Modeling De Novo Granulation of Anaerobic Sludge

The enigma of anaerobic sludge granulations is still exciting the minds of both experimental scientists and modeling experts. A unique combination of mechanical, physiochemical and biological forces influence granulation during processes of anaerobic digestion. However, knowledge of potential driving forces of granulation has not been transformed into a comprehensive model of anaerobic granulation. In this computational experiment, we address the role physiochemical and biological processes play in granulation and provide a literature-validated working model of anaerobic granule de novo formation. The model developed in a cDynoMiCs simulation environment successfully demonstrated a de novo granulation in a glucose fed system. The simulated granules exhibit experimental observations of radial stratification: A central dead core surrounded by methanogens then encased in acidogens. Practical applications of the granulation model was assessed on the anaerobic digestion of low-strength wastewater by measuring the changes in methane yield as model parameters were systematically swept. This model will be expanded in the future to investigate the influence of mechanical forces on the de novo granulation and the application of a model to anaerobic digestion of a complex protein-carbohydrate rich feedstock

Optimization of Biogas Production by Use of a Microbially Enhanced Inoculum

A renewable energy source, biogas, comprises of methane (80%) and carbon dioxide (15%), and is a great alternative to the conventional fossil-based fuels, such as coal, gas and oil. Biogas is created during anaerobic biological digestion of waste materials, such as landfill material, animal manure, wastewater, algal biomass, industrial organic waste etc. A biogas potential from organic waste in the United States is estimated at about 9 million tons per year and technology allows capture of greenhouse gases, such as methane and carbon dioxide, into a form of a fuel. In the light of global climate change and efforts to decrease carbon footprint of fuels in daily life, usage of biogas as an alternative fuel to fossil fuels looks especially promising. The goal of this research was to develop and test an approach for optimization of biogas production by engineering microorganisms digesting organic waste. Specifically, bacteria that can digest algal biomass, collected from the wastewater lagoons or open waterbodies. The research also expands on the previous efforts to analyze microbial interactions in wastewater treatment systems. A computational model is developed to aid with prognosis of microbial consortia ability to form complex aggregates in reactors with upflow mode of feeding substrate. Combining modeling predictions and laboratory experiments in organic matter digestion will lead to more stable engineered systems and higher yields of biogas

Growth and break-up of methanogenic granules suggests mechanisms for biofilm and community development

Methanogenic sludge granules are densely packed, small, spherical biofilms found in anaerobic digesters used to treat industrial wastewaters, where they underpin efficient organic waste conversion and biogas production. Each granule theoretically houses representative microorganisms from all of the trophic groups implicated in the successive and interdependent reactions of the anaerobic digestion (AD) process. Information on exactly how methanogenic granules develop, and their eventual fate will be important for precision management of environmental biotechnologies. Granules from a full-scale bioreactor were size-separated into small (0.6–1 mm), medium (1– 1.4 mm), and large (1.4–1.8 mm) size fractions. Twelve laboratory-scale bioreactors were operated using either small, medium, or large granules, or unfractionated sludge. After >50 days of operation, the granule size distribution in each of the small, medium, and large bioreactor sets had diversified beyond—to both bigger and smaller than—the size fraction used for inoculation. Interestingly, extra-small (XS; <0.6 mm) granules were observed, and retained in all of the bioreactors, suggesting the continuous nature of granulation, and/or the breakage of larger granules into XS bits. Moreover, evidence suggested that even granules with small diameters could break. “New” granules from each emerging size were analyzed by studying community structure based on high-throughput 16S rRNA gene sequencing. Methanobacterium, Aminobacterium, Propionibacteriaceae, and Desulfovibrio represented the majority of the community in new granules. H2-using, and not acetoclastic, methanogens appeared more important, and were associated with abundant syntrophic bacteria. Multivariate integration (MINT) analyses identified distinct discriminant taxa responsible for shaping the microbial communities in different-sized granules

