Evaluation of the Efficiency of Wastewater Treatment Plants in Taiz City and their Suitability for Irrigation

Abstract A field study was carried out for influent and effluent wastewater from Two treatment plants in Taiz city. The aim of the study is to evaluate and increase the efficiency of the treatment plants in Al-Buriahy and Nadfood factories (Al-Qurf), in order to ensure the safe and suitable use of wastewater for irrigation. Four samples of sewage were collected from influent and effluent of different locations within the areas of Al-Qurf, Al-Hawjlah, Hidran Al-Dabab and Al-Buraihy. The results of the chemical analysis showed that the samples of the partially treated wastewater compared with the untreated wastewater were higher in total dissolved solids. The values of the trace elements remained at the level of the sewage influent before and after the treatment plant in Al-Buraihy, the level of treatment did not decrease the concentration of a number of these elements. The results of the study indicate that the concentration of Biochemical Oxygen Demand (BOD5) for effluent wastewater from the treatment plants recorded a significant decrease in their values. In contrast the results were close in the concentration of the BOD5 influent from the treatment plant in Al-Buraihy with the BOD5 concentration effluent from the treatment plant in the Nadfood has, reached 457mg/l, because the influent of the sewage from the industrial processes in the treatment plant of the Nadfood was too high, reaching an average of 7791 mg / l compared with 553 mg / l in the municipal influent sewage at the treatment plant in Al-Buraihy. The results of bacteriological analyses showed that the treated wastewater recorded a significant reduction in the number of fecal coliform compared with the number of fecal coliform at influent from treatment plant at Al-Buraihy area.These indications for treatment in wastewater stabilization ponds in Al-Buraihy, and treatment  plant for industrial wastewater, that include the aeration and sedimentation units in Al-Qurf Nadfood factories, indicate that the degree of treatment is below the required level and still exceeds the limit allowed for irrigation purposes according to Yemeni and International standards. This suggests an action of rehabilitation of existing sewerage system, completion of the sewerage network and the establishment of the new treatment plant by using stabilization ponds with floating surface aerator in the facultative ponds at north of Taiz City. In addition, increase the efficiency of the current treatment plant by division of wastewater stabilization ponds in Al-Buraihy, into anaerobic, facultative and maturation ponds, providing each pond with two devices/tools to measure the flows, and the  establishment of the new treatment plant at the Nadfood factories. It should consist of screening, oil /fat removal, primary and secondary clarifiers, high rate trickling filters (1st and 2nd stage), sludge digester, sand drying beds, and chlorination. Keywords: Taiz city, sewage, biochemical oxygen demand, fecal coliform,treatment plant, efficiency, municipal, industrial.