Research

Interactions of graphene-based nanomaterials with microwaves: Towards technology to regenerable nano-adsorbents

Inadequate access to clean water and increasing levels of pollution are among the most concerning global problems with expected increases in severity in coming decades. Therefore, transformative and ingenious solutions that can overcome the barriers presented by difficult-to-remove pollutants are needed in wastewater reuse or potable water treatment to protect the environment and address the clean water scarcity that are challenging for traditional approaches. In the past two decades, bottom-up fabricated carbon-based nanomaterials (e.g., carbon nanotubes, graphene nanosheets) have been shown to be superior and targeted adsorbents for organic pollutants (e.g., pharmaceuticals and personal care products, illicit drugs, perfluorinated chemicals, endocrine disrupting compounds, dyestuff, pesticides and herbicides) compared against traditional granular activated carbon produced from top-down methods starting from coal, peat, or other heterogeneous materials. Nanomaterial-based sorbents have higher selectivity towards adsorbates, greater adsorption capacity, and faster reaction kinetics. Despite the advantages of using nano-adsorbents in drinking water treatment, there remains a substantial cost barrier to applying them broadly. Nanomaterials are currently orders of magnitude more expensive to produce than the conventional carbon-based adsorbents, and may only be cost-effective if used multiple times before disposal. Therefore, regenerating and reusing carbon-based nano-adsorbents encompass an opportunity to help overcome the predominant cost limitation of applying carbon-based nano-adsorbents in drinking water treatment, enable their ubiquitous use, and sustainably improve current practice.

Recently, carbon-based nanoparticles were reported to generate extraordinary heating responses under microwave irradiation, which leads to pollutant oxidation or volatilization; however, the underlying microwave heating mechanisms are not fully understood. Materials with favorable dielectric properties such as silicon carbide, magnetic iron oxide, and other transition metal containing oxides can convert microwave energy into heat at common microwave frequency (i.e., 2.45 GHz). Nanomaterials exert more reactivity due to their exceptionally small sizes because there are more atoms/electrons on their surfaces that respond to the changes in the surrounding environment when compared to bulk materials. Carbon nanomaterials’ extraordinary ability to convert microwave energy into heat has the potential to shift the paradigm of carbon-additive enhanced microwave heating. Advancing in this research field can influence an array of industries including biomedicine (e.g., microwave-enabled imaging), food industry (e.g., food drying, pasteurization and other heat involved processing), telecommunication (e.g., microwave and radio wave communication), energy industry (e.g., efficient combustion of fuels), and environmental remediation (e.g., ex-situ soil remediation, spent carbon regeneration).

Immobilization of nano-scale adsorbents into polymeric matrices: Tradeoff between pore accessibility and physical integrity

The disposition of nanoparticles in the electrpspun polymeric macrostructure can be tuned to develop superior hybrid polymer/nanomaterial adsorbents. These nanomaterials can be fully or partially encapsulated by the fibrous polymers. The thin polymer film surrounding the particles is hypothesized to influence the adsorption of pollutants by the adsorbent surfaces. By tuning nanoparticle size and hydrophobicity of the polymer (e.g., polystyrene) the dispersion state and exposure of the nanoparticle can be engineered and the diffusion of adsorbate into the pores of the adsorbent can be predicted. This would give the novel hybrid material superior tunable adsorbent characteristics that can selectively remove pollutants from water.

The fabricated material will be evaluated as filtration/pre-filtration units, pipe filters, sediment caps and it can be evaluated as suspended adsorbent scaffolding. Physical characteristics of these materials such as permeability, durability and integrity will be tested in addition to their functionalities. Eventually, these novel materials containing new generation nano adsorbents are going to be optimized for good water permeability, ease-of-operation, in-situ and ex-situ regeneration performances, minimal nanoparticle and polymer loss. Integrating this technology into a unit water treatment process is the long-term outcome of the projected work. In addition, investigating the interactions between nanoparticles, contaminants, and polymers will let us gain a mechanistic insight to the removal mechanism and fundamental knowledge will be generated while a novel technology is being generated.

