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.

中文翻译：

---

流经废水处理厂第三阶段水培泻湖的废水中颗粒的粒度组成的变化

摘要由于营养物去除效率高，半自然系统中的废水处理（例如作为第三级净化的水培泻湖）变得越来越受欢迎。水培沟渠中的处理过程常常受到藻类生长的支持，这可能导致废水处理厂流出的总悬浮固体浓度增加。本研究的目的是分析波兰城市污水处理厂 (WWTP) 废水净化第三阶段的水培泻湖中颗粒的粒度组成的变化。使用激光衍射法进行粒径的测量。结果表明，水培池中颗粒的尺寸在0.01至1000μm之间变化。对平均直径D(3.2)和D(4.3)的分析表明，颗粒的反应活性较低，但沉降性能良好，分形维数通常大于2.0，表明颗粒具有发达的表面。从污水处理厂流出的大部分颗粒可能是藻类或可以将其他污染物吸附到其表面的颗粒。使用激光粒度测定法进行颗粒识别可能有助于表征总悬浮固体，并有助于开发更便宜、更有效的去除方法。