Establishment And Research Of Electrochemical-osmotic System For Simultaneous Recovery Of Resource And Energy

With the rapid development of economy and industrialization,heavy metal pollution in the environment is getting worse.In particular,the discharge of wastewater rich in large amounts of heavy metal ions in natural waters poses a huge threat to public health and the ecological environment.However,metal-laden wastewater contains valuable resources,and traditional wastewater treatment technology requires a lot of power and chemical consumption when recycling these metal resources.Therefore,developing a new type of environmental-friendly treatment technology has becomes an important field in environmental engineering,which is also one of the effective ways to realize the resource and energy of heavy metal wastewater and ecological sustainability.This paper creatively presented a new nature-friendly paradigm for co-resource and energy symbiosis of metal-laden wastewater treatment.Firstly,we present a self-sustained hybrid electrochemical-osmotic system（EOS）in which an autonomous Fe（s）/Cu²⁺（aq）galvanic cell utilizes simulated copper-laden wastewater for power generation while simultaneously achieving copper recovery by Cu²⁺electro-reduction.With electrochemical redox reactions occurring in the draw and feed（i.e.,synthetic wastewater）solutions,the EOS extracts water from the wastewater across an FO membrane installed between the two solution chambers.We conduct process performance simulation to explore the key driving forces of the EOS and predict the variation of electric charge,solution p H,and membrane water flux.We proceed to experimentally evaluate the performance of a semi-batch EOS,including water and ion permeation behavior across the FO membrane and the related electrochemical properties of the system.By further assessing a scaled-up,modular EOS,we demonstrate long-term feasibility of electrical energy production,metal recovery,and water extraction from synthetic wastewater.Process efficiency and limiting factors of the EOS are also analyzed and discussed.We demonstrate that the system can generate a maximum electric power density of 1.05 m W cm^-2 by a spontaneous Fe/Cu²⁺galvanic cell,while simultaneously achieving copper recovery(11.53 g m^-2 h^-1)from wastewater.With an osmotic pressure difference generated by the deployed electrochemical reactions,water is osmotically extracted from the feed solution by the EOS at a water flux of 5.09 L m^-2 h^-1.Overall,the proposed prototype EOS accomplishes multi-resource recovery from a simulated metal-laden wastewater,demonstrating its promise as a new technology at the water-energy nexus.Then we investigated the differences in the effectiveness of using several membranes to install in EOS.For using nanofiltration（NF）membrane modified by polyelectrolyte,the system possessed a higher water flux value and output power density,while effectively suppressed the forward salt flux of Cu²⁺in the feed solution through the repulsive property between the charges.The results showed that,compared with the traditional EOS,the 1.5 bilayer polyelectrolyte modified NF membrane increased the maximum output power density by 18%,the water flux by 2.8 times,and the forward salt flux of Cu²⁺was also reduced by 69%,respectively.In order to explore the practical applications of EOS after optimizing,electroplating wastewater was used as the feed solution.The system could be able to extract clean water at 9.38 L m^-2 h^-1,and the maximum output power density reached 0.35 m W cm^-2.The experimental results confirmed EOS has good prospects for application,which not only achieved the treatment of electroplating wastewater but also produced electricity and recovered metal resources.Lastly,we present an autonomous photoelectrochemical-osmotic system（PEOS）that can recover a wide range of metals from simulated metal-laden wastewater with sunlight illumination while generating electricity.The PEOS comprises a draw solution chamber with a nickel nanoparticle-functionalized titanium nanowire（Ni-Ti NA）photoanode,a feed solution chamber containing synthetic wastewater and an immersed carbon fiber cathode,and a FO membrane mounted between the chambers as a separator.Using a Na2-EDTA anolyte as a draw solution at neutral p H,we demonstrate that a sunlit PEOS achieves copper recovery at a rate of 5.5 g m^-2 h^-1of membrane area from simulated copper-laden wastewater while simultaneously producing a maximum power density of 221.8 m W m^-2.Moreover,due to the osmotic pressure difference generated by the photoelectrochemical reactions,the PEOS reduces the wastewater volume by extracting fresh water through the FO membrane at a water flux of 0.84 L m^-2 h^-1.We further demonstrate the feasibility of the PEOS in recovering diverse metals from metal-laden wastewater under sunlight irradiation.Our proof-of-concept PEOS prototype provides a green,sustainable technological solution that leverages sunlight in an electrochemical-osmotic system to recover multiple resources from wastewater.