A novel approach to evaluate the production kinetics of extracellular polymeric substances (EPS) by activated sludge using weighted nonlinear least-squares analysis

Challenges and opportunities in bioprocessing of gellan gum: A review

Gellan gum (GG) - the microbial exopolysaccharide is increasingly being adopted into drug development, tissue engineering, and food and pharmaceutical products. In spite of the commercial importance and expanding application horizon of GG, little attention has been directed toward the exploration of novel microbial cultures, development of advanced screening protocols, strain engineering, and robust upstream or downstream processes. This comprehensive review not only attempts to summarize the existing knowledge pool on GG bioprocess but also critically assesses their inherent challenges. The process optimization design augmented with advanced machine learning modeling tools, widely adopted in other microbial bioprocesses, should be extended to GG. The unification of mechanistic insight into data-driven modeling would help to formulate optimal feeding and process control strategies.

Understanding the N-acylated homoserine lactones(AHLs)-based quorum sensing for the stability of aerobic granular sludge in the aspect of substrate hydrolysis enhancement

Efficient substrate metabolism is the premise for stable operation of aerobic granular sludge and can be regulated by quorum sensing (QS). In this study, starch and acetate were selected to represent complex and simple substrates to provide comparable amount of metabolic energy for granules cultivation. Starch-fed granules were larger in size and contained higher EPS content than acetate-fed granules, though both granules exhibited similar substrate-degradation rates during sequencing batch reactor (SBR) cycle. Three N-acylhomoserine lactones (AHLs), including C8-HSL, 3OHC8-HSL and 3OHC12-HSL, were detected as dominant autoinducers in granules. They accumulated more in starch-fed granules than acetate-fed granules. The batch experiments were implemented to investigate QS regulation for granular stability in terms of substrate hydrolysis and transformation. The addition of three AHLs increased the activity of α-amylase, the main starch hydrolase, 4-6 times, significantly (p < 0.01) higher than the control treatment without AHLs amendment. While activity of dehydrogenase, the main simple substrate degradation enzyme, was increased only 1-2 times. Higher enzyme activity, especially α-amylase, significantly (p < 0.05) promoted the substrate-degradation rate (65 % than control group) and EPS yield in starch-fed system. Overall, QS can facilitate complex substrate uptake via hydrolysis enhancement and EPS secretion, which together promote sludge granulation and stability.

External resistance acclimation regulates bio-anode: new perspective from biofilm structure and its correlation with anode performance

External resistance is important for the anode and cell performance. However, little attentions were paid on the effect of external resistance on the variation of biofilm structure. Here, we used external resistance ranged from 4000 to 500 Ω for anodic acclimation to investigate the correlation between anode performance and biofilm structure. With the reduce of external resistance, the maximum current density of anode increased from 1.0 to 3.4 A/m², which was resulted from a comprehensive effect of reduced charge transfer resistance and increased diffusion resistance. Biological analysis showed that with the reduce of external resistance, biomass and extracellular polymeric substances content increased by 109 and 286%, cell viability increased by 22.7%, which contributed to the reduced charge transfer resistance. But the porosity of anodic biofilm decreased by 27.8%, which led to an increased diffusion resistance of H⁺. This work provided a clear correlation between the electrochemical performance and biofilm structure.

Using stable isotope probing and fluorescence spectroscopy to examine the roles of substrate and soluble microbial products in extracellular polymeric substance formation in activated sludge process

In this study, we used stable isotope-labeled soluble microbial products (SMP) and substrates to explore their assimilation into the formation of new biological products (i.e., extracellular polymeric substances and biomass) in two adjacent sequencing batch reactors. The isotope labeling approach along with fluorescence spectroscopy allowed us to distinguish between refractory and labile portions of SMP constituents as well as their roles in the formation of extracellular polymeric substances (EPS). Comparison of SMP fluorescence and the specific UV absorbance values between the two reactors revealed the presence of humic-like aromatic substances in the non-consumable part of SMP, which can be ultimately released as effluent organic matter. Parallel factor analysis modeling of fluorescence spectra showed that the hydrolysis of EPS contents mostly resulted in humic-like components in SMP rather than protein-like components, which were initially abundant in EPS (>80%). From variations in carbon and nitrogen isotopic contents in EPS and biomass, it was found that carbon-containing substrates were enriched faster than their nitrogenous counterparts. The contributions to new EPS formation reached 87.5% for carbon and 60.5% for nitrogen. Meanwhile, the isotopic tracking of the labeled SMP revealed that only 11.0% and 11.9% of carbon and 13.3% and 11.6% of nitrogen from the influent SMP were finally assimilated into EPS and biomass, respectively. In contrast, the isotopic enrichment in SMP was higher (~50%) than that of EPS and biomass, indicating the low bioavailability and refractory nature of the feed SMP. This study proposed a promising approach for estimating the relative contributions of different forms of labile substrate and SMP to the formation of EPS in activated sludge processes. This approach could be suggested as a versatile method for establishing the kinetics, substrate element flow, mass balance on organic substrates and nutrients, as well as for tracking the consumption and uptake pathways of hazardous materials.

Identification of Biokinetic Models Using the Concept of Extents

The development of a wide array of process technologies to enable the shift from conventional biological wastewater treatment processes to resource recovery systems is matched by an increasing demand for predictive capabilities. Mathematical models are excellent tools to meet this demand. However, obtaining reliable and fit-for-purpose models remains a cumbersome task due to the inherent complexity of biological wastewater treatment processes. In this work, we present a first study in the context of environmental biotechnology that adopts and explores the use of extents as a way to simplify and streamline the dynamic process modeling task. In addition, the extent-based modeling strategy is enhanced by optimal accounting for nonlinear algebraic equilibria and nonlinear measurement equations. Finally, a thorough discussion of our results explains the benefits of extent-based modeling and its potential to turn environmental process modeling into a highly automated task.

