The 4th Euro-Mediterranean Conference for Environmental Integration (EMCEI-2022) held in Sousse, Tunisia from the 1st to 4th of November 2022,  aimed to gather high-quality, original research papers on various multidisciplinary topics linked to the evolution and development of the Euro-Mediterranean environment in the past, present, and future. 

The main objectives of the Conference are to support research and innovation, to promote the exchange of scientific knowledge, and to foster collaboration among Euro-Mediterranean communities.  

Our colleagues of the Institute of Arid Regions (IRA), on this occasion, has successfully presented their research paper based on the results of MEDISS pilot project in Tunisia, with the contribution of researchers from Higher Institute of Sciences and Techniques of Water of Gabes (ISSTEG, University of Gabes, Tunisia) and Olive Tree Institute (IO), Tunisia. 

We are pleased to present herewith a synthesis of their work.

Phyto-purification by cattails of the Typha latifolia type in a wastewater treatment process by infiltration percolation on sand and clay*

Authors: Saifeddine Eturki⁽¹⁾, Feryel Hajjaji^(1,2), Faiza Souid⁽¹⁾, Haifa Rajhi⁽¹⁾, Rim Werhani⁽¹⁾ and Yassine Hidri⁽³⁾.

(1) Eremology and combating desertification laboratory (LR16IRA01), Institute of Arid Regions (IRA), 6051 Nahal Gabes, Tunisia;
(2) Higher Institute of Sciences and Techniques of Water of Gabes (ISSTEG), University of Gabes, Tunisia;
 (3) Olive Tree Institute (IO), Tunisia.

Introduction 

Tunisia is one of the least endowed countries in terms of water resources. The prospects of water scarcity have become evident. The latter are available in space according to the local conditions of underground and surface resources. These limited water resources threaten the sustainability of agricultural activity. As a result, irrigation with treated wastewater can constitute a potential and sustainable additional water resource. Indeed, these waters can be beneficial at different levels. This unconventional irrigation technique would contribute in particular to improving agricultural yields as well as fertilizing the soil with biodegradable substances. 

Hence, as in Tunisia, the reuse of non-conventional waters is becoming increasingly popular in arid and semiarid regions of the world [1][2].  

Advanced treatment techniques such as ultrafiltration, reverse osmosis, ion exchange can be used to improve the quality of secondary wastewater effluents before they could be reused to supplement declining water supplies. However, the use of these advanced techniques is quite limited because of operational costs. Infiltration-percolation (I-P) is an extensive process for the treatment of urban wastewater, allowing the degradation of organic matter and the oxidation of nitrogen.[1][2][3][4][5] 

The objective of this work is to study the efficiency of the I-P process using three filtration mixtures as a complementary treatment to activated sludge. The pilot site is located in the region of Wadi Echerka Bechima in the West of Gabes City and the North-West part of El Hamma district. The installation of this wastewater treatment system in the region of Bechima (funded by MEDISS project "Mediterranean Integrated System for Water Supply" financed by the EU under the ENI CBC Mediterranean Sea Basin Programme), aims to improve the irrigation water quality by using an innovative infiltration-percolation system and promote the farmers of the region to use non-conventional water as an alternative for irrigation of agricultural land and protect the environment.

Materials and Methods 

The monitoring of the pilot wastewater treatment system is carried out through sampling and analysis of various water quality parameters and tracers at the input and the output of the filters. The operation mode conditions of the pilot wastewater treatment system were performed on a weekly feeding cycle: 1-day flooding period and 2-days drying period. During the feeding operation of the three reactors, the daily hydraulic load is about 1.5 m3/silo. The feeding is provided by a feeding system to ensure a uniform distribution of the wastewater on the filter surface. Wastewater samples are collected from the input and the outlet of the three silos. The secondary effluent and filtrated water were analyzed in laboratory, according to standard methods. 

The removal efficiencies of the Total Nitrogen (TN) before and after treatment are shown in Fig.2, where we note a very remarkable purification efficiency in all the reactor. 

However, the highest removal efficiency for TN was achieved by the second silo, where we plant the macrophyte (Typha latifolia).  The mean removal rate of nitrogen was around 75%, which confirmed the high ability of the mixture filter combination (second reactor) to adsorb and remove NTK from wastewater. 

The fig.3 indicate that even though nitrate is typically absent in raw wastewater, results showed an increase in NO3–N concentration over time [6]. The increase of nitrate concentration in the effluent can be explained by the nitrification of ammonia favored by autotrophic bacteria. 

Low concentrations of nitrite at fig.4 show that nitrite was rapidly transformed into nitrate during the process of nitrification this explains the good oxygenation of the filter bed.

Results

• The mean removal rates of Total Coliforms obtained in the three reactors were 1.4; 2.3 and 1.9 log unit, respectively. 
• The reduction rates of E.Coli were 1.8; 2.8 and 2.4 log units, respectively.  
• The infiltration-percolation device proves to be very efficient with regard to the elimination of biodegradable organic matter and the reduction of bacteriological pollution of treated water. The results obtained show the effectiveness of the water treatment system in improving the physicochemical and bacteriological quality of irrigation water. The treatment of water by infiltration-percolation is ensured by different processes involved:
• Mechanical filtration and retention of particles at the level of the pores of the filter medium.- Ion exchange, adsorption and precipitation of dissolved salts by clays. 
• Biodegradation of organic matter by bacterial biofilm. 
• The absorption and bioaccumulation of certain pollutants by the Typha Latypholia plant planted on the surface of the filter medium. 
• The reactor planted by the Typha Latypholia plant shows a high purification rate compared to the other two reactors. The results prove the effectiveness of the plant used in the treatment of wastewater.

