A Research Study Discussion For Practical Usage


Polyquaternium-10 polymers, often abbreviated as PQ-10, are chemicals frequently found in beauty and self-care products like hair conditioners, lotions, and makeup. They serve multiple purposes such as moisturizers, thickness controllers, and they help deposit other ingredients onto your skin or hair. Given their wide usage, they inevitably end up in our wastewater.

Like many other chemicals with a positive charge (cationic polymers), PQ-10 can harm aquatic life, which is why it’s crucial that they’re removed during wastewater treatment.

One common way this is achieved is by having the chemicals stick to (adsorb onto) activated sludge solids, which are parts of the wastewater that can be removed.

The study we’ll be looking at:

Some researchers have studied the removal of PQ-10 from wastewater by assuming that the primary component of the activated sludge is humic acid, a common component in soil. They used partition coefficients, a measure of how a chemical distributes between liquid and solid states, to describe the process.

But this approach assumes that adsorption follows a straight line pattern, which isn’t typically the case for polymers like PQ-10.

Furthermore, the activated sludge isn’t just humic acids. It’s more accurate to describe it as particles covered by a cocktail of large molecules that bacteria secrete, which are primarily proteins, polysaccharides (large sugar molecules), and humic substances.

Also, once these polymers are adsorbed, they usually stay put; the process isn’t easily reversible. The pattern they tend to follow is typically either Langmuir or “high-affinity” type—meaning if there’s enough of the polymer, it will stick until it can’t anymore.

This study’s goal was to delve deeper into how PQ-10 polymers get adsorbed by activated sludge. The researchers looked at adsorption patterns of several common PQ-10 polymers to better understand the environmental implications of these chemicals.

Testing the interactions: the process

In this study, four types of Polyquaternium-10 (PQ-10) polymers were used, each having different sizes and charge properties. These polymers were provided by The Dow Chemical Company, and their specific labels were JR-125, LR-400, JR-30 M, and LR-30 M.

The researchers created a testing environment similar to actual wastewater, following international guidelines set by the Organisation for Economic Co-operation and Development (OECD).

They mixed small amounts of various chemicals, including calcium chloride, ferric chloride, and magnesium sulfate, with a phosphate buffer and a large volume of deionized water.

The water was purified using a high-quality purification system known as the GenPure™ Thermo Electrone LED GmbH system.

The team studied how these polymers attach themselves to activated sludge, which was collected from a wastewater treatment plant in Easton, Maryland. They gathered two sets of sludge samples: one for initial testing, and a second batch for more detailed examination conducted almost a year later.

Each batch of sludge was filtered through a screen to remove larger particles and then allowed to settle. The clear liquid on top (the supernatant) was removed, and the remaining sludge was put in a container and spun at a high speed in a centrifuge. This process separates the sludge from the remaining water.

The water (supernatant) was removed, measured, and then replaced with an equal amount of the testing solution. This mixture was then vigorously mixed and centrifuged again.

The sludge washing process was repeated, and the washed sludge was stored in a cool environment until needed for the experiments, which were carried out within five days.

The amounts of PQ-10 polymers that were attached to the sludge were calculated based on the dry weight of the sludge after it had been heated to roughly 105 degrees Celsius.

Results: How the polymers interacted with the activated sludge

This study’s findings suggest a few important points about how these particular polymers interact with activated sludge in water.

When the researchers tested the polymers, they found that at lower doses, the polymers were fully absorbed by the sludge – the concentration of the polymer in the water was nearly zero. This was termed the “total adsorption” phase.

As they increased the dose, the amount of polymer in the water also increased, marking a transition to the “solution concentration rising” phase.

The relationship between the amount of polymer in the water and the amount absorbed by the sludge was not straightforward – it didn’t follow a straight line but instead displayed a “high-affinity” pattern. This means the sludge had a high ability to absorb the polymer.

The researchers identified what they called “threshold loadings” for each polymer. This is the point at which the sludge has absorbed as much polymer as it can and any additional polymer stays in the water.

The “threshold loading” was between 50 and 100 milligrams of polymer for every gram of sludge.

Interestingly, the “threshold loadings” identified in this study are a lot higher than the amount of polymer you would normally find in domestic sewage that gets treated in wastewater treatment plants.

What this could mean, and potential benefits in the real world:

In terms of the real-world impact, these findings could suggest that activated sludge in wastewater treatment plants is likely able to remove these types of polymers from the water effectively, as the amounts typically present in domestic sewage are well below the identified “threshold loadings”.

Here are some specific areas these findings could potentially be applied usefully:

Wastewater Treatment

Traditional wastewater treatment plants are designed to remove organic matter, solids, and some pathogens. However, these facilities often struggle to adequately remove certain chemicals like PQ-10 polymers, which are found in many personal care products.

This study suggests that activated sludge – a key component of many wastewater treatment processes – might have a surprisingly high capacity to absorb these chemicals. This could be a game-changer in improving the efficiency of wastewater treatment plants, leading to cleaner discharged water.

For instance, treatment plants could potentially adjust their processes to optimize the conditions for maximum absorption of these polymers, based on the findings of this study.

Environmental Impact

If wastewater treatment plants can improve their efficiency in removing such chemicals, it could have significant benefits for the environment. When not adequately removed, these polymers can enter our rivers, lakes, and oceans, posing a threat to aquatic life and potentially entering the food chain.

By better understanding and leveraging the adsorption capacity of activated sludge, we can limit the release of these potentially harmful substances into the environment.

Regulation and Policy

The study’s findings may also have implications for environmental regulation and policy. For example, regulators could use these insights to establish more effective standards for the removal of such chemicals at wastewater treatment plants.

It may also inform policies around the manufacturing and use of these polymers, particularly in products that end up in the wastewater stream.

Public Health

Lastly, this research might have implications for public health. While this study does not address this directly, if these polymers are not effectively removed in the wastewater treatment process, they could end up in drinking water sources.

Further studies could explore the impact of these polymers on human health and how effectively removing them in wastewater treatment might mitigate any potential risks.

In summary, this study adds a valuable piece to the puzzle of how we can more effectively treat wastewater to remove harmful chemicals, contributing to cleaner water, healthier ecosystems, and potentially better public health outcomes.

However, more research would be needed to confirm this and to determine the best ways to implement such a process.

Citation For This Study:

Author(s): Ponizovsky, Alexander Schaefer, Edward Stanton, Kathleen Heisler, Ryan

Title: Adsorption isotherms of Polyquaternium-10 polymers by activated sludge solids

Journal: Chemosphere

Volume: 307, Part 2

Publication Date: November 2022

Page Numbers: 135891

URL: https://doi.org/10.1016/j.chemosphere.2022.135891