Pilot Digester Research Articles

Process characterization in industrial vessels by flow-following sensor particles

Instrumented flow-following sensor particles have been developed for investigation of hydrodynamic and biochemical processes in chemical reactors and bioreactors, where standard measurement techniques are not applicable. The sensor particles allow autonomous long-term measurement of spatially distributed process parameters in the chemically and mechanically harsh environments of e.g. agitated industrial vessels. Each sensor particle comprises of an on-board measurement electronics that logs the signals of the embedded sensors. A buoyancy control unit enables automated taring to achieve neutral buoyancy of the sensor particles. Moreover, controlled floating of the sensor particles is possible to expose them for recovery from the liquid surface. Macro-flow tracking of the sensor particles is validated with circulation time reference measurements by means of salt tracer experiments in a stirred model reactor and computational fluid dynamics (CFD) simulations. Moreover, process characterization with sensor particles is demonstrated in three further applications, namely a biogas pilot digester, an air–water column and a biological wastewater treatment basin. Acquired data were used to fit mixing model parameters, namely effective circulation time, circulation number, degree of suspension and Péclet number.

Photosynthetic upgrading of biogas from anaerobic digestion of mixed sludge in an outdoors algal-bacterial photobioreactor at pilot scale

Anaerobic digestion can biotransform the biodegradable fraction of sewage sludge into biogas, while the symbiotic action of algal-bacterial consortia can remove both the CO2 and H2S from biogas and nutrients from digestate. A 100 L anaerobic digester operated at 20 days of retention time coupled with a 180 L high-rate algal pond (HRAP) engineered to upgrade the biogas and treat the liquid fraction of the pilot digester was optimized along four operational stages: (I) operation with a greenhouse during winter; (II) operation without greenhouse; (III) process supplementation with NaHCO3; (IV) process supplementation with Na2CO3. The biogas produced was composed of 63.7 ± 2.9% CH4, 33.7 ± 1.9% CO2, 0.5 ± 0.3% O2 and 1.6 ± 1.1% N2. An average methane productivity of 324.7 ± 75.8 mL CH4 g VSin−1 and total COD removals of 48 ± 20% were recorded in the digester. The CH4 concentration in the biomethane gradually decreased to 87.6 ± 2.0% and 85.1 ± 1.3% at the end of stage I and II, respectively, attributed to the loss of inorganic carbon in the HRAP. The supplementation of NaHCO3 and Na2CO3 mediated an increase in the CH4 content to 90.4 ± 1.5 and 91.2 ± 0.7% in stages III and IV, respectively. Steady state CO2 removals of 90% and 88% in stages I and II, and 95.7 and 97.6% in stages III and IV, respectively, were recorded. A constant biomass productivity of 22 g m−2 d−1, set by daily harvesting 26.5 g dry algal-bacterial biomass from the bottom of the settler, was maintained concomitantly with a complete removal of the N and P supplied via centrate.

New findings on the anaerobic co-digestion of thermally pretreated sludge and food waste: laboratory and pilot-scale studies.

Co-digestion of thermally pretreated sewage sludge with food waste is an innovative strategy that could improve the balance and availability of nutrients needed to increase the efficiency of anaerobic digestion in terms of biogas production. In this context, the aim of this research was to evaluate the impact of different proportions of sewage sludge/food waste in laboratory- and pilot-scale reactors. Special focus was placed on the impact of the variability of food waste composition on the behaviour of the pilot digester. Our results show that by adding 40% of co-substrate, a higher biogas production was possible during laboratory operation. Interestingly, using a co-substrate of variable composition had no negative impact on the reactor's stability at pilot-scale, promoting an increase in biogas production through a more efficient use of organic matter. In both the lab and pilot experiences there was an impact on the amount of nitrogen in the digestate compared to digester operating in monodigestion. This impact is more significant as the proportion of co-substrate rises. Overall, our results show that co-digestion of thermally pretreated sewage sludge with food waste allows better management of food waste, especially when their composition is variable.

