Critical Analysis of Methods Adopted for Evaluation of Mixing Efficiency in an Anaerobic Digester

The effect of slurry mixing in an anaerobic digester on biogas production was intensively studied in the last few years. This subject is still debatable due to fact that this process involves three phases, solid-gas-liquid, along with the involvement of microbes during biochemical reactions, which are highly vulnerable to changes in hydrodynamic shear stresses and mixing conditions. Moreover, the complexity in the direction of optimization of mixing magnifies due to the implication of both fluid mechanics and biochemical engineering to study the effect of mixing in anaerobic digestion (AD). The effect of mixing on AD is explored using recent literature and theoretical analysis, concentrating on the multi-phase and multi-scale aspects of AD. The tools and methods available to experimentally quantify the function of mixing on both the global and local scales are summarized in this study. The major challenge for mixing in an anaerobic digester is to minimize dead zones and maintain uniform distribution of viscosity and shear at low mixing intensities without disrupting the microbial flocs and syntrophic relationships between the bacteria during the AD process. This study is a critical analysis of various techniques and approaches adopted by researchers to evaluate the effectiveness of mixing regimes and mixing equipment. Most studies describe biogas production performance and hydrodynamic characteristics of the digesters separately, but the evaluation of mixing requires interdisciplinary experts, which include mechanical engineers, microbiologists and hydrodynamic experts. Through this review, the readers will be guided through intensive literature regarding agitation, the best possible way to scrutinize the agitation problems and the approach to answering the question “why is the optimization of mixing in an anaerobic digester still a debatable subject?”.

Isolation, Separation and Identification of the Extracellular Polymeric Substance (EPS) Protein Fraction from the Activated Sludge Floc

The purpose of this study was to expand the current knowledge of the composition of extracellular polymeric substances (EPS), principally EPS proteins, and their influence on structure, stability and surface chemistry of microbial flocs in activated sludge. It was proposed that a substantial portion of EPS proteins contains glycoproteins or proteins that are strongly bound noncovalently to carbohydrates. Various buffer additives, purification and precipitation methods were employed for protein purification and several glycoprotein detection methods were utilized for glycoprotein detection in the EPS. The proteins were separated with success, with a substantial portion suggesting either a possible glycosylation or strong noncovalent interactions with carbohydrate moiety. An enzyme, oligoendopeptidase F from M3B family was tentatively identified as a major protein present. These results suggest that proteins in the activated sludge EPS may exist in a very intricate arrangement. Furthermore, the EPS peptides may get degraded by naturally present enzymes in the EPS after the protein is digested prior to mass spectrum (MS), making the identification challenging.

Isolation, Separation and Identification of the Extracellular Polymeric Substance (EPS) Protein Fraction from the Activated Sludge Floc

The purpose of this study was to expand the current knowledge of the composition of extracellular polymeric substances (EPS), principally EPS proteins, and their influence on structure, stability and surface chemistry of microbial flocs in activated sludge. It was proposed that a substantial portion of EPS proteins contains glycoproteins or proteins that are strongly bound noncovalently to carbohydrates. Various buffer additives, purification and precipitation methods were employed for protein purification and several glycoprotein detection methods were utilized for glycoprotein detection in the EPS. The proteins were separated with success, with a substantial portion suggesting either a possible glycosylation or strong noncovalent interactions with carbohydrate moiety. An enzyme, oligoendopeptidase F from M3B family was tentatively identified as a major protein present. These results suggest that proteins in the activated sludge EPS may exist in a very intricate arrangement. Furthermore, the EPS peptides may get degraded by naturally present enzymes in the EPS after the protein is digested prior to mass spectrum (MS), making the identification challenging.

