Characterization of potassium hydroxide (KOH) modified hydrochars from different feedstocks for enhanced removal of heavy metals from water

Abstract

Hydrochars produced from different feedstocks (sawdust, wheat straw, and corn stalk) via hydrothermal carbonization (HTC) and KOH modification were used as alternative adsorbents for aqueous heavy metals remediation. The chemical and physical properties of the hydrochars and KOH-treated hydrochars were characterized, and the ability of hydrochars for removal of heavy metals from aqueous solutions as a function of reaction time, pH, and initial contaminant concentration was tested. The results showed that KOH modification of hydrochars might have increased the aromatic and oxygen-containing functional groups, such as carboxyl groups, resulting in about 2-3 times increase of cadmium sorption capacity (30.40-40.78 mg/g) compared to that of unmodified hydrochars (13.92-14.52 mg/g). The sorption ability among different feedstocks after modification was as the following: sawdust> wheat straw > corn stack. Cadmium sorption kinetics on modified hydrochars could be interpreted with a pseudo-second order, and sorption isotherm was simulated with Langmuir adsorption model. High cadmium uptake on modified hydrochars was observed over the pH range of 4.0-8.0, while for other heavy metals (Pb(2+), Cu(2+), and Zn(2+)) the range was 4.0-6.0. In a multi-metal system, the sorption capacity of heavy metals by modified hydrochars was also higher than that by unmodified ones and followed the order of Pb(II) > Cu(II) > Cd(II) > Zn(II). The results suggest that KOH-modified hydrochars can be used as a low cost, environmental-friendly, and effective adsorbent for heavy metal removal from aqueous solutions.

Hydrothermal Carbonization: Modeling, Final Properties Design and Applications: A Review

“…Especially with the push to find more sustainable pathways for wet agricultural residues and decrease their environmental impact, more non-traditional chars often with high mineral content are being produced via the HTC-process and evaluated for their adsorption capacities. It may be possible to utilize both the organic as well as mineral content in the chars to remove contaminants [69]. Their potential as a precursor material for the production of activated carbon is also being tested.…”

“…Feedstocks for HCs that have been tested for their sorption ability range from woody landscape/forestry residues (sawdust [69]; bamboo sawdust [70]), bioenergy crops (switchgrass [71]) agricultural residues (animal manures [72,73]; wheat straw and corn stalk [69]) to food processing (rice husks [74]; penaut husks [75]; banana peels [76]; orange waste, olive pomace, compost [74]) and domestic wastewater sludges (digested sewage sludge [77]; faecal sludge [78]). …”

“…The environmentally relevant target compounds that have been studied as sorbates span the range from organic agrochemicals, such as pesticides and herbicides (fluridone, norflurazon [79]; isoproturon [80]; atrazine [77]), pharmaceuticals and personal care products (tetracycline [81]; diclofenac, salicylic acid, fluriprofen [82]; triclosan, estrone, acetaminophen, carbamazepine [73]; sulfamethoxazole, carbamazepine, bezafibrate, diclofenac [77]), PAHs, endocrine disrupting chemicals and dyes (phenanthrene [83]; pyrene [72], bisphenol A, 17a-ethinyl estradiol [83]; methylene blue [84][85][86]; Congo red, 2-napthol [70]) to heavy metals Pb (II), Cu (II), Cd (II), Sb (III), Zn (II), As, and phosphate [69,71,[73][74][75]78,[84][85][86][87].…”

Removal of Escherichia coli by Intermittent Operation of Saturated Sand Columns Supplemented with Hydrochar Derived from Sewage Sludge

“…In order to increase the adsorptive capacity, the raw hydrochar was activated by KOH solution [17,19,20]. Washed hydrochar powders were suspended in a 1 M KOH solution at a concentration of 5 g hydrochar (dry weight)/L and stirred for 1 h at room temperature.…”

Hydrothermally Treated Banana Empty Fruit Bunch Fiber Activated Carbon for Pb(II) and Zn(II) Removal

“…Thus, the obtained hydrochar material obtained virtually no framework of confined pores. Its surface area arises only from inter-particle voids (Sun et al 2015).…”