The impact of immersed liquid circulation on anaerobic digestion of rice straw bale and methane generation improvement

Immersed liquid circulation is assumed to improve solid-state anaerobic digestion (SS-AD) with digestate flow convection on the surface of solid-state bed (SSB), which depends on SSB concentration and circulation rate (CR). In this study, the impact of CR on rice straw SS-AD was investigated within a 30 L pilot digester. Results showed that SSB threshold concentration for efficient biogas conversion was 10%–12% TS, achieving the methane yield of 185.3 mL/g VS. Within the threshold, methane production progress and VFAs release could be enhanced simultaneously by rational CR increasing, but no significant methane yield improvement was observed; above, the rapid and stable biogas generation could be acquired with a competitive methane yield of 174.7 mL/g VS (150% CR). No matter within or above the threshold, efficient lingo-cellulosic degradation was always accompanied by the moderate CR for effective methane generation. SSB was proposed to be above threshold for industrial application.

Enhancement of organic household waste anaerobic digestion performances in a thermophilic pilot digester

Performances of organic household waste anaerobic digestion was investigated in a new horizontal thermophilic pilot digester of 50 L total capacity. The operation was performed under favorable conditions without any chemical additives. The presence of predigested cattle manure in the digester provided an interesting buffer capacity that was able to balance the produced fatty acids during the digestion process.The biomethane production reached 0.44 m3 CH4/Kg VS while achieving a COD removal of 70%.The operating time and the anaerobic digestion steps were shortened under thermophilic wet digestion. Only 4 days were sufficient to reach the daily maximum methane production (0.084 m3 CH4/(kgVS.day)) and 10 days to reach 80% of the overall biomethane potential. The process efficiency in removing volatile solid was found to be more than 35% within 5 days.Therefore, wet anaerobic digestion under thermophilic temperature is suitable for industrial scale anaerobic digestion of biowaste regarding the high biomethane yield, the large COD and solid removing and the shortness of process operating time.

Anaerobic Digestion of Liquid Waste from an Attiéké Factory: From the Experimental Scale to the Semi-Industrial Scale

This study focused on the transfer of experimental results of anaerobic digestion of liquid waste from an attieke (steamed cassava semolina) factory to a 6 m3 pilot digester. The experimental digester and the pilot were powered as follows: Lw + U + C (liquid waste + urine + cow dung). To the results, the experimental digester mesophilic with a progressive elimination of COD. Also, the nitrogen concentrations in the experimental reactor had little removal with alkaline pH. As for the biogas product in this digester, a volume of 3.6 m3 was obtained with a positive flammability test. The transition from the laboratory scale to the semi-industrial scale retains the results of purification and fuel biogas production of the experimental digester.

Energy performance evaluation of ultrasonic pretreatment of organic solid waste in a pilot-scale digester

It has been proven that ultrasonic pretreatment (UP) has positive effect on biogas generation from previous lab-scale studies. However, that is not always the case in larger scale processes. The purpose of this study was to evaluate the effectiveness of UP to biogas generation in terms of anaerobic digestion process and energy efficiency. Parameters including total solids (TS) and ultrasonic treatment operational parameters of organic solid waste (OSW) resulted from our past lab scale UP studies were applied in this study. OSW with 6–10% TS was treated using a lab-scale ultrasonic processor using various power densities (0.2–0.6 W/mL) at different time periods up to 30 min. Results of lab scale confirmed that OSW with 6% TS sonicated with 0.2 W/mL power density in 30 min gave the best outcome for the pilot scale experiment. To simulate the condition of an actual scale, in addition to energy analysis, two different organic loading rates (OLR), namely 500 and 1500 gVS/m3day were examined. The pilot digester was fed with OSW with or without the pretreatment based on the aforementioned specifications. The results showed that UP effectively improves biogas generation in terms of quantity and quality (CH4/CO2). Furthermore, it decreases the time to reach the maximum cumulative biogas volume comparing to the untreated feed. The key achievement of this research has confirmed that although the relative increase in the energy gain by the influence of UP was more remarkable under the 500 gVS/m3day OLR, energy analysis showed a better energy gain and energy benefit as well as jumping in biogas yield up to 80% for UP treated OSW under 1500 gVS/m3day OLR.