A Model for Bioaugmented Anaerobic Granule

In this study, we have created a simulation model which is concerned about digesting cellulose, as a major component of microalgae in a bioreactor. This model is designed to generate a computational model that simulates the process of granulation in anaerobic sludge and aims to investigate scenarios of possible granular bioaugmentation. Once a mature granule is formed, protein is used as an alternative substrate that will be supplied to a mature granule. Protein, being a main component of cyanobacteria, will promote growth and incorporation of a cell type that can degrade protein (selective pressure). The model developed in a cDynoMiCs simulation environment successfully demonstrated the process of granule formation and bioaugmentation in an Anaerobic granule. Bioaugmentation is a common strategy in the field of wastewater treatment, used to introduce a new metabolic capability to either aerobic or anaerobic granules. The end product of our work is a model that can visually demonstrate varying stratifications of different trophic microbial groups that will be of help for the engineers and researchers, who are operating both laboratory and industrial-scale anaerobic digesters and wish to enhance reactor performance. The working model that we have developed has been validated using the existing literature and lab experiments. The model successfully demonstrates granulation in a cellobiose fed system with formation of 0.63 mm mature granule in 59 days with the production of good amount of methane that could be used commercially as a green fuel. This model is extended to perform bioaugmentation by chaining different simulations

Free boundary problems for mixed-species biofilms: modelling and simulation

This dissertation proposes a modelling study on biofilms, with a special interest in phototrophic biofilms, one of the most promising innovative biological technologies in the field of wastewater treatment. Novel mathematical models are derived and presented here, with the aim of describing exhaustively the formation and the growth of planar and granular biofilms, specifically phototrophic-heterotrophic biofilms, anaerobic granular biofilms and oxygenic photogranules. The introduction of novel mathematical formulations allows to describe crucial aspects and processes of these ecosystems, never or not exhaustively explored by mathematical models present in literature. Models presented here are formulated as one-dimensional free boundary problems, which describe the evolution of planar and granular biofilms. The processes taking place within the biofilm are modelled through systems of nonlinear partial differential equations (PDEs), derived using a continuum approach: non-linear hyperbolic PDEs model the advective transport and growth of sessile biomasses which constitute the biofilm, while quasi-linear parabolic PDEs govern the diffusive transport and conversion of soluble substrates, and the phenomena of microbial invasion by planktonic cells inhabiting the surrounding environment. The first proposed model consists of a free boundary problem describing the role of planktonic cells in the formation and evolution of planar multispecies biofilms, by modelling the phenomena of initial attachment and microbial invasion. Moreover, a theorem of existence and uniqueness of the solutions, based on the fixed-point theorem, is presented. The second model is formulated as a free boundary problem which describes the ecology of phototrophic-heterotrophic biofilms. It considers the processes of microbial invasion and focuses on the metabolic activities of phototrophic and heterotrophic species, their interactions and main factors involved in this biofilm ecosystem, such as light conditions and attenuation, photoinhibition, phototrophic release of organic matter, production of extracellular polymeric substances (EPS). In order to model the process of initial formation and growth of anaerobic granular biofilms, known as de novo granulation, a free boundary problem is formulated within a spherical domain with radial symmetry. In this case, a multiscale approach is used, by modelling both the evolution of granular anaerobic biofilms and the dynamics of the bioreactor where such biofilms develop. Hence, such model allows to simulate the global treatment process occurring in anaerobic granular systems and to draw engineering conclusions. Finally, the latest model is aimed to describe for the first time the oxygenic photogranules (OPGs), biofilm granules composed of cyanobacteria and microalgae, recently recognised as an attractive biological technology to remove polluting compounds from wastewaters. As the previous one, this multiscale model is formulated as a spherical free boundary problem with radial symmetry, and allows to accurately describe the genesis and growth processes of oxygenic photogranules within a sequencing batch reactor (SBR) and to investigate the treatment efficiency of this system. The model considers the main biotic and abiotic factors involved, the symbiotic and competitive microbial mechanisms driving the treatment process, the metabolic differences between cyanobacteria and microalgae and the key role that cyanobacteria play in the photogranulation. All models are integrated numerically through the development of original numerical softwares in MatLab platform. The main numerical methods used are the method of characteristics, the Euler explicit method and the method of lines. Furthermore, the models presented are used to carry out numerical studies of relevant engineering, biological and ecological interest

Aerobic granular sludge technology for fish-canning wastewater treatment: optimisation and scale up

