This paper evaluates the performance and potential of a full-scale hybrid multi-soil-layering (MSL) system for the treatment of domestic wastewater for landscape irrigation reuse. The system integrates a solar septic tank and sequential vertical flow MSL and horizontal flow MSL components with alternating layers of gravel and soil-based material. It operates at a hydraulic loading rate of 250 L/m2/day. Results show significant removal of pollutants and pathogens, including total suspended solids (TSS) (97%), chemical oxygen demand (COD) (88.57%), total phosphorus (TP) (79.93%), and total nitrogen (TN) (88.49%), along with significant reductions in fecal bacteria indicators (4.21 log for fecal coliforms and 3.90 log for fecal streptococci) and the pathogen Staphylococcus sp. (2.43 log). The principal component analysis confirms the effectiveness of the system in reducing the concentrations of NH4, COD, TP, PO4, fecal coliforms, fecal streptococci, and fecal staphylococci, thus supporting the reliability of the study. This work highlights the promising potential of the hybrid MSL technology for the treatment of domestic wastewater, especially in arid regions such as North Africa and the Middle East, to support efforts to protect the environment and facilitate the reuse of wastewater for landscape irrigation and agriculture.

  • High removal of TSS (97%), COD (88.57), TN (88.49), TP (79.93) achieved by MSL system.

  • Significant removal rates of fecal coliforms (4.21 log) and fecal streptococci (3.90 log).

  • Principal component analysis showed a positive correlation between COD, NH4+, TP removal, and pathogens.

  • Treated water met Moroccan and FAO guidelines for safe irrigation.

  • MSL sustainably reduces the environmental impact and health hazards of wastewater.

Over the past few decades, Marrakech and its surrounding region have experienced significant economic, demographic, and urban growth, characterized by a notable construction boom. The expansion of the developed area has been remarkable, increasing from 2,000 ha in the early 1970s to nearly 20,000 ha by 2020 (Lachir et al. 2016). This rapid development has been particularly evident in the last 20 years, as Marrakech has established itself as the number one tourist destination in Morocco, attracting approximately 3 million visitors each year (Analy & Laftouhi 2021). The region is also a major center for mining, accounting for 28% of the country's total production, and is known for its extensive agricultural activities (Kahime et al. 2018; Analay & Laftouhi 2021). However, this rapid growth has put immense pressure on natural resources, particularly groundwater, which is used extensively for agricultural irrigation, golf courses, and various other purposes (Hssaisoune et al. 2020). The availability of groundwater in the shallow aquifer has decreased significantly, from 331 Mm3 in 1962 to 207 Mm3 in 2019 (Analy & Laftouhi 2021). More alarmingly, during the critical period between 2002 and 2019, groundwater resources declined at an average annual rate of 8.5 Mm3, resulting in a significant reduction from 353 to 207 Mm3. This represents a dramatic 41% decrease in just 17 years and the water demand for agricultural irrigation has increased dramatically, from 500 Mm3 in 1961 to 13,500 Mm3 in 2014, with 70% coming from surface water and 30% from groundwater (FAO 2015).

Like many arid countries, Morocco faces significant pressures on its water supply due to limited water resources and increasing demand from various sectors, including agriculture, industry, and domestic use. Water availability, especially in arid and semi-arid regions, is further strained by erratic rainfall patterns and recurrent droughts due to the effects of climate change (World Bank 2017; Ben-Daoud et al. 2021). Wastewater treatment and reuse is emerging as a key strategy to address this challenge. By implementing efficient wastewater treatment technologies, Morocco can recover and reuse water from a variety of sources, including domestic, industrial and agricultural wastewater, and significantly reduce the demand for freshwater resources. In addition, public health and water quality can be protected through proper wastewater management. The implementation of wastewater treatment and reuse initiatives is in line with sustainable water management practices and offers a pragmatic solution to increase water availability and resilience in the face of increasing water scarcity challenges in Morocco (Mandi et al. 2022).

To relieve pressure on traditional water sources, researchers, and policymakers are actively seeking alternative approaches to urban irrigation, and one promising solution is the use of domestic wastewater (Zidan et al. 2023). The World Bank has projected a significant increase in wastewater volumes, from 666 Mm3 in 2014 to 750 Mm3 in 2020 and 900 Mm3 in 2050 (World Bank 2017). This indicates a significant potential resource that can be harnessed for sustainable irrigation practices. However, concerns about waterborne diseases and the safety of water reuse have increased in recent years (Labhasetwar & Yadav 2023; Bibi et al. 2021). Public perception of wastewater exposure and associated health risks is a significant barrier to water reclamation and reuse. Among the various contaminants present in wastewater, pathogens are of particular concern due to their potential to cause human disease. Therefore, it is crucial to develop effective technical methods to remove pathogens from domestic wastewater to prevent contamination. The importance of such research in the context of sustainable development is paramount. As water scarcity becomes more prevalent, particularly in arid regions such as North Africa and the Middle East, the need for innovative wastewater treatment technologies that can reduce pressure on freshwater resources is urgent.

The multi-soil-layering (MSL) system, as elucidated by Guan et al. (2014), has been adopted as a decentralized approach for wastewater treatment. MSL takes advantage of the soil structure to enhance the wastewater treatment capacity, as highlighted by Sy et al. (2021). According to Masunaga et al. (2007), the standard configuration includes a permeable gravel layer surrounding a soil mixture (charcoal, iron granules, sawdust, and soil). The use of gravel is crucial to improve the treatment by increasing permeability, aeration, and preventing clogging, as emphasized by Chen et al. (2009). The soil mixture layer was found to have low porosity and lack of aeration (Latrach et al. 2018). Maintaining a balance between aerobic and anaerobic conditions is crucial for the efficiency of this system, especially for nitrogen removal through nitrification–denitrification processes (Attanandana et al. 2000). These factors are crucial for MSL technology to effectively treat wastewater and remove nitrogen (Sbahi et al. 2021). Numerous studies and adaptations using different approaches and stages have led to extensive changes in the MSL system. A vertical hybrid system, which combines the MSL system with a trickling filter, was introduced in China by Luo et al. (2013) and is effective in treating wastewater from simulated septic tanks. In this regard, the trickling filter was modified by Zhang et al. (2015) by incorporating the MSL system. Subsequently, Tang et al. (2020) used this system to remove sodium dodecyl benzene sulfonate from the effluent. Latrach et al. (2016) conducted another study in which a sand filter was integrated with the MSL system. The goal of this configuration is to improve performance while maintaining a low hydraulic retention time, particularly by removing organics and nutrients. In addition, in Morocco, Zidan et al. (2023) designed a hybrid MSL system using vertically and horizontally flowing MSL units to treat domestic wastewater in urban areas. The MSL system was shown to be capable of treating domestic wastewater by incorporating biological (biodegradation), chemical (precipitation, adsorption), and physical (sedimentation, filtration) mechanisms as highlighted by Zidan et al. (2022). The MSL system has successfully treated other types of wastewater, including polluted river water (Wei & Wu 2018), textile wastewater (Sy & Kasman 2019), turtle aquaculture wastewater (Song et al. 2015), industrial wastewater (Attanandana et al. 2000), laboratory wastewater (Sy et al. 2021), and wastewater contaminated with sodium dodecyl benzene sulfonate (Tang et al. 2020), thereby expanding its scope. This wastewater treatment plant is characterized by its ability to provide low-cost, high-performance treatment and its unique ability to accommodate higher hydraulic loads (Sbahi et al. 2020). It is highly adaptable to the environment. It minimizes the risk of clogging and requires less maintenance. Furthermore, as demonstrated in studies by Latrach et al. (2015), Guan et al. (2014), and Chen et al. (2009), the MSL system has a lifespan of more than 20 years. Zhang et al. (2015) noted that another advantage of MSL is the availability of microbial communities. In addition, the MSL system requires a relatively small area for implementation (Latrach et al. 2018) and shows resilience to negative impacts such as odor and insects as shown by Zidan et al. (2022). Very few works have been focused on hybrid MSL systems, except for the studies by Zidan et al. (2023) and Tang et al. (2020). In addition, pathogen removal by MSL and the suitability of treated wastewater for irrigation purposes have received very little attention.

