A review of pesticides sorption in biochar from maize, rice, and wheat residues: Current status and challenges for soil application.

The use of pesticides has been increasing in recent years for maintaining traditional agricultural practices. However, these chemicals are associated with several environmental impacts, demanding urgent remediation techniques. Biochar is a carbonaceous material produced by pyrolysis that has the potential for pesticide sorption and remediation. In this context, this interdisciplinary review systematically assessed the state of the knowledge of crop residues to produce biochar for pesticide sorption. We focused on maize, rice, and wheat residues since these are the three most-produced grains worldwide. Besides, we evaluated different biochar handling, storage, and soil dispersion techniques to ease its implementation in agriculture. In general, pyrolysis temperature influences biochar characteristics and its potential for pesticide sorption. Furthermore, biochar amended soils had greater pesticide sorption capacity, limiting potential leaching and runoff. Most studies showed that the feedstock and specific surface area influence the biochar sorption properties, among other factors. Also, biochar reduces pesticides' bioavailability, decreasing their toxicity to soil organisms and improving soil fertility and crop yields. Nonetheless, the retrieved papers assessed only 21 pesticides, mainly consisting of lab-scale batch experiments. Therefore, there is still a gap in studies evaluating biochar aging, its potential desorption, pesticide co-contaminations, the associated microbiological processes, and field applications. Determining flow properties for biochars of different sizes and pellets is vital for reliable handling equipment design, and performing techno-economic assessment under different farm contexts is encouraged. Ultimately, coupling biochar production with residue management could address this challenge on sustainable agricultural systems.

Feeding spent coffee grounds into reactors: TFM simulation of a non-mechanical spouted bed type feeder.

Due to the increasing coffee production, Spent Coffee Grounds' (SCGs) generation has grown dramatically, hence appropriate management of this solid biomass waste is imperative. SCGs can be used as feedstocks for renewable energy and fuel generation provided that a stable feeding of powders to reactors is maintained. Recently, a non-mechanical spouted bed feeder proved itself an excellent alternative in feeding SCGs to a pilot-scale circulating fluidized bed reactor. Nonetheless, further studies are necessary for the feeder's implementation in commercial applications. Here the feeding of SCGs with the spouted bed feeder is addressed by using Computational Fluid Dynamics. Firstly, a Two-Fluid Model (TFM) is validated against experimental data, and then the effects of five operating and design parameters were analyzed aiming at improving the handling of SCGs. The solids flowrate (WS) in the reactor could be stably controlled from 4 to 30 g/s depending on the settings. The feeder performance is enhanced by operating it under high gas flowrate (Q), high entrainment length (z), and high mass of solids in the feeder (HS). Using feeders with low cone angle (γ) or reactors with large diameter (DR) increases WS, which is appealing for the operation of medium-to large-scale units. The proposed TFM is a cost-effective tool for implementing spouted bed feeders in commercial applications. With the feeder coupled to the process, SCGs are treated continuously in the reactor for energy generation, thus reducing the disposal problems associated with this waste and improving the management of SCGs globally.