Monitor The Wastewater Filtration Process Using UV-VIS Spectroscopy

Monitoring wastewater characteristics is critical for the effective management of a water resource recovery facility (WRRF). Laboratory measurement of grab or composite samples is the dominant method of compliance monitoring. However, process monitoring is increasingly being done with measurements from online analytical instrumentation. Continuous monitoring improves decision-making and reduces the burden on staff for sampling and measuring process parameters multiple times per day. The information allows managers to minimize inputs of chemicals and energy and avoid conditions leading to process upsets. The selection and reliability of sensor technology has improved in the last decade. For example, sensors based on spectrophotometry are now available for direct measurement of important parameters without using costly reagents that need replenishing often.

The objective of this post is to provide guidance on the proper selection, commissioning, maintenance, operation, and application of sensors based on spectrophotometry for process monitoring of wastewater treatment. Many important substances in wastewater, including nitrate, nitrite, and organic carbon parameters, can be measured based on the absorption of UV and visible light (UV-Vis).

Basic Principles

UV-Vis spectroscopy operates on the principle that certain pollutants in water can absorb light within the ultraviolet to visible spectrum at specific wavelengths. This absorption is due to the transition of electrons from a lower energy state to a higher one, which results in a decrease in the intensity of light that passes through. The relationship between the absorption characteristics and the concentration of pollutants is utilized to identify and quantify contaminants in water. Each type of pollutant has a unique absorption profile, producing distinct spectral curves, with many showing significant absorption in the UV-Vis spectrum. By analyzing these absorption patterns, it is possible to determine the levels of various pollutants. The water quality parameters include chemical oxygen demand (COD), heavy metal content, nitrate nitrogen (NO₃⁻N). For instance, the absorption ranges for nitrate NO₃⁻N and nitrite NO₂⁻N ions are typically between 200 nm and 250 nm. Similarly, organic compounds and measures of water clarity are absorbed in the range of 380 nm to 750 nm (See table 1).

Table 1: Absorption spectrum range and substance characteristics of various substances.

Important wastewater parameters exhibit a distinguishable absorption of light in the UV-Vis range. Typical spectra of urban wastewater and some of its constituents are shown in Figure 1. The spectrum for each pure substance may be considered a unique fingerprint. The spectrum for urban wastewater (the black line) is formed from the individual contributions of each component substance. Particles that cause turbidity may increase absorbance across the spectrum.

Figure 1: Typical spectra of municipal wastewater and its constituents.

Measurement system

The setup consists of two essential elements: a light source that directs light onto the water's surface and a spectrometer that records the light that is reflected. The data collected by the spectrometer is processed by a computer to ascertain the levels of pollutants present in the water.

Figure 2: Maya 2000Pro spectrometer.

Intins Company provides advanced solutions for wastewater monitoring through the supply of Ocean Insight products. This spectrometer is particularly suited for detecting various contaminants in wastewater, such as nitrous oxide, aldehydes, organic matter, and turbidity, which have absorption characteristics between 200nm – 750nm. The Maya 2000 Pro Spectrometer is an advanced optical instrument designed for precise spectral analysis across a broad wavelength range. With its capability to measure spectra from 200 nm to 750 nm, it is an ideal tool for applications in both scientific research and industrial environments. Its high-resolution performance and sensitivity make it suitable for capturing detailed spectral information in fields such as biochemistry, material science, and quality control processes. The Maya 2000 Pro's robust design and user-friendly interface ensure reliable measurements and ease of use for professionals seeking accurate spectral data.

To complement the spectrometer, we also offer the HPX-2000 Xenon light source, which delivers a high-intensity, broad-spectrum light, essential for accurate absorbance readings. Together, these products form a robust system for environmental professionals seeking reliable and efficient tools for water quality analysis and pollution control.

Result and Conclusion

Figure 3: This graph shows absorption spectra of 10 concentrations of COD samples. The main absorbance spectra range from 200nm – 300nm. As the COD Concentration Rises, so does absorbance.