A presente tese de doutoramento céntrase na optimización e escalado da tecnoloxía de biomasa granular aerobia para o tratamento de augas residuais da industria conserveira. A optimización do proceso consistiu na avaliación de distintas configuracións de reactores, así como a implementación dunha nova estratexia de aeración baseada no aporte de aire de forma pulsante. O tratamento de efluentes da industria conserveira foi primeiro estudado a escala laboratorio. Posteriormente, operouse unha planta piloto, localizada nunha conserveira galega, para o tratamento das augas residuais xeradas. Ademais, elabotorouse un modelo biolóxico cos datos experimentais obtiedos, para determinar o efecto desta auga industrial salina na actividade biolóxica dos gránulos

Relating Anaerobic Digestion Microbial Community and Process Function

Anaerobic digestion (AD) involves a consortium of microorganisms that convert substrates into biogas containing methane for renewable energy. The technology has suffered from the perception of being periodically unstable due to limited understanding of the relationship between microbial community structure and function. The emphasis of this review is to describe microbial communities in digesters and quantitative and qualitative relationships between community structure and digester function. Progress has been made in the past few decades to identify key microorganisms influencing AD. Yet, more work is required to realize robust, quantitative relationships between microbial community structure and functions such as methane production rate and resilience after perturbations. Other promising areas of research for improved AD may include methods to increase/control (1) hydrolysis rate, (2) direct interspecies electron transfer to methanogens, (3) community structure–function relationships of methanogens, (4) methanogenesis via acetate oxidation, and (5) bioaugmentation to study community–activity relationships or improve engineered bioprocesses

Augmenting Anaerobic Digestion of Microalgal Biomass

Anaerobic digestion of microalgal biomass cannot be achieved without specialized hydrolytic microorganisms. Potentially algalytic bacteria belonging to Citrobacter and Alcaligenes species were isolated from a wastewater lagoon system. A combination of two potentially algalytic bacteria was successfully incorporated into the granular anaerobic consortia. A series of anaerobic cultures were prepared with different microbial combinations to test the methane production from algal biomass collected from a local wastewater treating trickling filter. The anaerobic microbial community mixed with two algalytic bacteria produced 10% more methane when compared to the methane produced by a native granular consortium. The presence of the algalytic bacteria of interest was confirmed by PCR using bacteria specific primers at the conclusion of the study. A computer-simulated model was designed to prove the possibility of incorporating algalytic bacteria into a mature methane-producing granule. Future research will address the anaerobic degradation potential of the modified granular consortia on other types of the microalgal biomass

Processo de granulação aeróbia em reatores em bateladas sequenciais em condições de baixa carga orgânica

