Linking hydrolytic activities to variables influencing a submerged membrane bioreactor (MBR) treating urban wastewater under real operating conditions

Isolation of a quorum quenching bacterium effective to various acyl-homoserine lactones: Its quorum quenching mechanism and application to a membrane bioreactor

Biofouling, caused by microbial biofilm formation on the membrane surface and in pores, is a major operational problem in membrane bioreactors (MBR). Many quorum quenching (QQ) bacteria have been isolated and applied to MBR to reduce biofouling. However, for more effective MBR biofouling control, novel approaches for isolating QQ bacteria and applying them in MBR are needed. Therefore, Listeria grayi (HEMM-2) was isolated using a mixture of different N-acyl homoserine lactones (AHLs). HEMM-2 degraded various AHLs, regardless of the length and oxo group in the carbon chain, with quorum sensing (QS) inhibition ratios of 47-61%. This QQ activity was attributed to extracellular substances in HEMM-2 cell-free supernatant (CFS). Furthermore, the HEMM-2 CFS negatively regulated QS-related gene expression, inhibiting Pseudomonas aeruginosa and activated sludge-biofilm formation by 53-75%. Surprisingly, when the HEMM-2 CFS was directly injected into a laboratory-scale MBR system, biofouling was not significantly affected. Biofouling was only controlled by cell suspension (CS) of HEMM-2, indicating the importance of QQ bacteria in MBR. The HEMM-2 CS increased operation time to reach 0.4 bar, a threshold transmembrane pressure for complete biofouling, from 315 h to 371 h. Taken together, HEMM-2, which is effective in the degradation of various AHLs, and its applicable method to MBR may be considered a potent approach for controlling biofouling and understanding the behavior of QQ bacteria in MBR systems.

The biological performance of a novel microalgal-bacterial membrane photobioreactor: Effects of HRT and N/P ratio

A microalgal-bacterial membrane photobioreactor (MB-MPBR) was developed for simultaneous COD and nutrients (N and P) removals from synthetic municipal wastewater in a single stage for a long-term operation over 350 days. The effects of hydraulic retention time (HRT) and N/P ratio on the biological performance were systematically evaluated for the first time. The results showed that a lower N/P ratio (3.9:1) and shorter HRT (2 d) promoted more biomass production, as compared to a high HRT (3 d) and a high N/P ratio (9.7:1). The highest biomass concentration (2.55 ± 0.14 g L^-1) and productivity (127.5 mg L^-1·d^-1) were achieved at N/P ratio of 3.9:1 and HRT of 2 d due to the highest nitrogen and phosphorus loadings under such conditions. A COD and ammonia-N removal efficiency of over 96% and 99%, respectively, were achieved regardless of HRTs and N/P ratios. In the absence of nitrogen or phosphorus deficiency, shorter HRT (2 d) yielded a higher nitrogen and phosphorus uptake but lower removal efficiency. In addition, the imbalance N/P ratio (9.7:1) would decrease nitrogen or phosphorus removal. Overall, the results suggested that it was feasible to simultaneously achieve complete or high removal of COD, nitrogen, and phosphorous in MB-MPBR under the appropriate conditions. This study demonstrated for the first time that MB-MPBR is a promising technology that could achieve a high-quality effluent meeting the discharge standards of COD and nutrients in one single step.

A high-throughput assay to quantify protein hydrolysis in aerobic and anaerobic wastewater treatment processes

Proteins, an important fraction of the organic matter in wastewater, typically enter a treatment facility as high molecular weight components. These components are degraded by extracellular protein hydrolytic enzymes, denoted as proteases. Adequate protein hydrolysis monitoring is crucial, since protein hydrolysis is often a rate-limiting step in wastewater treatment. However, current monitoring tools lack a high sample throughput and reliable quantification. Here, we present an improved assay for high-throughput protein hydrolysis rate measurements in wastewater treatment applications. A BODIPY FL casein model substrate was implemented in a microplate format for continuous fluorescent quantification. Case studies on a conventional and a high-rate aerobic municipal wastewater treatment plant and a lab-scale, two-stage, anaerobic reactor provided proof-of-concept. The assay presented in this study can help to obtain monitoring-based process insights, which will in turn allow improving biological performance of wastewater treatment installations in the future. KEY POINTS: • Protein hydrolysis is a crucial step in biological wastewater treatment. • Quantification of the protein hydrolysis rate enables in-depth process knowledge. • BODIPY FL casein is a suitable model substrate for a protein hydrolysis assay. • High sample throughput was obtained with fluorescent hydrolysis quantification. Graphical abstract.

