Enhancing Resource Recovery

Abstract

This thesis examines the feasibility of Selectrodialysis as an innovative and efficient technology for nutrient recovery from greenhouse wastewater. The study aims to address the critical challenges of water quality degradation and Na+ accumulation in greenhouse operations, where the selective recovery of ions such as Na⁺, Ca²⁺, and Mg²⁺ is essential for maintaining optimal plant health and agricultural productivity.

The research evaluates the performance of SED by investigating the effects of various operational parameters, particularly voltage, and the presence of competing cations on ion transport efficiency. Experimental analysis revealed that SED could effectively achieve selective ion separation at an optimal voltage of 9V, which maximizes ion fractionation and migration rates while maintaining moderate energy consumption. However, higher voltages resulted in increased energy demands, water dissociation, and concentration polarization, which adversely impacted the selectivity of specific ions, particularly Na⁺.

The presence of competing cations, such as Ca²⁺ and Mg²⁺, was shown which significantly impacts the Na⁺ transport by reducing its migration rate and recovery efficiency. These effects are primarily due to competitive interactions and increased membrane resistance caused by concentration polarization, particularly at higher concentrations of divalent cations. Understanding these interactions is crucial for optimizing the recovery process and energy efficiency in systems where competing cations are prevalent.

The study also highlights the economic implications of implementing SED compared to conventional methods like RO. While SED demonstrates technical advantages in terms of selective ion recovery and reduced chemical usage, its broader adoption is constrained by significantly higher capital and operational costs. The total capital cost for SED was found to be over 13 times higher than that of RO, primarily due to the specialized membranes required for selective ion transport and the additional electrical components necessary for ion migration. Additionally, operational costs for SED are elevated due to higher energy consumption, which is more than double that of RO, and increased maintenance expenses resulting from the complexity of the system.

Despite its technical feasibility, the economic analysis suggests that SED may be better suited for niche applications where selective ion recovery is critical, such as in high-value greenhouse operations where precise nutrient control is essential. To improve the economic viability of SED, future research should focus on integrating renewable energy sources, experimenting with new membrane materials, and exploring different operational modes to reduce energy consumption and overall costs.