Improvement of MBBR-MBR Performance by the Addition of Commercial and 3D-Printed Biocarriers

Moving bed biofilm reactor combined with membrane bioreactor (MBBR-MBR) constitute a highly effective wastewater treatment technology. The aim of this research work was to study the effect of commercial K1 biocarriers (MBBR-MBR K1 unit) and 3D-printed biocarriers fabricated from 13X and Halloysite (MBBR-MBR 13X-H unit), on the efficiency and the fouling rate of an MBBR-MBR unit during wastewater treatment. Various physicochemical parameters and trans-membrane pressure were measured. It was observed that in the MBBR-MBR K1 unit, membrane filtration improved reaching total membrane fouling at 43d, while in the MBBR-MBR 13X-H and in the control MBBR-MBR total fouling took place at about 32d. This is attributed to the large production of soluble microbial products (SMP) in the MBBR-MBR 13X-H, which resulted from a large amount of biofilm created in the 13X-H biocarriers. An optimal biodegradation of the organic load was concluded, and nitrification and denitrification processes were improved at the MBBR-MBR K1 and MBBR-MBR 13X-H units. The dry mass produced on the 13X-H biocarriers ranged at 4980-5711 mg, three orders of magnitude larger than that produced on the K1, which ranged at 2.9-4.6 mg. Finally, it was observed that mostly extracellular polymeric substances were produced in the biofilm of K1 biocarriers while in 13X-H mostly SMP.

Membrane Fouling Controlled by Adjustment of Biological Treatment Parameters in Step-Aerating MBR

A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the direction of improvement of the membrane filtration. In this work, these parameters were investigated in a step-aerating pilot MBR that treated municipal wastewater, in order to control the filamentous population. When F/M loading in the first aeration tank (AT₁) was ≤0.65 ± 0.2 g COD/g MLSS/d at 20 ± 3 °C, DO = 2.5 ± 0.1 mg/L and HRT = 1.6 h, the filamentous bacteria were controlled effectively at a moderate filament index of 1.5-3. The moderate population of filamentous bacteria improved the membrane performance, leading to low transmembrane pressure (TMP) at values ≤ 2 kPa for a great period, while at the control MBR the TMP gradually increased reaching 14 kPa. Soluble microbial products (SMP), were also maintained at low concentrations, contributing additionally to the reduction of ΤΜP. Finally, the step-aerating MBR process and the selected imposed operating conditions of HRT, F/M and DO improved the MBR performance in terms of fouling control, facilitating its future wider application.

LCA of a Membrane Bioreactor Compared to Activated Sludge System for Municipal Wastewater Treatment

Membrane bioreactor (MBR) systems are connected to several advantages compared to the conventional activated sludge (CAS) units. This work aims to the examination of the life cycle environmental impact of an MBR against a CAS unit when treating municipal wastewater with similar influent loading (BOD = 400 mg/L) and giving similar high-quality effluent (BOD < 5 mg/L). The MBR unit contained a denitrification, an aeration and a membrane tank, whereas the CAS unit included an equalization, a denitrification, a nitrification, a sedimentation, a mixing, a flocculation tank and a drum filter. Several impact categories factors were calculated by implementing the Life Cycle Assessment (LCA) methodology, including acidification potential, eutrophication potential, global warming potential (GWP), ozone depletion potential and photochemical ozone creation potential of the plants throughout their life cycle. Real data from two wastewater treatment plants were used. The research focused on two parameters which constitute the main differences between the two treatment plants: The excess sludge removal life cycle contribution—where GWP_MBR = 0.50 kg CO₂-eq*FU⁻¹ and GWP_CAS = 2.67 kg CO₂-eq*FU⁻¹ without sludge removal—and the wastewater treatment plant life cycle contribution—where GWP_MBR = 0.002 kg CO₂-eq*FU⁻¹ and GWP_CAS = 0.14 kg CO₂-eq*FU⁻¹ without land area contribution. Finally, in all the examined cases the environmental superiority of the MBR process was found.

Evaluation of a novel quorum quenching strain for MBR biofouling mitigation

Membrane biofouling, due to Soluble Microbial Products (SMP) and Extracellular Polymeric Substances (EPS) deposition, results in reduction of the performance of Membrane Bioreactors (MBRs). However, recently, a new method of biofouling control has been developed, utilizing the interference of the bacterial inter- and intra-species' communication. Bacteria use Quorum Sensing (QS) to regulate the production of SMP and EPS. Therefore, disruption of Quorum Sensing (Quorum Quenching: QQ), by enzymes or microorganisms, may be a simple mean to control membrane biofouling. In the present study, a novel QQ-bacterium, namely Lactobacillus sp. SBR04MA, was isolated from municipal wastewater sludge and its ability to mitigate biofouling was evaluated by monitoring the changes in critical flux and transmembrane pressure, along with the production of EPS and SMP, in a lab-scale MBR system treating synthetic wastewater. Lactobacillus sp. SBR04MA showed great potential for biofouling control, which was evidenced by the ∼3-fold increase in critical flux (8.3 → 24.25 L/m²/h), as well as by reduction of the SMP and EPS production, which was lower during the QQ-period when compared against the control period. Furthermore, the addition of the QQ-strain did not affect the COD removal rate. Results suggested that Lactobacillus sp. SBR04MA represents a novel and promising strain for biofouling mitigation and enhancement of MBRs performance.