The New Jersey Institute of Technology's
Electronic Theses & Dissertations Project

Title:	Colloidal behavior of nanobubbles and their application in enhancing plant growth: mechanisms of nanobubble interactions with microbial and soil species
Author:	Xue, Shan
View Online:	njit-etd2023-047 (xxix, 230 pages ~ 7.2 MB pdf)
Department:	Department of Civil and Environmental Engineering
Degree:	Doctor of Philosophy
Program:	Environmental Engineering
Document Type:	Dissertation
Advisory Committee:	Zhang, Wen (Committee chair) Marhaba, Taha F. (Committee member) Liu, Changqing (Committee member) Rodriguez-Freire, Lucia (Committee member) White, James F., Jr. (Committee member)
Date:	2023-08
Keywords:	Agriculture Ceramic membrane Colloidal behavior Irrigation water Nanobubble Plant
Availability:	Unrestricted
Abstract:	Climate change has resulted in increasing uncertainties of water resources and disturbance on agricultural activities. For example, the shortage of water resources, land erosion and pollution from runoff significantly affect agricultural sustainability. This dissertation research focuses on the fundamental studies of nanobubble (NB) water and explores the benefits for irrigation to enhance plant germination and growth. Unlike bulk bubbles, NBs exhibit prolonged stability in water and possess large surface areas that facilitate efficient mass transfer and potential tailored reactions (e.g., disinfection). However, the enhancement mechanisms for NBs on seed germination and plant growth remain elusive. This research first evaluated the membrane bubbling method to produce NBs in water and provided insights into the optimization of bubble water with desirable quality such as high bubble concentrations and small bubble sizes. The results demonstrate that the ceramic membranes with a hydrophilic surface and hydrophobic pores produced greater levels of NBs with small sizes compared to the pristine or surface hydrophobized membranes. Additionally, this study discovered that dissolution kinetics of oxygen NBs are strongly influenced by the initial bubble size and the dissolution could lead to shrinkage or expansion of bubbles in water. Smaller NBs exhibit a faster increase in DO, while larger NBs can result in higher equilibrium dissolved oxygen (DO) levels. Oxygen NBs significantly enhanced the oxygen transfer efficiency compared to microbubble aeration, exhibiting a remarkable increase of up to 300%, as well as a mass transfer coefficient of 21.05 h-1. Lastly, this study provides compelling evidence that NBs have a positive impact on seed germination and plant growth through changing various soil properties such as soil pH, oxygen content, redox potential and nutrient release, enzymatic activities and microbial communities. For example, oxygen NBs significantly boosted peroxidase activity in tomato leaves, with an impressive increase of 100%-1000%. The composition and structure of rhizosphere microbial communities in early tomato plants were found to be influenced by irrigation frequency, NB concentration, and the specific types of NBs used. Through discovering and characterizing these intriguing nanoscale phenomena and processes, this research aims to deliver new insight into novel sustainable agricultural practices using NB water that may increase agricultural production and reduce water and chemical fertilizer uses.