Conclusion 

The MEDISS pilot water treatment system is an efficient system for the treatment of wastewater by the infiltration-percolation process combined with phytoremediation. It is a system that allows farmers to minimize the health risks caused by continuous pathogenic germs in water, to have irrigation water that meets standards, and to valorize georesources (sand and clay) in the treatment wastewater to use for irrigation. 

By comparing the first and the second reactors, It is important to highlight the primordial purifying power of the clay in (TN) elimination (by accelerating and improving the nitrification phenomenon). 

According to the results founded in the second reactor, T.L. appears to play an essential role in wastewater treatment. In effect, the roots of this macrophyte had a high sorption capacity for nitrogen nutrients. So we can conclude that the removal of various organic substances and nutrients in our filter bed is thought to be the result of several mechanisms, such as sedimentation, direct plant uptake, NH3 volatilization and degradation [7][8][9] 

A significantly higher removal rate for fecal coliforms and E.Coli  is observed in the second reactor.  

• The removal of bacteria occurred through mechanical filtration and adsorption. Mechanical trapping took place through surface filtration, whereby particles that were too large to pass through the pores were trapped at the top of the column. The adsorption occurred through physical trapping after deeper penetration into the sand bed [10].  
• Clay minerals are another class of adsorbents that offer themselves naturally as antimicrobials [11].  
• Similar study have been done proves that the rate of removal of bacteria from wastewater in the presence of macrophyte is enhanced and this has been attributed to a combination of several physical and biological processes [12] [13].

References 

[1]Eturki, S., Ayari, F., Kallali, H., Jedidi, N., & Ben Dhia, H. (2012). Treatment of rural wastewater by Treatment, 49(1-3), 65-73.
 

[2]Bali, M., & Gueddari, M. (2019). Removal of phosphorus from secondary effluents using infiltration–percolation process. Applied Water Science, 9(3), 1-8.
 

[3]Eturki, S., Makni, H., & H Ben, D. (2011). Study of the purification performance of sand filter drained in a complementary treatment of urban wastewater under soil and climatic conditions of the southern Tunisia. Journal of Water Resource and Protection, 2011.
 

[4]Cherfouh, R., Lucas, Y., Derridj, A., & Merdy, P. (2018). Long-term, low technicality sewage sludge amendment and irrigation with treated wastewater under Mediterranean climate: impact on agronomical soil quality. Environmental Science and Pollution Research, 25(35), 35571-35581.
 

[5]Cormier, J. A., & Duranceau, S. J. (2020). Comparison of a modified and traditional rapid infiltration basin for treatment of nutrients in wastewater effluent. Water Environment Research, 92(3), 441-454.
 

[6] Almeida, A., Carvalho, F., Imaginário, M. J., Castanheira, I., Prazeres, A. R., & Ribeiro, C. (2017). Nitrate removal in vertical flow constructed wetland planted with Vetiveria zizanioides: Effect of hydraulic load. Ecological engineering, 99, 535-542.
 

[7]Ghezali, K., Bentahar, N., Barsan, N., Nedeff, V., & Moșneguțu, E. (2022). Potential of Canna indica in Vertical Flow Constructed Wetlands for Heavy Metals and Nitrogen Removal from Algiers Refinery Wastewater. Sustainability, 14(8), 4394.
 

[8]Silvestrini, N. C., Maine, M. A., Hadad, H. R., Nocetti, E., & Campagnoli, M. A. (2019). Effect of feeding strategy on the performance of a pilot scale vertical flow wetland for the treatment of landfill leachate. Science of the Total Environment, 648, 542-549.
 

[9]Kraiem, K., Kallali, H., Ammeri, R. W., Salma, B., & Jedidi, N. (2021). Effects of Partial Saturation on Nitrogen Removal and Bacterial Community in Vertical-flow Constructed Wetlands. International Journal of Environmental Chemistry, 5(2), 38.
 

[10] ElBastamy, E., Ibrahim, L. A., Ghandour, A., Zelenakova, M., Vranayova, Z., & Abu-Hashim, M. (2021). Efficiency of Natural Clay Mineral Adsorbent Filtration Systems in Wastewater Treatment for Potential Irrigation Purposes. Sustainability, 13(10), 5738.
 

[11] Unuabonah, E. I., Ugwuja, C. G., Omorogie, M. O., Adewuyi, A., & Oladoja, N. A. (2018). Clays for efficient disinfection of bacteria in water. Applied Clay Science, 151, 211-223.
 

[12] Tlili, H., Bali, M., & Boukchina, R. (2021). Assessment of the performance of intermittent planted filters in treating urban wastewater under arid climate. Water Science and Technology, 84(7), 1704-1714.
 

[13] Latrach, L., Ouazzani, N., Masunaga, T., Hejjaj, A., Bouhoum, K., Mahi, M., & Mandi, L. (2016). Domestic wastewater disinfection by combined treatment using multi-soil-layering system and sand filters (MSL–SF): A laboratory pilot study. Ecological Engineering, 91, 294-301.

*This research was funded by MEDISS project "Mediterranean Integrated System for Water Supply" financed by the EU under the ENI CBC Mediterranean Sea Basin Programme