Performance of Sequencing Batch Reactor Treating Sewage Using Two Stage Anoxic Aerobic

Sequencing batch reactor technology (SBR) is an increasingly popular reactor configuration because of flexibility of operation in the treatment of domestic wastewater. However, the combined two stage anoxic-aerobic for further nitrogen removal has not been explored further. This study aims to determine the performance efficiency of two-stage anoxic-aerobic using sequencing batch reactor. 10 L of SBR reactor was operated twice daily. The system was operated on a 500 minutes cycle with 10 minutes of feeding, 300 minutes for reacting, 60 minutes of sedimentation, 10 minutes of decanting and 120 minutes for an idle period. Effluent quality (chemical oxygen demand (COD), ammoniacal nitrogen (NH4–N), total suspended solids (TSS)), particle size and sludge settleability have been analyzed over a period of 35 days of operation. Results shows that the overall efficiencies for COD, TSS and NH4–N were 93.8%, 98.4 % and 85.9%, respectively. In the lab scale SBR reactor unit, the 2 h anoxic/1.5 h aerobic period resulted in good process performance with COD, NH4–N and TSS removal of 66.0%, 78.5% and 59.4 %, respectively. Increasing the length of anoxic up to 1 h did not enhance the NH4–N removal with 4.5% in anoxic phase and 7.2% in aerobic phase. Sludge settleability became poorer as the ciliate species becomes rich. The particle size of the sludge was observed to increase from 117.743 μm to 127.310 μm. It is recommended that the duration of combined anoxic/aerobic periods should be optimized to achieve maximum performance and nutrient removal.

PERFORMANCE OF INTEGRATED TWO STAGE ANOXIC-AEROBIC SEQUENCING BATCH REACTOR IN THE TREATMENT OF SEWAGE

A 10 L SBR reactor was operated on a two cycles per day with total cycle time of 500 minutes. This study explored the impact of a 300 minute react period with alternating two stage anoxic-aerobic phases starting at 120 minutes to 30 minutes on effluent quality, sludge settleability and particle size distribution.The overall removal efficiencies for COD, TSS and NH4-N were 93.8%, 98.4 % and 85.9%, respectively. The results indicated a good process performance with the first 2h anoxic/1.5 h aerobic period with removals of 66.0%, 78.5% and 59.4 % for COD, NH4-N and TSS removal respectively.The NH4-N removal was not enhanced although the anoxic period was lengthened by 1 h with low removal of 4.5 % and subsequent 7.2% of the second aerobic phase. There was an increase in the particle size of the sludge from 117.743μm to 127.310μm over an operating period of 35 days.

Effect of Aluminium Salt Dosing on Activated Sludge Settleability Indicators: A New Settleability Model Development

There has been a significant rise in the use of aluminium salts (Al3+) for the chemical precipitation of phosphates in wastewater treatment plants due to growing stricter regulatory requirements for wastewater effluent release to the environment. The modelling of the settleability of the resultant Al3+ sludge in present engineering practice for design and optimisation are still based on conventional sludge settleability models. This paper describes a novel activated sludge settleability model which is designed to analyse the effects of Al3+ dosing on activated sludge settleability indicators, zone settling velocity (ZSV), and stirred specific volume index (SSVI). The impact of Al3+ dosing concentrations on ZSV and SSVI of full scale activated sludge plant were analysed in the laboratory over a three years’ period and the exponential form of the Vesilind equation was optimised and validated to include alum chemical dosing parameters. The proposed model equation was found to effectively describe the settleability of Al3+ dosed sludge for dosing concentrations range of 0 to 100 mg/L.