Kenya is an East African country with the third-largest economy in sub-Saharan Africa. The demand for metals and minerals continues to increase due to urbanization, population rise, and new infrastructure growth in different countries. Kenya formally confirmed the discovery of oil and various minerals in April 2013, launching itself as a new player in Africa’s rapidly expanding extractive sector. This review paper highlights the mining status in Kenya and the role of hydrometallurgical and flotation processes in the recovery of deficit metals from ores and mine wastes. The nation’s 2030 Vision is anticipated to benefit greatly from the proceeds from the sale of oil, gas, and valuable metals. Because Kenya was originally mapped as an agricultural region, less mineral prospecting was done in earlier times. The country’s mining industry is now dominated by the manufacture of non-metallic goods, and it is largely neglected for minerals. One of the most serious problems for the mining industry in Kenya is the production of tailings that hold strategic metals. The material is already ground, which means the most energy-consuming process has been already applied, and chemical engineering processes like leaching are more feasible at this point. Hydrometallurgical and flotation recovery of valuable metals from wastes, high and low-grade ores, or tailings is essential. The resources will be preserved, which ensures sustainability in the growth of the mining industry.

In present times, with increasing emphasis on circular economies, municipal wastewater treatment plants (WWTPs) are considered resource recovery facilities. The targeted resources are water, biogas, and sludge, organic residuals containing nutrients and elements needed by plants (nitrogen and phosphorus). Sludge is a byproduct that constitutes the largest volume of all other byproducts obtained in wastewater treatment plants. Its processing and disposal are challenging for environmental engineers because of its complexity. Thus, quick development and implementation in industrial practice of sludge valorization and utilization technologies is required, where high nutrient content must be taken into account. Also, the occurrence of a variety of pathogens in sewage sludge is a matter of concern, even in the case of developed countries. The use of untreated sludge or wastewater in agricultural activities poses a serious risk of bacterial and parasitic infection in human beings. To overcome such issues, the application of ionizing radiation processing, especially electron beam (EB), can be considered a promising method. Its effectiveness in pathogen removal has been proven by researchers. Water radiolysis products created during irradiation of water are highly reactive and cause some effects such as DNA damage, ${}_{ }{}^{•}OH$ radical production, etc. Additionally, ionizing radiation technologies in sewage sludge treatment enhance the efficiency of the methane fermentation process. Depending on specific needs, different types of ionizing radiation sources can be discussed. Based on the review information and our research results, the basic engineering parameters of hybrid installation have been presented as the conclusion of the report. In this technical solution, a notably effective additional step would be the use of EB irradiation, combined with conventional wastewater treatment, to achieve efficient removal of pollutants.

Large quantity of sewage sludge originating from wastewater treatment plants is becoming a growing problem from environmental and human health points of view. One of the ways to use sewage sludge is agricultural purpose due to its nutrients and organic matter content, but the condition is that it should be deprived of pathogenic bacteria and parasite egg contamination. Application of ionizing radiation to hygienize sewage sludge can make it appropriate for agricultural use. The process does not require addition of chemicals to sludge; it is environmentally friendly and effective in removal of biological threats. In the past, successful attempts of sewage sludge treatment using ionizing radiation were made. Pilot plants and commercial ones proved that pathogens can be easily removed from sewage sludge by ionizing radiation. The concept of ‘zero energy’ biogas plant is based on the construction of a complex system consisting of biogas plant and electron accelerator in the biofertilizer manufacturing line. Digestate originating from the methane fermentation of sewage sludge is irradiated to remove all pathogens using electron beam from an accelerator powered by electric energy obtained from burning biogas in a cogenerator. The product is a high-quality, biologically safe fertilizer.

Diclofenac (DCF) degradation in aqueous solution under electron beam (EB) irradiation after nanobubbling treatment was studied and compared with treatments using nanobubbling or EB irradiation alone. It was found that the removal efficiency of DCF increased by increasing the adsorbed dose, and it depended on the initial concentration of DCF in solution, being higher for the lower concentrations. Furthermore, when using the nanobubbling treatment alone, about 16% of the DCF was removed from the aqueous solution due to the OH radicals generated during the process. On the other hand, using EB treatment at 0.5 kGy, the degradation of DCF increased from 36% to 51% when adding a nanobubbling pretreatment before the EB radiation. At higher doses (5 kGy), the degradation of DCF was 96% using EB radiation and 99% using nanobubbling before EB radiation, indicating that the nanobubbling effect was not synergistic. With an increase in the adsorbed doses, EB radiation seemed to play a more important role on the degradation of DCF, probably due to the reactive species generated. Moreover, the solutions treated with nanobubbling and EB radiation presented higher COD values and radiolytic by-products with aromatic rings with chlorine. This work can support the development of innovative strategies to treat municipal wastewaters using ionizing radiation technologies.

Sulfamethoxazole (SMX), a widely used antibiotic, persists in aquatic environments due to its resistance to conventional wastewater treatments. This work examined the breakdown of SMX in both purified water and urban wastewater through the application of electron beam irradiation (EBI). Experiments were conducted across doses of 0.5–3.0 kGy and varying pHs (2.70, 6.13, 9.00 and 11.10) and initial concentrations (5, 10, 15, 20 and 30 mg/L), and the role of reactive species was investigated with the help of scavengers. The results showed that SMX degradation followed pseudo-first-order kinetics and was most efficient at lower pH and concentrations. The scavenger experiments confirmed hydroxyl radicals as the dominant oxidizing agents responsible for SMX degradation, while wastewater constituents slightly inhibited the process. Nevertheless, over 99% SMX degradation was achieved at higher doses (1.5–3.0 kGy). TOC analysis revealed the partial mineralization of SMX, indicating the persistence of intermediate by-products despite high degradation efficiency. LC-MS analysis revealed multiple transformation products including hydroxylated sulfonamides and nitro-substituted derivatives, reflecting diverse degradation pathways. These results demonstrate that EBI is a highly effective laboratory-scale method for degrading SMX from water and wastewater, with promising potential for practical application.

This work reports on municipal sludge hygienization using electron beams. Three types of sewage sludge from two municipal wastewater treatment plants were tested: preliminary sludge with 4% TS, postflotation sludge with 2.5% TS and thickened preliminary sludge with 10% TS. The analysis of reference samples demonstrated the presence of bacteria and helminths ova in all examined samples. For the study of hygienization, electron beams from two types of accelerators, linear (Elektronika 10/10) and single cavity (ILU-6), were applied. For each type of accelerator, different irradiation methods were used: irradiation in sealed polyethylene bags using conveyor and flow irradiation installation. Experiments showed that the doses necessary for the elimination of mentioned pathogens were 4 kGy for preliminary sludge, 4 kGy for postflotation sludge and 5.5 kGy for preliminary sludge. The differences between the amounts of initial pathogens in preliminary and thickened preliminary sludge were marginal. It is possible that the higher irradiation dose required to hygienize thickened sludge resulted from higher TS concentration.