From biomass to hydrochar and beyond
Hydrochar offers a dizzying range of applications, depending on the input biomass, the carbonization process, and the intended ultimate use of the char. We look at a few recent examples.
In the last newsletters we looked at wet biomass as input, the various carbonization processes, and the available uses of hydrochar (and biochar) to enable a sustainable carbon economy. In this newsletter, we offer a few examples from recent research about how these components tie together. We will get back to these and other examples in more detail later, so consider this a teaser for future newsletters.
Sedum alfredii to heavy metal recovery
Sedum alfredii is a perennial herb in areas of Asia, especially in China. Its most attractive feature is that it a hyperaccumulator. It is able to absorb high amounts of heavy metals, especially cadmium and zinc. This makes it an intriguing plant to use in the recovery of heavy metal-contaminated lands (the so-called phytoremediation). For this to work, it’s important that we find ways to remove the metals from the plant after they have been absorbed.
Hydrochar might offer a solution, as a recent paper by Jianwei Zhang et al proposed. In their most promising setup, they achieved removal efficiencies of 95.0% for cadmium and 89.3% for zinc, leaving behind a high-quality hydrochar that could be reused in agricultural sequestration as stable soil additive.
Orange peel into pollution sensors
Citrus fruits are among the most cultivated fruits in the world, with oranges accounting for some 55 million metric tons alone. Notoriously, citrus fruits aren’t only rich in flavor, but also in waste. Orange peel waste alone makes up some 50% of the total fruit weight. Claudia Espro et al of the University of Messina investigated if this peel waste could be turned into a useful end product.
Their experiment focused on producing high-performing electrochemical sensors for the detection of pollutants, in their case NO2 and dopamines. As their work showed, turning orange peel waste into hydrochar creates an economically attractive end product that could be, depending on application, also lead to mid-term sequestration as a stable solid carbon.
And if that’s not enough, we can also turn orange juice into supercapacitor electrodes.
Corn waste into clean drinking water
Jae Wok Chung, now of ZHAW Zürich, tackled the problem of purifying polluted water in his Ph.D. thesis at IHE Delft. Using both corn waste, a ubiquitous waste product of one of the most intensively cultivated crops, and sewage sludge, he demonstrated that cheaply produced hydrochar can increase the efficiency of sand columns in removing human pathogen from 20-70% to 90-99%.
This research was augmented by Kandis Leslie Abdul-Aziz and her colleagues at UC Riverside. In their research setup, corn waste-derived activated hydrochar managed to remove 98% of the pollutant vanillin from water.
Beyond the upcycling of agricultural waste, recent research also managed to employ hydrothermal processes using more pedestrian waste products of human civilization: cigarette butts, car tires, or chicken poop. We will have a special newsletter devoted to this end of the spectrum in the future.
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