Characterization of microbial aggregates in relation to membrane biofouling in submerged membrane bioreactors

The purpose of this study was to characterize microbial aggregates and extracellular polymeric substances (EPS) that contribute to biofouling of submerged polymeric microfiltration membranes. Two issues were addressed in this study, (1) the influence operational and recovery cleanings of membranes have on biofouling amelioration and (2) the influence physicochemical properties of microbial flocs have on biofouling. The experiments in this study employed two pilot scale Zee Weed™ membrane bioreactors (MBRs). In one MBR, a ZW-I0 module was installed to treat secondary municipal wastewater at a sludge retention time (SRT) of30 days and operated under permeate/relaxation conditions. In the other MBR, two ZW -10 modules were installed to treat secondary municipal wastewater at an SRT of 12 days. One module operated under permeate/relaxation conditions, while the other operated under permeate/backwash conditions. Sludge samples from the MBRs were characterized by measuring the surface charge, hydrophobicity, and EPS composition of the microbial flocs. Membrane fibre samples were collected from each ZW -10 module during permeation and after recovery cleanings. The biofoulant on the membrane was analyzed using confocal laser scanning microscopy (CLSM) after simultaneous staining with the lectins concanavalin A (ConA), wheat germ agglutinin (WGA), and soybean agglutinin (SBA). The CLSM analysis of the membrane fibres sampled showed that the biofoulant on the membrane was composed of a heterogeneous colonization of microbes and EPS known to contain glucose, mannose, N -acetylglucosamine, and galactose. The dominant carbohydrate in the biofoulant was shown to be N -acetylglucosamine, which is part of both the cell wall of bacteria and the extracellular matrix. The reversible biofoulant was composed of individual cells, aggregates of cells, and EPS. The major constituent of the irreversible biofoulant was inferred to be EPS, which was observed as a fibrous network of material that remained adhered to the membrane after recovery cleaning the modules with a 2000 ppm hypochlorite solution. By using a permeate backwash rather than relaxation as an operational cleaning method, the rate of biofouling may be reduced. The rate of biofoulant accumulation on hydrophilic membranes may be reduced at higher SR Ts because the biomass at higher SR Ts has a higher hydrophobicity when compared to the biomass at lower SRTs.

Characterization of microbial aggregates in relation to membrane biofouling in submerged membrane bioreactors

The purpose of this study was to characterize microbial aggregates and extracellular polymeric substances (EPS) that contribute to biofouling of submerged polymeric microfiltration membranes. Two issues were addressed in this study, (1) the influence operational and recovery cleanings of membranes have on biofouling amelioration and (2) the influence physicochemical properties of microbial flocs have on biofouling. The experiments in this study employed two pilot scale Zee Weed™ membrane bioreactors (MBRs). In one MBR, a ZW-I0 module was installed to treat secondary municipal wastewater at a sludge retention time (SRT) of30 days and operated under permeate/relaxation conditions. In the other MBR, two ZW -10 modules were installed to treat secondary municipal wastewater at an SRT of 12 days. One module operated under permeate/relaxation conditions, while the other operated under permeate/backwash conditions. Sludge samples from the MBRs were characterized by measuring the surface charge, hydrophobicity, and EPS composition of the microbial flocs. Membrane fibre samples were collected from each ZW -10 module during permeation and after recovery cleanings. The biofoulant on the membrane was analyzed using confocal laser scanning microscopy (CLSM) after simultaneous staining with the lectins concanavalin A (ConA), wheat germ agglutinin (WGA), and soybean agglutinin (SBA). The CLSM analysis of the membrane fibres sampled showed that the biofoulant on the membrane was composed of a heterogeneous colonization of microbes and EPS known to contain glucose, mannose, N -acetylglucosamine, and galactose. The dominant carbohydrate in the biofoulant was shown to be N -acetylglucosamine, which is part of both the cell wall of bacteria and the extracellular matrix. The reversible biofoulant was composed of individual cells, aggregates of cells, and EPS. The major constituent of the irreversible biofoulant was inferred to be EPS, which was observed as a fibrous network of material that remained adhered to the membrane after recovery cleaning the modules with a 2000 ppm hypochlorite solution. By using a permeate backwash rather than relaxation as an operational cleaning method, the rate of biofouling may be reduced. The rate of biofoulant accumulation on hydrophilic membranes may be reduced at higher SR Ts because the biomass at higher SR Ts has a higher hydrophobicity when compared to the biomass at lower SRTs.

