Carbon footprint analysis and carbon neutrality potential of desalination by electrodialysis for different applications.

Low-carbon water production technologies are indispensable for achieving sustainable development goals and mitigating global climate change. However, at present, many advanced water treatment processes lack a systematic assessment of related greenhouse gas (GHG) emissions. Thus, quantifying their life-cycle GHG emissions and proposing strategies toward carbon neutrality is urgently needed. This case study focuses on electrodialysis (ED), an electricity-driven desalination technology. To analyze the carbon footprint of ED desalination in various applications, a life cycle assessment model was developed based on industrial-scale ED processes. For seawater desalination, the carbon footprint is 59.74 kg CO2-eq/metric ton removed salt, which is one order of magnitude lower than that of high-salinity wastewater treatment and organic solvent desalination. Meanwhile, the power consumption during operation is the main hotspot of GHG emissions. Power grid decarbonization and improved waste recycling in China are projected to reduce the carbon footprint up to 92%. Meanwhile, the contribution of operation power consumption is expected to reduce from 95.83% to 77.84% for organic solvent desalination. Through sensitivity analysis, significant non-linear impacts of process variables on the carbon footprint were determined. Therefore, it is recommended to optimize the process design and operation to reduce power consumption based on the current fossil-based grid. GHG reduction for module production and disposal should also be emphasized. This method can be extended to general water treatment or other industrial technologies for carbon footprint assessment and reducing GHG emission.

Scheduling of Batch Operation for a Wastewater Treatment Plant under Time-of-Use Electricity Pricing.

High operating cost caused by electric energy consumption is a common problem challenging many municipal wastewater treatment plants (WWTPs). Due to the characteristics of intermittent inflow and aeration, WWTPs using sequencing batch reactor technology and its variants can be managed to relieve operating cost through taking advantage of time-of-use electricity pricing. However, little attention has been paid to the scheduling of treatment processes in the context of WWTPs. In this paper, a novel mixed-integer linear programming model is established for scheduling the batch operation of a WWTP under time-of-use electricity pricing, which considers constraints arising from task allocation, processing sequence, and processing duration. The modeling method is developed from the event-based continuous-time approach. The start time and end time of each treatment task are optimized to shift electricity consumption from peak hours to off-peak hours to the greatest extent, thus minimizing electricity cost. A case study demonstrates that the proposed model can quickly generate precise operational plans for the investigated WWTP. By implementing the optimum schedules, the WWTP can save on its electricity bill without changing the treatment capacity or the treatment process. The widening of peak and off-peak electricity pricing gap is favorable for the proposed model to display a more significant effect in reducing electricity cost.

Remediation of Urban River Water by Pontederia Cordata Combined with Artificial Aeration: Organic Matter and Nutrients Removal and Root-Adhered Bacterial Communities.

Macrophyte combined with artificial aeration is a promising in situ remediation approach for urban rivers polluted with nutrients and organic matter. However, seasonal variations and aeration effects on phytoremediation performance and root-adhered microbial communities are still unclear. In this study, Pontederia cordata was used to treat polluted urban river water under various aeration intensities. Results showed that the highest removal efficiencies of chemical oxygen demand (COD(Cr)) and total nitrogen (TN) were attained under aeration of 30 L min(-1) in spring and summer and 15 L min(-1) in autumn, while total phosphorus (TP) removal reached maximum with aeration of 15 L min(-1) in all seasons. Moderate aeration was beneficial for increasing the diversity of root-adhered bacteria communities, and the shift of bacterial community structure was more pronounced in spring and autumn with varying aeration intensity. The dual effect, i.e. turbulence and dissolved oxygen (DO), of aeration on the removal of COD(Cr) and TN prevailed over the individual effect of DO, while DO was the most influential factor for TP removal and the root-adhered bacterial community diversity. P. cordata combined with 15 L min(-1) aeration was deemed to be the best condition tested in this study.

[Spatial distribution and contamination assessments of heavy metals in sediments of Wenzhou River network].

In order to investigate the spatial distribution pattern and degree of heavy metal pollution in river network sediments of Wenzhou, 29 sediment samples were collected, and using atomic fluorescence spectrometry (AFS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) heavy metal concentration in the samples were analyzed. The Kriging interpolation map reflected the spatial distribution of heavy metal. Comprehensive geo-accumulation index based on the Nemerow index method was established to assess the pollution degree. Pearson correlation analysis method and principal component analysis method were employed in sources analysis. Results show that heavy metal concentration varies significantly at different sites. The area with highest Cd and Zn concentrations is the centralized urban and industrial area of the main stream of this river network, while the highest concentrations of As, Pb, Hg, Cu, Ni and Cr were found to be in machinery industrial park. Sediments are contaminated by Hg, Cd, Cu, Zn, Ni and Cr. The order of degree of contamination is as follows: machinery industrial park > urban areas of the main stream > Sanyang Wetland>outskirt and rural area > drinking water source area. Hg, Cd, Cu, Zn, Ni and Cr have similar pollution sources which are mainly anthropogenic sources.