Process Design for Advanced Biological Treatment of Petrochemical Wastewater

Abstract

Petrochemical industry produces a wide variety of chemicals, which include both organic and inorganic compounds. Petrochemical plants generate wastewater containing various conventional pollutants as well as specific petrochemical constituents like aromatics, phenolics, cyanides, sulphides, fluorides, halogenated compounds, polycyclic hydrocarbons and detergents etc., many of which are potentially toxic and carcinogenic besides being explosive and corrosive. Since the project will be on advance biological treatment of wastewater having high COD and turbidity from a specific polymer stream of plant, initially analytical studies on determination on Polyvinly alcohol (PVA) and Nonyl phenol (NP) was undergone. Later, enrichment of already available acclimatized cultures capable of degrading PVA & NP was carried out & and a Submerged Aerated Biofilter Column (SAB) was set up. Two columns were set up one with mixed culture S1, S2, S3, S4, S5 & S7 and another with mixed culture S2 & S7 (from shake flask study it showed better degradation). Synthetic water containing PVA 200 ppm, 100 ppm, NP 30 ppm, was treated at air flowrates of 100 and 200 mL/min and Water flowrates of 0.8 and 1.6 mL/min. The results indicate that with synthetic wastewater optimum conditions are pH 6.5-8.5 , DO approx 6.5, Water flowrate 0.8 mL/min for COD ranging 250-500 ppm, PVA concentration ≤ 200 ppm, NP concentration 30 ppm and Air flowrate 100 mL/min (No change at higher flowrate). Based on the results obtained with synthetic wastewater, a petrochemical (polymer manufacturing) wastewater stream having significant concentrations of COD (250 ppm), Turbidity (200-250 NTU), PVA (<30 ppm) and NP (4 ppm) was taken for SAF study. Its Conductivity was 150-160 uS, DO 6.5 and pH 6.5-8.5. The Total Solids was 250-350 ppm, TSS, 60-70 ppm and TDS, 200-300 ppm. Experiments were carried out at different flowrates (0.8 mL/min, 1.2 mL/min and 1.6 mL/min).Best result was obtained at 1.2 mL/min flowrate and in column having mixed culture S1, S2, S3, S4, S6 & S7 which shows COD 82%, Turbidity 87%, PVA 88%, NP 88% reduction. And column is running continuously since 8 months. Initial and final colony characteristics of microbial cultures were studied and microbial loading was calculated. Mechanical integrity & strength of used GAC, even after 8 months of study, have not changed much from fresh GAC. Design of the reactor was calculated for the petrochemical wastewater stream studied. Further study was performed with 40% petrochemical wastewater stream having color and 60% petrochemical wastewater stream having PVA and NP which I have used in this experiment. But clogging was occurring in the SAF columns. Hence another treatment must be added prior to SAF to avoid clogging and to get effective reduction in COD and Turbidity. Wastewater having color can be removed preliminary by Fenton oxidation experiments and carried by GAC adsorption and biofilteration.