Role of Mesh Pore Size in Dynamic Membrane Bioreactors.

Two identical bench-scale Self-Forming Dynamic Membrane BioReactors (SFD MBR) were set-up and operated for the treatment of real urban wastewater. The two bioreactors were equipped with meshes of different mesh pore size. Meshes having pore size values of 20 and 50 µm were tested under solid retention time (SRT) of 15 d, whereas meshes with 50 and 100 µm pore sizes were compared under SRT of 50 d. The results of long-term experiments showed very good overall performances by all systems at the steady state. High flux (in the range 61-71 L m-2 h-1) and very good effluent quality were obtained, with average suspended solids and chemical oxygen demanding values below 10 mg L-1 and 35 mg L-1, respectively. The mesh pore size did not have a major influence on the average cleaning frequency. However, the pore size affected the effluent quality in correspondence of two particular conditions: (i) immediately after mesh cleaning; and (ii) during operation under high suction pressures (mesh clogging not promptly removed through cleaning). Moreover, the mesh cleaning frequency was observed to be dependent on the SRT. In tests with 50 d SRT, the cleaning requirements were very low (one every five days), and this limited the influence of the mesh pore size on the effluent quality. In conclusion, in SFD MBR, the role of the mesh pore size on the effluent quality may be more or less relevant depending on the operating conditions that directly influence the Dynamic Membrane formation.

Reuse of ultrafiltered effluents for crop irrigation: On-site flow cytometry unveiled microbial removal patterns across a full-scale tertiary treatment.

Reuse of treated wastewater for crop irrigation has been widely adopted to mitigate the effects of water scarcity on agricultural yields and to help preserving the integrity of aquatic ecosystems. This paper presents the outcomes of one-year monitoring of a full-scale agro-industrial wastewater treatment plant designed for water reuse, with a multistage tertiary treatment based on sand filtration, membrane ultrafiltration, storage and on-demand UV disinfection. We aimed to test flow cytometry as a monitoring tool to provide on-site indications on tertiary treatment performances and on the quality of treated wastewater along the treatment scheme. Membrane ultrafiltration retained prokaryotic cells and E. coli (>3 log). During storage of treated effluents, a significant decay of E. coli was observed together with the growth of prokaryotic and eukaryotic cells, and the UV disinfection was effective only against fecal indicators. The microbial quality of the treated effluent was comparable to the control groundwater locally used for irrigation. On-site rapid assessments by flow cytometry allowed unveiling crucial aspects affecting the microbiological quality of ultrafiltration permeate and treated effluent immediately after sampling, including plant operating performances and microbial removal patterns across the treatment train.

The Self-Forming Dynamic Membrane BioReactor (SFD MBR) as a suitable technology for agro-industrial wastewater treatment.

Two bench-scale Self-Forming Dynamic Membrane BioReactors (SFD MBR), equipped with 50 µm nylon meshes were set up and operated under aerobic conditions in order to treat canning and winery wastewaters. The results showed different behaviors of the two systems, confirming the strong dependence of SFD MBR performance on the type of biomass and, in turn, on the type of stream being treated. Both plants achieved good results in terms of effluent quality, demonstrating the suitability of the proposed technology. Median values of effluent turbidity were 2.7 and 15.4 NTU (Nephelometric Turbidity Units) in the reactors fed with canning wastewater and winery wastewater, respectively. The removal of organic matter (as COD, Chemical Oxygen Demand) was consistently above 90 %, although the retention of suspended solids was variable and somewhat dependent on operating conditions and feed composition. The activated sludge characteristics were observed to affect filtration performance and in particular the capillary suction time (CST) was a possible indicator of efficiency, with a threshold value of 11 s above which filtration performance decreased. This parameter is proposed as an early warning tool for changes in the filtration performance of an SFD MBR, both for effluent quality and cleaning requirements.

Sludge cake and biofilm formation as valuable tools in wastewater treatment by coupling Integrated Fixed-film Activated Sludge (IFAS) with Self Forming Dynamic Membrane BioReactors (SFD-MBR).

