Efficiency of Suspended Activated Sludge System in Biological Removal of Phthalic Acid

Background & Objective: Phthalic acid is one of the toxic organic contaminats which can enter the environment through various industries. Biological removal of this pollutant before disposing the wastewater plays an important role for environmental protection and human health. This study is aimed to achieve the efficiency of suspended activated sludge system in biological removal of domestic and industrial wastewater contaminants. The variables of concentration and hydraulic retention time were studied to gain the best allowed volumetric loading time and hydraulic retention time.

Materials & Methods:  In this descriptive-analytic research 144 effluents and 23 sludge samples were studied. In this system for biological elimination of phthalic acid, four different hydraulic retention times of 6, 12, 24 and 48 hrs were used. The volumes of aeration and setteling were 6 and 3 liters respectively and total COD feed has been adjusted to 1000 mg/l along with Glucose. The concentrations of inlet phthalic acid were 10, 20, 50 and 500 mgl. COD , BOD₅ and phthalic acid concentrations (using HPLC- UV with wave length of 210 nm) have been measured in effluent. For analysing the data, variant analysis, Cheffe test and Pearson’s coefficient of correalation were used.

Results: In all four retention times phthalic acid was removed. The average phthalic acid removal in hydraulic retention times of 6, 12, 24 and 48 hrs with 10-500 mg/l inlet concentration were 87.5±10.5, 97.5±2.6, 99.6±0.3 and 99.8±0.03 percent respectively. The average COD removal were 88.6±11.6 , 95.5±3, 97.4±0.88 and 98±0.5 percent respectively. The rate of phthalic acid in sludge and the inlet phthalic acid viscosity were 100-320 mg/kg.

Discussion: This system has the ability to tolerate the phthalic acid in hydraulic retention times with different inlet concentration. The average removal of phthalic acid and COD in 24 and 48 hrs retention times are more stable. There was a meaningful relationship between removal rate of phthalic acid and COD with retention times. There was a complete reversed and meaningful relationship between the increase of inlet phthalic acid concentration and the removal rate of these parameters. If the concentration of inlet phthalic acid is less than 50mg/l., the 12hrs retention time is recommended but for over 50 mg/l, 24 hrs retention time is suggested. Allowed volumetric loading rates for 6, 12 and 24 hrs were 80, 100 and 500 g/m³d. The sludge of this system has high adsorption ability of phthalic acid.