Impact of primary sedimentation tank on wastewater treatment plant units using computer simulation program

Abstract

This study presents a computer program designed in Visual Basic 6 program. The capability of this program is to design wastewater treatment plant units and determination of its construction cost. The program deals with two types of wasted sludge the first type is wasted sludge from the aeration basin, while the second system is wasted sludge from the secondary clarifier. Also, there is a detailed output shows the design flowrate, mass balance analysis and composition of each stream in and out of each treatment unit. Program results are verified with hand calculations within the allowable recommended values and they showed a good accuracy. The volume of aeration basin and secondary sedimentation tank increased with the elimination of primary sedimentation tank from the design of the wastewater treatment plant. Generally, an increment of about (52-170) % for aeration basins and (58-185) % for secondary sedimentation tanks are observed in the present study. From other hand, gravity thickener volume is decreased by (29-42) %, anaerobic digester volume is decreased about (38-52) % and drying beds is decreased by (29-38) % approximately. The cost analysis showed that the cost of a wastewater treatment plant is increased after a certain amount of influent. That amount is nearly (36,708.33) m 3 /d when wasted sludge is taken from aeration basin and (24,833.33) m3/d when wasted sludge is taken from secondary clarifier.