TUESDAY, JAN 17, 2023: NOTE TO FILE
Module 2-8
Constructed wetlands
THE CONSTRUCTED wetlands in which these processes take place are built either as surface flow (SFCW) or sub-surface flow (SSFCW). The former uses plants growing in soil over an impermeable liner. The SFCW runs in a flooded condition. A SSFCW has about 700 mm of gravel installed above a liner and the wastewater flows horizontally about 100 mm under the surface of the gravel – hence “sub-surface”. Plants are grown in the gravel with their roots in the water under the gravel surface.
SSFCWs are further divided into vertical flow (VF), horizonal flow (HF) and hybrid systems.
Above is a diagram of a vertical flow system and below there is a horizontal flow and a hybrid.
Source: Environmental Engineering Research http://eeer.org/journal/view.php?number=963
In the example of a MSR (Multi-Stage Re-circulating) constructed wetland below, treatment takes place in 4 stages combining an anaerobic stage (a multiple compartment baffle tank with an option for an up flow anaerobic sludge blanket - a variant on the septic tank with biofilter - more on this later) to remove TSS (Total Suspended Solids) with a SSFCW treatment. Stage 2 the SSFCW and stage 3 is an aerobic stage where nitrification and denitrification take place. A ‘polishing’ stage runs the treated water through a rough filter and an UV treatment before it can be used for flushing toilets etc. and then recycled back as influent into the system. It is a neat and attractive closed-loop approach. When necessary, treated water can also be diverted for irrigation.
http://www.biomatrixwater.com/msr-constructed-wetlands/
Besides these constructed wetlands, other options are available to suit the size and scale of the projects they serve as well as local ecosystems: systems (), systems with floating ecologies (examples of which we have seen above), and We will look at examples of these systems before moving on to how they function in combination with other technologies such as a septic tank or a biodigester in a constructed wetland system.
An appendix will provide extra and more detailed information about construction for those participants who feel they might be interested in this topic as a specialisation. The appendix will also contain links to further reading.
Module 2, lesson 9
