Study on Treating Sewage Age Using Gravel Beds And Natural Vegetation

Human Activities result in the generation of wastewater that needs careful management in order to preserve the surrounding environment from pollution Several treatment processes are commonly used to provide adequate treatment for municipal wastewater ( sewage ) including natural systems and mechanically operated systems .Mechanically operated systems are encountered in congested areas while natural systems can be applied where available lands and smaller communities are encountered offering less operation and maintenance costs .Constructed wetlands have been widely used worldwide for treatment of various types of wastewater including domestic ,industrial and agriculture and storm water drainage enabling high contaminants removal efficiency .In thus study a pilot constructed wetland –subsurface flow type – was used to investigate the efficiency of the process in the Egyptian environment for treating domestic wastewater subjected to primary treatment (settling ).The study was conducted on both long / shallow beds and short /deep beds planted with phragmites australis in addition to using control beds to evaluate the effect of the different components on contaminants removal .The experimental runs included variable influent flow rates (from 20 l/min to 35 l min )by operating the system 16 to 20 hours /day .The study showed that the gravel beds plants with the natural vegetation can successfully remove the following contaminants up to the percentages quoted adjacent to each of them :BOD5 (89 %),TSS ( 96% ),NH3 –N (64%0 and Po4 (88% ).The control bed without vegetation removed the studied contaminants at the following rates :BOD5 (66% ) TSS (86%) NH3 –N (32%) and PO4 (39% ) .The effect of natural vegetation in contaminants removal was noted in the increased value of DO in treated effluent ( from nil to 6.12 mg/l )as the plants provide oxygen from the atmosphere to the root zone and the increase in effluent nitrate concentration .In addition ,the plants provide an additional filtering effect at the root zone thus enhancing the removal of fine suspended solids and colloidal organic matter .