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.

A global multinational survey of cefotaxime-resistant coliforms in urban wastewater treatment plants.

The World Health Organization Global Action Plan recommends integrated surveillance programs as crucial strategies for monitoring antibiotic resistance. Although several national surveillance programs are in place for clinical and veterinary settings, no such schemes exist for monitoring antibiotic-resistant bacteria in the environment. In this transnational study, we developed, validated, and tested a low-cost surveillance and easy to implement approach to evaluate antibiotic resistance in wastewater treatment plants (WWTPs) by targeting cefotaxime-resistant (CTX-R) coliforms as indicators. The rationale for this approach was: i) coliform quantification methods are internationally accepted as indicators of fecal contamination in recreational waters and are therefore routinely applied in analytical labs; ii) CTX-R coliforms are clinically relevant, associated with extended-spectrum ß-lactamases (ESBLs), and are rare in pristine environments. We analyzed 57 WWTPs in 22 countries across Europe, Asia, Africa, Australia, and North America. CTX-R coliforms were ubiquitous in raw sewage and their relative abundance varied significantly (<0.1% to 38.3%), being positively correlated (p < 0.001) with regional atmospheric temperatures. Although most WWTPs removed large proportions of CTX-R coliforms, loads over 103 colony-forming units per mL were occasionally observed in final effluents. We demonstrate that CTX-R coliform monitoring is a feasible and affordable approach to assess wastewater antibiotic resistance status.

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.

Functional Response of MBR Microbial Consortia to Substrate Stress as Revealed by Metaproteomics.

Bacterial consortia have a primary role in the biological degradations occurring in activated sludge for wastewater treatment, for their capacities to metabolize the polluting matter. Therefore, the knowledge of the main metabolic pathways for the degradation of pollutants becomes critical for a correct design and operation of wastewater treatment plants. The metabolic activity of the different bacterial groups in activated sludge is commonly investigated through respirometry. Furthermore, in the last years, the development of "omic" approaches has offered more opportunities to integrate or substitute the conventional microbiological assays and to deeply understand the taxonomy and dynamics of complex microbial consortia. In the present work, an experimental membrane bioreactor (MBR) was set up and operated for the treatment of municipal wastewater, and the effects of a sudden decrease of the organic supply on the activated sludge were investigated. Both respirometric and metaproteomic approaches revealed a resistance of autotrophic bacteria to the substrate stress, and particularly of nitrifying bacteria. Furthermore, metaproteomics allowed the identification of the taxonomy of the microbial consortium based on its protein expression, unveiling the prevalence of Sorangium and Nitrosomonas genera both before and after the organic load decrease. Moreover, it confirmed the results obtained through respirometry and revealed a general expression of proteins involved in metabolism and transport of nitrogen, or belonging to nitrifying species like Nitrosomonas europeae, Nitrosomonas sp. AL212, or Nitrospira defluvii.

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.

Metaproteomics Applied to Activated Sludge for Industrial Wastewater Treatment Revealed a Dominant Methylotrophic Metabolism of Hyphomicrobium zavarzinii.

In biological wastewater treatments, microbial populations of the so-called activated sludge work together in the abatement of pollutants. In this work, the metabolic behavior of the biomass of a lab-scale plant treating industrial pharmaceutical wastewater was investigated through a metaproteomic approach. The complete treatment process included a membrane biological reactor (MBR) coupled with an advanced oxidation process (AOP) for partial breakdown of non-biodegradable molecules. Proteins from biomass samples collected pre- and post-AOP application were investigated by two-dimensional gel electrophoresis (2DE), mass spectrometry (MS), and finally identified by database search. Results showed that most proteins remained constant between pre- and post-AOP. Methanol dehydrogenase (MDH) belonging to Hyphomicrobium zavarzinii appeared as the most constantly expressed protein in the studied consortium. Other identified proteins belonging to Hyphomicrobium spp. revealed a predominant methylotrophic metabolism, and H. zavarzinii appeared as a key actor in the studied microbial community.

Isolation of Squarebop I bacteriorhodopsin from biomass of coastal salterns.

