New Trend in Wastewater Treatment: Photovoltaic Wastewater Treatment-Hezhong Environment (Beijing) Co., Ltd. was established in 2003

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New Trend in Wastewater Treatment: Photovoltaic Wastewater Treatment

Published Time:

2023-08-07

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Introduction

As one of the national strategic emerging industries, China's photovoltaic industry has achieved a transition from catching up to surpassing others, and has gradually become a global leader in the photovoltaic industry. It is foreseeable that, driven by both policy support and technological innovation, the photovoltaic industry will steadily advance in its gradual maturation.

On August 3, the Ministry of Industry and Information Technology (MIIT) released the operating status of the national photovoltaic industry in the first half of 2023. In the first half of 2023, China's photovoltaic industry maintained a generally stable and positive development trend, with the output of major links in the industrial chain achieving rapid growth. According to the information of photovoltaic industry standard announcement enterprises and industry association calculations, the national output of polysilicon, silicon wafers, cells, and components hit new highs, with year-on-year growth exceeding 65%. The total export value of photovoltaic products reached US$28.92 billion, a year-on-year increase of 11.6%.

Specifically, in the polysilicon segment, the national output exceeded 606,000 tons from January to June, a year-on-year increase of 66.1%; in the silicon wafer segment, the national output exceeded 253.4 GW from January to June, a year-on-year increase of 65.8%; in the cell segment, the national output of crystalline silicon cells exceeded 224.5 GW from January to June, a year-on-year increase of 65.7%; in the component segment, the national output of crystalline silicon components exceeded 204 GW from January to June, a year-on-year increase of 65%; exports reached 108 GW, a year-on-year increase of 37.3%.

The photovoltaic industry is developing steadily, and the development of the industry must also meet people's new expectations and requirements for environmental protection. Therefore, the photovoltaic industry will also become a new outlet for industrial wastewater treatment.

Development History of China's Photovoltaic Industry

Currently, China's photovoltaic industry ranks among the top in the world in terms of manufacturing scale, industrialization technology level, application market expansion, and industrial system construction. It has formed a complete industrial chain ranging from high-purity silicon materials, silicon ingots/silicon rods/silicon wafers, cells/components, photovoltaic auxiliary materials, photovoltaic production equipment to system integration and photovoltaic product applications, and has a solid foundation for advancing towards intelligent photovoltaics.

Competitive Landscape of the Photovoltaic Industry

2.1 Regional Competition

Data on the cumulative installed capacity of photovoltaics in various provinces and cities in the first half of 2021 released by the National Energy Administration shows that, as of the first half of 2021, Shandong, Hebei, and Jiangsu ranked among the top three in the country in terms of cumulative installed capacity of photovoltaics, with Shandong Province ranking first with a cumulative installed capacity of 26.06 GW.

2.2 Enterprise Competition

Longi Green Energy took the lead in the top 10 list of Chinese photovoltaic companies in 2020.

The top 10 list of Chinese photovoltaic companies in 2020, compiled by 365PV, has been released. Among them, Longi Green Energy Technology Co., Ltd. ranked first, with operating revenue reaching 32.897 billion yuan in 2019. In addition, GCL-Poly Energy Holdings Limited, JinkoSolar Holding Co., Ltd., Trina Solar Co., Ltd., and Canadian Solar Inc. ranked second, third, fourth, and fifth, respectively.

Future Prospects and Trend Predictions of the Photovoltaic Industry

3.1 China's Energy Transformation Strategy

The "14th Five-Year Plan" outline proposes to build a clean, low-carbon, safe, and efficient modern energy system. During the "14th Five-Year Plan" period, the proportion of non-fossil energy in total energy consumption will increase to around 20%. Policies continue to promote industry development.

3.2 Development Goals for Distributed Photovoltaics

Distributed photovoltaic power generation is an inevitable trend in the development and promotion of the photovoltaic power generation industry. Provinces such as Zhejiang, Shandong, Jilin, and Guangdong have included the development of distributed photovoltaics as an important part of promoting energy transformation in their "14th Five-Year Plan".

3.3 Cumulative Installed Capacity of Photovoltaics May Exceed 700 GW in 2026

Driven by policy support and the decline in the cost of photovoltaic power generation, the installed capacity of photovoltaics will continue to climb. According to the prediction of the China Photovoltaic Industry Association, during the "14th Five-Year Plan" period, China's annual new installed capacity of photovoltaics will be between 70 and 90 GW. To achieve carbon peaking by 2030 and carbon neutrality by 2060, the photovoltaic industry will become one of the new energy industries that will remain in a period of rapid development for a long time. Based on this prediction, the cumulative installed capacity of China's photovoltaic power generation industry in 2026 may be between 673 and 793 GW.

