Thesis Defense Preperation (GAC)

How does mass spec separate ions based on their mass to charge ratio?

An electric field is applied and ions with the same charge but a lower molecular weight move faster than those with a higher molecular weight. While ions with the same molecular weight but a higher charge move faster than those with a lower charge.

Tandem mass spec over singular

improves resolution

UPLC vs HPLC

UPLC is an advanced form of HPLC that uses sub-2 m particle columns and higher pressures (up to 15,000+ psi) to achieve faster analysis times, higher resolution, and increased sensitivity compared to conventional HPLC. While HPLC typically uses 3–5 m particles and operates at lower pressures, UPLC significantly reduces solvent consumption and run times (2–5 minutes vs 10–60 minutes)

PDA detector

measures how much (UV?) light is absorbed by the sample passing through the flow cell at a range of wavelengths. The intensity of transmitted light then decreases (if absorbs UV) which the detector then compares transmitted ti its reference and converts it into an electrical signal which we see as peaks. UV detectors (im assumming pda is the same? allows quantification of compounds with UV absorbing functional groups (aromatic rings, double bonds)

why is uv 254 used to measure dissolved organic matter concentration

Ultraviolet light at 254 nm is strongly absorbed by conjugated double bonds and aromatic rings within organic compounds. As DOM concentration increases, light absorbance at this wavelength increases proportionally, serving as a real-time, inexpensive surrogate for total organic carbon (TOC) and COD

why do conjucated double bonds and aromatic rings absorb uv 254

Conjugated double bonds and aromatic rings absorb UV light at 254 nm because this specific wavelength corresponds to the energy required for -electrons to jump from a lower-energy bonding orbital () to a higher-energy antibonding orbital (). This process is known as a transition, enabled by the low energy gap in conjugated systems

Van der waals vs electrostatic

Van der Waals forces and electrostatic interactions are distinct mechanisms in granular activated carbon (GAC) adsorption, primarily differing in their dependence on molecular polarity, charge, and the range of action. Van der Waals forces are weak, non-specific, short-range intermolecular forces that attract all molecules (especially non-polar ones) functioning on induced dipoles, while electrostatic interactions are stronger, charge-dependent attractions between oppositely charged species

How does lime softening remove Ca and Mg

raises the pH and causes the metals to precipitate out

Why does conventional treatment work for internal but not external cyanotoxins?

because it is designed to remove particles, not small dissolved molecules. Conventional treatment (coagulation/flocculation, sedimentation, filtration) is highly effective at removing intact cells and thus cell bound toxins, because it targets particles: cells aggregate into flocs and are settled or filtered out. Conventional clarification and sand filtration do not remove such dissolved contaminants efficiently

Cyanotoxins vs metals

Cyanotoxins are neutral/weakly charged organic molecules, not multivalent cations. They usually do not precipitate as solids under drinking-water pH, nor bind strongly to metal hydroxide flocs the way metal ions do. Without a precipitation or strong adsorption step, coagulation–sedimentation–sand filtration has little effect on truly dissolved organics

Why doesn’t conventional treatment work for PFAS

PFAS are extremely stable, water soluble organic ions that don’t precipitate, biodegrade, or adsorb well under “normal” plant conditions, so conventional treatment has little to act on. • very stable (strong C–F bonds), resistant to oxidation and biodegradation. • often anionic and fairly hydrophilic, especially short chain PFAS, so they stay dissolved and do not precipitate or strongly sorb to metal hydroxide flocs

types of adsorption by GAC

Across contaminants, GAC adsorption is usually controlled by a mix of forces. Hydrophobic interactions are often primary for nonpolar/fluorinated species; electrostatic interactions dominate when strong charge complementarity is present; van der Waals and π–π interactions provide additional, sometimes secondary, contributions, especially for neutral or aromatic organics

How do hydrophobic interactions work

Hydrophobic interactions on granular or powdered activated carbon arise because water prefers to interact with itself rather than with water hating (hydrophobic) solutes. This drives those solutes out of bulk water and into the carbon’s hydrophobic pores and graphitic surfaces

Three main componants of natural organic matters

humic acids, fulvic acids, and humin

fulvic acids

smallest molecules soluble at any pH

Humic acid

larger molecuesl soluble in alkaline conditions but insoluble in acidic (< pH 2)

Humin

largest size, insoluble at all pH fraction

what is dissolved organic matter

a complex heterogenous mixture of organic compounds dervied from decomposing plants, animals and microbial activity. Also can be grouped a biomolecules

what is empty bed contact time

is equal to the volume of the empty bed divided by the flow rate. It is a measure of the time water is in contact with media, assuming all water passes through at the same velocity.

