Specialist Group on Use of Macrophytes in Water Pollution ... - IWA

AREA AND ENERGY REQUIREMENTS: COMPARISON BETWEEN CEPT-CWL,
TIDAL FLOW CWL AND FRENCH DESIGN CWL SYSTEMS FOR THE REMOVAL
OF ORGANICS AND NITROGEN COMPOUNDS
Eilon Guthman, Sheldon Tarre and Michal Green
Technion, Israel Institute of Technology, Haifa, 32000 Israel
Background
In smaller communities the environmental friendly, low cost and long-lived technology of
constructed wetlands becomes more and more important. However, the large land demand
with the accompanying water loss and increased salinity due to the high evaporation rate
typical to Mediterranean countries, limit the application of this technology, especially when
effluent re-use is practiced or desired. Moreover, while the efficiency of constructed wetlands
in the removal of BOD and TSS is very high, nitrogen removal in most of the present
generation of operating wetland systems (predominantly horizontal flow beds) is deficient,
mainly because of poor nitrification due to insufficient oxygen supply. Treated domestic
wastewater without nutrient removal can be beneficial for agricultural use, but unfortunately,
this water cannot be released uncontrolled to the environment due to their negative effect on the
environment: eutrophication, contamination of groundwater, ammonia toxicity, etc. In Israel
where currently about 70% of the wastewater produced is reclaimed for agricultural reuse, a
new standard for unrestricted irrigation, known as Inbar regulations have been approved
(Inbar, 2007). Among others, the regulations dictate (average values): COD=100 mg/l;
TSS=10mg/l; TN=25 mg/l; NH4-N=20 mg/l; Total P=5 mg/l.
Having in mind the main disadvantages of extensive systems in general and constructed
wetlands (CWL) specifically, i.e. large land requirements, water loss and increased salinity
and poor nutrients removal, and in order to comply with the Israeli Inbar regulations, a new
CEPT-CWL system was investigated. This system is characterized by the main advantages of
extensive systems (constructed wetlands) including simplification; cost effectiveness; and
reliability, with the additional important advantages of nutrients (N, P) removal and minimal
land requirement. The system consists of chemically enhanced primary treatment (CEPT) that
significantly reduces the organic load on the succeeding units, followed by the use of
constructed wetland units for nitrification and denitrification with recirculation between the
two units. In addition to reducing the organic load, the removal of COD and suspended solids
by CEPT results in an effluent with a C to N ratio more suited for nitrification and less prone
to wetland clogging. The process is characterized by low energy input since the oxygen
requirement for the removal of the organic matter is minimized (most of the residual COD is
used as the electron donor for denitrification).
This article focuses on the area and energy requirements of the CEPT-CWL system in
comparison to two other well known CWL system variations claiming nitrogen removal: the
‗tidal flow‘ wetland system (nitrification and denitrification) (Austin et al., 2003, 2006) and
the ‗French design‘ system (nitrification with minimal denitrification) (Molle et al., 2008;
Molle et al., 2005).
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IWA <strong>Specialist</strong> <strong>Group</strong> on Use of Macrophytes in Water Pollution Control: Newsletter No. 38 31