hydrogel. The combination improved the surface texture and firmness, which can be beneficial for biofilm initial attachment as well as biomass harvesting. In stage 3, this new chitin-hydrogel system was tested in a larger setup to evaluate how well it supports microalgae attachment. The study investigated a new method for biofilm attachment and biomass growth.

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