Rural drinking water treatment system combining solar-powered electrocoagulation and a gravity-driven ceramic membrane bioreactor

Electrocoagulation enhanced gravity driven membrane bioreactor for advanced treatment of rural sewage

The daily discharge of rural sewage in China occupies 30 % of the national wastewater discharge, and developing an energy-efficient, easy to operate, and decentralized rural sewage treatment technology becomes an important task. In this work, a novel rural sewage treatment technology, Electrocoagulation enhanced Gravity-Driven Membrane Bioreactor (EC-GDMBR) was exploited for the rural sewage treatment under long-term operation (160 days). Two EC-GDMBRs with various module structures of ceramic membrane (horizontal module and side module) not only displayed the desirable effluent quality, but also sustained the stable flux (8-13 LMH). The electrocoagulation, electrooxidation, biodegradation, and separation in EC-GDMBRs were able to synergistically remove the particle matter, organic (CODCr effluent <11.6 ± 1.2 mg/L) and nutrients (NH3-N effluent <0.1 mg/L, TN effluent <8.5 mg/L, TP effluent <0.05 mg/L). Besides, the high permeability of ceramic membrane and large porosity of biofilm on its surface improved the sustainability of stable flux during the long-term operation. Moreover, by analyzing bacterial abundance, Extracellular Polymeric Substances, Adenosine Tri-Phosphate and Confocal Laser Scanning Microscopy, a large number of microorganisms grew and accumulated on the carrier, as well as formed the biofilm (23.46-659.9 μm), while Nitrobacteria (1.6-4.1 %) and Nitrate (0.01-0.06 %) exited in the carrier biofilms, promoting the nitrogen removal. Compared with EC-GDMBR with side module of ceramic membrane, EC-GDMBR with horizontal module of ceramic membrane has advantages in flux behavior, organic/nutrient removal, microbial abundance/activity, abundance of nitrogen removal functional bacteria and water permeability of biofilm, because the ceramic membrane of horizontal module can promote the uniform growth of biofilm and improve the uniformity of flow penetration distribution. In general, the findings of this work verify the reliability of EC-GDMBR for the sustainable operation of wastewater treatment and improve its application value of rural sewage treatment.

Integrated electro-coagulation and gravity driven ceramic membrane bioreactor for roofing rainwater purification: Flux improvement and extreme operating case

The collected roofing rainwater with high water quality and large water volume, can alleviate the crisis of water resources and fit the Low-Impact Development (LID) concept. In this work, a novel water purification technology, Electro-Coagulation coupled with Gravity-Driven Ceramic Membrane Bio-Reactor (EC-GDCMBR) was developed for the roofing rainwater purification under long-term operation (136 days). EC-GDCMBR system not only exhibited the better effluent quality, but also obtained the greater flux (~32 LMH). The reason contributed to the high permeability of ceramic membrane and large porosity of biofilm formed by floc growth (~36 μm) during the EC process, which was also proved by SEM image. The coagulation, adsorption, biodegradation, and coprecipitation of EC-GDCMBR was able to synergistically remove the particulate matter, ammonia nitrogen (NH₃-N), Total Phosphorus (TP), organic substances, and heavy metal (i.e., Cr, Zn, and Cu). In particular, via the analysis of bacterial abundance, Extracellular Polymeric Substances (EPS), Assimilable Organic Carbon (AOC), Adenosine Tri-Phosphate (ATP) and Confocal Laser Scanning Microscopy (CLSM), EC could sweep most free bacteria on the ceramic membrane surface, enhancing the biological purification efficiency. Furthermore, a large amount of Pseudomonas (12.4 %-66.7 %) and Nitrospira (1.46 %-3.16 %) in the aggregates formed the biofilms, improved the NH₃-N removal. During the long-term operation, there are some unavoidable problems, such as the thick and ripened biofilm of EC-GDCMBR would crack and fall off. Based on this, the current work also studied the reliability of GDCMBR under "extreme operating case", and the results showed that neither the biofilm detachment nor the biofilm breakup had a significant impact on the effluent quality. Overall, the findings of this study suggest the reliability of EC-GDCMBR for the sustainable operation of roofing rainwater purification and improve the application value of decentralized rainwater harvest device.

Rheological characterization of biofouling layers developing in nanofiltration processes：macroscale rheological properties of biofouling layer and micro fluid field

Nanofiltration (NF) membrane promotes the rapid development of reclaimed water treatment technology. Biofouling significantly limits NF membranes' performance in the case of wastewater treatment. The rheological characteristics of NF biofouling layer and the microfluid field on the vicinity of membrane surface determine the strategies for alleviating biofouling. Here, we tested the biofouling layer generated on NF in a parallel plate rheometer operated in oscillation and stable shear mode, along with shear stress calculation using computational fluid dynamic simulations on the membrane surface. Results indicated that the biofouling layer was typical viscoelastic material, and the yield stress exhibited shear thinning behavior. The biofouling layer tended to show elasticity during long-term operation, and with higher COD content formed, showed stronger elasticity, larger viscosity, and yield stress. Compared with the shear stress on the membrane surface obtained using numerical simulation (0.57 Pa~1.22 Pa), the yield stress (0.59 Pa~266.98 Pa) of NF biofouling layer was relatively large. Our results suggest that the shear stress generated by water flow may not effectively cause formed biofouling layer shedding. The research will provide theoretical and technical support for biofouling control in NF membrane systems and can be applied in advanced wastewater treatment and reclamation processes.

Electrocoagulation Process: An Approach to Continuous Processes, Reactors Design, Pharmaceuticals Removal, and Hybrid Systems—A Review

The electrocoagulation (EC) process has been widely studied in recent years to remove a wide range of contaminants present in different types of water: fluorides, arsenic, heavy metals, organic matter, colorants, oils, and recently, pharmaceutical compounds. However, most of the studies have been aimed at understanding the process factors that have the most significant effect on efficiency, and these studies have been mainly on a batch process. Therefore, this review is focused on elucidating the current state of development of this process and the challenges it involves transferring to continuous processes and the recent exploration of its potential use in the removal of pharmaceutical contaminants and its implementation with other technologies.