Department of Environmental Engineering and Water Technology, IHE Delft Institute for Water Education, Westvest 7, 2611AX, Delft, The Netherlands.
Department of Biotechnology, Delft University of Technology, Van der Maasweg 9, 2629, HZ, Delft, The Netherlands.
Environ Sci Pollut Res Int. 2019 Nov;26(33):34285-34300. doi: 10.1007/s11356-019-04369-x. Epub 2019 Feb 8.
The operation of membrane bioreactors (MBRs) at higher than usual mixed liquor suspended solids (MLSS) concentrations may enhance the loading rate treatment capacity while minimizing even further the system's footprint. This requires operating the MBR at the highest possible MLSS concentration and biomass activity (e.g., at high loading rates and low solid retention times (SRTs)). Both a negative effect of the MLSS concentrations and a positive effect of the SRT on the oxygen transfer have been reported when using conventional fine bubble diffusers. However, most of the evaluations have been carried out either at extremely high SRTs or at low MLSS concentrations eventually underestimating the effects of the MLSS concentration on the oxygen transfer. This research evaluated the current limitations imposed by fine bubble diffusers in the context of the high-loaded MBR (HL-MBR) (i.e., high MLSS and short SRT-the latter emulated by concentrating municipal sludge from a wastewater treatment plant (WWTP) operated at a short SRT of approximately 5 days). The high MLSS concentrations and the short SRT of the original municipal sludge induced a large fraction of mixed liquor volatile suspended solids (MLVSS) in the sludge, promoting a large amount of sludge flocs that eventually accumulated on the surface of the bubbles and reduced the free water content of the suspension. Moreover, the short SRTs at which the original municipal sludge was obtained eventually appear to have promoted the accumulation of surfactants in the sludge mixture. This combination exhibited a detrimental effect on the oxygen transfer. Fine bubble diffusers limit the maximum MLSS concentration for a HL-MBR at 30 g L; beyond that point is either not technically or not economically feasible to operate; an optimum MLSS concentration of 20 g L is suggested to maximize the treatment capacity while minimizing the system's footprint.
膜生物反应器 (MBR) 在高于通常的混合液悬浮固体 (MLSS) 浓度下运行，可能会提高负荷处理能力，同时进一步最小化系统的占地面积。这需要将 MBR 操作在尽可能高的 MLSS 浓度和生物量活性（例如，在高负荷和低固体停留时间 (SRT) 下）。当使用传统的微孔曝气器时，已经报道了 MLSS 浓度对氧转移的负面影响和 SRT 的积极影响。然而，大多数评估要么在极高的 SRT 下进行，要么在最终低估 MLSS 浓度对氧转移影响的低 MLSS 浓度下进行。本研究评估了微孔曝气器在高负荷 MBR (HL-MBR) 中的当前限制（即高 MLSS 和短 SRT-后者通过浓缩来自污水处理厂的城市污泥来模拟，该污水处理厂的 SRT 约为 5 天）。原始城市污泥的高 MLSS 浓度和短 SRT 导致污泥中混合液挥发性悬浮固体 (MLVSS) 的很大一部分，促进了大量的污泥絮体，最终在气泡表面积累并降低了悬浮液的自由水含量。此外，原始城市污泥获得的短 SRT 似乎促进了污泥混合物中表面活性剂的积累。这种组合对氧转移表现出不利影响。微孔曝气器将 HL-MBR 的最大 MLSS 浓度限制在 30 g/L；超过该点，在技术上或经济上都不可行；建议采用 20 g/L 的最佳 MLSS 浓度，以最大限度地提高处理能力，同时最小化系统的占地面积。
