Upgrade of a petrochemical wastewater treatment plant by an upflow anaerobic pond

Abstract

A petrochemical plant producing terephthalic acid faced a saturation of its wastewater treatment facilities due to an increase in production. In fact, the plant has been growing in the last years, and the effluents have been treated by reproducing the original activated sludge design. However, due to lack of space, as well as energy consumption and sludge production reaching a certain level, the plant considered other options for coping with the new effluent flow and organic load. Based on the authors' previous experience with this wastewater, the consultant designed a process consisting in modifying an existing pond, in order to add an anaerobic step previous to the aerobic tanks already in operation. The anaerobic pond is a three stage process, all included in the same adapted basin, with a distribution system in the bottom of each stage that creates an upflow pattern. Terephthalic acid wastewater is a mixture of several organic acids, with different anaerobic degradation kinetics, acetic and benzoic acids being more rapidly removed; the staged design takes this into account. The first two stages have a plastic floating cover (5,813 m 3 and 8,719 m 3 volume, respectively), while the third one is a conventional UASB type reactor (6,276 m 3 volume) with a gas-liquid-solid separation device on top. The design wastewater flow is 230 m 3 /h, with 10,300 mg/l COD, a pH of 4.5 and a temperature of 40 0 C. There is an effluent recycling pump (510 m 3 /h) in order to control upflow velocities and eventual acidification problems in the first two stages. The reactor, seeded with anaerobically adapted waste sludge from the aerobic plant, is now under start up, with the expected performance.

Microbial Community Involved in Anaerobic Purified Terephthalic Acid Treatment Process

“…Thus, to complement the high global demand for PTA synthesis, it is necessary to effectively treat the by-products and residues generated from PTA manufacturing processes. Aerobic biological processes were initially applied to remediate PTA wastewater (Lau 1977;Noyola et al 2000) due to their efficient chemical oxygen demand (COD) removal. However, known potential disadvantages are long hydraulic retention time, high aeration requirement, large site area requirement, excess sludge production, and poor biomass settling property due to 'sludge bulking' or overgrowth of filamentous bacteria (Noyola et al 2000;Razo-Flores et al 2006).…”

“…Aerobic biological processes were initially applied to remediate PTA wastewater (Lau 1977;Noyola et al 2000) due to their efficient chemical oxygen demand (COD) removal. However, known potential disadvantages are long hydraulic retention time, high aeration requirement, large site area requirement, excess sludge production, and poor biomass settling property due to 'sludge bulking' or overgrowth of filamentous bacteria (Noyola et al 2000;Razo-Flores et al 2006). To overcome these obstacles, BP-Amoco has developed anaerobic treatment systems under mesophilic conditions (35 o C) and achieved over 80-85% reduction in COD in the late 1980s (Razo-Flores et al 2006).…”