Diversity and Abundance of Microbial Communities in UASB Reactors during Methane Production from Hydrolyzed Wheat Straw and Lucerne

The use of straw for biofuel production is encouraged by the European Union. A previous study showed the feasibility of producing biomethane in upflow anaerobic sludge blanket (UASB) reactors using hydrolyzed, steam-pretreated wheat straw, before and after dark fermentation withCaldicellulosiruptor saccharolyticus, and lucerne. This study provides information on overall microbial community development in those UASB processes and changes related to acidification. The bacterial and archaeal community in granular samples was analyzed using high-throughput amplicon sequencing. Anaerobic digestion model no. 1 (ADM1) was used to predict the abundance of microbial functional groups. The sequencing results showed decreased richness and diversity in the microbial community, and decreased relative abundance of bacteria in relation to archaea, after process acidification. Canonical correspondence analysis showed significant negative correlations between the concentration of organic acids and three phyla, and positive correlations with seven phyla. Organic loading rate and total COD fed also showed significant correlations with microbial community structure, which changed over time. ADM1 predicted a decrease in acetate degraders after a decrease to pH <= 6.5. Acidification had a sustained effect on the microbial community and process performance

Characterization and adaptation of Caldicellulosiruptor strains to higher sugar concentrations, targeting enhanced hydrogen production from lignocellulosic hydrolysates

Abstract Background The members of the genus Caldicellulosiruptor have the potential for future integration into a biorefinery system due to their capacity to generate hydrogen close to the theoretical limit of 4 mol H2/mol hexose, use a wide range of sugars and can grow on numerous lignocellulose hydrolysates. However, members of this genus are unable to survive in high sugar concentrations, limiting their ability to grow on more concentrated hydrolysates, thus impeding their industrial applicability. In this study five members of this genus, C. owensensis, C. kronotskyensis, C. bescii, C. acetigenus and C. kristjanssonii, were developed to tolerate higher sugar concentrations through an adaptive laboratory evolution (ALE) process. The developed mixed population C. owensensis CO80 was further studied and accompanied by the development of a kinetic model based on Monod kinetics to quantitatively compare it with the parental strain. Results Mixed populations of Caldicellulosiruptor tolerant to higher glucose concentrations were obtained with C. owensensis adapted to grow up to 80 g/L glucose; other strains in particular C. kristjanssonii demonstrated a greater restriction to adaptation. The C. owensensis CO80 mixed population was further studied and demonstrated the ability to grow in glucose concentrations up to 80 g/L glucose, but with reduced volumetric hydrogen productivities ( $$Q_{{{\text{H}}_{2} }}$$ Q H 2 ) and incomplete sugar conversion at elevated glucose concentrations. In addition, the carbon yield decreased with elevated concentrations of glucose. The ability of the mixed population C. owensensis CO80 to grow in high glucose concentrations was further described with a kinetic growth model, which revealed that the critical sugar concentration of the cells increased fourfold when cultivated at higher concentrations. When co-cultured with the adapted C. saccharolyticus G5 mixed culture at a hydraulic retention time (HRT) of 20 h, C. owensensis constituted only 0.09–1.58% of the population in suspension. Conclusions The adaptation of members of the Caldicellulosiruptor genus to higher sugar concentrations established that the ability to develop improved strains via ALE is species dependent, with C. owensensis adapted to grow on 80 g/L, whereas C. kristjanssonii could only be adapted to 30 g/L glucose. Although C. owensensis CO80 was adapted to a higher sugar concentration, this mixed population demonstrated reduced $$Q_{{{\text{H}}_{2} }}$$ Q H 2 with elevated glucose concentrations. This would indicate that while ALE permits adaptation to elevated sugar concentrations, this approach does not result in improved fermentation performances at these higher sugar concentrations. Moreover, the observation that planktonic mixed culture of CO80 was outcompeted by an adapted C. saccharolyticus, when co-cultivated in continuous mode, indicates that the robustness of CO80 mixed culture should be improved for industrial application