Overview of the Photovoltaic Industry Chain

Photovoltaic Industry Production Process

5.1 Silicon Material → Silicon Wafer

5.2

Silicon Wafer → Cell

1. Texturing: Roughen the surface of the silicon wafer to reduce reflectivity

2. Diffusion: Apply a layer of phosphorus to form a PN junction

3. Etching & Edge Isolation: Remove the PN junction from the side surface to prevent short circuits

4. Back Surface Passivation: Reduce light transmission and improve the photoelectric conversion rate.

5. Coating: Silicon nitride film, reduce reflection, protect the battery from corrosion, etc.

6. Screen Printing: Print metal electrodes

7. Sintering: Sinter electrodes and silicon wafers

8. Sorting: Sort cells with different efficiencies

5.3

Cell → Module

Photovoltaic Industry Wastewater Treatment

With the increasing emphasis on resource utilization and the popularization of solar energy applications, various industries are involved in solar energy, and the development of solar cells has enabled the photovoltaic industry to gradually occupy the market. The photovoltaic industry has become a new outlet for industrial wastewater treatment.

Photovoltaic industry wastewater mainly includes acid washing wastewater, alkali washing wastewater, fluorine-containing wastewater, and organic wastewater.

6.1 Acid and Alkali Washing Wastewater

Wastewater Source ：The texturing process uses alkali to corrode the surface of the silicon wafer to form a pyramid-shaped morphology. In the process, strong oxidizing solutions such as chromic acid, nitric acid, hydrofluoric acid, and sulfuric acid are used for cleaning.

6.2 Fluorine-containing Wastewater

Wastewater Source ：Mainly includes hydrofluoric acid and silicon-containing fluorine-containing rinsing wastewater

6.3 Organic Wastewater

Wastewater Source: The main organic pollutants come from the isopropyl alcohol used in the texturing tank.

Water Quality Characteristics ：High concentration of organic matter, difficult to degrade.

The presence of a large amount of wastewater will cause serious pollution to the ecological environment and also restrict the continuous and rapid development of industries and enterprises. The characteristics of photovoltaic industrial wastewater are strong acid-base corrosiveness and high content of suspended solids in the water. The pH value can be less than 2, showing high acidity; it can be greater than 12, showing high alkalinity; and the water contains a large amount of suspended solids, with the content of suspended solids in the water, i.e., SS value, as high as more than 6000 mg/L.
At the same time, the wastewater contains a high concentration of polyethylene glycol, a high molecular polymer, resulting in a high chemical oxygen demand (COD) of the wastewater, with a COD value as high as 10,000～20,000 mg/L, indicating that the water body is highly polluted by organic matter.

Various wastewaters are classified and pre-treated and pH adjusted according to their characteristics. Through treatment, suspended solids are removed from the industrial wastewater, acid-base corrosiveness is eliminated, and the COD content of the wastewater is reduced, so that the pH value, suspended solids content, and COD value of the wastewater meet the requirements of the subsequent biological treatment system.

Based on the comprehensive water quality characteristics, acidic wastewater and alkaline wastewater are pre-treated using a combination of natural sedimentation and plate-and-frame filter press separation. Wastewater mixing and pH adjustment technology is used to purify the water body and adjust the pH value, eliminating the impact of wastewater quality differences on wastewater treatment.

Different types of wastewater are mixed and homogenized as needed to improve the water quality, stabilize the wastewater quality, and reduce the acid-base corrosiveness of the wastewater. Because the wastewater has a high salt content and a high organic matter content, and considering the difficulty in degrading the high polymer in the wastewater, air flotation and flocculation sedimentation treatment processes are used for pre-treatment before the wastewater enters the biological system. After mixing with other wastewater, the wastewater undergoes physical and chemical flocculation sedimentation as a pre-treatment measure before entering the biological system.

After pretreatment and flocculation sedimentation, the SS value and salt content are greatly reduced, but the concentration of organic matter in the wastewater is still very high, and the high polymer is difficult to degrade. In addition, the wastewater is nutritionally unbalanced. Anaerobic and aerobic bacteria in activated sludge are used to degrade and remove organic matter in the wastewater. A multi-stage biological treatment process is used, and the pretreatment combined evaporation and concentration process of photovoltaic wastewater can better reflect the reliability and economy of the technology.