Hydrodynamics of high solids anaerobic reactor: Characterization of solid segregation and liquid mixing pattern in a pilot plant VALORGA facility under different reactor geometry

One of the main problems of dry anaerobic digestion plants treating urban solid waste is the loss of useful volume by the sedimentation of solids (inerts) into the bottom of the digester, or by accumulation of floating materials in its upper part. This entails a periodic cost of emptying and cleaning the digesters, a decrease in biogas production and complications in maintenance. Usually the sedimentation is a consequence of the heterogeneity of waste that, in addition to organic matter, drags particles of high density that end up obstructing the digesters. To reduce this bottleneck, URBASER has designed a new configuration of VALORGA reactor. That is, the VALORGA central wall has been removed and an inclined bottom has been added. To test the sedimentability and the overall performance of both configurations (current and new design), hydrodynamic tests have been carried out in a pilot digester (digester of 95 m3 capacity). To simulate the liquid phase and the solid phase of the reactor, lithium tracers and tags of different densities with RFID (radio frequency identification reader) have been used respectively. The results of the study showed an improvement in the performance of the new reactor design at pilot level.

Biogas Production from Partially Digested Septic Tank Sludge and its Kinetics

In developing countries, like India, there is no systematic approach for septage management. Treatment and possibility of methane recovery from this septage has not been explored previously. Hence, possibility of recovering methane from septic tank sludge in an anaerobic digester was explored with and without ultra-sonication pre-treatment in laboratory scale reactors and a 2 m3 pilot anaerobic digester was operated on raw septic tank sludge over a period of 1 year. Methane production potential of the raw septic tank sludge was 298.88 ± 9.7 L kg VS destroyed, which increased to 409.96 ± 13.25 L kg VS destroyed after sonication pre-treatment. Methane content in biogas increased from 73.15 to 81.83% upon sonication pre-treatment of the sludge. A first-order kinetic model best predicted biogas production from pilot digester fed with raw septic tank sludge, with minimum errors. Laboratory scale studies proved the feasibility and economic benefit of using sonicated sludge in the digester, with a net energy gain of 1.67 W-h/L of sludge digested. The kinetic constants derived from the laboratory experiments can be used for design of digester for field application using sonicated sludge to enhance digestion rate and methane recovery from septic tank sludge for better energy conservation.

The use of an industrial by-product as a sorbent to remove CO2 and H2S from biogas

Raw biogas, produced by anaerobic digestion of organic matter, is a methane-rich combustible gas. The CH4 content can be upgraded to reach the natural gas composition for vehicle fuel use (bio-CNG) or injection into the gas grid. This upgrading is performed by CO2 removal and pollutants treatment (H2S, water, etc.). The accelerated carbonation on BOF slag, a by-product from the steel industry containing calcium and iron oxides, was studied as a solution. The purpose of this work was to study the potential of slags to remove simultaneously CO2 with CaO (carbonation) and H2S with Fe2O3 (sulfuration) under atmospheric conditions. Firstly, batch experiments have confirmed the reactivity among CO2, H2S and slag. Removal capacities of 63 gCO2/kgBOF and 140 gH2S/kgBOF were estimated. The effect of the amount of water in the mix biogas/slag was studied on treatment performances, and an optimal L/S range between 0.05 and 0.2 Lwater/kgBOF was found. Secondly a field scale column experiment has been performed to treat the biogas of a pilot digester. This test under dynamic conditions using a BOF slags filter has given promising results (73 gCO2/kgBOF).

Anaerobic digestion and co-digestion of slaughterhouse wastes

The use of renewable energy is becoming increasingly necessary in order to address the global warming problem and, as a consequence, has become an high priority for many countries. Biomass is a clean and renewable energy source with growing potential to replace conventional fossil fuels. Among biomass, residual and waste ones represent a great resource for energy generation since they permit both to eliminate a possible waste and to produce energy. In the present work, the case of slaughterhouse wastes (SHWs) has been investigated. Anaerobic digestion is nowadays considered as one of the most important and sustainable conversion technology exploiting organic matter and biodegradable wastes. Biogas results from this bio-chemical process and mainly consists of methane and carbon dioxide, leading to produce thermal energy and/or electricity. In this paper, the European Regulations on animal by-products (ABPs) are described, and some previous study on anaerobic digestion and co-digestion of ABPs - more precisely SHWs - are considered and compared in order to fix a starting point for future tests on their co-digestion in a micro-scale pilot digester. This is to define optimal feed ratio values which ensure an increasing content of methane in the outgoing biogas.

