**5.4 Treatment wetlands (TW)**

TW are technically and economically feasible solutions for the treatment of different wastewater types. The technology is widespread around the world. Already ten years ago, more than 5,000 TW were operational in Europe (Vymazal et al., 1998). The performance is thoroughly documented and the systems are capable of reducing the concentration of target pollutants by different bacteriological, physical and chemical processes to acceptable levels before discharging to the environment and therefore mitigating the harmful effect that the disposal of untreated wastewater may have (Vymazal, 2007). TW imitate natural wetlands by using an array of natural processes to transform and remove the contaminants and as such they represent important part of ET. Compared to their natural counterpart, these processes are intensified. This is achieved with appropriate design, filling material, planting, and incorporation of technical equipment (pumps, aeration, pre-treatment) which ensures optimal utilization of the TW area and volume. As TW typically require less or no supplemental energy, their operational costs can be approximately two orders of magnitude lower than those of a standard three-stage waste water treatment plants (WWTP) (Grönlund et al., 2004). The TW removal efficiency usually assessed by the decrease in biochemical and chemical oxygen demand (BOD, COD), total suspended solids (TSS) and nutrient (N, P) load, has already been studied widely (Kadlec & Wallace, 2009). TW can also effectively remove a wide array of persistent pollutants such as pathogens, trace organic contaminants and heavy metals, which all have a negative influence if released into the environment. TW have been used as a treatment step before wastewater is reused in agriculture, but with very variable success. Although wetlands are effective for the treatment of wastewaters, the everchanging reality of more stringent discharge regulations by the local governments imply that the wastewater treatment systems have to meet high water quality standards before discharge.

Fig. 1. A simple sketch of horizontal subsurface flow treatment wetland (source: LIMNOS Ltd.)

#### **5.5 Phytoremediation of landfill sites**

This ET involves the treatment and recycling of leachate on a vegetative landfill cover in order to avoid additional pollution by treated leachate discharges into the environment, to achieve landfill stabilization and easier public recognition of a reclaimed site. The final aim is to reduce the wastes' impacts on the environment through a closed hydrological and pollution cycle within a landfill site and the utilisation of leachate as a nutrient source. Leachate recycling belongs to a phytoremediation method where the assimilation of plant nutrients from leachate into biomass and faster waste decomposition by enabling leachate infiltration into the landfill body take place. Discharge of treated leachate to vegetation caps can provide an opportunity for closing the nutrient cycling loop and producing an effluent of a suitable quality. A controlled input of leachate results in a better provision of soil with nutrients and organic substances, improved growth of vegetation and intensified microbiological activity in soil. Today, the phytotechnology employing ligneous plants is used for the treatment of various forms of pollution. With a large water uptake from soil pores, plants take up also water pollutants and create a new capacity for water accumulation in soil. Poplars and willows are capable of taking up diverse pollutants and nutrients (nitrate, ammonium, phosphorus), metals, metalloids and petrochemical compounds (fuels, solvents), pesticides and soluble radionuclides (Zupančič et al., 2005). The methods applied for the treatment of leachate are vegetation barriers, filters, vegetation caps and short rotation coppices (SRC) with fast growing woody species. In addition to landfill sites, the planting of trees is used for the remediation of watercourse banks, abandoned and polluted industrial areas, at the margins of intensive agricultural areas and other polluted areas, as well as for the treatment of wastewater and sludge (Griessler Bulc & Zupančič Justin, 2007).

#### **5.6 Watercourse revitalization**

204 Studies on Water Management Issues

TW are technically and economically feasible solutions for the treatment of different wastewater types. The technology is widespread around the world. Already ten years ago, more than 5,000 TW were operational in Europe (Vymazal et al., 1998). The performance is thoroughly documented and the systems are capable of reducing the concentration of target pollutants by different bacteriological, physical and chemical processes to acceptable levels before discharging to the environment and therefore mitigating the harmful effect that the disposal of untreated wastewater may have (Vymazal, 2007). TW imitate natural wetlands by using an array of natural processes to transform and remove the contaminants and as such they represent important part of ET. Compared to their natural counterpart, these processes are intensified. This is achieved with appropriate design, filling material, planting, and incorporation of technical equipment (pumps, aeration, pre-treatment) which ensures optimal utilization of the TW area and volume. As TW typically require less or no supplemental energy, their operational costs can be approximately two orders of magnitude lower than those of a standard three-stage waste water treatment plants (WWTP) (Grönlund et al., 2004). The TW removal efficiency usually assessed by the decrease in biochemical and chemical oxygen demand (BOD, COD), total suspended solids (TSS) and nutrient (N, P) load, has already been studied widely (Kadlec & Wallace, 2009). TW can also effectively remove a wide array of persistent pollutants such as pathogens, trace organic contaminants and heavy metals, which all have a negative influence if released into the environment. TW have been used as a treatment step before wastewater is reused in agriculture, but with very variable success. Although wetlands are effective for the treatment of wastewaters, the everchanging reality of more stringent discharge regulations by the local governments imply that the wastewater treatment systems have to meet high water quality standards before