Squarebop I bacteriorhodopsin is a light-activated proton pump present in the membranes of the archeon Haloquadratum walsbyi, a square-shaped organism representing 50-60% of microbial population in the crystallizer ponds of the coastal salterns. Here we describe: (1) the operating mode of a bioreactor designed to concentrate the saltern biomass through a microfiltration process based on polyethersulfone hollow fibers; (2) the isolation of Squarebop I bacteriorhodopsin from solubilized biomass by means of a single chromatographic step; (3) tightly bound lipids to the isolated and purified protein as revealed by MALDI-TOF/MS analysis; (4) the photoactivity of Squarebop I bacteriorhodopsin isolated from environmental samples by flash spectroscopy. Yield of the isolation process is 150 µg of Squarebop I bacteriorhodopsin from 1l of 25-fold concentrated biomass. The possibility of using the concentrated biomass of salterns, as renewable resource for the isolation of functional bacteriorhodopsin and possibly other valuable bioproducts, is briefly discussed.

Metaproteome analysis of sewage sludge from membrane bioreactors.

Microbial dynamics and enzymatic activities of activated sludge processes are not completely understood yet. A better understanding about the biology is indispensable for further process optimization. Since proteins play a key role as catalysts in sludge processes, a protocol for protein extraction and analysis by 2-D PAGE was established. It is based on phenol extraction of alkaline extracts and on a subsequent precipitation with ammonium sulphate. 2-D protein patterns obtained from different sludges collected from membrane bioreactors showed--besides common spots--significant differences. Selected proteins were identified with nano-HPLC-ESI-MS/MS. All membrane biological reactor (MBR) sludge samples investigated in this study contained elastase 3A, which implies that this human serine protease is a significant constituent of municipal wastewater. Although the identification of proteins from ammonia-oxidizing bacterium Nitrosomonas europaea was expected, the detection of a protein with homology to the marine bacterium Saprospira grandis in MBR1 was surprising.

Biomass growth and activity in a membrane bioreactor with complete sludge retention.

This work reports the main results of a bench scale membrane bioreactor operated for more than 100 days without sludge withdrawal and fed on real municipal wastewater. The experiments were oriented towards three main objectives. Firstly, the performance of the system was evaluated under two different volumetric loading rates (0.8 and 1.7 g CODL(react.)(-1)d(-1)). Secondly, biomass growth and accumulation of solids were assessed and a relationship between sludge concentration and volumetric loading rates was proposed. Thirdly, biomass activity was evaluated through respirometric tests, and endogenous and maximum respiration rates of heterotrophic and nitrifying bacteria were determined. The experimental campaign showed that these systems are easy to manage and very rapid to start-up. The SS concentrations under equilibrium conditions for both experimental periods were slightly lower than 10 times the volumetric loading rates, and the organic loading rates reached the same equilibrium value of 0.12 g CODgTSS(-1)d(-1). Furthermore, under equilibrium conditions the system showed very limited sludge production (0.12 g VSSgCOD(rem)(-1)) and low biomass activity, although it readily responded to load variations. Further work is being carried out to evaluate the performance over the long term.

Influence of aeration and sludge retention time on ammonium oxidation to nitrite and nitrate.

Partial nitrification to nitrite was reported to be technically feasible and economically favourable, especially when wastewater with high ammonium concentrations or low C/N ratios are treated. Nitritation can be obtained by selectively inhibiting nitrite oxidizing microrganisms through appropriate regulation of the system's pH, temperature, and sludge retention time. In addition to already known methods, the work showed that aeration patterns may play a relevant role too. Nitrification tests were performed in two lab-scale reactors operated under continuous and intermittent aeration, respectively. In both plants, temperature was maintained at 32 degrees C and pH was regulated at 7.2 by providing external buffer capacity when needed. The results showed that partial nitrification to nitrite was steadily obtained under oxygen limitation, independent of the sludge age. Therefore, the aeration pattern is proposed as an alternative parameter to the sludge retention time for controlling ammonium oxidation to nitrite.