No abstract

Concentrations of selenium (Se) in agricultural irrigation effluent increased stored soil Se to toxic levels in the wetland sediment at Kesterson Reservoir. Vegetation management (phytoremediation) may be a strategy to reduce these soil Se concentrations to nontoxic levels. Selenium in plant shoots and depletion of soil Se removal by selected plant species were evaluated over a 1‐yr period under greenhouse conditions. Two soils were used: a seleniferous Turlock soil (collected from Kesterson Reservoir) that contained high total Se (∼40 mg kg−1 soil), high water extractable B (∼10 mg B L−1), a soil salinity of ∼8 dS m−1, and a nonseleniferous Hanford sandy loam (collected from an agricultural field site). Three plant species tested were Brassica napus cv. Westar (canola), Hibiscus cannabinus L. cv. Indian (kenaf), and Festuca arundinacea Schreb. cv. Alta (tall fescue). Only canola and kenaf grown in Turlock soil showed significant lower shoot yield (P < 0.01) than on the Hanford soil. Leaf Se was as high as 470 mg Se kg−1 DM in canola, 45 mg Se kg−1 DM in kenaf and 50 mg Se kg−1 DM in tall fescue. The same crops contained mean leaf B concentrations as high as 415 mg B kg−1 DM in kenaf, 180 mg B kg−1 DM in canola, and 111 mg B kg−1 DM in first clipping of tall fescue. The cultivation of all species led to a significant reduction (P < 0.01) of total soil Se between preplant and the final harvest by the following percentages: canola (47%), kenaf (23%), and tall fescue (21%). Successively planting of canola and to a lesser extent kenaf and tall fescue, in Se‐laden soil has the potential to reduce total soil Se.

Waste Sedum plumbizincicola, a zinc (Zn) hyperaccumulator during phytoremediation, was recycled via a subcritical hydrothermal liquefaction (HTL) reaction into multiple streams of products, including hydrochar, bio-oil, and carboxylic acids. Results show approximately 90% of Zn was released from the S. plumbizincicola biomass during HTL at an optimized temperature of 220 °C, and the release risk was mitigated via HTL reaction for hydrochar production. The low-Zn hydrochar (∼200 mg/kg compared to original plant of 1558 mg/kg) was further upgraded into porous carbon (PC) with high porosity (930 m/g) and excellent capability of carbon dioxide (CO) capture (3 mmol/g). The porosity, micropore structure, and graphitization degree of PCs were manipulated by the thermal recalcitrance of hydrochar. More importantly, results showed that the released Zn could effectively promote the production of acetic acid via the oxidation of furfural (FF) and 5-(hydroxymethyl)-furfural (HMF). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with negative electrospray ionization analysis confirmed the deoxygenation and depolymerization reactions and the production of long chain fatty acids during HTL reaction of S. plumbizincicola. This work provides a new path for the recycling of waste hyperaccumulator biomass into value-added products.