Fig. 1. A simple sketch of horizontal subsurface flow treatment wetland (source: LIMNOS Ltd.)

This ET involves the treatment and recycling of leachate on a vegetative landfill cover in order to avoid additional pollution by treated leachate discharges into the environment, to achieve landfill stabilization and easier public recognition of a reclaimed site. The final aim

**5.4 Treatment wetlands (TW)** 

discharge.

**5.5 Phytoremediation of landfill sites** 

Natural watercourses have a great ability of water retention, a great diversity of habitats and biodiversity and high self-cleaning capacity. Regulations or canalizations of watercourses were common in the past but in some places sill appearing in the present with the main goal of flood protection and gaining space for agriculture and urbanization. Canalizations of watercourses do decreased flooding in a local scale but downstream floods were even more severe. Canalized watercourse has trapezium profile; river bed is straightened and often covered with stones or concrete. Habitats for different animal and plant species are destroyed, self-cleaning capacity is scarce and there is no water retention in the riverbed, banks and floodplains. In a canalized watercourse pollutants from surroundings can freely flow into the water. With revitalization of a watercourse ecological balance is restored using appropriate water management interventions. Revitalization of a watercourse enables restoration of habitats for aquatic plants and animals, increases water retention and self-cleaning capacity of a water body. The type of revitalization is chosen according to the scope of revitalization and space abilities in the environment. Where the space around watercourse is limited revitalizations can be implemented inside existing canal. With revitalization measures like stabilization of river banks with vegetation, construction of weirs, pools, rapids, water deflectors, buffer strips along the watercourse, purification beds, creation of meanders and floodplains, backwater etc. habitat and biotic diversity is improved, self-purification capability and water retention are increased (Vrhovšek et al., 2008).

### **5.7 Additional technologies for integration in ET systems**

Additional technologies can be integrated in ET systems in order to enhance the removal of target pollutants. Those technologies mainly target at different soluble pollutants like phosphorous, nitrogen, soluble heavy metals and specific micropollutants. Enhanced

Ecosystem Technologies and Ecoremediation for Water Protection, Treatment and Reuse 207

phosphorous and heavy metals is enabled by the characteristics of the filter materials. Filter materials that comprise a lot of dolomite (CaMg(CO3)2) or calcite (CaCO3) minerals are effective in P adsorption (Brix et al., 2001) and materials containing iron or alumina are shown to have good sorption capacities for heavy metals (Genc-Fuhrman et al., 2007).

Ultrasound: Sonication is mainly used for algae control and disinfection of water in different systems. Ultrasound breaks up large suspended particles in treated water. The effect of ultrasound to algal cells is not clearly known; however, it is known that ultrasound suppresses algae growth and causes their sedimentation in the open water (Griessler Bulc et

UV: UV is commonly used for disinfection of treated water, where it usually presents a final stage of the treatment train. The UV lamps produce ultraviolet light that enters cells and damages proteins and genetic material. An ideal wavelength for efficient disinfection is

