Phenolic refinery wastewater biodegradation by an expanded granular sludge bed reactor

Area of Science:

• Environmental Engineering
• Biotechnology
• Wastewater Treatment

Background:

• Refinery spent caustics (SC) and sour waters (SW) contain hazardous aromatic compounds like phenol and cresols.
• Anaerobic digestion is a promising technology for treating industrial wastewater.
• The biodegradability and treatment efficiency of SC/SW mixtures in EGSB reactors require further investigation.

Purpose of the Study:

• To evaluate the anaerobic biodegradation of phenol and cresols from refinery wastewater in an EGSB reactor.
• To assess the impact of nutrient supplementation on COD removal efficiency and methane production.
• To determine the maximum organic load an EGSB reactor can handle before toxicity occurs.

Main Methods:

• Refinery spent caustics were diluted with sour waters and neutralized with CO2.
• The SC/SW(CO2) mixture was treated in an expanded granular sludge blanket (EGSB) reactor under anaerobic conditions.
• Experiments were conducted with and without mineral supplements, and organic loading rates were varied.
• Chemical Oxygen Demand (COD) removal, methane production, and biodegradation of phenol and cresols were monitored.

Main Results:

• Initial treatment without nutrients resulted in low COD removal (23%), no methane production, and no biodegradation of phenol or cresols.
• Addition of nutrients and phenol significantly improved COD removal efficiency, reaching 90% at 1.6 gCOD L(-1) d(-1).
• High concentrations of cresols exhibited toxicity, causing COD removal efficiency to drop to 23% at the highest load (1.87 gCOD L(-1) d(-1)).

Conclusions:

• Nutrient supplementation is essential for effective anaerobic treatment of refinery wastewater in EGSB reactors.
• EGSB reactors can achieve high COD removal efficiency for phenol and cresols when properly supplemented.
• Cresols present in refinery wastewater can exert toxic effects on the anaerobic digestion process at higher concentrations.