Photovoltaic solar cells industry wastewater treatment

Abstract

Abstract Nowadays, in the photovoltaic (PV) industry there still remains a huge potential to be exploited, where markets are dominated by crystalline silicon PV-based cells. However, in the future it is expected that thin films PV will have a larger market share. Until recently, the prevailing technology based on mono-crystalline silicon has been gradually exceeded by poly-silicon technology due to its lower production cost. In PV industry, solar-graded silicon is the main material used in manufacturing process. In this industry, manufacturing and production processes require large amounts of water that result in important discharged industrial effluents containing different pollutants such as hydrogen fluorides, suspended solids, mixed acids, SiO2, and high oxide particles. Among discharged pollutants, the hydrofluoric acid is significantly used in photovoltaic’s (PV) manufacturing for both quartz cleaning and wafer etching. In fact, wastewaters from PV industries have high concentrations of fluoride, typically in a range of 500–2,000 mg/L. They are considered highly toxic and need to be strictly monitored and regulated. Three production phases that generate the highest flow of wastewaters are texturing (multi-crystalline silicon wafers need a mixture of HF/HNO3 dilution and also a hot caustic solution with IPA used for the multi-crystalline wafers mixture), etching, and formation of PV cells. Phosphorus diffusion leads to formation of phosphorus silicate layer that needs to be eliminated by means of hydrofluoric acid (HF) application. Classification of effluents from a point of source, concentration, chemical, or composition feature is compared. Wastewater treatment optimization is often conducted and we discussed major treatment methods in solar cells manufacturing: treatment of HF discharges, neutralization, and collection of isopropanol discharges. The article discusses design of wastewater treatment system that is operational in practice.