Effects of C/N in the substrate on the simultaneous production of polyhydroxyalkanoates and extracellular polymeric substances by Haloferax mediterranei via kinetic model analysis

A study of the effect of extracellular carbon source distribution on polyhydroxyalkanoates and extracellular polymeric substances byHaloferax mediterranei viakinetic model analysis.

Effect of wet oxidation on the fingerprints of polymeric substances from an activated sludge

Thermal pre-treatments of activated sludge involve the release of a high amount of polymeric substances into the bulk medium. The molecular size of these polymers will largely define the subsequent biological treatment of the liquid effluent generated. In this work, the effects of wet oxidation treatment (WO) on the fingerprints of the polymeric substances which compose the activated sludge, were analysed. For a better understanding of these transformations, the sludge was separated into its main fractions: soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS), tightly bound extracellular polymeric substances (TB-EPS) and naked cells, and then each one was subjected to WO separately (190 °C and 65 bar), determining the fingerprints evolution by size exclusion technique. Results revealed a fast degradation of larger molecules (over 500 kDa) during the first minutes of treatment (40 min). WO also increases the absorptive properties of proteins (especially for 30 kDa), which is possibly due to the hydroxylation of phenylalanine amino acids in their structure. WO of naked cells involved the formation of molecules between 23 and 190 kDa, which are related to the release of cytoplasmic polymers, and more hydrophobic polymers, probably from the cell membrane. The results allowed to establish a relationship between the location of polymeric material and its facility to become oxidised; thus, the more internal the polymeric material in the cell, the easier its oxidation. When working directly with the raw sludge, hydrolysis mechanisms played a key role during the starting period. Once a high degree of solubilisation was reached, the molecules were rapidly oxidised into other compounds with refractory characteristics. The final effluent after WO showed almost 90% of low molecular weight solubilised substances (0-35 kDa).

Mathematical modeling of autotrophic denitrification (AD) process with sulphide as electron donor

Autotrophic denitrification (AD) plays a critical role in nitrate removal from organic carbon-deficient wastewaters with a high level of nitrogen oxides. However, the AD process is not included in the current denitrification models, which limits the application of AD technology for wastewater treatment. In this work, a kinetic model for AD process involved 4 processes and 5 components with 9 parameters is established to describe the sulphide biooxidation and nitrite removal process. In this model, 4 oxidation-reduction reactions using sulphide as electronic donor in the AD process are taken into account. The model parameters are optimized by fitting data from the experiments with different combinations of sulphide, sulphur, sulphate, nitrate and nitrite at various concentrations. Model calibration and validation results demonstrate that the developed model is able to reasonably describe the removal rates of nitrate, nitrite, sulphide and sulphur in the AD process. The model simulation results also show that the sulphur term (η(S)) in the kinetic equations of nitrate, nitrite, sulphur and sulphate remains constant, rather than being controlled by its own concentration. Furthermore, with this model the products of sulphide biooxidation in the AD process, sulphur and sulphate, and their concentrations can be accurately predicted. Therefore, this model provides a strategy to control the sulphate concentration below the discharge limits or recover sulphur as the main end product from sulphide biooxidation.

Spectrometric characterization of the effluent dissolved organic matter from an anammox reactor shows correlation between the EEM signature and anammox growth

Anaerobic ammonium oxidation (anammox) is a cost-effective process to treat high-strength nitrogenous wastewater. Even without organic carbon input, the effluent contains bioproducts from autotrophic and heterotrophic bacteria. In this work, excitation-emission matrix (EEM) fluorescence spectroscopy was used to characterize the effluent dissolved organic matter (EfOM) from an anammox reactor treating synthetic wastewater. Two dominant EEM components were identified as humic acid-like (component 1) and protein-like (component 2) substances with excitation/emission peaks at <240, 355, 420/464 nm and <240, 280, 330/346 nm, respectively. The presence of both compounds in the effluent was tracked during an activity recovery period (nitrogen load increased from 0.2 to 1.3 kg Nm(-3)d(-1)). The effluent concentration of both components increased during this period, indicating correlation between production and bacterial activity. The dynamics of these bioproducts during both substrate consumption and starvation phases was analyzed in batch experiments. Component 1 was only formed during substrate consumption in a rate proportional to ammonium removal and was considered an up-take associated product characteristic of anammox activity. The results show that the composition of the EfOM was qualitatively and quantitatively influenced by process performance. Monitoring the EfOM could, therefore, offer a useful approach to assess anammox process performance and must be further explored.

Fractional, biodegradable and spectral characteristics of extracted and fractionated sludge extracellular polymeric substances

Correlation between fractional, biodegradable and spectral characteristics of sludge extracellular polymeric substances (EPS) by different protocols has not been well established. This work extracted sludge EPS using alkaline extractants (NH₄OH and formaldehyde + NaOH) and physical protocols (ultrasonication, heating at 80 °C or cation exchange resin (CER)) and then fractionated the extracts using XAD-8/XAD-4 resins. The alkaline extractants yielded more sludge EPS than the physical protocols. However, the physical protocols extracted principally the hydrophilic components which were readily biodegradable by microorganisms. The alkaline extractants dissolved additional humic-like substances from sludge solids which were refractory in nature. Different extraction protocols preferably extracted EPS with distinct fractional, biodegradable and spectral characteristics which could be applied in specific usages.