## 2 Results
Pearson correlation and principal component analysis (PCA) were introduced as major approaches and health risks posed to MSW workers exposed to heavy metals in MSW were assessed using a Monte Carlo simulation combined with the US Environmental Protection Agency Health Risk Assessment Model. The results showed that As, Cd, Hg, Cr, and Pb contents of the east Guangdong MSW were (0.76 \(\pm\) 0.75), (2.14 \(\pm\) 4.44), (0.11 \(\pm\) 0.14), (55.42 \(\pm\) 31.88), and (30.67 \(\pm\) 20.58) mg/kg, respectively. Hg, Cr, and Pb were most likely originating from glass, textile and food waste, whereas As and Cd were mostly coming from soil and food waste in the MSW. The study highlighted that the heavy metals in MSW might induce carcinogenic risks, with the likelihoods for male and female workers being 35% and 45%, respectively. In the subject of advanced oxidation processes, this special issue contains two very interesting articles, reporting recent developments in the field, highlighting potential applications in water and wastewater treatment. The first study [8] depicted the comparative performance of micropollutants' removal by FeSO\({}_{4}\)- and zero-valent iron (Fe(0))-catalytic Fenton oxidation explored the possibilities of minimizing the sludge production from the processes. The emerging micropollutants examined in this paper were gabapentin, sulfamethoxazole, diuron, terbutryn and terbuthylazine. Both FeSO\({}_{4}\)- and Fe(0)-catalytic Fenton oxidation were able to completely degrade the stated micropollutants. The Fe(0)-catalytic Fenton process accomplished better removal of dissolved organic carbon (DOC; 70%) than FeSO\({}_{4}\) catalytic Fenton oxidation (45%). The second study in this field, [9] used sodium hydroxide-modified graphene oxide to support manganese oxides aiming at the formation of nanocomposites via a one-pot preparation route for the degradation of Reactive Black 5. The nanocomposites were characterized by X-ray diffraction, nitrogen adsorption, Fourier transform infrared spectroscopy, potentiometric titration, and thermal analysis measurements. The nanocomposites shoed high activity for the abatement of Reactive Black 5 at ambient conditions, without light irradiation. The study concluded that RB5 degradation was mainly based on the release of H\({}_{2}\), the cleavage of -N=N- bonds and the formation of -NH\({}_{2}\) groups. The presence of H\({}_{2}\)O\({}_{2}\) could increase the RB5 degradation by producing hydroxyl radicals which are able to decompose the dye molecules. The field of wastewater treatment is covered by four articles in this special issue. The first article, [10] reported the development of a pilot-scale six-compartment hybrid anaerobic baffled reactor (HABR) with effective volume of 18 m\({}^{3}\) for the treatment of dyeing wastewater. The HABR system treated effectively the wastewater after pretreatment with FeSO4. This was shown considering the removal efficiencies of 33.7% for chemical oxygen demand (COD), 39.9% for suspended solid (SS), and 22.5% for sulfate (SO\({}_{4}\)\({}^{2-}\)) during a steady state operational period. Besides, it was found that the concentrations of several categories of organic compounds, such as alkanes, amides, organic acids, ketones, phenols, and esters were much lower in the effluent than those in the influent. In addition, many high-molecular-weight compounds such as cyclanes, quinolines, and phenols were successfully transformed to low-molecular-weight compounds. Based on the overall treating effectiveness, the optimized operation plan of the wastewater treatment by HABR was achieved as the hydraulic retention time (HRT) of 12 h for steady-state operation with an up-flow velocity of 1.7 m/h as well as OLR of 1.5-2.0 kg COD/(m\({}^{3}\cdot\)d)  
Next, [PERSON] and co-authors [11] reviewed the strategies for minimization of sewage sludge from wastewater treatment plants.