Response Surface Methodology for Optimization of Rotating Biological Contactor Combined With An External Membrane Filtration

A large amount of wastewater is directly discharged into water bodies without treatment causing surface water contamination. Conventional treatment techniques produce lower effluent quality and are energy extensive. Rotating biological contactor (RBC) is an attractive biological wastewater treatment that offers a low energy footprint. However, its unstable removal efficiency makes it less popular. This study optimizes operating parameters in RBC combined with external membrane filtration (RBC-ME) in which the latter acts as a post-treatment step to stabilize the biological performance. Response Surface Methodology (RSM) was employed to optimize the biological and filtration performance by exploiting three parameters of disk rotational speed, hydraulic retention time (HRT), and sludge retention time (SRT). Results show that RBC-ME exhibits excellent biological treatment capacity and higher effluent quality. It attained 87.9 ± 3.2% of chemical oxygen demand, 45.2 ± 0.7% total nitrogen, 97.9 ± 0.1% turbidity, and 98.9 ± 1.1% ammonium removals. The RSM data demonstrated that the experimental data and model predictions agreed well. Under the most optimum parameters, the permeability of 144.6 L/m2 h bar could be achieved at 36.1 rpm disk rotational speed, 18 h HRT, and 14.9 d SRT. This work demonstrates the effective use of statistical modeling to enhance RBC-ME system performance to obtain a sustainable and energy-efficient treatment process to prevent human health and the environment.

Membrane Filtration as Post-Treatment of Rotating Biological Contactor for Wastewater Treatment

A rotating biological contactor (RBC) offers a low energy footprint but suffers from performance instability, making it less popular for domestic wastewater treatment. This paper presents a study on an RBC integrated with membrane technology in which membrane filtration was used as a post-treatment step (RBC–ME) to achieve enhanced biological performance. The RBC and RBC–ME systems were operated under different hydraulic retention times (HRTs) of 12, 18, 24, and 48 h, and the effects of HRT on biological performance and effluent filterability were assessed. The results show that RBC–ME demonstrates superior biological performance than the standalone RBC. The RBC–ME bioreactor achieved 87.9 ± 3.2% of chemical oxygen demand (COD), 98.9 ± 1.1% ammonium, 45.2 ± 0.7% total nitrogen (TN), and 97.9 ± 0.1% turbidity removals. A comparison of the HRTs showed that COD and TN removal efficiency was the highest at 48 h, with 92.4 ± 2.4% and 48.6 ± 1.3% removal efficiencies, respectively. The longer HRTs also lead to better RBC effluent filterability. The steady-state permeability increased respectively by 2.4%, 9.5%, and 19.1% at HRTs of 18, 24, and 48 h, compared to 12 h. Our analysis of membrane fouling shows that fouling resistance decreased at higher HRTs. Overall, RBC–ME offered a promising alternative for traditional suspended growth processes with higher microbial activity and enhanced biological performance, which is in line with the requirements of sustainable development and environment-friendly treatment.

Energy consumption and performance of a rotating biological contactor treating high-strength wastewater

Clean water availability, energy costs and the environmental impact of energy usage are major concerns all over the world. At the same time, the Rotating Biological Contactor (RBC) has emerged as a low energy-consuming technology used in wastewater treatment which compares favorably with other treatment methods. RBC is a fixed-film bioreactor employing rotating discs to provide support medium for the microbial growth and to supply dissolved oxygen. RBCs, when applied in the treatment of high strength wastewater, demand some modifications such as the addition of aeration systems or change the flow configuration. Aeration systems certainly reduce the footprint but at the cost of energy consumption. Therefore, the optimization of energy consumption in a modified RBC is a very relevant research objective. This thesis is an investigation on energy optimization in a commercial scale RBC modified with an aeration system and treating high strength synthetic wastewater. The coarse bubble diffuser was replaced by fine bubble air diffusers. To study energy consumption a mono-block main drive system and the central compressed air supply were replaced by a three phase motor with variable frequency drive and an aeration blower respectively. Removal performance and unit energy consumption were studied at various combinations of rotating speed (2.5-5 RPM) and rate of aeration (0-15 SCFM). Constant hydraulic (0.017 m³/m²-day), organic (86.1 gCOD/m²-day) and ammonia (3.444 gNH₃-N/m²-day) loadings were maintained throughout the study. The modified RBC was able to remove 34 to 96% COD and 21 to 68% ammonia depending on the aeration rate and angular velocity. The suspended growth section of the modified RBC contributed 47 to 85% and 38 to 87% of the total removal of COD and ammonia respectively. Conversion of ammonia-nitrogen to nitrate-nitrogen was observed very negligible at 0.26 to 1.59%. The angular velocity, 3.66 RPM and the rate of aeration 8.13 SCFM, were found to be the optimum parameters to achieve minimum unit energy consumption of 1.31 KWH/kg CODr. A mathematical model correlating energy consumption per unit oxygen demand with the rate of aeration and the angular velocity was developed.

Energy consumption and performance of a rotating biological contactor treating high-strength wastewater

Clean water availability, energy costs and the environmental impact of energy usage are major concerns all over the world. At the same time, the Rotating Biological Contactor (RBC) has emerged as a low energy-consuming technology used in wastewater treatment which compares favorably with other treatment methods. RBC is a fixed-film bioreactor employing rotating discs to provide support medium for the microbial growth and to supply dissolved oxygen. RBCs, when applied in the treatment of high strength wastewater, demand some modifications such as the addition of aeration systems or change the flow configuration. Aeration systems certainly reduce the footprint but at the cost of energy consumption. Therefore, the optimization of energy consumption in a modified RBC is a very relevant research objective. This thesis is an investigation on energy optimization in a commercial scale RBC modified with an aeration system and treating high strength synthetic wastewater. The coarse bubble diffuser was replaced by fine bubble air diffusers. To study energy consumption a mono-block main drive system and the central compressed air supply were replaced by a three phase motor with variable frequency drive and an aeration blower respectively. Removal performance and unit energy consumption were studied at various combinations of rotating speed (2.5-5 RPM) and rate of aeration (0-15 SCFM). Constant hydraulic (0.017 m³/m²-day), organic (86.1 gCOD/m²-day) and ammonia (3.444 gNH₃-N/m²-day) loadings were maintained throughout the study. The modified RBC was able to remove 34 to 96% COD and 21 to 68% ammonia depending on the aeration rate and angular velocity. The suspended growth section of the modified RBC contributed 47 to 85% and 38 to 87% of the total removal of COD and ammonia respectively. Conversion of ammonia-nitrogen to nitrate-nitrogen was observed very negligible at 0.26 to 1.59%. The angular velocity, 3.66 RPM and the rate of aeration 8.13 SCFM, were found to be the optimum parameters to achieve minimum unit energy consumption of 1.31 KWH/kg CODr. A mathematical model correlating energy consumption per unit oxygen demand with the rate of aeration and the angular velocity was developed.