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Methanol induced biological nutrient removal in a full-scale sequencing batch reactor Louzeiro, Nuno

Abstract

The primary goal of this research was to determine the potential for denitrification and phosphorus removal of a full-scale SBR, with and without the use of methanol as an external carbon source. This study was conducted at the Kent Wastewater Treatment Plant, in Agassiz, British Columbia, Canada, which has two SBRs working in parallel; one SBR was used as a control, and the other was used for the experiment. Methanol was fed into the experimental SBR during the anoxic cycle to achieve approximate concentrations of 4.1, 8.1, and 12.2 mg CH₃OH/L. Each dosage was applied for a one-month period. The full-scale control SBR, without methanol addition, achieved negligible denitrification rates. However, two denitrification rates were observed in the full-scale experimental SBR, with methanol addition; an initial fast rate and a slower second rate. Methanol was utilized as the carbon source for denitrification during the first rate period. The denitrification rate (K[sub DN], mg NO[sub x]/g MLVSS/day) during this period increased with increasing methanol concentration (M, mg CH₃OH/L) according to the following relationship: K[sub DN] =-0.203•M² + 3.93•M, until a maximum denitrification rate of approximately 19 mg NOx/g MLVSS/day was attained. Following the depletion of the methanol, denitrification reactions continued by using the available natural carbon in the influent, resulting in a slower second denitrification rate. Biological phosphate uptake and release was only observed to a significant extent in the experimental SBR with methanol addition. The phosphate release, which commenced once a very low nitrate concentration was achieved, had a rate of approximately 2.7 mg P/g MLVSS/day and was likely caused by a supply of natural short chain carbon in the influent wastewater. Methanol was not utilized to a significant extent as the carbon source for the enhanced biological phosphorus removal (EBPR) process. However, methanol addition was critical to the EBPR process, since it depleted the available nitrates, and, thus, allowed EBPR to take place. It was demonstrated during the full-scale study that the settleability was linearly related to the denitrification rate. The average total change in the ORP, during a four-hour SBR cycle, was also linearly related to the denitrification rate.

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