Changes in the granulometric composition of particles in wastewater flowing through a hydroponic lagoon used as the third stage in a wastewater treatment plant

Abstract

Wastewater treatment in semi-natural systems, such as a hydroponic lagoon operating as the third stage of purification, is becoming more and more popular because of the efficiency of nutrient removal. Very often treatment processes in hydroponic ditches are supported by algal growth, which can cause an increase in the concentration of total suspended solids in the outflow from the wastewater treatment plant. The aim of this study was to analyse changes in the granulometric composition of particles in the hydroponic lagoon operating as the third stage of wastewater purification in a municipal wastewater treatment plant (WWTP) in Poland. Measurements of the particle sizes were made with the use of the laser diffraction method. The results showed that the size of the particles in the hydroponic lagoon varied from 0.01 to 1000 μm. Analyses of the average diameters D(3.2) and D(4.3) showed that particles have low reactivity but good sedimentation properties and their fractal dimensions are usually higher than 2.0, which indicated that they had well-developed surfaces. Most of the particles flowing out of the WWTP were probably algae or particles that could adsorb other pollutants onto their surfaces. The use of laser granulometry for particle identification might be useful in characterizing the total suspended solids as well as helping to develop cheaper and more efficient methods for its removal.