Assessing oxygen uptake rates in sewage treatment system / Jamaiatul Lailah Mohd Jais

Aerobic biological treatment of wastewater needs a sufficient supply of oxygen for it to proceed properly. Untreated wastewater if discharged into receiving waters would have a serious impact on the quality of the environment and a hazard to public health. The study assessed the oxygen uptake rate (OUR), which represents the consumption of dissolved oxygen over time of the biodegradation of organic substrates by microorganisms in the activated sludge treatment process, and its relationship with wastewater conditions, oxygen mass transfer and oxygenation efficiencies. Though OUR is a significant parameter for wastewater treatment process, very few relevant data are available to local wastewater treatment plants. Measurement of OUR was carried out by a respirometric method and the OUR values, determined by linear regression of the DO data points, has values ranging from 2.5 - 9.5 mg/L.h. The effects of wastewater conditions on the OUR profile showed a close and direct relationship with the dissolved oxygen content, the mixed-liquor volatile suspended solids and the biochemical oxidation demand loading, indicating that OUR can complement them as a control parameter in the activated sludge process, but OUR can be regarded as more superior since it is directly indicative of respiratory metabolic process by aerobic biomass. Aeration systems employing diffused-air and mechanical surface aeration systems were used for the assessment of transfer of atmospheric oxygen to the mixed liquor. The mass transfer coefficient for oxygen, ranging from 0.80 to 1.46 per hour for the aeration systems, were derived from the measured OUR values and incorporated into the field oxygen transfer rate for subsequent conversion into standard oxygen transfer rate (SOTR) which can serve as an important control parameter for the wastewater aeration process. The adequacies of oxygen supply for the wastewater treatment process by both the different aeration systems were assessed, and oxygenation efficiencies of the aeration systems for the diffusers and mechanical aerators vary from 1.12 to 1.26 and 1.06 to 1.19 kg02/kW.h respectively, indicating that energy consumption for the aeration process was optimal. The OUR measurement by respirometry was found to be simple and practical enough to be introduced for implementation into local wastewater treatment plants to monitor daily operational control, system performance and aeration efficiency. An on-line monitoring of OUR can have a potential for incorporation into larger local treatment plants already equipped with the Supervisory Control and Data Acquisition System for more efficient wastewater treatment process monitoring and management.