**6. ET systems in Slovenia**

206 Studies on Water Management Issues

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

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

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

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

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

LIMNOS Ltd.)

and iron, which have similar characteristics.

high to prevent reduction of ferric iron to ferrous iron.

water systems and therefore have the highest risk of causing harmful effects.

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, revitalization of watercourses, and wastewater separation and reuse.

Ecosystem Technologies and Ecoremediation for Water Protection, Treatment and Reuse 209

*Design:* In the period between 2000 and 2003, a pilot SFW and a pilot WSP were constructed at the outlet of wastewater treatment plant (WWTP). The SFW was planted with *Phragmites australis* and *Eichhornia crassipes*, while in the WSP development of algae was spontaneous. *Monitoring:* The systems were monitored under the same operating conditions. The efficiency was evaluated by means of physical and chemical parameters in the inflow and outflow water, by plant productivity and by the analysis of N and P contents in biomass.

*Results and Discussion:* The SFW proved more efficient in the elimination of suspended solids (64.6 %), settleable solids (91.8 %), organic N (59.3 %), total N (38 %), COD (67.2 %) and BOD5 (72.1 %) than the WSP. The WSP was more efficient in the treatment of ammonia nitrogen (48.9 %) and orthophosphate (43.9 %). The difference in treatment efficiency between the systems most probably originates from different primary producers (macrophytes vs. algae) and consequent food webs established. The results of this study provide data of help in optimising combinations of SFW and WSP (Šajn-Slak et. al., 2005).

*Design:* From 1989 to 2011, over 73 TW were constructed in different regions of Slovenia. Most TW are horizontal or/and vertical systems (VF, HSF), operating in combination or integrated in zero foot print unite. Most of them consist of several interconnected beds. Most TW were installed to treat sewage, industrial wastewater, highway run-off, gray water for toilet flushing, drinking water, water from fish farms and landfill leachate. Pre-treatment mostly comprised septic tanks or sedimentation basins. Excavations were sealed with PVC or HDPE membranes, clay or the combination of both. The medium was mostly a mixture of different material (peat, soil, sand, gravel, expended clay), varying in grain size and proportion. The depths of the TW varied from 0.5 to 0.8 m, and the bottom slope from 0 to 3 %. Most systems were between 20 and 1500 m2 in area (Table 1). Theoretical hydraulic loading of media was in each case at least 10-3 m/s. The TW for sewage vary in size with 2- 2.5 m2 per people equivalent on average. Wide adaptability to different environmental conditions, tolerance to stress, high productivity is evident characteristic of *P. australis* that favoured the use of this species in TW. Different parts of reed were used for planting, most frequently clumps. In shallow beds of integrated systems, where the depth was 0.4 m, other species, such as *Juncus effusus, J. inflexus, Carex gracilis, Schoenoplectus lacustris*, and *Thyphoides arundinacea,* were successfully tested. Systems were planted generally in spring

*Monitoring:* The efficiency of TW was monitored by sampling at the inlets and outlets in different periods between 1989 and 2011. TW for landfill leachate were monitored regularly on a long-term basis, from 1992 till 2003, while other systems were monitored monthly for one year or occasionally for one up to 5 years. The efficiency of TWs was evaluated by analyzing suspended and settlements solids, COD, BOD5, total phosphorus and ammonia nitrogen. Grab samples were taken mostly according to the measured retention time and analyzed by independent laboratories. Analyses were done according to Standard Methods (APHA, 2005). At sampling sites, flow, temperature, pH, dissolved oxygen and electric conductivity were measured. More extensive chemical and microbiological analyses were

**6.1.2 Waste stabilization ponds (WSP) / surface flow wetlands (SFW)** 

**6.1.3 Treatment wetlands (TW)** 

done occasionally.

or autumn when the environmental conditions were optimal.
