Hydroponic root mats for wastewater treatment—a review

Abstract

Hydroponic root mats (HRMs) are ecotechnological wastewater treatment systems where aquatic vegetation forms buoyant filters by their dense interwoven roots and rhizomes, sometimes supported by rafts or other floating materials. A preferential hydraulic flow is created in the water zone between the plant root mat and the bottom of the treatment system. When the mat touches the bottom of the water body, such systems can also function as HRM filter; i.e. the hydraulic flow passes directly through the root zone. HRMs have been used for the treatment of various types of polluted water, including domestic wastewater; agricultural effluents; and polluted river, lake, stormwater and groundwater and even acid mine drainage. This article provides an overview on the concept of applying floating HRM and non-floating HRM filters for wastewater treatment. Exemplary performance data are presented, and the advantages and disadvantages of this technology are discussed in comparison to those of ponds, free-floating plant and soil-based constructed wetlands. Finally, suggestions are provided on the preferred scope of application of HRMs.

Floating Wetlands: A Sustainable Tool for Wastewater Treatment

“…The plant growth and gain in biomass depend on plant species, age, type of wastewater, nutrients concentration, redox condition of water, trophic level of water, and supporting mat . High nutrient load and toxic compounds may affect development of plants especially at the young stage .…”

“…Some wetland plants are found to be sensitive to the variation of water level such as T. domingensis showing about 52% decrease in biomass due to water level fluctuation . Whereas some species, such as Juncus spp., Phalaris arundinacea , and P. australias , have great morphological adaption to the fluctuation of water levels . These plants can be utilized in stormwater ponds which show great fluctuations of the water level.…”

“…Total suspended solids (TSS) are mainly removed by physical settling and filtration process in FTWs. Minimized turbulence and free water layer between root mats and system's bottom create ideal conditions for the particle sedimentation . Moreover, roots of plants allow entrapping/filtering of the suspended particles.…”

“…The hanging roots of plants below mat provide a large area for biofilms development and wastewater treatment . This is the reason that FTWs even have been proved effective for treatment of polluted surface water, sewage, industrial, and agricultural wastewater . Retention ponds are efficient to remove coarse and particulate forms of contaminants but not capable of removing dissolved contaminants effectively .…”

Performance Evaluation of a Full‐Scale Constructed Wetland for Treating Stormwater Runoff

“…In comparison, Quek et al evaluated the performance of a pilot showcase of different wetland systems in an urban setting in Singapore, and reported the RE of 50.7–81.3% for total suspended solids (TSS), 22.0–44.9% for TN, and 5.4–56.7% for TP, respectively. Wetland configurations, flow rate, wastewater type, and plant species, among other operational variables, can affect the performance of wetland systems with respect to water treatment . Due to the paucity of available information in the literature, there is no general agreement on design criteria for stormwater CW systems, and the use of wetland systems for stormwater processing can be poorly characterized under various conditions …”