The present study is designed to (1) evaluate the treatment performance and behavior of a full-scale hybrid MSL plant combining vertical flow (VF) MSL and horizontal subsurface flow (HSSF) MSL with special attention to coliform and human pathogen removal; (2) explore the correlation between physicochemical and bacteriological parameters for the MSL system; (3) investigate the effect of each compartment on the hybrid MSL performance in an arid climate; and (4) compare the treated water quality with Moroccan water reuse standards to evaluate its suitability for irrigation.

Hybrid multi-soil-layering plant description

The hybrid MSL system is built in the annex of the Faculty of Law of the Cadi Ayyad University in Marrakech (Morocco) with 1,200 students. It covers an area of 175 m2. Figure 1 describes the flow process line of the treatment plant, which consists of a septic tank with dimensions of 6.5 × 3.5 × 3.5 m (length × width × depth), followed by a VF-MSL unit with dimensions of 5 × 4.5 × 1.5 m (length × width × depth) and a HF-MSL unit with dimensions of 7.4 × 4 × 0.6 m (length × width × depth) operating in series.
Figure 1

A schematic overview of the hybrid MSL system implemented at the Cadi Ayyad University, Marrakech (Morocco).

Figure 1

A schematic overview of the hybrid MSL system implemented at the Cadi Ayyad University, Marrakech (Morocco).

Close modal

Each unit of the hybrid MSL system consists of stratified layers filled with gravel (approximately 1–2 cm in diameter) alternating with a soil-based layer (SBL). The SBL consists of soil (70%) associated with granular ferrous metal (10%), charcoal (10%), and sawdust (10%) and has an effective pore space of 30%. SBL characteristics are shown in Table 1.

Table 1

Physicochemical characteristics and mineral composition of the SBL (mean ± standard deviation)

ParameterUnitValue
pH 8.335 ± 0.22 
EC μS/cm 448 ± 0.31 
Total organic carbon 12.48 ± 0.226 
Total organic matter 19.67 ± 0.424 
Mineral composition 
 LE mg/kg 86.85 
 Ca 2.45 
 Cl 3.87 
 Fe 4.06 
 Si mg/kg 5,685 
 K mg/kg 2,643 
 Al mg/kg 3,860 
 P mg/kg 1,542 
 Ti mg/kg 737 
 S mg/kg 675 
 Mn mg/kg 460 
 Sr mg/kg 244 
 Zr mg/kg 105 
 Zn mg/kg 70 
 Rb mg/kg 45 
 Pb mg/kg 27 
 Cu mg/kg 19 
 Y mg/kg 15 
 As mg/kg 
 Mg 1.15 
ParameterUnitValue
pH 8.335 ± 0.22 
EC μS/cm 448 ± 0.31 
Total organic carbon 12.48 ± 0.226 
Total organic matter 19.67 ± 0.424 
Mineral composition 
 LE mg/kg 86.85 
 Ca 2.45 
 Cl 3.87 
 Fe 4.06 
 Si mg/kg 5,685 
 K mg/kg 2,643 
 Al mg/kg 3,860 
 P mg/kg 1,542 
 Ti mg/kg 737 
 S mg/kg 675 
 Mn mg/kg 460 
 Sr mg/kg 244 
 Zr mg/kg 105 
 Zn mg/kg 70 
 Rb mg/kg 45 
 Pb mg/kg 27 
 Cu mg/kg 19 
 Y mg/kg 15 
 As mg/kg 
 Mg 1.15 

The VF-MSL unit contains six layers aerated by four PVC pipes that allow atmospheric air to penetrate and is continuously fed by vertical flow (VF). The HF-MSL unit contains only three layers without aeration, fed by a continuous subsurface flow.

To ensure a continuous inflow of wastewater, a primary solar pump first lifts the raw domestic wastewater from the sanitary manhole to the septic tank. The MSL units are then fed continuously by gravity (Figure 1). The treated water is temporarily stored in a storage tank and reused for landscape irrigation at the Cadi Ayyad University.

A hydraulic loading rate (HLR) between 160 and 250 L/m2/day and a continuous flow rate of 16 m3/day were applied to the hybrid MSL system. The system was monitored from December 2021 to June 2023 (1.5 years) with the exception of the period from August to October 2022. This period coincides with the closing of the institution for vacation, which renders the system inoperable. During this period, self-cleaning and maintenance activities will be carried out and no treatment will take place due to the absence of wastewater. When the academic year begins, the system resumes normal operation until the next vacation begins.

Sampling

Water samples from the MSL system were collected at regular intervals, approximately every two weeks, from the raw wastewater, septic tank, VF-MSL, and HF-MSL outlets to study the role of each treatment step. The collected water samples were analyzed for various physicochemical and bacterial parameters according to standardized methods described in references (AFNOR 1997; APHA 2005; Rodier et al. 2009). To ensure proper handling and maintain sample integrity, the samples, after being stored in sterile bottles, were placed in refrigerators at a temperature of 4°C and transported to the National Center for Research and Studies on Water and Energy for immediate analysis. In the laboratory, various physicochemical parameters were measured to evaluate the quality of wastewater. The chemical oxygen demand (COD) was determined using the dichromate open reflux method described in the APHA (2005) guidelines. In addition, electrical conductivity (EC), dissolved oxygen (DO), and pH were determined using a multiparameter probe-type instrument called WTW Multi 340i/set manufactured by Wissenschaftlich-Technische Werkstätten GmbH (WTW) in Weilheim, Germany. For nitrogen forms, several methods were used to measure nitrate-nitrogen , total Kjeldahl nitrogen (TKN), ammonium-nitrogen , and total nitrogen (TN). For total phosphorus (TP), the AFNOR standard (1997) was used for the measurement of after digestion with potassium peroxodisulfate. The orthophosphate content was determined by the molybdate and ascorbic acid method. The following formula represents the removal rate calculation for TP, TN, and COD, where Ci and Ce represent the concentrations in the inlet and outlet of the MSL system in mg/L:
formula
Bacterial analysis focused on several indicators, including fecal coliforms (FCs) and fecal streptococci (FS), as well as specific pathogens such as Staphylococcus sp. (S). To determine bacterial concentrations, the dilution method was used for both inlet and outlet samples from the hybrid MSL system (Moroccan Standard 2006). Bacterial concentrations were quantified and expressed as the decimal logarithm of colony forming units per 100 mL (log10 CFU/100 mL). This logarithmic scale provides a standardized unit of measurement for bacterial load. The bacterial removal efficiency of the MSL was expressed as the logarithm (log) of colony forming units per 100 mL (CFU/100 mL).
formula
where log (CFU/100 mL) in the influent are denoted as log influent and those in the effluent are denoted as log effluent for each MSL unit.

