Influence of Temperature and pH on Short-term Biochemical Oxygen Demand (BODst) Estimation

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Piyarat Premanoch
Patikon Saensing

Abstract

This research aims to study the influence of temperature and pH on short-term Biochemical Oxygen Demand (BODst) by measuring an oxygen uptake rate of activated sludge sample (microbe) taken from a return sludge pipe in an oxidation ditch at Maharaj Hospital, Nakhon Ratchasima Province, Thailand. The experiment was conducted by filtering solid materials and aerating sludge for not less than 12 hours without adding any substrates for sludge to enter the endogenous respiration condition. 20 mg/mL (13 mg COD/mL) of sodium acetate was used as a readily biodegradable COD substrate (rbCOD) and dosed to 2.2 liters of sludge sample. Final COD concentration was between 3.0 - 33.9 mg COD/L. Temperature, pH, oxygen and oxygen uptake rate were recorded every 3 seconds using an ultimate hybrid respirometer. Two experimental conditions were conducted, including uncontrolled and controlled conditions. The controlled experiment was conducted at 20, 25 and 30OC (± 0.5 OC) and pH was adjusted to 7.8±0.1 using NaOH 0.05N and HCl 0.05 N, while the uncontrolled experiment was conducted in the range between 25.6-27.6 ° C and pH was adjusted to 7.0-9.6.


The experimental results showed the linear relationship between BODst and COD substrate concentration for each sample of both conditions. The slope of the uncontrolled system was equal to 0.37 (r2 = 0.9917) while for the controlled system, the average slope was equal to 0.31 (r2 = 0.9950). Furthermore, it was also found that when temperature increases, the experimental duration was shorter from 9.7 minutes (20 OC) to 7.0 minutes (30OC) when COD concentration was 5.3 mg/L. Furthermore, the research results showed that temperature does not affect the estimated accuracy of BODst at a temperature range of 20 - 30 OC, which covers increasing temperature of wastewater throughout the year, while pH has a direct effect. Obviously, the findings of this research would be highly beneficial to develop a  hybrid respirator system that can be used to analyze BODst of wastewater and effluent in the activated sludge wastewater treatment system for practical operations in plants, which is called the BOD on-line Analyzer.

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References

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