Heterotrophic Kinetic Study and Nitrogen Removal of a Membrane Bioreactor System Treating Real Urban Wastewater under a Pharmaceutical Compounds Shock: Effect of the Operative Variables

Numerous studies have analyzed the viability of the biodegradation and removal of different compounds of emerging concern in biological systems for wastewater treatment. However, the effect on the heterotrophic biomass of organic matter removal is sometimes missed. The aim of the present research was to study the effect of the addition of a mix of three pharmaceuticals (carbamazepine, ciprofloxacin, and ibuprofen) on the behavior of the biomass in two different membrane-based biological systems treating urban wastewater. The present research studied a membrane bioreactor (MBR) pilot plant operating at a similar mixed liquor suspended solids (MLSS) concentration (about 5.5 g/L). This system works as an MBR and is combined with a moving bed biofilm reactor (MBBR-MBR) to treat real urban wastewater at 6 and 10 h of hydraulic retention time (HRT) under three different shocks of pharmaceuticals with increasing concentrations. In all cases, the organic matter removal was, in average terms, higher than about 92% of biochemical oxygen demand on the fifth day (BOD5), 79% of chemical oxygen demand (COD), and 85% of total organic carbon (TOC). Nevertheless, the removal is higher in the MBBR-MBR technology under the same HRT and the MLSS is similar. Moreover, the removal increased during the shock of pharmaceutical compounds, especially in the MBR technology. From a kinetic perspective, MBBR-MBR is more suitable for low HRT (6 h) and MBR is more effective for high HRT (10 h). This could be due to the fact that biofilm systems are less sensitive to hostile environments than the MBR systems. The removal of N-NH4+ decreased considerably when the pharmaceutical compounds mix was introduced into the system until no removal was detected in cycle 1, even when biofilm was present.

Effect of semi-permeable cover system on the bacterial diversity during sewage sludge composting

Sewage sludge composting is a profitable process economically viable and environmentally friendly. In despite of there are several kind of composting types, the use of combined system of semipermeable cover film and aeration air-floor is widely developed at industrial scale. However, the knowledge of the linkages between microbial communities structure, enzyme activities and physico-chemical factors under these conditions it has been poorly explored. Thus, the aim of this study was to investigate the bacterial dynamic and community structure using next generation sequencing coupled to analyses of microbial enzymatic activity and culturable dependent techniques in a full-scale real composting plant. Sewage sludge composting process was conducted using a semi-permeable Gore-tex cover, in combination with an air-insufflation system. The highest values of enzymatic activities such as dehydrogenase, protease and arylsulphatase were detected in the first 5 days of composting; suggesting that during this period of time a greater degrading activity of organic matter took place. Culturable bacteria identified were in agreement with the bacteria found by massive sequencing technologies. The greatest bacterial diversity was detected between days 15 and 30, with Actinomycetales and Bacillales being the predominant orders at the beginning and end of the process. Bacillus was the most representative genus during all the process. A strong correlation between abiotic factors as total organic content and organic matter and enzymatic activities such as dehydrogenase, alkaline phosphatase, and ß-glucosidase activity was found. Bacterial diversity was strongly influenced by the stage of the process, community-structure change was concomitant with a temperature rise, rendering favorable conditions to stimulate microbial activity and facilitate the change in the microbial community linked to the degradation process. Moreover, results obtained confirmed that the use of semipermeable cover in the composting of sewage sludge allow a noticeable reduction in the process-time comparing to conventional open windrows.