Anaerobic digestion and co-digestion of slaughterhouse wastes

The use of renewable energy is becoming increasingly necessary in order to address the global warming problem and, as a consequence, has become an high priority for many countries. Biomass is a clean and renewable energy source with growing potential to replace conventional fossil fuels. Among biomass, residual and waste ones represent a great resource for energy generation since they permit both to eliminate a possible waste and to produce energy. In the present work, the case of slaughterhouse wastes (SHWs) has been investigated. Anaerobic digestion is nowadays considered as one of the most important and sustainable conversion technology exploiting organic matter and biodegradable wastes. Biogas results from this bio-chemical process and mainly consists of methane and carbon dioxide, leading to produce thermal energy and/or electricity. In this paper, the European Regulations on animal by-products (ABPs) are described, and some previous study on anaerobic digestion and co-digestion of ABPs - more precisely SHWs - are considered and compared in order to fix a starting point for future tests on their co-digestion in a micro-scale pilot digester. This is to define optimal feed ratio values which ensure an increasing content of methane in the outgoing biogas.

Microaerobic desulphurisation unit: A new biological system for the removal of H2S from biogas

A new biotechnology for the removal of H2S from biogas was devised. The desulphurisation conditions present in microaerobic digesters were reproduced inside an external chamber called a microaerobic desulphurisation unit (MDU). A 10 L-unit was inoculated with 1L of digested sludge in order to treat the biogas produced in a pilot digester. During the 128 d of research under such conditions, the average removal efficiency was 94%. The MDU proved to be robust against fluctuations in biogas residence time (57-107 min), inlet H2S concentration (0.17-0.39% v/v), O2/H2S supplied ratio (17.3-1.4 v/v), and temperature (20-35°C). Microbiological analysis confirmed the presence of at least three genera of sulphide-oxidising bacteria. Approximately 60% of all the H2S oxidised was recovered from the bottom of the system in the form of large solid S(0) sheets with 98% w/w of purity. Therefore, this system could become a cost-effective alternative to the conventional biotechniques for biogas desulphurisation.

In this issue

Engineering in Life SciencesVolume 11, Issue 5 p. 455-455 In this issueFree Access In this issue First published: 14 October 2011 https://doi.org/10.1002/elsc.201190033AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Dairy manure mixing for biogas production Rico et al., Eng. Life Sci. 2011, 11, 476–481. Dairy manure can either be disposed or turned into valuable products by anaerobic digestion: (i) biogas, which can be used as a source for green electricity, heat or fuel; (ii) digested substrate, also called digestate, a fertilizer in agriculture. While many studies have investigated mixing strategies in anaerobic digesters, there is only limited information for mixing in anaerobic digestion of manure. In this issue, researchers from the University of Cantabria, Santander, Spain, evaluate the influence of reactor content recirculation rate on biogas production during mesophilic anaerobic digestion of airy manure in a 1.5 m3 pilot digester. The key determinants of biogas production are the hydraulic retention time (HRT) of the substrate and the degree of contact between the incoming substrate and the viable bacterial population. The authors conclude that for long HRTs the degree of mixing has only a minimal effect on biogas production……………476. http://dx.doi.org/10.1002/elsc.201100010 Honey mushroom culture: Aeration rate and antioxidant property Lung and Hsieh, Eng. Life Sci. 2011, 11, 482–490. Armillaria mellea, also called honey mushroom, is an edible mushroom used in traditional Asian medicine. Bioreactive compounds derived from mushrooms, including polysaccharides, display a variety of immunomodulating, antitumor and antioxidant activity. Submerged cultures are efficiently used for polysaccharide production from these mushrooms. Although several studies have focused on optimization of submerged culture conditions, the effects of the aeration rate have not been studied in detail. In this issue, optimized production of biomass and exopolysaccharide (EPS) is studied by authors from Taiwan. They evaluate changes of the aeration rate of an A. mellea culture performed in a 5L-stirred-tank bioreactor. EPS produced in the proposed optimal two-stage aeration rate culture is not only produced at a high yield, but also displays a high molecular weight with effective antioxidant properties.……………482 http://dx.doi.org/10.1002/elsc.2011000003 Plant cell culture system for gymnemic acid production Nagella et al., Eng. Life Sci. 2011, 11, 537–540. Traditional medicine uses plant extracts or infusions from wild or cultivated plants. For efficient use as pharmaceuticals large-scale septic and controllable production processes are needed. Gymnema sylvestre, an important medicinal plant, contains the bioactive gymnemic acids, which have anti-diabetic properties and may also be used to treat obesity. Preliminary reports have already described callus and cell suspension cultures of G. sylvestre. In this issue, authors from Seoul, South Korea, and Dharwad, India, present the first systematic approach to establish a suspension culture system for the production of gymnemic acid. Inoculum density, medium components, the carbon source, as well as the concentration of sucrose in the medium were optimized for efficient productivity of gymnemic acid. The results of the current study are the first step for large-scale production of gymnemic acid in cell culture.……………537 http://dx.doi.org/10.1002/elsc.2010000167 Volume11, Issue5October 2011Pages 455-455 RelatedInformation

