Lahbib Latrach

Removal of bacterial indicators and pathogens from domestic wastewater by the multi-soil-layering (MSL) system

Abstract This paper presents the performance and behavior of a multi-soil-layering (MSL) system to remove fecal contamination bacteria indicators and pathogens from domestic wastewater. The experimental setup was performed using a laboratory-scale MSL system (depth 30 × width 36 × height 65 cm). The MSL system was composed of soil mixture blocks (SMB) arranged in a brick-like pattern and surrounded by permeable gravel layers (PL). The SMB comprised sandy soil, charcoal, sawdust and metal iron at a dry weight ratio of 7:1:1:1. The hydraulic loading rate was 200 L m−2 day−1. Bacteriological analyses comprised total bacterial count at 22 and 37°C, fecal coliforms, total coliforms, Escherichia coli, streptococci, intestinal enterococci and pathogenic bacteria: Clostridium sp., Staphylococcus sp., Pseudomonas sp. and Salmonella sp. The best removal efficiency was achieved for Staphylococcus sp. by 1.42 log unit, while the lowest removal efficiency was found for E. coli by 1.01 log unit. The mean removal efficiencies of total suspended solids (SS), biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorous (TP) were 93, 86, 81, 78 and 80%, respectively. Based on these results, the MSL system could efficiently remove organic matter, phosphorus and nitrogen. However, the performance to reduce bacterial indicators and pathogens was still moderate.

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

This paper investigates the removal efficiency of organic matter, nitrogen, phosphorus, coliforms and pathogens from rural domestic wastewater in a two-stage vertical flow multi-soil-layering (MSL) system. The effects of wastewater quality, season and arid climate conditions on pollutants removal efficiency by the system were examined for one year. The experimental setup included two similar MSL systems composed of two layers: soil-mixture-layers (SML) and gravel permeable layers (PL) that are arranged in a brick like pattern. The applied hydraulic loading rate was 1000Lm-2day-1. Results showed that most of the physicochemical contaminants elimination occurred while the wastewater percolated through the first MSL stage. The second stage demonstrated an improvement in the reduction of all pollutants, especially fecal bacteria indicators and pathogens. The mean overall removal rates performed by the two-stage MSL system were 97% for TSS, 96% for BOD5, 91% for COD, 96% for TN and 95% for TP. For bacterial indicators, the combination of two-stage MSL system achieved high log removals between 2.21 and 3.15 log units. Contaminants reduction processes in MSL technology are more dependent on internal than external environmental factors. The effectiveness of the two-stage MSL system to treat domestic wastewater was strongly influenced by wastewater quality. Significant relationships between influent contaminants level and their removal efficiency were found. The efficiency of MSL technology to reduce contaminants is not sensitive to season and air temperature fluctuations. This is due to the capacity of MSL system materials to withstand the air temperature variation, which highlights one of the advantages of MSLs technology. Wastewater quality is the most important factor affecting the removal of contaminants in the MSL, which could be a critical parameter to considered when designing MSL system. Two-stage MSL system achieved a high treated wastewater quality amenable for treated wastewater reuse in agriculture recommended by Moroccan code of practice. Therefore, the combination of two-stage vertical flow MSL system could be considered an efficient and promising domestic wastewater treatment solution in arid countries to promote environmental protection and wastewater reuse.

Phytoremediation of domestic wastewater using a hybrid constructed wetlands in mountainous rural area

ABSTRACT The purpose of this study is to evaluate the efficiency of hybrid constructed wetlands (HCWs) in a rural mountainous area. The experiment was set up in small rural community named Tidili within the region of Marrakech, Morocco. The wastewater treatment plant was composed of three vertical flow constructed wetlands (VFCWs) working in parallel, followed by two parallel horizontal-subsurface flow constructed wetlands (HFCWs), with hydraulic loading rates of 0.5 and 0.75 m3/m2.d, respectively. The two units were planted with Phragmites australis at a density of 4 plants/m2. Wastewater samples were collected at the inlet of the storage tank and at the outlet of the whole system (VFCWs, HFCWs) stages. The main removal percentages of total suspended solids (TSS), biochemical oxygen demand measured in a 5-day test (BOD5), chemical oxygen demand (COD), total nitrogen, and total phosphorus were respectively 95%, 93%, 91%, 67%, and 62%. The system showed a very high capacity to remove total coliforms, fecal coliforms, and fecal streptococci (4.46, 4.31, and 4.10 Log units, respectively). Artificial neural networks (ANNs) were used to model the quality parameters (TSS, BOD5, COD) and total coliforms and fecal streptococci. Based on the obtained results, the ANN model could be considered as an efficient tool to predict the studied phytoremediation performances using HCWs.