The optimal MBR configuration: hybrid versus stand-alone - comparison between three full-scale MBRs treating municipal wastewater

Construction or modernization of a wastewater treatment plant (WWTP) with membrane bioreactor (MBR) technology requires the selection of an optimal configuration and design. The objective of this paper is to evaluate a stand-alone MBR in comparison to a hybrid MBR, i.e., a combination of a conventional activated sludge (CAS) process and an MBR. This paper evaluates two different hybrid MBR configurations, i.e., in series and in parallel, and a stand-alone MBR. The impact of these MBR configurations on operation, performance, energy consumption and economy is evaluated. A hybrid MBR operated in series provides certain operational flexibility, ensures more stable conditions for the activated sludge leading to a more stable MBR operation at energy and cost efficient conditions. Nevertheless, determination of the optimal plant configuration depends on the particular local situation such as the presence and condition of old infrastructure, availability of equalization tanks and space requirement. © 2011 Elsevier B.V..status: publishe

The influence of solids retention time on activated sludge bioflocculation and membrane fouling in a membrane bioreactor (MBR)

Membrane fouling remains a significant drawback for membrane bioreactors (MBRs). The solids retention time (SRT) has been widely acknowledged to be an important factor influencing membrane fouling. In general, lower membrane fouling rates are observed at elevated SRTs, however, the direct mechanisms through which a high SRT alleviates fouling are unclear. Since it has also been reported that activated sludge bioflocculation is an important factor in membrane fouling, this paper studies the impact of SRT on bioflocculation with respect to membrane fouling. A pilot-scale MBR was operated for more than two years at three different SRTs during which bioflocculation was closely monitored by means of an automated image analysis procedure while the fouling rate was recorded on-line for different fluxes and different filtration/relaxation cycles. In addition, the Delft filtration characterization method (DFC m) was employed to assess the activated sludge fouling propensity. Based on these data, it is shown that stable operation of a membrane bioreactor requires a good activated sludge condition and that bioflocculation is a crucial factor within that context. In the tested SRT range (10-30-50 days), a higher SRT contributes to better activated sludge bioflocculation and as a consequence, to lower fouling rates. © 2012 Elsevier B.V.status: publishe

Activated sludge characteristics affecting sludge filterability in municipal and industrial MBRs: unraveling correlations using multi-component regression analysis

In the field of membrane bioreactors (MBRs) many membrane fouling related questions still remain unanswered. The goal of this research is to unveil some of the black-box features of activated sludge filterability by correlating the results from activated sludge filterability measurements following the Delft Filtration Characterization method (DFCm) with a large set of activated sludge characteristics. Ten different MBRs in Belgium and the Netherlands were sampled in both winter and summer. All samples were subjected to the DFCm, automated image analysis and an extensive set of standardized measurements. No clear correlation could be found between a single sludge parameter and activated sludge filterability. However, a combination of sludge morphology and relative hydrophobicity (RH) allows for a clear classification of activated sludge into two classes, i.e., bad and poor to good, implying that deflocculation and a low RH have a negative impact on activated sludge filterability. Furthermore, for sludge samples having poor to good filterability, accurate estimations of sludge filterability can be made when including more parameters. The main conclusion is that filterability can be predicted by analyzing the bioflocculation state of the activated sludge. © 2011 Elsevier B.V.status: publishe

Microfiltration of pretreated sanitary landfill leachate

A laboratory study using a bench scale model of two units operation involving coagulation process with Moringa oleifera seeds extract as a coagulant and filtration process using hollow fibre microfiltration membrane, was adopted to treat Air Hitam Sanitary Landfill leachate in Puchong, Malaysia. The performance of the microfiltration membrane in pretreated sanitary landfill leachate treatment was investigated through a continuous process. The leachate sample was passed through conventional coagulation process before being filtered through a hollow fibre microfiltration membrane of 0.1 µm surface pores. The hollow fibre microfiltration membrane decreased the turbidity, colour, total suspended solids, total dissolved solids and volatile suspended solids in the leachate by 98.30, 90.30, 99.63, 14.71 and 20%, respectively. The results showed that microfiltration is capable of removing high percentage of solids from leachate and might be considered as a polishing stage after on-site biological treatment for sanitary landfill leachate