Reducing pollution and carbon emissions is an important direction for wastewater treatment plants to achieve sustainability. This study established a comprehensive evaluation system based on three indicators, namely, effluent quality index (EQI), operating cost index (OCI), and greenhouse gas emissions (GHG), to systematically compare traditional and emerging wastewater treatment processes. Fourteen kinds of wastewater treatment processes under six inflow and outflow scenarios were simulated using GPS-X software. EQI calculations show that biofilm processes such as biological aerated filter (AO-BAF) achieve the best effluent quality under various scenarios, with a removal value of 2.28 kg EQI/m3. OCI calculations reveal that the average proportions of chemical addition, electricity usage costs, and sludge transportation costs for all processes are 47.69%, 24.62%, and 27.69% respectively, with anammox processes having the lowest OCI (0.047 $/m3)) for the baseline scenario. Carbon emission accounting results showed that direct emissions of CH4 from wastewater treatment, indirect emissions of electricity and chemicals were the main sources of GHG. Finally, through non-dominated sorting considering EQI, OCI and GHG indices, AO-BAF and AAO-VMBR processes were the preferred processes for most scenarios. This study provides valuable insights for the selection and upgrading of wastewater treatment processes from a low-carbon perspective.
UV light absorption by aquatic systems affect the physicochemical characteristics of graphene oxide (GO) nanoparticles which ultimately influence its aggregation behavior in water. Regarding this research, various humic and fulvic acids (HA/FA), extracted from China’s different climate zones, were treated with 2 h UV irradiated large (~500 nm) and (~200 nm) GO in 200 mmol/L NaCl. UV irradiated GO particles displayed aggregation even at low humic acid/fulvic acid (HA/FA) concentrations ranging from 0.2 to 1.0 mgC/L, whereas pristine GO particles did not exhibit such behavior. Reduction of functional groups, containing Oxygen (C=O/C–O), via UV irradiation is responsible for this aggregation phenomenon and conversion of GO to reduced graphene oxide (rGO). Consequently, rGO exhibits lower dispersibility, facilitating its agglomeration. Moreover, both small and large-sized GO particles exhibited less aggregation in HAs compared to FAs due to large molecular weight and high polarity of HAs. Aggregation of GO was more obvious with Makou FA and Maqin HA from Plateau and Mountain climate zone and Subtropical Monsoon climate zone, respectively, owing to DOM’s lower molecular weight and aromaticity that reduced their adsorption. The application of the Derjaguin-landau-verwey-overbeek (DLVO) theory did not reveal any significant interaction energy barrier between the 2 h UV irradiated GO particles even in the presence of DOM, indicating that aggregation prevailed despite the addition of DOM. These findings highlight that UV irradiation poses a significant threat to the GO stability in aquatic environments, particularly in the presence of DOM.
Iron-based nanoparticles (Fe-NPs) exhibit promising potential for soil remediation. However, their toxic effects on plants have also been reported. Typical Fe-NPs have been introduced into soil–plant systems to examine their possible nanotoxicity and other impacts on plants, while Fe-NPs have been added to pollutant–soil–plant systems to evaluate their performance as remediation agents. Mixed opinions and results have been reported regarding interactions between Fe-NPs and soil or plants. Here, meta-analysis was conducted to evaluate the effects of Fe-NPs on plant morphological and physiological characteristics in soil–plant and pollutant–soil–plant systems. Interestingly, morphological characteristics (dry and fresh weight) were significantly improved by Fe-NPs in both soil–plant and pollutant–soil–plant systems. In terms of plant physiological characteristics, Fe-NPs exerted negative effects on plant pigments in soil–plant systems, but positive effects in pollutant–soil–plant systems. In addition, Fe-NPs greatly increased the Fe contents and decreased the pollutant contents of plants. This study also provides a comprehensive review of the positive and negative effects of Fe-NPs on soil–plant systems and summarizes the pollutant remediation mechanisms of Fe-NPs in soil–plant systems. The results underscore the potential of Fe-NPs in agricultural applications and the future development of food safety.
