The U.S. spends $5 billion a year to repair damages to road infrastructure from winter snow and ice control operations and the use of traditional deicers.
A team of researchers at WSU is developing a more sustainable solution using grape skins and other agricultural waste.
The researchers, including graduate student Mehdi Honarvar Nazari and Xianming Shi, associate professor in Civil and Environmental Engineering, determined that their deicer containing grape extract outperformed commonly used deicers, including road salt and what is thought to be a more environmentally friendly blend of salt brine and beet juice.
They published their results in the December issue of the Journal of Materials in Civil Engineering.
Every year, roughly 27 million tons of sodium chloride, commonly known as road salt, is used on U.S. roadways for winter maintenance.
The chlorides do not degrade in the environment and may pose long term environmental risks. Commercial deicers typically contain chemicals that are corrosive toward metals, asphalt, concrete, and pose some risk to aquatic species.
Beet juice has become a common additive used by highway departments and cities to enhance the performance of deicers while reducing their corrosive impacts.
However, when beet juice enters water bodies, it can deplete oxygen and endanger aquatic organisms.
Working to develop a greener additive, the WSU researchers derived chemicals from waste grape skins through chemical degradation and natural fermentation.
Shi said their novel process to make the formula produces no waste of any kind.
The researchers found that their grape extract-based solution melts ice faster than other deicers and causes significantly less damage to concrete and asphalt, the two most ubiquitous materials used in bridges and roads.
The solution also poses less risk to nearby water bodies.
“We delivered a more sustainable solution because we’re introducing less chlorides into the road operations and are achieving comparable or better performance,” Shi said. “It’s one step in the right direction.”
Shi first thought of using biotechnology to derive deicer additives out of agricultural waste materials several years ago when tasked by the Alaska Department of Transportation to develop locally sourced and performance-enhanced brine formulations for anti-icing.
His group has also successfully applied this technology to waste peony leaves, sugar beet leaves, dandelion leaves, and waste from apples and grapes.
“The beauty of this approach is that it allows us to diversify,” he said. “We can use this same platform technology in different regions of the country but choose a different agricultural product, depending on what source of waste is available.”
Salt pollution is a long-term environmental concern, potentially threatening soil, lake, and stream ecosystems, and groundwater supplies, as well as coastal regions [1–7]. In particular, road salt crystals and brines used to de-ice roads have become major sources of salt pollution in cold regions of the world, while their use has increased substantially over the past decades [2, 8, 9] (Fig 1).
Even as the frequency of snow storms and total accumulation have diminished due to climate change, larger and more intense winter precipitation events are leading to increased demand for application of road salt.
Global climatic trends are predicted to further increase these extreme events, including record-breaking storms [10–12]. This trend will likely continue, especially in north-central USA, where climate change models predict an increase in the intensity of snowfall and ice storm events [12].
Salt pollution causes damage to roadside vegetation, material goods, and infrastructure, including roads and bridges, as well as water systems. Salt removal from drinking water supplies requires installation of expensive desalination systems [15].
In the 2017/18 winter season, nearly 22 million metric tons of road salt was applied for de-icing in the USA [16]. Estimated damage due to road salt application was between $803 and $3,401 per ton applied [15] resulting in annual costs of up to $75 billion in the USA.
Negative impacts of salt pollution on human health primarily include the effects from rising sodium concentrations in fresh-water drinking reservoirs, where elevated sodium levels contribute to hypertension and consequently an increased burden on health care systems [17–19].
Salt pollution also affects biodiversity and the composition of microbial communities [20–22] which can indirectly impact human health. Increasing salt levels in freshwater systems favor salt-tolerant cyanobacteria, including some that can produce harmful toxins [22–26]. Furthermore, rising salt levels have been linked to the increased release of toxins by cyanobacteria into the air and water [24, 25, 27, 28].
Consumption of or exposure to these toxins is known to cause liver damage and possible carcinogenic effects [27, 29–33]. Moreover, harmful blooms can adversely affect the tourism and food industries, causing additional economic hardship [34].
Other negative effects of salt pollution include changes in soil biogeochemistry, composition, and characteristics such as decreased aeration and decreased soil permeability with increased erosion [22]. In aquatic environments, salt pollution may impact stratification of lakes and shift biological communities towards more salt tolerant species and reduction of biodiversity [20–22, 35, 36].
Increased salt concentrations heighten osmotic stress which in turn results in inhibition of non-halophilic microbial species and stimulation of halophilic ones.
The most sensitive microbes are non-halophilic species which tolerate less than 0.2 M sodium chloride (NaCl). These microbes become osmotically stressed in the presence of even small increases in salt concentrations and may only survive in pockets of lower salinity or in dormant spore forms.
Growth of slight halophiles (tolerating up to 0.85 M NaCl), moderate halophiles (tolerating up to 3.4 M NaCl), and extreme halophiles, which require high salt concentrations for growth and tolerate up to 5.2 M (saturated) NaCl, may be promoted when salt concentrations are substantially [37–39].
Sodium chloride is the primary salt used to de-ice roads in the USA, employing halite crystals from salt mines and solar salterns. These have long been known to be rich sources of halophilic microorganisms, harboring a wide variety of species which includes Bacteria and their spores, Archaea, and some Eukaryotes, such as green algae [37, 40–43].
In this initial study, we address whether any halophilic microorganisms are becoming either seasonal or persistent members of proximal microbial communities and if their presence may be used as indicator and biomarkers for salt pollution.
More information: Mehdi Honarvar Nazari et al, Developing Renewable Agro-Based Anti-Icers for Sustainable Winter Road Maintenance Operations, Journal of Materials in Civil Engineering (2019). DOI: 10.1061/(ASCE)MT.1943-5533.0002963