Growth, antioxidant system, and immunological status of shrimp in bioflocs and clear water culture systems

The objective of this work was to evaluate the effect of the traditional culture system in clear water and of the one in microbial flocs on the antioxidant and immunological status of Litopenaeus vannamei shrimp. Samples (gill, hemolymph, and hepatopancreas) were collected on days 15, 30, and 60 of the experimental period. The following immunological parameters were analyzed at each evaluation time: granular and hyaline hemocytes, total protein, and apoptosis. Assays on glutamate-cysteine ligase (GCL) activity and on the concentrations of reduced glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) were also performed. The evaluated immunological parameters did not differ significantly between treatments. Shrimp reared in clear water showed higher levels of lipid peroxidation in the gills and of GCL activity in the hemolymph on days 15 and 30. Shrimp in microbial floc had a higher survival rate, and the water did not have to be renewed during the experimental period. The microbial floc system improves production levels and provides a healthier culture environment.

EVALUATION OF MICROBIAL FLOC AND MICROALGAE Spirulina platensis COMBINATION FOR JUVENILE COBIA Rachycentron canadum DIETS ON GROWTH AND PHYSIOLOGICAL RESPONSES AFTER IMMERSION IN FRESHWATER

In marine aquaculture, immersing marine fish species in fresh water can remove ectoparasite that adhere to all over the fish body. This study aimed to evaluate the impacts of combining microbial floc and microalgae Spirulina platensis in juvenile cobia diet on growth performance and stress responses after immersion in aerated fresh water for 15 minutes. The fishes were reared in concrete tanks for 40 days before collecting data on their growth performance. The stress response was determined by mea-suring both glucose and cortisol levels before (0 h) and after (1, 2, 4, 6, 24 hours) immersion. The fish-es fed on the 15% of combining microbial flock and microalgae Spirulina platensis diet showed the highest growth rate with the lowest feed conversion ratio compared to other treatments. The cortisol level of juvenile cobia in both the 15% and 30% combination of microbial floc and microalgae Spiru-lina platensis treatments did not increase during the first hour following the immersion compared to the control treatment. The glucose level also increased after one hour immersion in freshwater of all treatments. This indicated that feeding juvenile cobia on microbial flocs and microalgae diets had a retarding effect on the physiological responses (cortisol and glucose) after immersion in fresh water.Keywords: microbial, microalga, Spirulina, glucose, cortisol, stress, cobia

EVALUATION OF MICROBIAL FLOC AND MICROALGAE Spirulina platensis COMBINATION FOR JUVENILE COBIA Rachycentron canadum DIETS ON GROWTH AND PHYSIOLOGICAL RESPONSES AFTER IMMERSION IN FRESHWATER

<p>In marine aquaculture, immersing marine fish species in fresh water can remove ectoparasite that adhere to all over the fish body. This study aimed to evaluate the impacts of combining microbial floc and microalgae <em>Spirulina platensis </em>in juvenile cobia diet on growth performance and stress responses after immersion in aerated fresh water for 15 minutes. The fishes were reared in concrete tanks for 40 days before collecting data on their growth performance. The stress response was determined by mea-suring both glucose and cortisol levels before (0 h) and after (1, 2, 4, 6, 24 hours) immersion. The fish-es fed on the 15% of combining microbial flock and microalgae <em>Spirulina platensis</em> diet showed the highest growth rate with the lowest feed conversion ratio compared to other treatments. The cortisol level of juvenile cobia in both the 15% and 30% combination of microbial floc and microalgae <em>Spiru-lina platensis</em> treatments did not increase during the first hour following the immersion compared to the control treatment. The glucose level also increased after one hour immersion in freshwater of all treatments. This indicated that feeding juvenile cobia on microbial flocs and microalgae diets had a retarding effect on the physiological responses (cortisol and glucose) after immersion in fresh water.</p><p><strong>Keywords</strong>: microbial, microalga, Spirulina, glucose, cortisol, stress, cobia</p>