Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Madhumita B. Ray

Abstract

Benzalkonium chlorides (BACs) are a type of cationic surfactant and are highly adsorptive to negatively charged surfaces during the wastewater treatment process. They can, therefore, enter the aquatic environment via the suspended organic matter in wastewater effluents, and the terrestrial environment through the application of biosolids as a soil amendment for crop production or by the use of reclaimed wastewater for irrigation. This research investigated the fate of the two most commonly used BACs, benzyl dimethyl dodecyl ammonium chloride (BDDA; C12-alkyl chain) and benzyl dimethyl tetradecyl ammonium chloride (BDTA; C14-alkyl chain), individually and in mixture in various natural and engineered systems.

Under laboratory conditions, the following potential fate processes of these BACs were investigated: bacterial biodegradation, adsorption and leaching in various agricultural soils amended with biosolids, and plant uptake. A pure Pseudomonas strain biodegraded BACs, but BDTA was more toxic and inhibited the biodegradation of BDDA. Radiolabelled [U-14C-benzyl] BDDA showed about 85% of the initial concentration mineralized within 300 h. Adsorption studies of BACs to agricultural soils showed, BDTA adsorbed more on soil compared to BDDA. Organic carbon normalized adsorption coefficients (Log Koc, L kg–1) for BACs in the soils were >4, which suggested that BACs tend to retain on the organic fraction of soils. Soil column experiments indicated very low leaching (–1 BACs inhibited plant growth to 50% and BACs were found in the root and shoot tissues of both garden cress (Lepidium sativum) and lettuce (Lactuca sativa).

An advanced oxidation process (AOP) based on O3/H2O2 showed that about 1.28 g h–1 O3 and 200 mg L–1 of H2O2 at pH 11 degraded 90% of the initial BACs within 30 min. The AOP treated water was not toxic to two species of algae (Chlorella vulgaris and Chlamydomonas reinhardtii); growth rate was about 0.38 d-1 for treated and control samples compared to 0.01 d-1 for samples contained BACs without AOP. About 25 transformation products were identified in the AOP processes following six different degradation pathways.


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