Statistical analysis

In this study, the application of Fisher's exact test (F) and Fisher's test allows the comparison of the means of different parameters to determine the presence of statistically significant effects. The principal component analysis (PCA) is used to evaluate the influence of each compound on the removal of pollutants. A correlation test is used to investigate possible relationships between the different parameters.

Characteristics of urban domestic wastewater

Raw wastewater has pH values ranging from 7.62 to 8.71, indicating a slightly alkaline nature (Table 2). This alkalinity can be attributed to the prevalence of anaerobic conditions in these waters, as observed by Luanmanee et al. (2002). The concentrations of parameters such as COD, TP, TN, FC, FS, and S ranged from 288.40 to 820.89 mg/L, 4.76 to 11.30 mg/L, 20.63 to 62.87 mg/L, 6.04 to 6.29 log, 6.28 to 6.08 log, and 5.29 to 5.59 log, respectively. These concentrations are consistent with the previous findings of Zidan et al. (2023) who did monitoring of the system some years ago.

Table 2

Composition of raw wastewater

VariablesUnitMinMaxMeanSD
pH Unit 7.62 8.71 8.18 0.047 
DO mg/L 0.79 1.99 1.40 0.061 
EC μS/cm 953.33 1,762.66 1,286.64 47.44 
TSS mg/L 101.6 326 213.8 0.92 
COD mg/L 288.40 820.89 520.90 0.036 
 mg/L 1.79 7.73 4.43 0.11 
TP mg/L 4.76 11.30 6.72 0.017 
TN mg/L 20.63 62.87 41.75 0,13 
TKN mg/L 13.06 42 24.23 0.092 
 mg/L 13.32 39.48 18.08 0.013 
 mg/L 0.28 1.88 0.77 0.002 
FC log (CFU/100 mL) 6.04 6.29 6.18 0.083 
FS log (CFU/100 mL) 5.89 6.28 6.08 0.12 
log (CFU/100 mL) 5.29 5.59 5.44 0.069 
VariablesUnitMinMaxMeanSD
pH Unit 7.62 8.71 8.18 0.047 
DO mg/L 0.79 1.99 1.40 0.061 
EC μS/cm 953.33 1,762.66 1,286.64 47.44 
TSS mg/L 101.6 326 213.8 0.92 
COD mg/L 288.40 820.89 520.90 0.036 
 mg/L 1.79 7.73 4.43 0.11 
TP mg/L 4.76 11.30 6.72 0.017 
TN mg/L 20.63 62.87 41.75 0,13 
TKN mg/L 13.06 42 24.23 0.092 
 mg/L 13.32 39.48 18.08 0.013 
 mg/L 0.28 1.88 0.77 0.002 
FC log (CFU/100 mL) 6.04 6.29 6.18 0.083 
FS log (CFU/100 mL) 5.89 6.28 6.08 0.12 
log (CFU/100 mL) 5.29 5.59 5.44 0.069 

In situ parameters

Figure 2 illustrates the variations in pH, EC, and DO at various points in the system during the monitoring period. These points include the MSL inlet, septic tank outlet (ST-outlet), VF-MSL outlet, and HF-MSL outlet.
Figure 2

Temporal changes of DO (a), pH (b), and EC (c) during the treatment process in the hybrid MSL system.

Figure 2

Temporal changes of DO (a), pH (b), and EC (c) during the treatment process in the hybrid MSL system.

Close modal

At the ST-outlet, DO values range from 1 to 2.31 mg/L. At the VF-MSL outlet, DO concentrations range from 2.43 to 5.11 mg/L, while at the HF-MSL outlet, DO concentrations range from 4.02 to 5.72 mg/L (Figure 2(a)). The increase in oxygen levels at the hybrid MSL system outlet is attributed to the introduction of aeration pipes at the VF-MSL level, which results in increased oxygen levels in the effluent. Placement of the HF-MSL unit after the VF-MSL unit, which benefits from increased oxygen transfer capacity due to the permeable gravel layer, resulted in the highest DO concentration (Zidan et al. 2022). Previous studies by Latrach et al. (2018) have shown that wastewater treatment systems combining two stages of VF-MSL have increased levels of oxygenation in the effluent. Similarly, Ávila et al. (2015) obtained consistent results using a system combining VF–HF constructed wetlands (CWs). The pH values showed a significant decrease, starting at 8.14 in the hybrid MSL influent, reaching 8.01 in the S-outlet, followed by a further decrease to 7.71 in the VF-MSL outlet. However, a slight increase to 7.72 was observed in the HF-MSL effluent (Figure 2(b)). The decrease in pH values in the VF-MSL effluent can be attributed to the release of hydrogen ions resulting from oxidation processes and organic acids generated by the decomposition of organic matter (Latrach et al. 2016). These pH values can be used as an indicator to adjust the aeration rate in the MSL system to improve contaminant removal (Luanmanee et al. 2002). Throughout the hybrid MSL system study, pH values generally ranged between 6.84 and 8.73, an interval considered optimal for microbial growth and nutrient adsorption in porous systems. In addition, it is noteworthy that nitrification and denitrification processes can have a small effect on pH values (Sbahi et al. 2022).

For EC, Figure 2(c) shows significant variations in EC values among the different components of the hybrid MSL system. The average values recorded in the hybrid MSL system were 1,212.86 μS/cm at the inlet, 1,093.13 μS/cm at the S-outlet, 917.96 μS/cm in the VF-MSL outlet, and 850.18 μS/cm in the HF-MSL outlet. The decrease in EC is primarily attributed to the presence of free ions, such as , that enhance EC. Furthermore, the decrease in EC is associated with the conversion of and to molecular nitrogen (N2), as noted by Rasool et al. (2018).

