Application Research of Solar Energy Technology in Wastewater Treatment

【introduction】

Efficient solar energy conversion and utilization is seen as a major demand for national energy. Among them, light-heat (steam) conversion has shown good application prospects in the fields of desalination, fractionation and sterilization. However, due to optical and thermal losses, conventional photo-thermal (steam) conversion efficiency is low (~40%), which greatly limits its wide application.

[Introduction]

Professor Zhu Jia of the School of Modern Engineering and Applied Science of Nanjing University has made a series of work in the field of high-efficiency interface photothermal conversion: Firstly, the preparation of the blackest plasmon absorber has been successfully realized (Science Advances, 2, e1501227 ( 2016)); on this basis, the first solar seawater desalination device based on plasmon enhancement effect (Nature Photonics, 10, 393-398 (2016)) was realized, which greatly solved the optical loss problem of the absorber. Then, through the design of the two-dimensional water channel, the indirect contact between the absorber and the water body is achieved, which greatly reduces the heat conduction loss of the device to the water body (PNAS, 113, 13953-13958 (2016)).

Recently, the group focused on maximizing the optical loss and thermal loss (heat conduction, heat convection and heat radiation) caused by the constant change of solar incident angle in practical applications and made good progress. The latest research was published in the Natio nal Science Review under the title "Three-dimensio nal artificial transpiration for efficient solar waste water treatment".

[Graphic introduction]

Figure 1 Schematic diagram of different solar steam generators

(a) Schematic diagram of conventional photo-thermal (steam) conversion devices

(b) Schematic diagram of three-dimensional (3D) artificial transpiration device

(ce) Electron micrograph of the absorber, water extension layer and one-dimensional water path

Figure 2 Temperature distribution of different solar steam generators

(ac) Two-dimensional direct contact, two-dimensional indirect contact, and three-dimensional artificial transpiration device pictures

(df) temperature of the graphene oxide layer before illumination

(gi) Temperature of the graphene oxide layer after 30 min of solar illumination

Figure 3 Performance of solar steam generators under light conditions

(a) Quality versus time for two-dimensional direct contact transpiration devices under illumination and non-light conditions

(b) Quality versus time of two-dimensional indirect contact transpiration device under illumination and non-light conditions

(c) Quality versus time curve of 3D artificial transpiration devices under illumination and non-light conditions

(d) Two-dimensional direct contact, two-dimensional indirect contact and three-dimensional artificial transpiration devices under outdoor sunlight

Two ways solar wastewater treatment Figure 4

(a) Different metal ion concentrations before and after treatment, blue line reference to World Health Organization drinking water standards

(b) Copper ion concentration before and after treatment at different pH conditions

(c) Stable cycle performance of 3D artificial transpiration device, treating lead ion contaminated water for 50 cycles, each cycle lasting 1h

(d) Purified water output during irradiation time

【summary】

This work first proposed and realized the "artificial transpiration" structure, breaking through the limitations of the traditional two-dimensional planar device, and designing a three-dimensional hollow cone structure, which greatly alleviated the dependence of the device on the incident angle of sunlight in the real environment. At the same time, the evaporation temperature of the device is effectively reduced, thereby effectively controlling the loss of heat convection and heat radiation. Another advantage of the "artificial transpiration" structure is that the heat conduction loss is effectively controlled by the one-dimensional water supply channel, thereby achieving the light-steam conversion efficiency of more than 85% without external assistance and normal illumination conditions for the first time. At the application level, this work extends the interface light-steam conversion to heavy metal wastewater treatment for the first time. The experimental results show that the technology can not only obtain water that meets drinking standards, but also effectively recover heavy metals (such as gold, copper, etc.), providing new ideas for efficient solar light-heat (steam) utilization and development.