Although avoiding polluting should be a primary goal of any industry, there are many processes and practices — not to mention accidents like oil spills — which inevitably will result in pollution. 

In these circumstances, pollution remediation is often the best way to hand a crutch to a contaminated site on the long walk to recovery. However, there are even issues with remediation itself. 

“The goal of remediation is to regain that clean, pristine, safe environment, right? That’s what we desire. But that comes at the cost. The cost could be straightforward money you need to pay someone for the procedure, or the cost could also be environmental,” Adeyemi Adeleye, a professor in the department of civil and environmental engineering at UC Irvine and an alumnus of UCSB, said.

On June 1, the Bren School of Environmental Science & Management invited Adeleye onto Zoom for an online seminar titled “Green Chemistry Approaches for Improving the Sustainability of Pollution Remediation.” 

Adeleye spoke on two particular ways that his graduate students have been developing methods and processes to improve remediation and mitigate these costs with green chemistry. 

According to Adeleye, the EPA defines “green chemistry” as the “design of chemical products and processes to reduce waste or eliminate the generation of hazardous substances.” Oftentimes, this means finding different ways of doing things to decrease the associated hazards of a process. 

There are 12 principles of green chemistry; Adeleye and his students focused on two, aiming to “design chemical products that are fully effective yet have little or no toxicity” and “use renewable feedstocks,” which are the raw materials used to fuel an industrial process. 

In regard to the former principle, a student of Adeleye, Ziwei Han, has been developing methods to reduce the toxicity of arsenic, a contaminant found in groundwater. 

A schematic diagram showing nanoscale zerovalent iron and the mechanism of arsenic remediation. Courtesy of Adeyemi Adeleye

Some methods to address the problem of arsenic in water have included things like bioremediation, using microorganisms and plants in order to sequester arsenic and soft washing with acids, but both of these have problems. 

“The plants that can actually cause sequestration of arsenic cannot grow everywhere,” meanwhile, acids “directly [impact] organisms. And when you wash with acids or bases, you can also wash all that very useful nutrients from the soil,” Adeleye said. 

Instead, Han looked into nanoscale zerovalent iron (nZVI), which can be used to immobilize arsenic in soil. Specifically, Han wanted to learn how one could better nZVI’s performance in remediation by reducing solubility and reactivity.  

“When the [nZVI] accepts a contaminant like arsenic upon its dissolution, it can release what it has already absorbed previously… The second problem is that it can adjust the pH of the soil. So, if there are organisms that cannot tolerate large change in pH, they would be negatively impacted. Last is that it can increase the iron concentration in water,” Adeleye said. 

The researchers modified nZVI with the aim of preventing reactions from occurring which contribute to nZVI’s toxicity, and studied the effects of these modified particles over four weeks. 

“Between week one and week four, the amount of arsenic that can be leaked is decreasing compared to increasing without any modification,” Adeleye said.  

“So, we think this modified material is not working as fast as the unmodified work but on a long-term basis, it may be more promising in that arsenic that has been immobilized will not be remobilized because this particle is more chemically stable.”

Then, the researchers looked into how the modified particles affected other life forms, namely earthworms, and observed that the toxicity appeared to be reduced. However, Adeleye admitted that another experiment looking at just the pH of the soil and the survival rate of the worms would be beneficial data to have. 

The second project, led by a graduate student in the Adeleye Lab, Omobayo Salawu, looked into alternatives to the use of conventional activated carbon in adsorbing organic contaminants. 

Photo “a” shows raw shrimp shell, which is then ground and pyrolyzed. Photo “b” shows the ground shell under an electron microscope. Photo “c” shows the small volume pores of a shell which received further treatment via activation. Courtesy of Adeyemi Adeleye

Activated carbon, despite being seen as a standard for adsorption, has a number of issues. It is made from charcoal and often sourced illegally from countries with weak or poorly enforced environmental regulations. Activated carbon also lacks “specificity,” according to Adeleye. 

“It’s a cross-spectrum adsorbent and in general, water treatment plants are trying to remove contaminants that are present at very low concentrations. So they need to use a lot more activated carbon than is really needed, because there is competition between a low concentration of the contaminant and other things that may be present at a much higher concentration,” Adeleye said. 

Shrimp shells seemed like a good candidate for use as a renewable feedstock in adsorbing contaminants, ordinarily being a waste product which could be diverted from a landfill and also being plentiful with largely little to no competition for use. 

Crushing the shrimp shells resulted in carbon with good physical properties for carbon removal, having high surface area compared to conventional activated carbon and also nitrogen, the presence of which researchers noticed increased the absorption of target contaminants.

In promising experiments with ciprofloxacin, a common pharmaceutical found in biosolids, they found that “for every gram of the activated carbon we use, we removed about six to 0.66 grams of ciprofloxacin,” Adeleye said.

“To put it into context, it is very high.” 

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