Document Type

Dissertation - Open Access

Award Date

2018

Degree Name

Doctor of Philosophy (PhD)

Department / School

Civil and Environmental Engineering

First Advisor

Guanghui Hua

Abstract

Eutrophication is one of the most widespread water quality problems in lakes and reservoirs. Frequent cyanobacterial blooms resulting from eutrophication can greatly damage aquatic ecosystems and pose a high risk to human health. Phosphorus (P) and nitrogen (N) are the major causes for eutrophic conditions and can enter to the aquatic ecosystem via different sources. The combination of phosphorus precipitation and sediment capping are promising technologies to minimize internal P loading and control harmful algal blooms in eutrophic lakes. Denitrification bioreactors have emerged as an important edge-of-field treatment technology to reduce nitrate-nitrogen loads from external sources. The objective of this study was 1) to evaluate the use of natural minerals to enhance the precipitation of phosphorus and cyanobacteria during alum coagulation, 2) to reduce phosphate release during sediment capping, 3) to evaluate the synergistic effects of polyaluminum chloride (PAC) and phoslock on phosphate and cyanobacteria removal during coagulation of eutrophic lake water, and 4) to evaluate the quantity and quality of dissolved organic carbon (DOC) leaching from agricultural residues including corn cobs, corn stover and barley straw to develop a new denitrification bioreactor system that uses a combination of an agricultural residue and woodchips for enhancing the nitrate removal efficiency. Laboratory coagulation experiments were conducted on a lake water spiked with Anabaena sp. using alum and four natural minerals (zeolite, calcite, limestone, and sand) to determine the effect of natural minerals on chlorophyll α, phosphate and turbidity removal. Long-term column sediment capping experiments were also conducted using different minerals after alum coagulation to evaluate their effectiveness in reducing phosphate release. The results showed that alum coagulation was able to remove 85-90% of phosphate and chlorophyll α from Anabaena sp. enriched lake water samples. The added natural particles did not substantially affect the removal of phosphate and chlorophyll α during combined alum and particle coagulation. However, natural particles substantially increased the floc settling kinetics during coagulation. The combined treatment with alum and particles also increased the resistance of the sediment to disturbance by mixing. The long-term sediment capping experiments showed that capping with natural minerals substantially reduced the levels of phosphate released from the sediment. Lake water samples were also treated with PAC, phoslock, and the combination of these two technologies to evaluate their removal efficiencies for phosphate, chlorophyll α, and DOC. The impact of doses, pH, DOC levels on the removal efficiencies were investigated. The results showed that PAC alone achieved 90% removal for phosphate and chlorophyll α, and 23.6% removal for DOC at the maximum dose of 8 mg Al/L. Phoslock alone removed phosphate, chlorophyll α, and DOC by 70%, 73.3% and 4%, respectively, at a dose of 800 mg/L. The combination of PAC (4 mg Al/L) and phoslock (300 mg/L) resulted in the removal of phosphate, chlorophyll α, and DOC by 90%, 100%, and 35%, respectively, suggesting that the combination of PAC (4 mgAl/L) and phoslock (300 mg/L) is able to significantly enhance the phosphate, chlorophyll α, and DOC removal efficiencies. The combined use of PAC and phoslock exhibited high tolerances to variations in pH and DOC levels for phosphate and chlorophyll α removal. The combination of PAC and Phoslock also increased the settling kinetics of the flocs. The final set of experiments showed that the DOC leaching potential followed the order of barley straw > corn stover > corn cobs > woodchips. Agricultural residues also exhibited faster DOC leaching kinetics and higher biodegradation potentials than woodchips. Although agricultural residues leached higher concentrations of nutrients during initial flush, those concentrations quickly declined within several days of leaching.

Library of Congress Subject Headings

Algal blooms -- Control.
Eutrophication.
Cyanobacteria.
Lake ecology.

Description

Includes bibliographical references (pages 94-112)

Format

application/pdf

Number of Pages

127

Publisher

South Dakota State University

Download

Share

COinS
 

Rights Statement

In Copyright