Enzymes as Enhancers for the Biodegradation of Synthetic Polymers in Wastewater

Synthetic polyesters are today the second-largest class of ingredients in household products and are entering wastewater treatment plants (WWTPs) after product utilization. One approach to improve polymer biodegradation in wastewater would be to complement current processes with polyester-hydrolyzing enzymes and their microbial producers. In this study, the hydrolysis of poly(oxyethylene terephthalate) polymer by hydrolases from wastewater microorganisms was investigated in vitro and under realistic WWTP conditions. An esterase and a cutinase from Pseudomonas pseudoalcaligenes and a lipase from Pseudomonas pelagia were heterologously expressed in Escherichia coli BL21-Gold(DE3) and were purified by a C-terminal His₆ tag. The hydrolases were proven to hydrolyze the polymer effectively, which is a prerequisite for further biodegradation. The hydrolases maintained high activity up to 50 % upon lowering the temperature from 28 to 15 °C to mimic WWTP conditions. The hydrolases were also not inhibited by the wastewater matrix. Polyester-hydrolyzing enzymes active under WWTP conditions and their microbial producers thus have the potential to improve biological treatment of wastewater rich in synthetic polymers.

Extracellular enzymatic activity of two hydrolases in wastewater treatment for biological nutrient removal

Due to the complex nature of the wastewater (both domestic and non-domestic) composition, biological processes are widely used to remove nutrients, such as carbon (C), nitrogen (N), and phosphorous (P), which cause instability and hence contribute to the damage of water bodies. Systems with different configurations have been developed (including anaerobic, anoxic, and aerobic conditions) for the joint removal of carbon, nitrogen, and phosphorus. The goal of this research is to evaluate the extracellular activity of β-glucosidase and phosphatase enzymes in a University of Cape Town (UCT) system fed with two synthetic wastewaters of different molecular complexity. Both types of waters have medium strength characteristics similar to those of domestic wastewater with a mean C/N/P ratio of 100:13:1. The operation parameters were hydraulic retention time (HRT) of 10 h, solid retention time (SRT) of 12 days, mean concentration of the influent in terms of chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) of 600, 80, and 6 mg/L, respectively. According to the results obtained, statistically significant differences have been found in the extracellular enzyme activities with the evaluated wastewaters and in the units comprising the treatment system in some of the cases. An analysis of principal components showed that the extracellular enzymatic activity has been correlated to nutrient concentration in wastewater, biomass concentration in the system, and metabolic conditions of treatment phases. Additionally, this research has allowed determining an inverse relationship between wastewater biodegradability and the extracellular enzyme activity of β-glucosidase and phosphatase. These results highlight the importance of including the analysis of biomass biochemical characteristics as control methods in wastewater treatment systems for the nutrient removal.

Micropollutant degradation via extracted native enzymes from activated sludge

A procedure was developed to assess the biodegradation of micropollutants in cell-free lysates produced from activated sludge of a municipal wastewater treatment plant (WWTP). This proof-of-principle provides the basis for further investigations of micropollutant biodegradation via native enzymes in a solution of reduced complexity, facilitating downstream protein analysis. Differently produced lysates, containing a variety of native enzymes, showed significant enzymatic activities of acid phosphatase, β-galactosidase and β-glucuronidase in conventional colorimetric enzyme assays, whereas heat-deactivated controls did not. To determine the enzymatic activity towards micropollutants, 20 compounds were spiked to the cell-free lysates under aerobic conditions and were monitored via LC-ESI-MS/MS. The micropollutants were selected to span a wide range of different biodegradabilities in conventional activated sludge treatment via distinct primary degradation reactions. Of the 20 spiked micropollutants, 18 could be degraded by intact sludge under assay conditions, while six showed reproducible degradation in the lysates compared to the heat-deactivated negative controls: acetaminophen, N-acetyl-sulfamethoxazole (acetyl-SMX), atenolol, bezafibrate, erythromycin and 10,11-dihydro-10-hydroxycarbamazepine (10-OH-CBZ). The primary biotransformation of the first four compounds can be attributed to amide hydrolysis. However, the observed biotransformations in the lysates were differently influenced by experimental parameters such as sludge pre-treatment and the addition of ammonium sulfate or peptidase inhibitors, suggesting that different hydrolase enzymes were involved in the primary degradation, among them possibly peptidases. Furthermore, the transformation of 10-OH-CBZ to 9-CA-ADIN was caused by a biologically-mediated oxidation, which indicates that in addition to hydrolases further enzyme classes (probably oxidoreductases) are present in the native lysates. Although the full variety of indigenous enzymatic activity of the activated sludge source material could not be restored, experimental modifications, e.g. different lysate filtration, significantly enhanced specific enzyme activities (e.g. >96% removal of the antibiotic erythromycin). Therefore, the approach presented in this study provides the experimental basis for a further elucidation of the enzymatic processes underlying wastewater treatment on the level of native proteins.