Contribution to on-line kraft pulping control

In this paper, an on-line sensor, based on ultra-violet absorption of the black liquor in a Kraft pulping process is described. The sensor, tested and improved on a 45-liters pilot digester, appeared to be accurate and to give reproducible measurements which compared favourably with off-line ultra-violet absorption measurements.In order to verify the theoretical relation between the signal and the extent of reaction, a set of experiments were carried out in six 0,5-liter laboratory scale digesters.The lignin content of the liquor appears to be linearily related to the U.V. absorption, however the kappa number must be taken relative to the initial dry weight of wood in order to obtain a linear relation with the U.V. signal.A mathematical model is developed to simulate the sensor experimental recordings with interesting results.

Contribution to On-Line Kraft Pulping Control

In this paper, an on-line sensor, based on ultra-violet absorption of the black liquor in a Kraft pulping process is described. The sensor, tested and improved on a 45-1iters pilot digester, appeared to be accurate and to give reproducible measurements which compared favourably with off-line ultra-violet absorption measurements.In order to verify the theoretical relation between the signal and the extent of reaction, a set of experiments were carried out in six 0,5-liter laboratory scale digesters.The lignin content of the liquor appears to be linearily related to the U.V. absorption, however the kappa number must be taken relative to the initial dry weight of wood in order to obtain a linear relation with the U.V. signal.A mathematical model is developed to simulate the sensor experimental recordings with interesting results.

Design criteria and operational guidelines for a pilotscale anaerobic digester

Design considerations for constructing a pilot anaerobic digester are presented. A 4.34 m 3 pilot digester was constructed using these criteria. Operational guidelines are presented. Also included is an iterative technique for sizing an internal heat exchanger, suggestions for selecting pumps, meters, and other equipment, and an electrical control system that permits automation of the entire system. The pilot digester operated successfully for more than 4 years with swine manure as a feedstock at a loading rate of 4 kg volatile solids per m 3 per day with a 15-day detention time at 35°C. Energy balances indicate that the overall energy efficiency of the digester is a function of ambient temperature surrounding the digester, amount of agitation, and amount of insulation.

Studies on Continuous Rapid Vapor-Phase Alkaline Cooking and High Sulfidity Chemical Recovery

This report summarizes the results of both laboratory scale and pilot scale tests for rapid vapor-phase alkaline cooking and high sulfidity chemical recovery processes. The pilot plant tests include rapid vapor-phase alkaline cooking of various wood species by a 0.5 ton per day scale continuous pilot digester and operation of a 0.5 ton per day scale (as Na2CO3·H2O crystal) pilot crystallizer which is one of the most important parts of the newly developed high sulfidity chemical recovery system. The works were performed in cooperation of Jujo Paper Mfg. Co., Ltd. and Mitsubishi Heavy Industries Ltd.