Organic matter removal

Figure 3(a) shows the evolution of total suspended solids (TSS) along the hybrid MSL system. The average values obtained are 128.63 mg/L at the inlet of the hybrid MSL system, 20.32 mg/L at the VF-MSL outlet, and 1.68 mg/L at the HF-MSL outlet. Filtration phenomena occur due to the impaction of particles in the soil mixture layers or gravel layer. The voids and media grain structure visible in the permeable layers (PLs) have a remarkable influence on TSS and trapping during the flow path, as reported by several authors (Akratos & Tsihrintzis 2007; García-Mesa et al. 2010). Statistical analysis shows a significant difference in TSS removal at the outlets of the VF-MSL and hybrid MSL systems, which reached 75 and 97%, respectively the same results, were obtained by Zidan et al. (2023). The variations of COD concentrations in the different units of the hybrid MSL system are shown in Figure 3(b). At the inlet of the MSL plant, the average COD concentrations were 393.51 mg/L, followed by 322.97 mg/L at the ST-outlet, 97.15 mg/L at the VF-MSL outlet, and finally 51.98 mg/L at the HF-MSL outlet. The MSL system can efficiently treat urban domestic wastewater, achieving 87.76% removal of organic matter. Throughout the study period, the quality of urban wastewater experienced significant fluctuations due to its sensitivity to water use patterns. The removal of organic matter by the hybrid MSL system was attributed to microbial degradation and/or physicochemical absorption (Sato et al. 2011). More specifically, within the porous structure of the MSL, microorganisms facilitate the biological decomposition of organic matter under oxygenated conditions. Initially, organic matter is adsorbed on the layers of the soil mixture and on the specific surface area of the gravel before being decomposed by microorganisms (Latrach et al. 2018). Other studies suggest that organic matter is initially adsorbed and retained by the MSL, which promotes the growth of aerobic microorganisms that intercept organic pollutants, resulting in the simultaneous removal of COD (Sato et al. 2011). Chen et al. (2009) reported similar results to the hybrid MSL system, achieving an average COD reduction of 80% with a VF-MSL system operating under aerobic and anaerobic conditions to treat contaminated river water in China. However, Ho & Wang (2015) reported a lower average COD removal ranging from 57 to 65%. Furthermore, Zidan et al. (2023) highlighted a removal efficiency of 70%. The results of the investigated hybrid MSL system exceeded those documented by Ho & Wang (2015), demonstrating its superior performance compared to previous studies.
Figure 3

Temporal changes in TSS (a) and COD (b) during the treatment process in the hybrid MSL system.

Figure 3

Temporal changes in TSS (a) and COD (b) during the treatment process in the hybrid MSL system.

Close modal

The Fisher exact text (F) statistic was used to measure the ratio of the variance observed between groups and within groups. A value close to one indicates similarity between samples, while a larger deviation indicates greater differences. However, the F value alone does not indicate the significance of the difference. To determine significance, the F value is compared to the degrees of freedom and used to calculate a p-value. In this study, we obtained a very low p-value, which provides strong evidence against the null hypothesis (H0) that the COD concentrations are similar. This supports the alternative hypothesis (H1) that COD concentrations differ between groups. It is important to note that a significant p-value only confirms the presence of a difference, but does not quantify the magnitude or significance of that difference. To further evaluate the impact of the hybrid MSL system on COD concentrations, we calculated the effect size using omega (ω). The analysis revealed an effect size of 0.72, indicating a significant effect of the system on COD concentrations. This indicates that the MSL system has a significant effect on the observed COD levels.

Phosphorus removal

Figure 4 shows the changes in phosphorus concentrations in the influent and effluent of the hybrid system throughout the experimental period. The average concentrations of and TP were 3.44 and 5.42 mg/L, respectively, in the hybrid MSL inlet. In the ST-outlet, the concentrations were 2.92 mg/L for and 4.34 mg/L for TP. In the VF-MSL outlet, the concentrations were 1.39 mg/L for and 1.76 mg/L for TP, while in the HF-MSL outlet, the concentrations were 0.99 mg/L for and 1.17 mg/L for TP. The hybrid MSL technology showed excellent performance in phosphorus removal, mainly through the processes of adsorption and precipitation facilitated by the addition of iron metal to the SBL (Sato et al. 2011). The added iron is converted to ferrous iron ( ) and subsequently to ferric ions () (Wei & Wu 2018) through its aerobic oxidation process in the PL. Latrach et al. (2016) noted that the adsorption and precipitation of , leading to the formation of the Fe complex, occurs before the formation of Fe(OH)3 deposits.
Figure 4

Temporal changes in (a) and TP (b) during the treatment process in the hybrid MSL system.

Figure 4

Temporal changes in (a) and TP (b) during the treatment process in the hybrid MSL system.

Close modal

The treatment performance of TP reached 60.43% for the VF-MSL effluent and 78.47% for the hybrid MSL effluent. These results exceed the previous results of Zidan et al. (2023), who studied the same hybrid MSL system and observed average TP removal efficiencies of 47% in VF-MSL and 76% in hybrid MSL effluents. Furthermore, these results exceed those obtained by Luo et al. (2014), who achieved a TP removal efficiency of 47.3% in a one-unit MSL pilot. Compared to CW technologies, MSL technology has demonstrated superior efficiencies in TP removal. For example, Elfanssi et al. (2018) worked with a hybrid CW plant and reported a TP removal rate of 69%, while Zhai et al. (2011) and Lesage et al. (2007) documented TP removal rates of 68.1 and 44.5%, respectively, in two-stage CW treatment systems.

Nitrogen removal

Figure 5 shows the monthly nutrient concentrations of the MSL plant influent and effluent during the monitoring period. In the influent, the average concentrations of TKN and ammonium ions were 23.64 and 14.92 mg/L, respectively. The MSL system demonstrated significant reductions in TKN (Figure 5(a)) and (Figure 5(b)), with average removal efficiencies of 84.79% for TKN and 95.71% for . Our results exceed those of Zidan et al. (2023), who found that the hybrid system removes 73% for TKN and 83% for . Previous studies have highlighted the ability of the MSL system to decontaminate domestic wastewater by adsorbing TKN on the surface of gravel and soil mixture layers, thereby facilitating its mineralization into (Sato et al. 2011; Sbahi et al. 2022). The removal of can be attributed to both adsorption processes and aerobic nitrification, where is converted to nitrite by ammonia-oxidizing bacteria, followed by oxidation of the intermediate substrate to nitrate by nitrite-oxidizing bacteria (Sbahi et al. 2022). These microbial communities, with their high nitrification potential, play a crucial role in removal (Zidan et al. 2023). In particular, the VF-MSL unit with multiple PLs was particularly effective in removing and enhancing the nitrification process within the system.
Figure 5

Temporal changes in TKN (a) and (b) during the treatment process in the hybrid MSL system.

Figure 5

Temporal changes in TKN (a) and (b) during the treatment process in the hybrid MSL system.

Close modal
The concentration showed a significant increase in the treated water due to the favorable conditions provided for nitrification in the VF-MSL unit. In the raw wastewater, the concentration of nitrates was 1.24 mg/L. It increased to 21.17 mg/L in the VF-MSL unit before decreasing to 12.65 mg/L in the HF-MSL unit due to the presence of anaerobic conditions in this unit (Figure 6(a)). This observation can be explained by the conversion of to under aerobic conditions, followed by the denitrification process in which is converted to N2 under anaerobic conditions (Zhang et al. 2015). The increased concentration of nitrates in the VF-MSL unit indicates successful nitrification, while the subsequent decrease in the HF-MSL unit indicates efficient denitrification.
Figure 6

Temporal changes in nitrates, (a) and TN (b) during the treatment process in the hybrid MSL system.

