Constructed wetlands for the Mediterranean countries: hybrid systems for water reuse and sustainable sanitation

One of the main problems in adopting extensive treatment for wastewater purification in hot climate countries, when also the effluent reuse is aimed, is the high evapotranspiration rate. This factor can play a key role in reducing the water output, a desirable effect in some cases but completely adverse when water reuse is a primary resource for the area. Constructed wetlands have an higher evapotranspiration rate in comparison with ponds or lagoons but they also have the shortest hydraulic retention time (HRT) amongst the whole group of extensive treatment techniques. The water loss can also be minimised using a particular design and configuration of the constructed wetland system. The most powerful combinations seems to be the coupling of horizontal and vertical submerged flow beds, called hybrid systems, which performances are analysed in the present paper. In terms of overall performances the following mean removal rates were obtained: COD 94%, BOD5 95%, total suspended + solids 84%, NH4 86%, total nitrogen 60%, total phosphorus 94%.

Acknowledgments The hybrid constructed wetland (horizontal subsurface flow + vertical subsurface flow) system, realised for the treatment of wastewater produced by a medium-size hotel, was found proper for the removal of pathogens and all the monitored chemical parameters in this study. The use of septic tanks and secondary treatment subsurface CWs for small populations have been used increasingly in the Mediterranean countries. The use of hybrid systems incorporating both surface and subsurface-flow sections is now becoming more common, as well as the powerful combination of VF and HSSF. The outlet of the hybrid system used here started complaining with the national limits for the reuse after about 6 months from the start-up and it’s currently maintaining these performances. Assuming that Constructed Wetland systems have proven to be a reliable treatment, especially advised for small medium size settlements and for the decentralised sanitation approach, this hybrid configuration permits a considerable reduction of the total surface needed for the treatment and, consequently, a reduction of the water losses by evapotranspiration. The monitored hybrid system has shown only in the hottest summer water losses for about the 30–35% of the total inlet. This configuration should be deeply tested in hotter climates, like the North African countries, in order to assess the effective water balances in such meteo-climatic conditions. The treatment plant observed in this study has an official permission for discharge in freshwater, as well there’s a discharge pipe. Because the hotel owners wished to optimise their water consumption, they monitored the effluent for a couple of years in order to ask the authorities for the reuse permission for gardening, and recently they have obtained it; one suggestion we gave them was anyway to set a small UV lamp just after the pump in the reuse tank to ensure E. coli parameter in the effluent.