## 6 Final Remarks and Future Outlooks  
In the drinking water industry, commercially available activated carbon used in adsorption processes can cause significant operating and management costs. Biochar produced by pyrolyzing biomass, on which the scientific literature has been focusing more and more in recent years, can be a sustainable adsorbent alternative. This review paper focuses on waste deriving from the rice industry as adsorbent material because it presents a series of non-negligible advantages: (i) easily recoverable, (ii) at low cost, (iii) reusable in a circular economy perspective, and (iv) easily manageable even in rural areas of developing countries. In addition, the adsorption treatment can be (i) applied with simple plant configurations, (ii) adapted to different scales, even very small ones, and (iii) characterized by plant engineering and management simplicity. Almost all the experimental tests showed in the scientific literature and collected in the review paper were conducted in laboratory-scale reactors with synthetic waters. At the laboratory scale, the operating conditions (such as pH, temperature, initial concentration of the pollutant tested) of the experimental tests are very controlled and, in most cases, kept constant in each test performed. In the real field, the situation can change, even significantly, also varying the efficiencies (adsorption capacities) of the adsorbent materials obtained from the controlled laboratory conditions. In more scientific research, groundwater from existing realities should be tested, and not just synthetic waters recreated in laboratories with aqueous solutions. Usually, waters are tested with the addition of individual pollutants such as fluoride or arsenic. The removal mechanisms are studied individually without interfering substances. The next and necessary step would be to study multicomponent adsorption, to get closer to the treatments performed on a large scale on groundwater. In this way, the interaction mechanisms between different pollutants which are present simultaneously in real waters could be investigated. There are few scientific studies conducted at the pilot scale and most are batch tests. It is important to conduct batch experiments as they allow to identify the optimal operating conditions of the adsorption mechanisms, but the next step must consist in carrying out (i) more pilot-scale studies, (ii) continuous tests, or at least semi-batch, and (iii) experiments on a scale ever closer to future real applications of the technology. Thanks to these research approaches, it is possible to get closer to the real functioning to evaluate and verify the actual application at full and industrial scale. There are other critical issues related to the intrinsic properties of biochar that represent a limit to its application in the water sector. Some fundamental properties that must be improved are the specific surface, surface functionality, pore volume, and pore distribution to consequently increase both the adsorption and the catalytic capacity of the biochar [133; 134]. There are several treatments to increase the specific surface of biochar, including vapor activation, metal doping, hydrothermal pyrolysis, and high temperature pyrolysis [133]. Studies have shown an increase in the surface area of rice straw biochar