The use of ET, as a new, wider concept of understanding of natural treatment systems has started in Slovenia in the late eighties. The idea of ET was introduced in Slovenia first by floating macrophytes and later by subsurface flow TW for water treatment. An experimental period of treating wastewater with plants, mostly as different types of TW followed. During this period experiences were based on certain European researchers such us Kickuth (1984) and Clayton (1988). The basic design was developed in a project started in 1991 in Austria (Perfler & Haberl, 1992) which was modified to select, apply, and compare various options in situ. After 1995, innovative ET were developed for different applications (*e.g.* protection of lakes and watercourses from non-point pollution) based on design and experiences of TW, primarily regarding geographical, demographical and water management characteristics of Slovenia. The introduction of ET was not systematic, since this alternative way of wastewater treatment was not accepted by the government as a state of the art before the nineties. Most installed systems were pilot-systems, destined above all for experimental work. Nevertheless, from 1989 to 2011, several ET systems were installed in Slovenia; 73 TW, 12 sections of river revitalization, 2 VDD, 2 ET for landfill restoration and 1 WSP were constructed in the Karst, coastal, mountain and agricultural lowland regions of Slovenia. The Karst region, covering about 44 % of the surface, is marked by expressive shortage of surface water and soil, and by scattered communities. All this is reflecting in pollution, which is a serious threat for the extremely sensible underground sources of drinking water, based on the complex underground systems with numerous caves (under UNESCO protection). Similar difficulties are recognized also in the coastal region at the Adriatic Sea, where treated wastewaters are discharged into the sea or in its catchment area in the mountain region, which is conserved because of its ecological and scenic values, and in agricultural lowlands characterized by a high contamination with pesticides and other agricultural contaminants. The majority of inhabitants (60 %) live in the settlements with less than 5,000, most of them even 200 to 500 inhabitants, so usually the only way of treatment is the septic tank. Particular problems are tourist centres with large quantities of wastewater in the high seasons. Nowadays, the ET development in Slovenia is mainly focused on the reduction of dispersed pollution, protection of drinking water sources,

al., 2010; Krivograd Klemenčič & Griessler Bulc, 2010).

believed to be of approximately 254 nm (Modak, 2008).

revitalization of watercourses, and wastewater separation and reuse.

**6. ET systems in Slovenia** 

removal of dissolved and colloidal pollutants is especially important in case of a discharge into a sensitive recipient and in case of further production of drinking water. Different treatment units can be combined, e.g. coagulation, flocculation and subsequent sedimentation, plant uptake, sorption of dissolved and colloid matter to surfaces, etc. In contrast to sedimentation, the mentioned processes enable higher removal of dissolved and colloidal pollutants. Dissolved and colloidal pollutants are known for its mobile nature in water systems and therefore have the highest risk of causing harmful effects.

Fig. 2. An example of revitalization measures in a short segment of a watercourse (source: LIMNOS Ltd.)

Flocculation: Aluminum salts form insoluble aluminium hydroxide flocks Al(OH)3 in bulk water. The flocks have good settling properties and high sorption capacity for phosphate, heavy metals, organic micropollutants and algae (El Samrani et al., 2008). Accordingly, these pollutants are removed by sorption to the flocks in bulk water and subsequent sedimentation in the pond. Besides aluminum also lime and iron salts are used, and calcium and iron, which have similar characteristics.

Sediment and media enrichment: Sediment and media in ET can be enriched with minerals that have high sorption capacity for target pollutants. E.g. Ferric iron (Fe(OH)3) binds phosphate and several heavy metals under aerobic conditions (Kadlec & Wallace, 2009). In an aqueous environment, Fe(OH)3 is least soluble at pH between 7 and 10 and provides sorption sites for a number of pollutants. Besides adsorption of pollutants to Fe(OH)3, also insoluble precipitates with iron can be formed, e.g. FePO4 and complexes with metals. Using Fe to adsorb pollutants, it is essential that the redox potential of the media is sufficiently high to prevent reduction of ferric iron to ferrous iron.

Sorption filters: One of the possible technologies for upgrading existing ET is an installation of sorption filters after the system. Dissolved and colloidal pollutants as heavy metals and phosphorous are thus removed by sorption to the filter media. However filter clogging and saturation of the media may be of a concern. Elimination of dissolved pollutants like phosphorous and heavy metals is enabled by the characteristics of the filter materials. Filter materials that comprise a lot of dolomite (CaMg(CO3)2) or calcite (CaCO3) minerals are effective in P adsorption (Brix et al., 2001) and materials containing iron or alumina are shown to have good sorption capacities for heavy metals (Genc-Fuhrman et al., 2007).

Ultrasound: Sonication is mainly used for algae control and disinfection of water in different systems. Ultrasound breaks up large suspended particles in treated water. The effect of ultrasound to algal cells is not clearly known; however, it is known that ultrasound suppresses algae growth and causes their sedimentation in the open water (Griessler Bulc et al., 2010; Krivograd Klemenčič & Griessler Bulc, 2010).

UV: UV is commonly used for disinfection of treated water, where it usually presents a final stage of the treatment train. The UV lamps produce ultraviolet light that enters cells and damages proteins and genetic material. An ideal wavelength for efficient disinfection is believed to be of approximately 254 nm (Modak, 2008).