Figure 6

Temporal changes in nitrates, (a) and TN (b) during the treatment process in the hybrid MSL system.

Close modal

The efficiency of TN removal in the MSL system is strongly influenced by the coexistence of aerobic and anaerobic processes. The concentration of TN was significantly reduced from 38.38 mg/L at the inlet to 4.38 mg/L at the outlet of the hybrid MSL system (Figure 6(b)). Therefore, the combination of aerobic and anaerobic processes plays an important role in the overall efficiency of TN removal in the MSL system.

Microbial parameters removal

Bacterial pathogens, including FCs, FS, and staphylococci (S), were monitored at both the inlet and outlet of the hybrid MSL system (Figure 7). The hybrid MSL system exhibited a higher log removal efficiency of bacteria (3.32 log) compared to a single-stage MSL system (1.92 log) operating at a HLR of 250 L/m2/day. These results suggest that relying solely on a single-stage MSL system may not be sufficient to achieve efficient FC removal (Latrach et al. 2015). Our study demonstrated greater efficacy when compared to the results of Zidan et al. (2023), who reported that the FC removal performance of the hybrid MSL system was higher (2.88 log) than a single-stage MSL system (1.59 log). The hybrid MSL system showed significant removal of Streptococcus (3.90 log) and Staphylococcus (2.43 log). The effectiveness of the filtration system in removing bacteria varies by species because different bacteria have different cell sizes and shape characteristics. Wang et al. (2021) explain that FS and Gram-positive S are known to be more resistant to environmental stress and generally have longer survival times. This explains their higher removal rates when compared to Gram-negative bacteria.
Figure 7

Temporal changes of FC (a), FS (b), and Staphylococcus, S (c) during the treatment process in the hybrid MSL system.

Figure 7

Temporal changes of FC (a), FS (b), and Staphylococcus, S (c) during the treatment process in the hybrid MSL system.

Close modal

MSL technology uses a variety of mechanisms, including physical filtration, adsorption, microbial death, and predation, to effectively reduce bacterial concentrations (Latrach et al. 2018; Sbahi et al. 2022). Filtration primarily occurs in the soil mixture layers, which have lower porosity compared to the permeable gravel layers, making them more efficient at reducing bacteria. Adsorption of bacteria is expected to occur primarily in the soil mixture layers. These initial stages of filtration and adsorption are followed by microbial degradation and natural mortality of bacteria. The mechanism of natural mortality in the soil mixture layers also plays a critical role in the removal of bacteria from domestic wastewater (Stevik et al. 2004).

Predation of bacteria by protozoa has been documented in several studies. Favorable aeration conditions in the PLs of the MSL system stimulate the formation of predator communities (Garcıa et al. 2013). Additional predators, such as Bdellovibrio and Ensifer adhaerens, contribute significantly to bacterial reduction (Wang et al. 2021). Previous research has emphasized that maintaining a minimal bacterial population in porous environments promotes the presence of predators, whose concentration increases proportionally to the bacterial concentration. For example, in a study where Escherichia coli was introduced into the soil, a sixfold increase in the protozoan population was observed, accompanied by a reduction in the number of E. coli bacteria (Garcıa et al. 2013). Natural mortality of living cells is another critical factor in the bacterial elimination process, which has been studied in both planted and unplanted sand columns (Wand et al. 2007). The conditions for microbial mortality are influenced by temperature, while pH emerges as an essential factor affecting bacterial survival. The consistent removal of bacterial indicators during the experimental period indicates a continuous elimination of bacteria at a certain rate in the hybrid MSL system (Figure 3). This observation implies the absence of bacterial accumulation, and instead suggests continuous removal by microbial degradation or natural death. The bacterial removal rate in the MSL system is likely explained by either bacterial adsorption or filtration (Stevik et al. 2004).

Correlation between studied parameters

The use of correlation analysis is a statistical approach designed to assess the links or relationships between different quantitative variables. Based on the concept of a linear relationship between these variables, this method involves the calculation of a correlation coefficient, which measures both the strength and direction of the relationship and ranges from −1 to +1. A correlation coefficient of +1 or −1 reflects a perfect positive or negative linear relationship, respectively, while a coefficient of 0 indicates that there is no linear relationship between the variables under study (Gogtay & Thatte 2017). The monitoring period, consisting of 31 observations, is summarized in Figure 8, which shows the Pearson linear correlation coefficients between the different variables of the hybrid system.
Figure 8

Analyzing correlations between physicochemical and bacteriological parameters during monitoring.

Figure 8

Analyzing correlations between physicochemical and bacteriological parameters during monitoring.

Close modal

Notably, a positive correlation (r = 0.586) was observed between the removal rate of TP and the pH of the treated wastewater by MSL. As the pH of the treated wastewater decreased, the efficiency of TP removal decreased. In addition, a strong negative correlation (r = −0.904) was found between DO and TP. This suggests that improved oxygenation in the MSL system, achieved through enhanced iron oxidation, can effectively reduce TP levels in the MSL units. Similar results have been reported by Hong et al. (2019) and Wei & Wu (2018). Gallionellaceae, as identified by Song et al. (2020), contributes to phosphorus removal through anaerobic iron oxidation and binding with ferric hydroxide. In addition, Acidimicrobiia, known to promote phosphorus removal by producing ferric hydroxide colloids in SBLs, plays a role in phosphorus removal in the hybrid system. In addition, a significant and strong correlation between TN removal efficiency and pH of the treated water was observed in the MSL system (r = 0.677). In the MSL system, aeration enhances nitrification but inhibits denitrification (r = −0.907). This leads to a significant increase in the concentration of (r = 0.628) and a subsequent decrease in the pH of the effluent (Figure 8(a)). Conversely, denitrification occurs in the anaerobic zones.

Significant linear relationships were also found between , TP, and COD in the hybrid MSL system. This indicates that the system is efficient in reducing both organic matter and nutrients. Degradation of COD and nitrogen (N) (r = 0.912) occurs primarily through biological processes within the MSL pores (Chen et al. 2009). Since most denitrifiers are heterotrophic organisms that rely on carbon as an electron donor, COD, which represents organic matter, becomes a critical carbon source for microorganisms involved in the denitrification process (Zidan et al. 2023). Consequently, the increase in NO3 concentration corresponds to a decrease in COD content (r = −0.732).