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

With an increasing number of low-grade primary ores starting to be cog-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circular economy that requires a shift in business models, policies and improvements in process technologies. This review discusses the evolution towards low-grade primary ore and secondary raw material mining that will allow for sufficient supply of critical raw materials as well as base metals. Seven low-grade ores, including primary (Greek and Polish laterites) and secondary (fayalitic slags, jarosite and goethite sludges, zincrich waste treatment sludge and chromium-rich neutralisation sludge) raw materials are discussed as typical examples for Europe. In order to treat diverse and complex low-grade ores efficiently, the use of a new metallurgical systems toolbox is proposed, which is populated with existing and innovative unit operations: (i) mineral processing, (ii) metal extraction, (iii) metal recovery and (iv) matrix valorisation. Several promising novel techniques are under development for these four unit-operations. From an economical and environmental point of view, such processes must be fitted into new (circular) business models, whereby impacts and costs are divided over the entire value chain. Currently, low-grade secondary raw material processing is only economic and environmentally beneficial when the mineral residues can be valorised and landfill costs are avoided and/or incentives for waste processing can be taken into account

Design of kinetic models for assessment of critical aspects in bioprocess development : A case study of biohydrogen

The world faces major climate challenges and extensive efforts need to be taken to combat this issue. Replacing fossil-derived fuels and chemicals with renewables are one important step on the way. Hydrogen has a great potential as a renewable energy carrier for the transport sector and as a green chemical for the industry. Today, the production of hydrogen stems primarily from fossil resources. A sustainable alternative to the current methods of hydrogen production are via biological methods using micororganisms and renewable substrates. Caldicellulosiruptor species are thermophilic bacteria able to produce hydrogen close to the theoretical maximum of 4mol H2/mol hexose. Due to economic reasons, it is preferable if the microorganism can utilize different kinds.of substrates containing both pentose and hexose sugars as well as to withstand high amounts of sugar in the feed. These two aspects were quantitatively evaluated in this research by using kinetic models. Modelling is an important tool in bioprocess development since it can contribute to an increased understanding of the process and function as a predictor for future process performance and hence strive towards in silico assessments which are more cost effective.When a microorganism is exposed to several sugars a phenomenon called diauxic-growth can occur. Caldicellulosiruptor saccharolyticus was exposed to an industrial substrate, wheat straw hydrolysate (WSH), containing glucose, xylose and arabinose, as well as to an artifical sugar mixture containing the same amount of sugars as in the WSH. It was displayed that Caldicellulosiruptor saccharolyticus expresses a diauxic-like behaviour; simultaneously taking up different sugars (hexose and pentose) but with a preference for the pentoses. When the pentoses are depleted, there is a short lag phase followed by the continued uptake of the hexoses, however, at an altered rate. This is displayed as a biphasic growth curve, most visible in the hydrogen and carbon dioxide productivity profile. We hypothesize that there are several enzyme systems involved in the uptake that are either upregulated or downregulated depending on which sugar that is preferred. By using cybernetic variables that describe which transport system that is active this phenomenon could be describedmathematically.Caldicellulosiruptor owensensis’ tolerance towards high sugar and end-product concentration (i.e., high osmolarity) were evaluated and described mathematically. The kinetic growth model was appropriate to describethe behaviour of growth when exposed to 10 and 30 g/L of glucose. At higher sugar concentration, 80 g/L, the model slightly overestimated the growth. A critical osmolarity parameter was quantified and showed a fourfold increase in value with an increasing osmolarity. This means that Caldicellulosiruptor’s tolerance to a high osmolarity had increased in the adaptive laboratory evolution experiments conducted earlier. Producing biohydrogen with microorganisms such as Caldicellulosiruptor species has great potential in the transformation from a fossil to a bio-based economy. Further efforts in constructing and tuning kinetic models for biohydrogen production would be benficial from a process development point of view