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Ambiental, Florianópolis, 2015.A tecnologia de grânulos aeróbios tem sido amplamente estudada para a remoção de nitrogênio e fósforo de águas residuárias. Entretanto, a maioria dos estudos tem sido realizada utilizando efluentes sintéticos de média e elevada carga orgânica volumétrica (COV). Existem poucos relatos sobre a granulação aeróbia com efluentes reais de baixa COV, como os esgotos domésticos. Neste contexto, o processo de granulação aeróbia em condições de baixa COV foi avaliado utilizando três Sistemas Experimentais (SE) distintos. No SE-I foi explorada a remoção de nitrogênio durante a formação e a maturação dos grânulos aeróbios em um reator em bateladas sequenciais (RBS) alimentado com esgoto doméstico. Após 160 dias de operação, o processo de granulação estava completo no reator. Os grânulos maduros apresentavam uma estrutura esférica e densa, com diâmetro médio de 473 µm e IVL30 (índice volumétrico de lodo) de 75,6 mL·gSST-1. A assimilação da amônia para o crescimento celular foi mais expressiva durante o período de start-up do reator. Após a formação dos grânulos, a assimilação foi menor do que 5% e a remoção do nitrogênio ocorreu, principalmente, por nitrificação-desnitrificação via nitrito. O SE-II teve como objetivo compreender como a presença de matéria orgânica particulada (XS) afeta a formação dos grânulos e a qualidade do efluente tratado sob diferentes condições operacionais. Para isso, dois reatores alimentados com esgoto sintético foram operados na ausência (R1) ou presença (R2) de XS. Os grânulos cultivados na presença de XS apresentaram uma estrutura irregular e filamentosa, a qual afetou a capacidade de sedimentação da biomassa e, consequentemente, a qualidade do efluente tratado. A operação em volume constante (enchimento ascendente pela parte inferior do reator e descarte simultâneo pela parte superior do reator) mostrou-se favorável para uma maior eficiência de remoção de substrato e também para o suprimento do crescimento filamentoso na presença de XS. No SE-III buscou-se entender como a velocidade ascensional de esgoto (VWW) aplicada durante a fase de enchimento-descarte simultâneos (volume constante) influencia as propriedades do lodo e a conversão do substrato. Para isso, o reator utilizado foi alimentado com esgoto doméstico de baixa carga orgânica em diferentes VWW: 1, 5,9, 8, 12,5 e 16 m·h-1. Elevadas eficiências de remoção de sustrato foram obtidas a uma VWW de 1 m·h-1, uma vez que houve uma maior retenção de biomassa no reator sob essas condições. Em média, 96 ± 4% de amônia e 89 ± 7% de fósforo foram removidos a uma baixa VWW de 1 m·h-1. No entanto, o processo de desnitrificação foi a etapa limitante na remoção de nitrogênio. De maneira geral, os sistemas estudados mostraram que é possível desenvolver grânulos maduros e estáveis com esgoto doméstico de baixa carga orgânica utilizando RBS. Além disso, também foi possível remover carbono, nitrogênio e fósforo em uma única unidade operacional compacta. Entretanto, o modo de operação do RBS deve ser adaptado de acordo com o tipo de efluente a ser tratado, principalmente aqueles que contêm XS em sua composição.Abstract : The aerobic granular sludge (AGS) technology has been widely studied for the biological nutrient removal from wastewater. However, most of the studies have been performed using synthetic wastewaters at high or middle-high organic loading rates (OLR). Only few studies reported successful granulation with real influents at low OLR, such as domestic wastewater. In this context, three different Experimental Systems (ES) were used in order to evaluate the aerobic granulation process under conditions of low OLR. In the ES-I the performance of a sequencing batch reactor (SBR) was evaluated in terms of nitrogen removal during the formation and maturation of aerobic granules fed with real domestic wastewater. The granulation process was complete after 160 days of operation. The mature granules had a nearly spherical structure, an average size of 473.0 µm, and a good settling ability (SVI30 of 75.6 mL·g-1). Ammonium assimilation for cell growth was more significant during the reactor start-up period. After granule formation, assimilation accounted for less than 5% and nitrogen was mainly removed by nitrification-denitrification via nitrite. The ES-II aimed at understanding how the presence of XS affects the formation of the granules and the quality of the treated effluent under different operating conditions. Two reactors fed with synthetic influents were operated in absence (R1) or presence (R2) of particulate organic matter (XS). The granules grown in presence of XS had irregular and filamentous outgrowths in the surface, which affected the settleability of the biomass and therefore the quality of the effluent. Operating at constant volume (simultaneous fill from the bottom of the reactor and draw from the upper part of the reactor) showed to be beneficial for the substrate removal efficiency and for suppressing filamentous overgrowth in presence of XS. In the ES-III the focus was on understanding how the wastewater upflow velocity (VWW) applied during the fill-and-draw phase (constant volume) influenced the sludge properties and in turn the substrate conversion. The reactor was fed with low-strength domestic wastewater at different VWW: 1, 5.9, 8, 12.5 and 16 m h-1. High efficiencies for substrate removal were obtained at VWW of 1 m·h-1, due to the higher biomass retention in the system under these conditions. Average removal efficiencies of 96 ± 4% for ammonium and 89 ± 7% for phosphorus were obtained at very low VWW of 1 m·h-1. However, denitrification was the limiting step for nitrogen removal. Overall, the studied systems showed that it is possible to develop mature and stable aerobic granules in SBR using low-strengthdomestic wastewater. Besides, it was also possible to efficiently remove carbon, nitrogen, and phosphorus in a single and compact reactor unit. However, the operation mode of such reactors must be adapted according to the composition of the influent, especially the ones containing XS