Physicochemical parameters play an important role in the removal and destruction of pathogenic bacteria in wastewater (Zidan et al. 2023). In order to understand the relationship between the concentrations of pathogenic bacteria (FC, FS, and S) during their passage through the MSL system and various physicochemical parameters, a correlation analysis was performed. The results showed positive correlations between COD, TSS, TN, TP, and the levels of FC, FS, and ST in the effluent during treatment. The correlation between COD and pathogenic bacteria was statistically significant. Similarly, TSS and TN showed significant relationships with FC, FS, and S (Figure 8(b)). These results indicate that the physicochemical parameters (COD, TSS, TN, and TP) decrease as the wastewater passes through the MSL system. These observations are in agreement with previous studies. For example, Zidan et al. (2023), working on the same plant in Morocco, reported a positive correlation between TSS and nitrogen content with pathogenic bacteria. Furthermore, Tyagi et al. (2008) reported positive correlations between TSS and FCs in the effluent of the hybrid MSL plant. The efficient removal of pathogenic bacteria by sedimentation, especially when they are attached to larger particles, may reveal the association between their removal and the reduction of TSS (Wei & Wu 2018). Thus, this mechanism may explain the positive correlation between the TSS and indicator bacteria. Previous studies have also found a positive correlation between the levels of bacterial indicators (E. coli and Enterococci) and TN concentrations in CWs, suggesting that the presence of available nitrogen could increase bacterial survival (Díaz et al. 2010).

Statistical analysis by PCA of physicochemical and bacteriological parameters

PCA was used to assess the impact of each compound on the efficiency of contaminant removal (Figure S1, Supplementary Material). The dataset used in this study consists of 14 variables and 4 individuals representing the temporal sampling. Data analysis was performed using R software, with an emphasis on the use of the FactoMineR and factoextra packages. These tools are well suited and easily navigated to perform a thorough PCA. The primary objective of the statistical analysis through PCA is to explore the variability between different phases of water treatment in the hybrid MSL system. Prior to this study, data preprocessing is performed to remove outliers from our database. The goal is to identify individuals based on the complete set of information related to the movement process. The examination of the results shows that the factorial plan formed by Dim1 and Dim2, summarizes 84% of the information, with the first axis alone representing 80% of this variability. The analysis of cos², represented by a color gradient (where values closer to 1 or marked by larger spheres indicate better representation in the chosen plane), shows that the majority of variables and individuals are well represented in the chosen plan. In addition, the analysis shows that and DO are positively correlated with Dim1, while the other variables are negatively correlated. To study the effect of different phases of the hybrid MSL system on the variability of physicochemical and bacteriological elements in the water, the individuals of each phase were colored with a specific color. The PCA results indicate that the VF-MSL and HF-MSL effluents have high DO and nitrate levels (Figure S1(A), Supplementary Material). This can be attributed to the occurrence of nitrification, which generates nitrate and accounts for the high nitrate levels observed (nitrification reaction):
formula
formula

Conversely, the high concentrations of TP, COD, and TN at the inlet of the system and at the outlet of the septic tank indicate the presence of pollutants in the incoming wastewater. Based on the cos2 analysis (Figure S1(B), supplementary material), it can be concluded that the variables and individuals are well represented in the plane (PC1 and PC2), with the majority of them having cos2 values greater than 0.65.

Figure S1(B) (supplementary material) shows a variation in the representation of the parameters within the PCA plane, mainly characterized by the decrease of COD cos2. This decrease can be attributed to the absence of oxygen, which affects the degradation of organic matter by aerobic bacteria.

Quality of treated water

The combination of the VF-MSL unit with the HF-MSL unit is effective in successfully removing organic matter, nutrients, and pathogenic bacteria from urban domestic wastewater, which explains the positive performance of the hybrid MSL system. In addition, no significant problems such as clogging, odor, or insect infestation were observed throughout the monitoring period. Table 3 shows that the levels of pH, EC, TSS, , and FC in the treated effluent were within acceptable ranges according to Moroccan irrigation water quality standards. This indicates that the effluent from the hybrid MSL system maintained a quality within the permitted limits for direct wastewater discharge, making it potentially suitable for reuse in irrigation in accordance with Moroccan regulations.

Table 3

Guidelines for reusing treated wastewater in irrigation

ParametersUnitRaw wastewaterTreated wastewaterRemovalAdmissible limits for direct discharge (Valeurs Limites Spécifiques de Rejet Domestique 2006)Admissible limits for wastewater reuse (Normes de qualité des eaux destinées à l'irrigation au Maroc 2007)
DO mg/L 1.47 ± 0.047 4.63 ± 0.055 – – – 
pH Unit 8.10 ± 0.061 7.57 ± 0.031 – – 6.5–8.5 
EC μS/cm 1,286.64 ± 47.44 847.90 ± 32.2 – – 12,000 
COD mg/L 520.20 ± 0.92 47.97 ± 0.74 87.76% 250 – 
TSS mg/L 128.63 ± 0.036 1.68 ± 0.071 97% 150 100 
 mg/L 5.05 ± 0.11 1.15 ± 0.23 70.59% – – 
TP mg/L 6.72 ± 0.017 1.11 ± 0.046 78.47% – – 
 mg/L 18.06 ± 0,13 0.61 ± 0.17 95.71% – – 
TKN mg/L 24.23 ± 0.092 3.73 ± 0.064 84.79% – – 
 mg/L 0.77 ± 0.013 13.02 ± 0.021 – – 30 
TN mg/L 14.24 ± 0.002 1.38 ± 0,012 91.65% – – 
FC log (CFU/100 mL) 6.23 ± 0.083 2.02 ± 0.089 4.21 log – ≤3 
FS log (CFU/100 mL) 6.15 ± 0.12 2.29 ± 0.33 3.90 log – – 
log (CFU/100 mL) 5.46 ± 0.069 3.06 ± 0.089 2.43 log – – 
ParametersUnitRaw wastewaterTreated wastewaterRemovalAdmissible limits for direct discharge (Valeurs Limites Spécifiques de Rejet Domestique 2006)Admissible limits for wastewater reuse (Normes de qualité des eaux destinées à l'irrigation au Maroc 2007)
DO mg/L 1.47 ± 0.047 4.63 ± 0.055 – – – 
pH Unit 8.10 ± 0.061 7.57 ± 0.031 – – 6.5–8.5 
EC μS/cm 1,286.64 ± 47.44 847.90 ± 32.2 – – 12,000 
COD mg/L 520.20 ± 0.92 47.97 ± 0.74 87.76% 250 – 
TSS mg/L 128.63 ± 0.036 1.68 ± 0.071 97% 150 100 
 mg/L 5.05 ± 0.11 1.15 ± 0.23 70.59% – – 
TP mg/L 6.72 ± 0.017 1.11 ± 0.046 78.47% – – 
 mg/L 18.06 ± 0,13 0.61 ± 0.17 95.71% – – 
TKN mg/L 24.23 ± 0.092 3.73 ± 0.064 84.79% – – 
 mg/L 0.77 ± 0.013 13.02 ± 0.021 – – 30 
TN mg/L 14.24 ± 0.002 1.38 ± 0,012 91.65% – – 
FC log (CFU/100 mL) 6.23 ± 0.083 2.02 ± 0.089 4.21 log – ≤3 
FS log (CFU/100 mL) 6.15 ± 0.12 2.29 ± 0.33 3.90 log – – 
log (CFU/100 mL) 5.46 ± 0.069 3.06 ± 0.089 2.43 log – – 