Identification of technical and process related problems and potential for developments at biogas plants

Biogasanläggningar, som behandlar fler än en typ av substrat, så kallade samrötningsanläggningar, är relativt unga anläggningar. De första byggdes under tidigt 90-tal och står idag för omkring 28% av Sveriges totala biogasproduktion. Felaktigt inkommande material och det matavfall som tas in som substrat ställer höga krav på anläggningarnas utrustning, med därtill kopplade problem. Syftet med detta examensarbete var att genom intervjuer genomföra en kartläggning av befintliga tekniska och processrelaterade problem för två biogasanläggningar med samrötning samt en förbehandlingsanläggning. För att undersöka alternativa tekniker och utrustningar till identifierade problem genomfördes litteraturstudier och kontakt togs med leverantörer av biogasutrustning. Slutligen genomfördes en kostnadskalkylering för en specifik anläggning för att få en uppfattning om vad ett byte av problematisk utrustning skulle innebära rent ekonomiskt. Resultatet av kartläggningen visade att anläggningarnas förbehandling stod för de flesta problemen. Ett gemensamt problem för samtliga anläggningar var svårigheten att separera oönskat material från matavfall. Plast och annat oönskat material avskiljs inte i tillfredställande grad utan följer med vidare i processen och orsakar driftproblem samt att allt för mycket rötbart material följer med utgående rejekt och går till förbränning istället för rötning. Provtagning och analys av substrat och rejekt visade att vid avskiljning med skruvpress återfanns mer än 40% av substratets potentiella teoretiska metanutbyte i rejektfraktionen. Separation med bioseparator samt separation med en kombination av separerings­bassäng, trappstegsgaller och silpress visade en mindre förlust av metan i det avskiljda rejektet. Övriga identifierade problem omfattas av slitage och låg servicevänlighet hos utrustningen och outnyttjad utrustningskapacitet samt problem på grund av att utrustning ursprungligen ej var avsedd för biogasanläggningar. Litteraturstudier och kontakter med leverantörer av biogasutrustning visade att det finns alternativa tekniker och utrustningar till de identifierade problemen. Uppvärmning av substrat innan separation samt skifte till papperspåsar som insamlingsmetod är två potentiella lösningar. Det finns ett flertal utrustningar på marknaden för avskiljning av oönskat material, som potentiellt skulle kunna ersätta ineffektiva separationsutrustningar vid de aktuella anläggningarna. Huruvida sådana utrustningar skulle ge en förbättrad avskiljning och därmed minskad förlust av rötbart material i rejekt är svårt att avgöra innan tester med aktuellt substrat under aktuella förutsättningar genomförts. Resultatet av kostnadskalkyleringen visade att de största årliga drift- och underhålls­kostnaderna för befintlig separationsutrustning var lön till personal samt kostnader för slitage och haverier. En nyinvestering visade sig vara mycket kapitalintensivt i form av den initiala investeringskostnaden. Däremot frigör ett eventuellt byte till ny separationsutrustning personaltimmar då ny utrustning potentiellt kan kräva mindre drift- och underhållstid. Frigjorda personaltimmar kan istället användas till förebyggande underhåll eller som en besparingsåtgärd. Bättre uppföljning av rejektmängder och oplanerade driftstopp vid anläggningarna är viktiga initiala steg för att få kunskap om vilka problem som är av störst betydelse för att därefter kunna förbättra processen. Befintliga separationstekniker på anläggningarna fungerar inte optimalt och en vidareutveckling alternativt ersättning av dessa bör undersökas ytterligare.Biogas plants treating more than one type of substrate, so called co-digestion plants, are relatively new facilities. Mainly they were established in the early nineties and in Sweden these digesters produce approximately 28% of the total amount of biogas produced today. Faultily incoming material and the food waste used as substrate at the plants set high demands on the equipment used at the plants and many problems occur. The purpose of this thesis was to identify technical and process related problems at two co-digestion plants and one pretreatment plant by performing interviews with staff at the plants. Investigation of alternative techniques and equipment to abate the identified problems were performed by a literature study and contacts with distributors of biogas plant equipment. Finally, a cost-estimation was made at a specific plant in order to investigate the economic aspects of a replacement of old equipment. The result of the problem identification showed that the pretreatment units of the plants caused most of the problems. A common issue at the three plants was the problem to separate unwanted material from the food waste. Plastics and other unwanted material aren’t separated to a full extent and thereby cause problems downstream. Furthermore a large amount of food waste aimed for digestion, are separated together with the reject fraction and goes to incineration instead. Analysis of the incoming substrate and reject showed that by separation with a screw press more than 40% of the substrates theoretical methane yield were lost in the reject fraction. However, separation with a bio-separator or with a combination of sedimentation/flotation, a grid and a strain press showed a smaller loss of methane in the reject. Additional problems identified included extensive wear and tear at the equipment, unused equipment and problems caused by the fact that the equipment was not originally constructed for biogas plants. The literature study and contact with distributors of biogas plant equipment revealed alternative techniques and equipment to remediate the identified problems. The warm-up of substrate before separation and the replacement of plastic bags for paper bags for the collection of food waste are two potential solutions. There are several different equipments available, in order to separate unwanted material, which could potentially replace the ineffective equipment at the plants. Whether these would result in better separation and reduced loss of food waste via the reject is hard to tell before tests have been made at prevalent substrate and operation conditions. The result of the cost-estimation showed that the largest operating and maintenance costs for the old equipment were the labor cost and the cost for wear and tear. An investment in new equipment is very capital-intensive because of the large purchasing and installation cost.  On the other hand, a new equipment could potentially result in a release in working hours compared to a continuous operation of the old equipment. These extra hours could instead be used to maintain the new equipment and prevent break downs.  A better follow-up at the plants regarding the amount of reject and the number of occasions of unwanted stop is a first step towards gaining knowledge on the major problems in order to be able to improve the process. Current used separation techniques at the plants are not working as expected and an optimization or replacement of these should be evaluated