Two lab-scale Self Forming Dynamic Membrane BioReactors (SFD-MBR), equipped with 50 µm nylon meshes were set up and operated for the treatment of real municipal wastewater. Plastic carriers were added in one of the two bioreactors to generate a combination of the Integrated Fixed-film Activated Sludge (IFAS) and the SFD-MBR technologies. Overall, the two systems performed very well, achieving excellent effluent quality under steady state conditions and showing good resilience to extreme organic loading conditions. Continuous air scouring and periodical mesh cleaning by jet rinsing with tap water were effective in maintaining stable and high productivity (membrane flux around 67 L m2 h-1) over a period of 140 days. The application of the IFAS process resulted in lower production of excess sludge and improved denitrification. On the other hand, under the tested conditions the combined IFAS-SFD-MBR showed a higher tendency to mesh clogging with respect to the SFD-MBR.

Influence of air scouring on the performance of a Self Forming Dynamic Membrane BioReactor (SFD MBR) for municipal wastewater treatment.

The Membrane BioReactor (MBR) is a well-established filtration-based technology for wastewater treatment. Despite the high quality of the effluent produced, one of the main drawbacks of the MBR is membrane fouling. In this context, a possible evolution towards systems having potentially lower installation and operating costs is the Self Forming Dynamic Membrane BioReactor (SFD MBR). Key of this technology is the self-formation of a biological filtering layer on a support of inert material. In this work, a lab-scale aerobic SFD MBR equipped with a nylon mesh was operated at approximately 95Lm-2h-1. Two mesh pore sizes (20 and 50µm) and three air scouring flow rates (150, 250, and 500mLairmin-1) were tested at steady state. Under all the tested conditions, the SFD MBR effectively treated real municipal wastewater. The quality of the produced effluent increased for lower mesh size and lower air scouring intensity.

A full-scale plug-flow reactor for biological sludge ozonation.

The reduction of biological excess sludge production using ozone is a well-known technology and is applied in several full-scale plants around the world. Nevertheless, optimisation of the process is not yet adequately documented in the literature. Operational parameters are usually chosen by assuming a direct proportionality between ozone dose and excess sludge reduction. This paper investigates the role of ozone concentration on process efficiency and demonstrates the (non-linear) inverse relationship between ozone dose and specific particulate chemical oxygen demand solubilisation in plug-flow contact reactors. The influence of total suspended solids concentration is also studied and described. No short-term lethal effects on heterotrophic biomass have been observed.

Phragmites sp. physiological changes in a constructed wetland treating an effluent contaminated with a diazo dye (DR81).

The role of Phragmites sp. in phytoremediation of wastewaters containing azo dyes is still, in many ways, at its initial stage of investigation. This plant response to the long-term exposure to a highly conjugated di-azo dye (Direct Red 81, DR81) was assessed using a vertical flow constructed wetland, at pilot scale. A reed bed fed with water was used as control. Changes in photosynthetic pigment content in response to the plant contact with synthetic DR81 effluent highlight Phragmites plasticity. Phragmites leaf enzymatic system responded rapidly to the stress imposed; in general, within 1 day, the up-regulation of foliar reactive oxygen species-scavenging enzymes (especially superoxide dismutase, ascorbate peroxidase (APX), glutathione peroxidase (GPX) and peroxidase) was noticed as plants entered in contact with synthetic DR81 effluent. This prompt activation decreased the endogenous levels of H2O2 and the malonyldialdehyde content beyond reference values. Glutathione S-transferase (GST) activity intensification was not enough to cope with stress imposed by DR81. GPX activity was pivotal for the detoxification pathways after a 24-h exposure. Carotenoid pool was depleted during this shock. After the imposed DR81 stress, plants were harvested. In the next vegetative cycle, Phragmites had already recovered from the chemical stress. Principal component analysis (PCA) highlights the role of GPX, GST, APX, and carotenoids along catalase (CAT) in the detoxification process.