The ratio of metabolically active versus total Mycolata populations triggers foaming in a membrane bioreactor

The abundance of total and metabolically active populations of Mycolata was evaluated in a full-scale membrane bioreactor (MBR) experiencing seasonal foaming, using quantitative PCR (qPCR) and retrotranscribed qPCR (RT-qPCR) targeting the 16S rRNA gene sequence. While the abundance of total Mycolata remained stable (10(10) copies of 16S rRNA genes/L activated sludge) throughout four different experimental phases, significant variations (up to one order of magnitude) were observed when the 16S rRNA was targeted. The highest ratios of metabolically active versus total Mycolata populations were observed in samples of two experimental phases when foaming was experienced in the MBR. Non-metric multidimensional scaling and BIO-ENV analyses demonstrated that this ratio was positively correlated to the concentrations of substrates in the influent water, F/M ratio, and pH, and negatively correlated to temperature and solids retention time. It the first time that the ratio of metabolically active versus total Mycolata is found to be a key parameter triggering foaming in the MBR; thus, we propose it as a candidate predictive tool.

Biomass viability: An experimental study and the development of an empirical mathematical model for submerged membrane bioreactor

This study investigates the influence of key biomass parameters on specific oxygen uptake rate (SOUR) in a sponge submerged membrane bioreactor (SSMBR) to develop mathematical models of biomass viability. Extra-cellular polymeric substances (EPS) were considered as a lumped parameter of bound EPS (bEPS) and soluble microbial products (SMP). Statistical analyses of experimental results indicate that the bEPS, SMP, mixed liquor suspended solids and volatile suspended solids (MLSS and MLVSS) have functional relationships with SOUR and their relative influence on SOUR was in the order of EPS>bEPS>SMP>MLVSS/MLSS. Based on correlations among biomass parameters and SOUR, two independent empirical models of biomass viability were developed. The models were validated using results of the SSMBR. However, further validation of the models for different operating conditions is suggested.

Quantitative response of nitrifying and denitrifying communities to environmental variables in a full-scale membrane bioreactor

The abundance and transcription levels of specific gene markers of total bacteria, ammonia-oxidizing Betaproteobacteria, nitrite-oxidizing bacteria (Nitrospira-like) and denitrifiers (N2O-reducers) were analyzed using quantitative PCR (qPCR) and reverse-transcription qPCR during 9 months in a full-scale membrane bioreactor treating urban wastewater. A stable community of N-removal key players was developed; however, the abundance of active populations experienced sharper shifts, demonstrating their fast adaptation to changing conditions. Despite constituting a small percentage of the total bacterial community, the larger abundances of active populations of nitrifiers explained the high N-removal accomplished by the MBR. Multivariate analyses revealed that temperature, accumulation of volatile suspended solids in the sludge, BOD5, NH4(+) concentration and C/N ratio of the wastewater contributed significantly (23-38%) to explain changes in the abundance of nitrifiers and denitrifiers. However, each targeted group showed different responses to shifts in these parameters, evidencing the complexity of the balance among them for successful biological N-removal.

Exploring the links between population dynamics of total and active bacteria and the variables influencing a full-scale membrane bioreactor (MBR)

Long-term dynamics of total and active bacterial populations in a full-scale membrane bioreactor (MBR) treating urban wastewater were monitored during nine months by temperature-gradient gel electrophoresis (TGGE) of partial 16S-rRNA genes, amplified from community DNA and RNA templates. The bacterial community, dominated by Alphaproteobacteria, displayed the required characteristics for a successful and steady contaminant removal under real operating conditions. The evolution of population dynamics showed that a fully-stable microbial community was not developed even after technical stabilization and steady performance of the MBR were achieved. Non-metric multidimensional scaling and BIO-ENV demonstrated that the trends of the populations were often mostly explained by temperature, followed by the concentration of volatile suspended solids and C/N ratio of the influent. These variables were mainly responsible for triggering the shifts between functionally redundant populations. These conclusions contribute to the prediction of the complex profiles of adaptation and response of bacterial populations under changing conditions.