A non-linear model of hydrogen production by Caldicellulosiruptor saccharolyticus for diauxic-like consumption of lignocellulosic sugar mixtures

Background: Caldicellulosiruptor saccharolyticus is an attractive hydrogen producer suitable for growth on various lignocellulosic substrates. The aim of this study was to quantify uptake of pentose and hexose monosaccharides in anindustrial substrate and to present a kinetic growth model of C. saccharolyticus that includes sugar uptake on defined and industrial media. The model is based on Monod and Hill kinetics extended with gas-to-liquid mass transfer and acybernetic approach to describe diauxic-like growth.Results: Mathematical expressions were developed to describe hydrogen production by C. saccharolyticus consuming glucose, xylose, and arabinose. The model parameters were calibrated against batch fermentation data. Theexperimental data included four different cases: glucose, xylose, sugar mixture, and wheat straw hydrolysate (WSH) fermentations. The fermentations were performed without yeast extract. The substrate uptake rate of C. saccharolyticuson single sugar-defined media was higher on glucose compared to xylose. In contrast, in the defined sugar mixture and WSH, the pentoses were consumed faster than glucose. Subsequently, the cultures entered a lag phasewhen all pentoses were consumed after which glucose uptake rate increased. This phenomenon suggested a diauxic-like behavior as was deduced from the successive appearance of two peaks in the hydrogen and carbon dioxideproductivity. The observation could be described with a modified diauxic model including a second enzyme system with a higher affinity for glucose being expressed when pentose saccharides are consumed. This behavior was morepronounced when WSH was used as substrate.Conclusions: The previously observed co-consumption of glucose and pentoses with a preference for the latter was herein confirmed. However, once all pentoses were consumed, C. saccharolyticus most probably expressed anotheruptake system to account for the observed increased glucose uptake rate. This phenomenon could be quantitatively captured in a kinetic model of the entire diauxic-like growth process. Moreover, the observation indicates a regulationsystem that has fundamental research relevance, since pentose and glucose uptake in C. saccharolyticus has only been described with ABC transporters, whereas previously reported diauxic growth phenomena have been correlatedmainly to PTS systems for sugar uptake