This study focuses on the investigation of a full-scale hybrid MSL ecotechnology for the treatment of urban domestic wastewater. Monitoring of the treatment process revealed high removal efficiencies of various pollutants. The hybrid MSL plant demonstrated significant reductions in organic matter, nitrogen, and phosphorus, with removal rates of 97% for TSS, 88.57% for COD, 88.49% for TN, and 79.93% for TP. In addition, the plant effectively removed bacterial indicators present in the domestic wastewater, achieving removal rates of 4.21 log for FC, 3.90 log for FS, and 2.43 log for S. PCA showed a positive correlation between COD, , TP removal, and bacterial pathogens. The treated water from the hybrid MSL system met the irrigation standards set by Moroccan regulations and the FAO guidelines for water reuse. Therefore, the treated water can be safely reused for irrigation purposes in green spaces or agriculture. This hybrid MSL ecotechnology represents a promising solution that effectively treats wastewater and provides a quality of water that can be reused for landscape irrigation and agriculture without health risks. This dual benefit is consistent with the principles of sustainable development by promoting environmental protection and resource conservation. By enabling the safe reuse of treated wastewater, the hybrid MSL system contributes to water conservation efforts and reduces reliance on dwindling freshwater sources, thereby supporting long-term sustainability goals. Thus, this study highlights the critical role of technological innovation in addressing water challenges and promoting sustainable development goals, particularly in water-stressed areas.

This work was supported by the project I-MAROC ‘Artificial Intelligence/Applied Mathematics, Health/Environment: Simulation for Decision Support’, the APRD Program (Morocco) and the National Center for Studies and Research on Water and Energy, Cadi Ayyad University, Morocco.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

