Digital microscopic image application (DMIA), an automatic method for particle size distribution analysis in waste activated sludge

Abstract

An important physical property in environmental samples is particle size distribution. Several processes exist to measure particle diameter, including change in electrical resistance, blocking of light, the fractionation of field flow and laser diffraction (these being the most commonly used). However, their use requires expensive and complex equipment. Therefore, a digital microscopic imaging application (DMIA) method was developed adapting the algorithms used in the helminth egg automatic detector software coupled with a neural network (NN) and Bayesian algorithms. This allowed the determination of particle size distribution in samples of waste activated sludge (WAS), recirculated sludge (RCS), and pre-treated sludge (PTS). The recirculation and electro-oxidation pre-treatment processes showed an effect in increasing the degree of solubilization, decreasing particle size and breakage factor with ranges between 44.29%, and 31.89%. Together with a final NN calibration process, it was possible to compare results. For example, the 90th percentile of equivalent diameter value obtained by the DMIA with the corresponding result for the laser diffraction method. DMIA values: 228.76 μm (WAS), 111.18 μm (RCS), and 84.45 μm (PTS). DMIA processing has advantages in terms of reducing complexity, cost and time, and offers an alternative to the laser diffraction method. HIGHLIGHTS Adaptation of HEAD software algorithms, image processing techniques, and neural network fitting, allowed the evaluation of the particle size distribution.; Electro-oxidation pre-treatment improves the subsequent anaerobic digestion process.; Larger sludge particles are the most affected by the electro-oxidation process.;

Keywords

• electro-oxidation
• equivalent diameter
• image processing
• laser diffraction
• particle size
• waste activated sludge