Benchmarking av gödselsamrötning med avloppsslam mot förbränning av häst- och djurparksgödsel

Owners of stables and owners of zoos have difficulty finding an economically sustainable deposition of their produced manure. More than two million tons of horse manure are produced in urban environments in Sweden every year. If the manure cannot be used as fertilizer on farm land it is classified as a waste fraction and should be handled according to current regulations. The manure is a valuable waste fraction that contains both energy and nutrients. If the manure cannot be spread on farm land more applications need to be identified, where the energy and nutrients in the manure can be used. The focus in this study is to investigate possible applications for the usage of horse and zoo manure within Borås municipality where, among other things, a waste water treatment plant and a combined heat and power plant are available. Horse and zoo manure have been investigated in the following applications: co-digestion with sewage sludge at a waste water treatment plant (lab experiments), co-digestion with food waste (theoretical), co-incineration with waste (full scale) and co-incineration with biomass (theoretical). Potential quantity of manure and economical and legal aspects have been studied as well. There is no compilation of the number of horses in the country which makes it hard to estimate the true quantity of manure. The quantity of manure from the zoos are somewhat easier to estimate since the zoo owners are fewer and have knowledge of their manure production. The co-digestions experiments in this study showed that addition of horse manure to digestion can be of interest in many ways, among other things it can give a more stable biogas production and a possible decrease in the Cd/P-ratio in the end product. Horse manure turned out to have a faster degradation rate compared to zoo manure, however the degradation rate was lower than that of sewage sludge. Zoo manure gave a relatively low biogas production compared to horse manure at thermophilic conditions. The co-incineration trial with waste and manure gave no negative effect with regard to emissions and operation. However, the amount of manure added to the incineration trial was low. The theoretical studies regarding the co-incineration with biomass, showed two potential alternatives that need to be investigated further. Interesting aspects to look further upon, based on this study, are for example: • Laws and regulations in the EU regarding manure. • Co-digestion of manure and sewage sludge in a larger scale. • Laws and regulations and costs regarding incineration of manure with biomass

Techno-economic evaluation of biogas upgrading using ionic liquids in comparison with industrially used technology in Scandinavian anaerobic digestion plants

The process of biogas upgrading with ionic liquids, i.e. pure 1-butyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide ([bmim][Tf2N]), aqueous choline chloride/urea (ChCl/Urea), and aqueous 1-allyl-3-methyl imidazole formate ([Amim][HCOO]), was simulated in Aspen Plus and compared with the conventional water scrubbing upgrading technique. The comparisons of the performances on the amount of recirculated solvents and energy usage show the following order: aqueous [Amim][HCOO]<aqueous ChCl/Urea<[bmim][Tf2N]<water. Six different co-digestion plants (anaerobic digestion, AD, plants) were surveyed to acquire data for comparison. The selected plants had different raw biogas production capacities and produced gas with differing methane content. The data confirmed the simulation results that the type of substrate and the configuration of AD process are two factors affecting energy usage, investment cost, as well as operation and maintenance costs for the subsequent biogas upgrading. In addition, the simulation indicated that the energy usage of the ionic liquid-based upgrading was lower than that of the conventional upgrading techniques in Scandinavian AD plants. The estimated cost including investment, operation and maintenance for the ionic liquid technology showed to be lower than that for the water scrubbing upgrading process

Near-zero-waste processing of low-grade, complex primary ores and secondary raw materials in Europe: technology development trends

status: publishe