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With growing environmental consciousness, biomaterials (BMs) have garnered attention as sustainable materials for the adsorption of hazardous water contaminants. These BMs are engineered using surface treatments or physical alterations to enhance their adsorptive properties. The lab-scale methods generally employ a One Variable at a Time (OVAT) approach to analyze the impact of biomaterial modifications, their characteristics and other process variables such as pH, temperature, dosage, etc., on the removal of metals via adsorption. Although implementing the adsorption procedure using BMs seems simple, the conjugate effects of adsorbent properties and process attributes implicate complex nonlinear interactions. As a result, artificial neural networks (ANN) have gained traction in the quest to understand the complex metal adsorption processes on biomaterials, with applications in environmental remediation and water reuse. This review discusses recent progress using ANN frameworks for metal adsorption using modified biomaterials. Subsequently, the paper comprehensively evaluates the development of a hybrid-ANN system to estimate isothermal, kinetic and thermodynamic parameters in multicomponent adsorption systems.

Growing concerns of emissions from wildfires and burning of crop residues demand cleaner and efficient technologies to convert and utilize this residual biomass. The present study demonstrates a pilot scale moving bed biomass torrefaction reactor operating in oxidative medium to produce biochar for soil amendment. A series of experiments are conducted on pine shavings and rice husk, at conditions corresponding to different values of index of torrefaction (Itorr), ratio of higher heating value of torrefied biomass (i.e. biochar) to that of raw biomass. Air-biomass equivalence ratio dominantly governs the operating temperature and affects torrefaction more than the residence time. Product yields of scaled-up reactor differed from those of a smaller bench-top reactor, primarily because of differences in heat transfer within reactor and losses to the surrounding. A relatively linear relationship of Itorr is observed with biochar properties such as specific surface area, water retention capacity, bulk density, and electrical conductivity. When tested for soil amendment, the raw biomass and biochar treatments reduced soil pH by 0.2–0.3 in a season, with lowest pH values in case of pine shavings. Estimated nitrogen release and organic matter decreased with increasing Itorr, but most amendments had no significant effect on seed germination and the number of green shoots. Comparatively, heavy torrefied biomass treatments showed highest shoot heights and crop yield followed by light torrefied or raw biomass and control. Successful demonstration of a pilot scale reactor and encouraging effects on soil and plant growth suggest that commercial-scale oxidative torrefaction of various residual biomass is possible for soil amendment application.

The performance of photocatalytic advanced oxidation must be improved in order for the technology to make the jump from academic research to widespread use. Research is needed on the factors that cause photocatalysis to become self-limiting. In this study, we introduced, for the first time, nanobubbles continuously into a running photocatalytic reactor. Synthetic air, O2, and N2 bubbles in the size range of 40 to 700 nm were added to a reaction system comprising P25 TiO2 photocatalyst in stirred aqueous solution excited by UV-A lamps, with methyl orange as a target contaminant. The removal of methyl orange was tested under conditions of changing pH and with the addition of different radical scavengers. Results indicated that the oxygen and air nanobubbles improved the photocatalytic degradation of methyl orange—the removal efficiency of methyl orange increased from 58.2 ± 3.5% (N2 aeration) to 71.9 ± 0.6% (O2 aeration). Dissolved oxygen (DO) of 14.93 ± 0.13 mg/L was achieved using O2 nanobubbles in comparison to 8.43 ± 0.34 mg/L without aeration. The photodegradation of methyl orange decreased from 70.8 ± 0.4% to 53.9 ± 0.5% as pH increased from 2 to 10. Experiments using the scavengers showed that O2− was the main reactive species in photocatalytic degradation under highly dissolved oxygen conditions, which also accounted for the observation that the removal efficiency for methyl orange decreased at higher pH. However, without photocatalyst, nanobubbles alone did not improve the removal of methyl orange, and nanobubbles also did not increase the degradation of methyl orange by only photolysis. These experiments show that oxygen and air nanobubbles can act as environmentally friendly catalysts for boosting the performance of photocatalytic water treatment systems.