AFNOR
.
1997
Recueil de normes françaises: eau, méthodes d' essai, 2ème édition. Paris, France
.
Akratos
C. S.
&
Tsihrintzis
V. A.
2007
Effect of temperature, HRT, vegetation and porous media on removal efficiency of pilot-scale horizontal subsurface flow constructed wetlands
.
Ecological engineering
29
(
2
),
173
191
.
APHA
2005
Standard Methods for the Examination of Water and Wastewater
, 21st edn.
American Public Health Association/American Water Works Association/Water Environment Federation
,
Washington, DC, USA
, p.
541
.
Attanandana
T.
,
Saitthiti
B.
,
Thongpae
S.
,
Kritapirom
S.
,
Luanmanee
S.
&
Wakatsuki
T.
2000
Multi-media-layering system for food service wastewater treatment
.
Ecological Engineering
15
(
1–2
),
133
138
.
Ávila
C.
,
Bayona
J. M.
,
Martín
I.
,
Salas
J. J.
&
García
J.
2015
Emerging organic contaminant removal in a full-scale hybrid constructed wetland system for wastewater treatment and reuse
.
Ecological Engineering
80
,
108
116
.
Ben-Daoud
M.
,
Mahrad
B. E.
,
Elhassnaoui
I.
,
Moumen
A.
,
Sayad
A.
,
ELbouhadioui
M.
,
Moroșanu
G. A.
,
Mezouary
L. E.
,
Essahlaoui
A.
&
Eljaafari
S.
2021
Integrated water resources management: An indicator framework for water management system assessment in the R'Dom Sub-basin, Morocco
.
Environmental Challenges
3
,
100062
.
https://doi.org/10.1016/j.envc.2021.100062
.
Bibi
S.
,
Ahmad
A.
,
Anjum
M. A. R.
,
Haleem
A.
,
Siddiq
M.
,
Shah
S. S.
&
Al Kahtani
A.
2021
Photocatalytic degradation of malachite green and methylene blue over reduced graphene oxide (rGO) based metal oxides (rGO-Fe3O4/TiO2) nanocomposite under UV-visible light irradiation
.
Journal of Environmental Chemical Engineering
9
(
4
),
105580
.
Bolzman
C.
,
Fokkema
T.
,
Guissé
I.
&
Van Dalen
D.
2021
Starting a new life in the south? Swiss, Dutch and flemish ageing in Morocco: A lifecourse perspective
.
Ageing & Society
41
(
6
),
1240
1266
.
Chen
X.
,
Luo
A. C.
,
Sato
K.
,
Wakatsuki
T.
&
Masunaga
T.
2009
An introduction of a multi-soil-layering system: A novel green technology for wastewater treatment in rural areas
.
Water and Environment Journal
23
(
4
),
255
262
.
Díaz
F. J.
,
O'Geen
A. T.
&
Dahlgren
R. A.
2010
Efficacy of constructed wetlands for removal of bacterial contamination from agricultural return flows
.
Agricultural Water Management
97
(
11
),
1813
1821
.
Elfanssi
S.
,
Ouazzani
N.
,
Latrach
L.
,
Hejjaj
A.
&
Mandi
L.
2018
Phytoremediation of domestic wastewater using a hybrid constructed wetland in mountainous rural area
.
International Journal of Phytoremediation
20
(
1
),
75
87
.
FAO
.
2015
AQUASTAT – FAO's Global Information System on Water and Agriculture: Country Profile–Morocco
.
Food and Agriculture Organization of the United Nations
,
Rome, Italy
.
García-Mesa
J. J.
,
Poyatos
J. M.
,
Delgado
F.
&
Hontoria
E.
2010
The influence of biofilm treatment systems on particle size distribution in three wastewater treatment plants
.
Water, Air, & Soil Pollution 212, 37–49
.
García
J. A.
,
Paredes
D.
&
Cubillos
J. A.
2013
Effect of plants and the combination of wetland treatment type systems on pathogen removal in tropical climate conditions
.
Ecological Engineering 58, 57–62
.
Gogtay
N. J.
&
Thatte
U. M.
2017
Principles of correlation analysis
.
Journal of the Association of Physicians of India
65
(
3
),
78
81
.
Guan
Y. D.
,
Xu
D. F.
,
Chen
X.
,
Luo
A. C.
,
Fang
H.
&
Song
Y. Z.
2014
Flow patterns of multi-soil-layering systems
.
Desalination and Water Treatment
52
(
22–24
),
4165
4169
.
Ho
C.-C.
&
Wang
P.-H.
2015
Efficiency of a multi-soil-layering system on wastewater treatment using environment-friendly filter materials
.
Int. J. Environ. Res. Public Health
12
,
3362
3380
.
https://doi.org/10.3390/ijerph120303362.
Hssaisoune
M.
,
Bouchaou
L.
,
Sifeddine
A.
,
Bouimetarhan
I.
&
Chehbouni
A.
2020
Moroccan groundwater resources and evolution with global climate changes
.
Geosciences
10
(
2
),
81
.
Kahime
K.
,
Ben Salem
A.
,
El Hidan
A.
,
Messouli
M.
&
Chakhchar
A.
2018
Vulnerability and Adaptation Strategies to Climate Change on Water Resources and Agriculture in Morocco: Focus on Marrakesh-Tensift-Al Haouz Region
.
Int. J. Agric. Environ. Res. 2018 (4), 58–77
.
Labhasetwar
P. K.
&
Yadav
A.
2023
Membrane Based Point-of-use Drinking Water Treatment Systems
.
IWA Publishing, London, UK
.
Lachir
A.
,
Bounoua
L.
,
Zhang
P.
,
Thome
K.
&
Messouli
M.
2016
Modeling the urban impact on semiarid surface climate: A case study in Marrakech, Morocco
.
Canadian Journal of Remote Sensing
42
(
4
),
379
395
.
Latrach
L.
,
Masunaga
T.
,
Ouazzani
N.
,
Hejjaj
A.
,
Mahi
M.
&
Mandi
L.
2015
Removal of bacterial indicators and pathogens from domestic wastewater by the multi-soil-layering (MSL) system
.
Soil Science and Plant Nutrition
61
(
2
),
337
346
.
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
.
Latrach
L.
,
Ouazzani
N.
,
Hejjaj
A.
,
Mahi
M.
,
Masunaga
T.
&
Mandi
L.
2018
Two-stage vertical flow multi-soil-layering (MSL) technology for efficient removal of coliforms and human pathogens from domestic wastewater in rural areas under arid climate
.
International Journal of Hygiene and Environmental Health
221
(
1
),
64
80
.
Lesage
E.
,
Rousseau
D. P. L.
,
Meers
E.
,
Tack
F. M. G.
&
De Pauw
N.
2007
Accumulation of metals in a horizontal subsurface flow constructed wetland treating domestic wastewater in Flanders, Belgium
.
Science of the Total Environment
380
(
1–3
),
102
115
.
Luanmanee
S.
,
Boonsook
P.
,
Attanandana
T.
,
Saitthiti
B.
,
Panichajakul
C.
&
Wakatsuki
T.
2002
Effect of intermittent aeration regulation of a multi-soil-layering system on domestic wastewater treatment in Thailand
.
Ecological Engineering
18
(
4
),
415
428
.
Luo
W.
,
Yang
C.
,
He
H.
,
Zeng
G.
,
Yan
S.
&
Cheng
Y.
2014
Novel two-stage vertical flow biofilter system for efficient treatment of decentralized domestic wastewater
.
Ecological Engineering
64
,
415
423
.
Mandi
L.
,
Ouazzani
N.
&
Aziz
F.
,
2022
Constructed wetlands as a green and sustainable technology for domestic wastewater treatment under the arid climate of rural areas in Morocco
. In:
Constructed Wetlands for Wastewater Treatment in Hot and Arid Climates. Wetlands: Ecology, Conservation and Management
,
Vol. 7
(
Stefanakis
A.
ed.).
Springer
,
Cham, Switzerland
.
https://doi.org/10.1007/978-3-031-03600-2_1
.
Masunaga
T.
,
Sato
K.
,
Mori
J.
,
Shirahama
M.
,
Kudo
H.
&
Wakatsuki
T.
2007
Characteristics of wastewater treatment using a multi-soil-layering system in relation to wastewater contamination levels and hydraulic loading rates
.
Soil Science and Plant Nutrition
53
(
2
),
215
223
.
Moroccan Standards 2006 Norme Marocaine homologuée par arrêté du ministre de l'Industrie, du commerce et de la mise à niveau de l'économie; Service de Normalisation Industrielle Marocaine (SNIMA) (2006).
Normes de qualité des eaux destinées à l'irrigation au Maroc
2007
Secrétariat d'état auprès du ministère de l'énergie, des mines, de l'eau et de l'environnement, chargé de l'eau et de l'environnement, Maroc
.
Rodier
J.
,
Bazin
C.
,
Broutin
J. P.
,
Chambon
P.
,
Champsaur
H.
&
Rodi
L.
2009
Water Analysis, 9th edn
.
Dunod, Paris, France, p. 157
.
Sbahi
S.
,
Ouazzani
N.
,
Hejjaj
A.
&
Mandi
L.
2021
Nitrogen modeling and performance of multi-soil-layering (MSL) bioreactor treating domestic wastewater in rural community
.
Journal of Water Process Engineering
44
,
102389
.
Song
Y.
,
Huang
Y. T.
,
Ji
H. F.
,
Nie
X. J.
,
Zhang
Z. Y.
,
Ge
C.
&
Chen
X.
2015
Treatment of turtle aquaculture effluent by an improved multi-soil-layer system
.
Journal of Zhejiang University. Science. B
16
(
2
),
145
.
Stevik
T. K.
,
Aa
K.
,
Ausland
G.
&
Hanssen
J. F.
2004
Retention and removal of pathogenic bacteria in wastewater percolating through porous media: A review
.
Water Research
38
(
6
),
1355
1367
.
Sy
S.
&
Kasman
M.
2019
Reduction of pollutant parameters in textile dyeing wastewater by Gambier (Uncaria gambir Roxb) using the multi soil layering (MSL) bioreactor
. In:
IOP Conference Series: Materials Science and Engineering
,
Vol. 546
,
No. 2
.
IOP Publishing, Bristol, UK
, p.
022032
.
Sy
S.
,
Ardinal
A.
,
Sofyan
S.
,
Anova
I. T.
,
Munaf
H.
,
Marlusi
M.
&
Wakatsuki
T.
2021
Application of the multi soil layering (MSL) system to treat laboratory wastewater
.
AIP Conference Proceedings
2349
(1)
.
Valeurs Limites Spécifiques de Rejet Domestique
.
2006
Arrété n°1607–06 du Joumada II 1427, Secŕetariat d'Etat Auprès du Ministère de l'Energie, des Mines, de l'Eau et de l'Environnement, Chargé de l'Eau et de l'Environnement, Département de l'Eau. Royaume du Maroc, p. 50
.
Wand
H.
,
Vacca
G.
,
Kuschk
P.
,
Krüger
M.
&
Kästner
M.
2007
Removal of bacteria by filtration in planted and non-planted sand columns
.
Water Research
41
(
1
),
159
167
.
World Bank
.
2017
Managing Urban Water Scarcity in Morocco. Water Global Practice, Summary Report, Washington, DC, USA
.
Zhai
J.
,
Xiao
H. W.
,
Kujawa-Roeleveld
K.
,
He
Q.
&
Kerstens
S. M.
2011
Experimental study of a novel hybrid constructed wetland for water reuse and its application in Southern China
.
Water Science and Technology
64
(
11
),
2177
2184
.
Zidan
K.
,
Sbahi
S.
,
Hejjaj
A.
,
Ouazzani
N.
,
Assabbane
A.
&
Mandi
L.
2022
Removal of bacterial indicators in on-site two-stage multi-soil-layering plant under arid climate (Morocco): Prediction of total coliform content using K-nearest neighbor algorithm
.
Environmental Science and Pollution Research
29
(
50
),
75716
75729
.
Zidan
K.
,
Mandi
L.
,
Hejjaj
A.
,
Sbahi
S.
,
El Fels
A. E. A.
,
Ouazzani
N.
&
Assabbane
A.
2023
Efficiency of a new hybrid multi-soil-layering eco-friendly technology for removing pollutants from domestic wastewater under an arid climate
.
Journal of Water Process Engineering
51
,
103482
.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/).

Supplementary data