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Abstract
Biological treatment of domestic wastewater using constructed wetlands is gaining acceptance worldwide due to low cost and simple operation and maintenance. Previous studies showed that long treatment beds are more efficient than short beds in the elimination of nutrients and pathogens from secondary treated domestic wastewater. A biological wastewater treatment system (BIOWATSYST) was established in Abu-Attwa Experimental Station, Ismailia, Egypt. The system was designed to examine the treatment performance of short-deep beds as alternatives to long beds using standard physicochemical and microbiological parameters. The role of somatic coliphage as pollution indicator was examined in correlation with various classical indicators such as total coliforms, fecal coliforms and fecal enterococci. On the other hand, the role of bacteriophages against Escherichia coli, Salmonella, Shigella, Vibrio and Pseudomonas were investigated in order to establish a possible natural defense line in short-deep beds which could be used in the elimination of pathogenic bacteria from domestic wastewater.
Removal efficiency for both biochemical and chemical oxygen demand was about 70 %, that for total suspended solids and organic matter was about 45 %, 15 % for total nitrogen and 8 % for total phosphorus. Removal efficiency from primary-treated domestic wastewater for pathogenic bacteria and coliphages was 45 - 60 %.
The plant species was a factor that may slightly affect the treatment process and Phragmites beds had slightly better efficacy than Papyrus beds. In contrary, the bed filling materials were more effective in the treatment processes. The highest percentage removal of all parameters except total phosphorus were observed in the sand bed. Also, the depth of filling materials affected the treatment process.
High correlation between somatic coliphages and either bacterial indicators or pathogenic bacteria were found in the system, which may suggest the role of somatic coliphages as alternative indicators of wastewater treatment.
Regarding the role of bacteriophage in the elimination of bacterial pathogens from secondary treated domestic wastewater, it was found that various phages with different diameters have various activities against E. coli [NRRL B-3704]. Moreover, mixing two morphologically different phages together gave far more phage counts than either of them alone, which show the synergistic effect of mixed phages. The percentage removal of E. coli using the bacteriophage suspension was 37 % during 24 hours.