Graduation Year

2022

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

Albert Rubin, Ph.D.

Committee Member

Treavor Boyer, Ph.D.

Keywords

Magnesium ammonium phosphate (MAP), Ultrafiltration, Zeolite regeneration

Abstract

Increasing global populations will result in a rise of eutrophic wastewater and an increased need in food supply. Both problems share a commonality: nutrients. Not all communities are equipped to handle one or both of those challenges, considering that typical solutions require large and energy intensive technologies. Wastewater treatment in most major cities is done through centralized treatment plants, which is not feasible for places with limited resources. Decentralized wastewater treatment systems (DWTS) have been developed as an alternative solution for those communities, but they still struggle to sustainably treat nutrients such as ammonium (NH4) and phosphate (PO4^(3-)). Zeolite has shown promising results at removing NH4 over long periods of time in a decentralized context, but it is limited by its need to be regenerated (Castro et al., 2021). Another treatment alternative is the precipitation of ammonium magnesium phosphate (MAP), a crystal that forms in the presence of at least equimolar concentrations of NH4, magnesium (Mg) and phosphate (PO4(3-)). MAP precipitation technology has been explored in both centralized and decentralized contexts for its ability to recover nutrients in the form of a slow-release fertilizer. Creating an opportunity to address the two global challenges previously described. MAP precipitation technology almost exclusively relies on sedimentation as the main tool for separating and recovering solids (Regy et al., 2002; Stratful et al., 2004). To offer an approach that could expedite the process and treat larger volumes at once, the concept of membrane assisted recovery of solids (MARS) was created. MARS pairs together a MAP crystallization reactor with a tubular ultrafiltration (UF) membrane for the purposes of nutrient treatment and recovery. The development of MARS was tested under a concentration of 5 g/L NH4-N to simulate wastewater generated from zeolite regeneration. Multiple experiments were conducted to assess the quality of the effluent produced, the overall membrane performance, and the solids being generated. Preliminary studies showed that MAP precipitation achieved over 90% removal of NH4 and that the membrane was able to sustain MAP filtration for 3 days before showing signs of fouling. MARS under batch operation confirmed that a reaction period prior to filtration is needed to reach chemical equilibrium. The batch studies also confirmed that the membrane specific flux is able to be restored up to 20% using a combination of physical and chemical cleaning strategies. MARS was tested under continuous flow, which included a solid harvesting loop to protect the life of the membrane. Although there is still room for improvement in design, the overall concept of MARS showed promising results. Possible applications will be described in detail to serve as motivation for others to continue the development of MARS.

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