Sewage Flow Conditions in a Hydroponic Lagoon in Terms of Quality of Treated Wastewater

K Marek,J Baran,K Pawęska,A Bawiec

doi:10.1007/s11270-021-05235-8

Abstract

The aim of this study was to analyse the impact of velocity in the hydroponic lagoon used as the 3rd stage of municipal wastewater treatment on washing out of the particles suspended in the sewage as well as settled on the bottom of the hydroponic ditch. In order to analyse the flow velocity in the lagoon, 12 cross-sections were determined at points where the speed and motion of particles can change. Wastewater samples were taken in the summer month from each of the 12 sampling points (the depth of 0.1 m) and the basic physicochemical parameters of sewage were determined (BOD5, COD, TOC, TSS, turbidity). In selected cross-sections, a granulometric analysis of particles was made to determine the characteristics of suspended solids in the wastewater flow path. Based on the analysis, it was found that velocities in the lagoon during aeration can be ten times higher (0.070 m·s−1) than those assumed by designers (0.006 m·s−1). Such a large difference means that the sedimentation conditions assumed in the project cannot be met, which may result in an increase in the total suspended solids and organic matter concentrations at the outflow to the receiving water body. During the flow through the hydroponic ditch, the highest efficiency of pollutant removal was indicated for BOD5 — 88.7% and TSS — 80%, while the COD removal occurred with the lowest efficiency — 34.1%. Improving flow conditions as designed in the hydroponic lagoon technological project may increase the efficiency of wastewater treatment at the third stage of treatment.

Highlights

Higher and higher standards for the quality of treated wastewater discharged to the receiver became a motivation to look for high-performance technological solutions
The main objective of the research was to assess the conditions of sewage flow in the hydroponic lagoon by measuring the flow velocity and related selected quality parameters of treated sewage (BOD5, chemical oxygen demand (COD), total organic carbon (TOC), turbidity, total suspended solids (TSS)) as well as the particle size distribution of suspended solids
– Speed values caused by frequent and rapid work of aerators cause dynamic movement of organic matter and prevent slow sedimentation of particles to the bottom of the lagoon. This leads to outflow of organic matter to the receiving water body

Summary

Introduction

Higher and higher standards for the quality of treated wastewater discharged to the receiver became a motivation to look for high-performance technological solutions. The total suspended solids (TSS) concentration largely influence organic matter content in the water courses sediments which became a significant factor in water pollution (Zhu et al, 2017). Ensuring appropriate sewage flow rates through the wastewater treatment plant (WWTP) significantly influences the organic matter content in the sewage stream. The most popular semi-natural systems include constructed wetlands, sewage oxidation or stabilisation ponds, and hydroponic systems (Maiga et al, 2017). This type of solutions is used as the third or fourth stage of treatment of sewage and as a purification system for contaminated water from aquaculture (Keeratiurai, 2013). Plants floating on the surface of wastewater with the roots freely immersed in sewage can uptake nutrients directly from the solution and are perfect habitat to many desirable bacteria, protozoa, molluscs and invertebrates (Bawiec et al, 2020)

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