Graduation Semester and Year

2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

L Melanie Sattler

Abstract

ABSTRACT: Landfill leachates are considered now as a reusable source of water. Even irrigation projects are now considering use of non-traditional water sources, including treated wastewater, to augment supplies. Treated wastewater or leachate, however, may still contain many inorganic and organic pollutants of emerging concern, because traditional wastewater treatment plants are unable to remove all of them. Adsorbents have been demonstrated to effectively remove heavy metals and recalcitrant organics from leachate/wastewater more effectively, at lower cost, and using less chemicals and energy than many competing techniques. A single adsorbent with one pre-treatment, however, is not effective for simultaneously removing different types of water pollutants. This work proposes a novel solution: waste materials - rice husk (RH) and sewage sludge (SS) - will be modified with different physical/chemical pre-treatments to create a multi-sorbent mixture MultiSorb, which will be able to simultaneously remove different inorganics like heavy metal (Cu, Fe) and organics like per- and polyfluoroalkyl substances (PFAS) and Pharmaceutical and Personal Care Products (PPCP). The principal goal of this project was to develop a multiple sorbent mixture “MultiSorb” from readily available waste materials, to cost-effectively remove heavy metals and organics from leachate/wastewater. Specific objectives were: 1. Prepare/characterize adsorbents from rice husk and sewage sludge, using varied pre-treatments. 2. Develop and test PreSorb for removing natural organic matter (NOM), using batch tests. 3. Develop and test MultiSorb for removing perfluorinated compounds (PFAS), pharmaceutical and personal care products (PPCPs), and metals using batch tests. 4. Compare costs for leachate/wastewater treatment using PreSorb/MultiSorb with commercial activated carbon. The overarching hypothesis was that various tailored physical or chemical pretreatments on two waste materials, namely rice husk and sewage sludge, would produce a multiple sorbent mixture (“MultiSorb”) capable of simultaneously adsorbing greater amounts of metals, PFAS and PPCPs than regular commercial activated carbon (CAC). “PreSorb” was also developed, to be used in a pretreatment step to remove fulvic acid (i.e., NOM) from leachate/wastewater, prior to use of MultiSorb. The experimental design included 48 powdered adsorbents: 4 base materials (RH; rice husk ash, RHA; SS; sewage sludge char, SSC) x 4 chemical treatments (phosphoric acid, H3PO4; potassium hydroxide, KOH; zinc chloride, ZnCl2; none/physical activation only) x 3 temperatures (500, 650, 800ºC). Five controls were tested: unmodified RH, SS, RHA, SSC, and commercial AC (CAS#7440-44-0). Based on ability to adsorb NOM, 3 adsorbents were selected and combined to form ‘Presorb’: Rice Husk Ash-physically activated at 800°C (RHA-800), Sewage Sludge-chemically activated with ZnCl2 at 650°C (SS-650) and Rice Husk Ash-without modification (Cont. 2: RHA). In tests with real leachate, adsorption of NOM (represented by fulvic acid) by waste-made Presorb equaled or exceeded that of CAC. Since the cost of Presorb is lower than CAC, it could be used to adsorb NOM and then potentially disposed of without regeneration. Adsorbents were chosen to form Multisorb based on their ability to remove PFAS (PFOA and PFBA), PPCP (Atenolol, Naproxen, DEET, and Triclosan) and heavy metals (Cu and Fe). The selected adsorbents were Rice husk chemically modified with ZnCl2 at 500°C (RH-500-Zn), Sewage sludge chemically modified with ZnCl2 at 500°C (SS-500-Zn), and Sewage Sludge Char physically activated at 500°C (SSC-500). RH-500-Zn was found to be highly effective in adsorbing PFAS/PPCP, exceeding CAC by a factor of 2 for PFBA and a factor of 1.6 for PFOA. SS-500-Zn was a good adsorber for PFAS and PPCP, with percent adsorbed >73% relative to CAC in all cases except two. In terms of metals adsorption, SS-500-Zn was a strong performer, equaling or exceeding CAC. The waste-made best-performer adsorbents comprising ‘Presorb’ and ‘Multisorb’ were characterized using Scanning Electron Microscopy (SEM), Optical Microscopy, Brunauer–Emmett–Teller (BET) analysis, CHONS analysis, and Energy-Dispersive X-ray Spectroscopy (EDS). Most of these adsorbents are dominated by mesopores (favorable for PFAS and PPCP), with a very high pore volume and rough surface area. The surface area of one of the adsorbents (634 m2/gm) was close to that of commercial activated carbon (~700 m2/g). The adsorbents are dominated by several elements like C, O, Zn, Cl, Si, which can form functional groups favorable for adsorption. Finally, the waste-made adsorbents’ cost is found to be 22% of the cost of Commercial Activated Carbon.

Keywords

Leachate treatment, Wastewater treatment, Waste-made activated carbon, Sustainable waste management, Rice husk, Sewage sludge

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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