GAC typical use

Plants use GAC to remove DBP precursors (NOM and other organics) and thereby reduce formation of trihalomethanes (THMs), haloacetic acids (HAAs), and many unregulated DBPs after chlorination

what is hydrualic loading rate

The

hydraulic loading rate (HLR) for Granular Activated Carbon (GAC) is the speed at which water passes through the filter bed

breakthrough not being 100%

Breakthrough in granular activated carbon (GAC) occurs when the adsorption capacity of the carbon bed is partially exhausted, causing the mass transfer zone (MTZ)—the active zone where contaminants are transferred from water to carbon—to move through the bed and exit the effluent. The system still removes a portion of the contaminant during this phase because the entire column is not yet fully saturated, meaning some fresh or partially used GAC still exists to adsorb the passing contaminants, even though the effluent concentration has begun to rise

PD vs CD RSSCT

CD assumes that the surface diffusivity of the GAC will be the same regardless of the particle size

PD assumes that the change in surface diffusivity of the GAC is linearly related to the particle size of the GAC

This reflects the size exclusion that can occur for larger molecules such as MCs and DOM as PD-RSSCT has been shown to better predict full scale organic matter breakthrough. However, the assumption of constant diffusivity does not apply to the adsorption of large molecules such as humic and fulvic acids, which may be prone to size exclusion in small GAC pores. However, this might provide less accurate scaling of PFAS due to its smaller size

what factors play into adsorption strenght

charge and size since hydrophobic and electrostatic are usually dominant

What does the ohio epa rulw fo rMCs entail

public water systems are required to test for toxins during HABs season. Exceedences trigger immediate resampling increased monitoring, and public notification

GAC surface charge

This surface charge (Fig. 4) will depend on the solution pH and the surface characteristics of the carbon. A negative charge results from the dissociation of surface oxygen complexes of acid character such as carboxyl and phenolic groups. Therefore, these surface acid sites are of Br€oonsted type. The origin of the positive surface charge is more uncertain because, in carbons without nitrogen functionalities, it can be due to surface oxygen complexes of basic character like pyrones or chromenes, or to the existence of electron-rich regions within the graphene layers acting as Lewis basic centres, which accept protons from the aqueous solution

what influences gac phpzc

functional groups present on the carbon which are form the source material and activation method

SUVA

the more it adsorbs per unit mass (TOC) at UV254 the more aromatic it is

DBP formation

When NOM reacts w/ chlorine, chloramine, or bromine

What is kow?

Log (octanol-water partition coefficient) is the logarithm of the ratio of a chemical's concentration in n-octanol to its concentration in water at equilibrium. It measures a substance's lipophilicity (fat solubility) vs. hydrophilicity (water solubility), indicating how a chemical distributes between organic phases and water. Low kow indicates more hydrophilic and high indicates more hydrophobic

Terrestial DOM

tends to have higher amounts of high mw and hydrophobic fractions from lignin and tanin inputs

microbial dom

usually containts more low molecular weight and hydrophilic dom fractions

terrestrial and microbial dom

bother contain biomolecules (carbohydrates, lipids, and peptides) bcs both are derived from living organisms

E2/E3

a measure of spectral slope (decrease in absorbance in the UV region to the visible light region) is inversely correlates w/ DOM size and electron donating capacity. tends to be higher for microbial DOM. 250/365

Reason for less steep breakthrough curvees

The Mass Transfer Zone (MTZ) is the active region within an adsorption column where the adsorbate is transferred from the fluid phase to the adsorbent surface. It moves along the bed, and the breakthrough curve represents the concentration of this zone exiting the column over time. A slowly increasing breakthrough curve (a gradual slope rather than a sharp step) indicates a wide, dispersed MTZ. This occurs when mass transfer resistance, axial dispersion, or kinetic limitations prevent the sharp separation of the adsorbate from the carrier fluid.

AI Overview

The

Mass Transfer Zone (MTZ) is the active region within an adsorption column where the adsorbate is transferred from the fluid phase to the adsorbent surface. It moves along the bed, and the breakthrough curve represents the concentration of this zone exiting the column over time. 

A slowly increasing breakthrough curve (a gradual slope rather than a sharp step) indicates a wide, dispersed MTZ. This occurs when mass transfer resistance, axial dispersion, or kinetic limitations prevent the sharp separation of the adsorbate from the carrier fluid.

Key Reasons for a Slowly Increasing Breakthrough (Broad MTZ)

• Low Adsorption Kinetics (Slow Rate): If the adsorbent has slow internal diffusion (pore diffusion) or surface reaction rates, the adsorbate cannot be captured instantly as it moves through the bed. The molecules pass through the top layers before being captured, spreading out the concentration front.

• High Axial Dispersion/Backmixing: Axial mixing or longitudinal dispersion causes the concentration front to blur as it travels. This occurs in turbulent flows, or when there is significant velocity variation within the column (channeling), causing parts of the fluid to bypass the dense packing.

• Non-Favorable Adsorption Isotherms: If the equilibrium isotherm is not favorable (e.g.,Type 3 or 5), the adsorption is weak at lower concentrations, leading to a broader, shallower MTZ.

• Unfavorable Operating Conditions:

  • High Flow Rates: Higher velocities reduce the contact time between the fluid and adsorbent, allowing the front to disperse, resulting in a gradual breakthrough.

  • Low Initial Concentration: Low-concentration feeds often lead to a slower, wider MTZ.

  • High Temperature: For physical adsorption, high temperatures can reduce capacity and broaden the front.

• Particle Size and Bed Packing: Larger particles and non-uniform packing can cause wider zones due to longer diffusion paths and flow nonuniformity