Back in 1967 an iconic scene from the movie The Graduate, perhaps unwittingly so, was a harbinger of what was to come when Dustin Hoffman was given career advice with the single word “plastics.”

When the Ellen MacArthur Foundation submitted its report “The New Plastics Economy” to the 2016 World Economic Forum, it indicated that: “Plastics have become the ubiquitous workhorse material of the modern economy — combining unrivaled functional properties with low cost. Their use has increased twenty-fold in the past half-century and is expected to double again in the next 20 years. Today nearly everyone, everywhere, every day comes into contact with plastics — especially plastic packaging…” 

Too much of a good thing can hurt you. In recent years plastic use has moved into the environmental spotlight with stories of large floating continents of plastic waste in our oceans, whales washing up on beaches with bellies full of plastic bags and bottles, and animals crippled by six-pack holders. 

Efforts to stem the tide of plastic waste invoked movements away from single-use plastics toward a recycled material designed to lessen the flow of new material entering the environment. Until January 2018, China imported 45 percent of the world’s waste recycled plastic. China’s recent moves to curtail import of recycled materials has created confusion and a glut of materials that has slowed momentum towards a circular economical use of recycled plastics. Innovative and disrupting ideas to improve the efficiencies of collection are providing alternatives. While these are good ideas it does very little to actually reduce the total quantity of material in the environment. 

In a June 2018 article “We Made Plastic. We Depend On It. Now We’re Drowning In It.” National Geographic wrote, “Because plastic wasn’t invented until the late 19th century, and production really only took off around 1950, we have a mere 9.2 billion tons of the stuff to deal with. Of that, more than 6.9 billion tons have become waste. And of that waste, a staggering 6.3 billion tons never made it to a recycling bin.” What is interesting is that it goes on to say: “Most of it isn’t thrown off ships, but is dumped carelessly on land or in rivers.”

Now it enters our house

Those of us in the wastewater industry are very familiar with handling discarded materials. Many of the issues we face come from a throw-away-and-forget mentality prevalent with the communities whose wastes are collected and treated. Recent issues with “flushable wipes” are a perfect example of this. Between awareness campaigns to educate the public and pressure on the industry producing the wipes, there has been a measurable effect. This was buttressed by developing and employing technology that could better intercept and remove the offending wipes.

Plastic waste provides a similar challenge to the wastewater treatment process. As we have seen in recent days, the increase in conversation around accumulating plastics in the environment is raising public awareness. Movements to recycle the waste plastic are well underway. But as mentioned in the National Geographic article, over two-thirds of the waste plastic evades collection and recycling. As a result, wastewater treatment facilities are tasked with extracting and handling a significant quantity of fugitive plastic elements within the waste flow stream entering the facility.

The challenge is related to the proportionately steady increase of these plastic wastes overall. A significant number of existing wastewater treatment plants were built before there was a noticeable issue with plastic wastes as a dominant concern. Many components in the treatment system were not designed to target and extract these plastic wastes. Changing missions for wastewater facilities moving toward resource recovery created a focus on identifying and converting wastes into usable resources such as biosolids and energy. These treatment changes introduced technologies that were more intricate and created fouling challenges to the new technologies from the bypassed debris. 

One thing leads to another

Practical operational effect and regulatory pressure underscored the imperative to develop solutions that would extract the plastic waste from the treatment flow stream. From a practical basis, the ability to generate energy from the sludge in the plant and accelerate the volume reduction of the sludge provided new justifications to create or enhance anaerobic digesters to produce biogas for fuels and electricity generation.

This also opened an opportunity to utilize waste fats, oils and grease from surrounding businesses to increase gas yield in the digesters. The FOG was typically laden with discarded plastics and other undesirable materials that created both a maintenance and safety issue for the operators. The plastic wastes along with other debris such as rags and grit would begin to accumulate and proportionately diminish efficiency — ultimately leading to a premature interruption of service and cleaning by filling the digester with the debris. This resulted in expensive servicing and extended downtime for the digesters.

As techniques such as dewatering were employed for sludge volume reduction, plastic wastes could possibly disrupt operations or even disable some types of equipment. Sludge drying techniques expanded the possible use of the sludge to create Class A sludge material that could be land-applied for agricultural purposes. Regulatory pressure in certain areas prohibited the presence of visible plastics and similar type debris.

Similar to the disposable wipes issue, technologies were employed to safely extract these nuisance wastes at key points in the flow. This was especially useful with existing facilities being repurposed to develop the resource conversion opportunities.

Out of sight is not out of mind

Interestingly enough, much of what comes to mind when we consider plastic wastes are bottles, bags and packaging. This is most likely due to this type of plastic waste being common and easily visible. Work done by Washington State University identifies microplastics generated from synthetic fibers as a possible source of microplastics in wastewater. They indicate the microfibers, which are mainly released when clothes are washed, end up in wastewater plants where a significant proportion pass through water filtration systems. Even the ones that are filtered end up in the sewage sludge that can be applied to farm soils as fertilizer or dumped in landfills.

In January 2019 it was reported by water-technology.net that researchers at Chinese Academy of Sciences analyzed wastewater in China to determine the quantities and fraction of plastics in wastewater. What they found was 54.8 percent was polyamide, or nylon. They theorized these microplastic particles may have come from the wastewater discharged by clothes washing and polymer manufacturing firms. 

As it stands right now the ability to reliably extract microplastics from the outfall of a wastewater plant or from sludge is limited. Efforts to develop a biodegradable plastic are showing promise. In reality a combination of factors can be employed to provide a sustainable solution to curb the mounting plastic waste problem. The Ellen MacArthur Foundation report to the 2016 World Economic Forum outlines a combination of recycling, reuse and compostable packaging as important first steps. Some early adopters, such as London-based Marks & Spencer and Henkel, are proactively integrating plastic recycling and reuse techniques in their products and manufacturing. The end goal is to develop plastics that are not fossil-fuel based and learning to do more with less plastic.

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