Graduation Year

2023

Document Type

Thesis

Degree

M.S.E.V.

Degree Name

MS in Environmental Engr. (M.S.E.V.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Daniel Yeh, Ph.D.

Committee Member

Maya Trotz, Ph.D.

Committee Member

Albert Rubin, Ph.D.

Keywords

Decentralized Wastewater Treatment, ion exchange regeneration, Non-sewered sanitation systems, struvite, ultrafiltration, zeolite, nitrogen

Abstract

The effective management of nutrients, such as nitrogen and phosphorus, in decentralizedwastewater treatment environments is a pressing challenge. These nutrients pose significant risks to the environment and public health when discharged into water bodies, while their recovery and reuse can help alleviate nutrient shortages in various industries, including agriculture. Conventional biological treatment methods used in centralized facilities are not suitable for decentralized systems due to operational complexities and space limitations. Chemical treatment mechanisms, such as adsorption, ion exchange, precipitation, and air-stripping, offer potential solutions but are accompanied by challenges like high costs and logistical issues. Therefore, finding a sustainable and efficient approach to nutrient management in decentralized wastewater treatment systems (DWTS) is crucial.

This thesis investigates the membrane-assisted recovery of solids (MARS) technology andits potential applications in various industries, with a specific focus on wastewater treatment. MARS technology offers a distinctive and effective solution for efficiently extracting nutrients from high-strength waste streams. The successful implementation of MARS relies on achieving optimal operation based on several criteria, including chemical transformation, effluent water and product quality, and membrane performance. However, achieving optimal operation often requires balancing different factors and complying with specific constraints determined by the application and characteristics of the wastewater source. The precipitation of Magnesium Ammonium Phosphate (MAP) solids, extensively studied as a crystallization process, emerges as a promising approach to enhance the design and performance of the MARS system. As a result, particularly the work described in Chapter 4, aimed to address the identified limitations of the MARS system from previous studies to improve its overall effectiveness.

On the other hand, the regeneration of ion-exchange reactors in non-sewered sanitationsystems poses numerous challenges, including limited regenerant volumes and high ammonium concentrations. Natural zeolites offer a cost-effective alternative to synthetic ion-exchange materials. To address slow and ineffective regeneration, Chapter 5 of this thesis integrates the MARS system with the regeneration process. It assesses the impact on regeneration kinetics and efficiency, explores regenerant solution reuse, and investigates regenerating zeolite-based systems at less alkaline pH levels to support nitrogen recycling efforts as well as prolong their operational lifespan.

MARS v2.4, the final design iteration, demonstrated the highest performance and stability.The integration of the optimized MARS system successfully enhanced the regeneration of a zeolite-based cation-exchange reactor, increasing the desorption rate by around 50% and removing 52% of the total ammonium during two regeneration-recovery cycles. However, the co-desorption of potassium ions resulted in the formation of unwanted co-precipitates, affecting magnesium availability and chemical conversion rates. Purity testing revealed the presence of magnesiumcontaining co-precipitates and trace amounts of heavy metals in the solid products.

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