Transformation and removal of cannabinoids from engineered aquatic systems

Cannabis, commonly known as marijuana, is the most widely used illicit drug with about 192 million users (3.9% of world’s population) worldwide, aged between 15 to 64 as per 2016 estimates (UNODC, 2018). In the United States, cannabis was categorized as a schedule I (the most stringent controlled-substance category) drug with the passage of the Control Substance Act of 1970 (US DEA, 2018). There have been multiple failed lawsuits (e.g., United States v. Oakland Cannabis Buyers’ Cooperative) (Gonzales v. Raich, 2005) to federally reschedule marijuana and approve for medical use over the past few decades. However, 31 states, including Washington D.C., have independently enacted laws that are in direct contradiction with the federal schedule since California’s passage of Proposition 215 in 1996 (Proposition 215, 1996). This state-legalization effort is generally linked with the increasing cannabis usage (Cerdá, Wall, Keyes, Galea, & Hasin, 2012). The compassionate medical use of marijuana and continued non-federal legalization efforts have increased its reach to over $22 billion by 2022 (Business Marijuana Daily, 2018), which raises questions on their environmental release and potential impacts. The literature on THC and its metabolites is sparse with a few studies focusing on detection of these compounds in the natural environment at a trace level (Pal et al., 2013; Peng, Hall, & Gautam, 2016). A few studies have examined the destructive removal of THC-COOH from waste- and surface-waters with photo-degradation (Boix et al., 2014; Y. Park, Mackie, MacIsaac, & Gagnon, 2018), chlorination (Boix et al., 2014; González-Mari˜no, Rodríguez, Quintana, & Cela, 2013), and zerovalent iron (Mackie, Park, & Gagnon, 2017; Mackuľak et al., 2016). These processes can completely remove and/or transform THC-COOH , however, its transformation by-products can be equally or be even more toxic in surface waters (González-Marino et al., 2013). Effective removal of these compounds from water and wastewater continues to be a critical gap in the environmental literature. 

Increasing biogas production from wastewater residual sludge by nano-amplified microwave pretreatment method

Anaerobic digestion converts organic constituents of waste activated sludge to biogas in the absence of free oxygen. There are four key biological mechanisms of anaerobic digestion: hydrolysis, acidogenesis, acetogenesis and methanogenesis. Among these steps hydrolysis is the rate-limiting step that is responsible from breaking complex molecules into simpler sugars and fatty acids. There are several studies in the literature reporting successfully achieving hydrolysis prior to anaerobic digestion by employing mechanical, chemical or biological methods. The technology idea that is being investigated in this project is enhancement of biogas quality and quantity using a single-step thermal pretreatment method prior to anaerobic digestion. 

Proposed Technology: Nano-Enabled Microwave Pre-treatment prior to Anaerobic Digestion
Proposed Technology: Nano-Enabled Microwave Pre-Treatment Prior To Anaerobic Digestion
Massachusetts: A Hotspot for Municipal Wastewater Sludge Generation Presenting an Opportunity to Maximize Biogas Revenue and Minimize Digested Sludge via Nano-Enabled Microwave Irradiation.
Massachusetts: A Hotspot For Municipal Wastewater Sludge Generation Presenting An Opportunity To Maximize Biogas Revenue And Minimize Digested Sludge Via Nano-Enabled Microwave Irradiation.

Capacitive deionization for selective bromide removal from surface waters

Bromine is a trace element in the Earth's crust and is commonly detected in natural waters at various levels. In water treatment plants bromide (Br-) reacts directly to produce disinfection byproducts (DBPs) and will form intermediates in the formation of organic DBPs (e.g., THM, HAA, and haloacetonitriles).  The toxicity of brominated DBPs are concerning. However, very few studies directly consider Br- removal  from natural waters because of its low concentration relative to chloride and the poor selectivity of separation processes. Thus, Br- poses a harm to consumers and can limit the capacity of water utilities to be compliant with current DBP regulations.

Capacitive deionization (CDI) has recently gained popularity as an alternative way of deionizing natural waters. Unlike reverse osmosis and distillation, the CDI process does not require high pressures or temperatures. It can operate at room temperature with the application of a small voltage (e.g., 1.0 - 1.2 V) and process can be reversed by lifting the electric current. During operation, raw water is passed through porous electrodes while a potential difference is applied to the cell. Applied voltage forms the electric double layer, causing ions to migrate towards the electrodes, which leads to adsorption of ions and decreases the overall ionic strength of water. The main objective of this study is to utilize the principles of capacitive deionization and the difference in electrochemical oxidation of bromide and chloride ions to selectively remove bromide from natural waters. Our results indicate that it is possible to selectively remove bromide from natural waters utilizing the lower electrochemical formation potential of bromine gas (1.09 V vs. standard hydrogen electrode) compared to chlorine formation (1.36 V vs. standard hydrogen electrode).