Rapid Correction of Turbidity and CDOM Interference on Three-Dimensional Fluorescence Spectra of Live Algae Based on Deep Learning

Abstract

In natural aquatic environments, the existence of colored dissolved organic matter (CDOM), suspended particles, and colloids can cause scattering and reflection of light and even emit fluorescence itself. Such interference negatively impacts algal fluorescence, further making it unreliable to measure the algal concentration using three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy. In this study, we proposed a novel algal fluorescence anti-interference network (AFAI-Net) based on a convolutional neural network. The main procedure of this model can be divided into two parts: (1) to quickly determine if there is an interference of CDOM or turbidity in the detected algal samples; (2) to correct the interfered samples and output the fluorescent components of the algae. We trained the model using the 3D-EEMs of pure algal samples (non-interfered) and mixed samples of algae and CDOM or turbidity (interfered); as a result, the well-trained model achieved a total classification accuracy of 96.82%, and the RMSE of CDOM and turbidity removal fitting effects were 0.2274 and 0.3423, respectively. Compared with the non-negative weighted least squares (NNLS) regression analysis method, using the CNN model for CDOM correction resulted in 13.11%, 0.65%, and 5.69% reductions in the average deviation rate for PD, PG, and CM, respectively. Furthermore, the spectra corrected by the model predicted algal densities that were closer to the true algal densities. This study provides a new way to remove non-algal factors that affect algal fluorescence spectra in water bodies, which is beneficial to monitoring eutrophication and red tide in aquatic systems.

Measurement of Total Dissolved Solids and Total Suspended Solids in Water Systems: A Review of the Issues, Conventional, and Remote Sensing Techniques

“…Suspended sediments in water may not be toxic, but an excessive amount leads to a high level of turbidity. Turbidity is a visual characteristic of the water consisting of biotic and abiotic elements that indicate its clarity or lack of it due to the presence of organic and inorganic suspended materials or matter (SM), plankton, and microscopic organisms causing scattering and absorbing of light [4,28,90,91]. Turbidity in water could be measured conventionally in the laboratory through the nephelometric method and by measurements using optical in situ sensors often called turbidimeters as described in Section 2130B and 2130A, respectively, of the standard methods for the examination of water and wastewater [4].…”

Insights into Asphaltene Adsorption on Sandstone Surface by Experiment and Simulation: Performance and Mechanism Investigation

“…3D-FS technology has been proven to be an important analysis method with the obvious advantages of high manipulation simplicity, little sample damage, and less sample consumption . 3D-FS has been widely applied in the distribution characterization of dissolved organic matter − and toxic tide algae . As typical polycyclic aromatic compounds with large conjugated systems, asphaltenes are anticipated to produce strong fluorescence with characteristics including (1) aromatic or heterocyclic structures, (2) high conjugation degree of π electrons, and (3) rigid planar structures for molecular vibration reduction.…”