A Study of Single Stage Semi‐Dry Anaerobic Digestion of Organic Fraction of Municipal Solid Waste

Solid waste generation is a natural consequence of human activity and is increasing along with population growth, urbanization and industrialization. Improper disposal of the huge amount of solid waste seriously affects the environment and contributes to climate change by the release of greenhouse gases. Practicing anaerobic digestion (AD) for the organic fraction of municipal solid waste (OFMSW) can reduce emissions to environment and thereby alleviate the environmental problems together with production of biogas, an energy source, and digestate, a soil amendment. The amenability of substrate for biogasification varies from substrate to substrate and different environmental and operating conditions such as pH, temperature, type and quality of substrate, mixing, retention time etc. Therefore, the purpose of this research work is to develop feasible semi-dry anaerobic digestion process for the treatment of OFMSW from Kerala, India for potential energy recovery and sustainable waste management. This study was carried out in three phases in order to reach the research purpose. In the first phase, batch study of anaerobic digestion of OFMSW was carried out for 100 days at 32°C (mesophilic digestion) for varying substrate concentrations. The aim of this study was to obtain the optimal conditions for biogas production using response surface methodology (RSM). The parameters studied were initial pH, substrate concentration and total organic carbon (TOC). The experimental results showed that the linear model terms of initial pH and substrate concentration and the quadratic model terms of the substrate concentration and TOC had significant individual effect (p < 0.05) on biogas yield. However, there was no interactive effect between these variables (p > 0.05). The optimum conditions for maximizing the biogas yield were a substrate concentration of 99 g/l, an initial pH of 6.5 and TOC of 20.32 g/l. AD of OFMSW with optimized substrate concentration of 99 g/l [Total Solid (TS)-10.5%] is a semi-dry digestion system .Under the optimized condition, the maximum biogas yield was 53.4 L/kg VS (volatile solid).. In the second phase, semi-dry anaerobic digestion of organic solid wastes was conducted for 45 days in a lab-scale batch experiment for substrate concentration of 100 g/l (TS-11.2%) for investigating the start-up performances under thermophilic condition (50°C). The performance of the reactor was evaluated by measuring the daily biogas production and calculating the degradation of total solids and the total volatile solids. The biogas yield at the end of the digestion was 52.9 L/kg VS for the substrate concentration of 100 g/l. About 66.7% of volatile solid degradation was obtained during the digestion. A first order model based on the availability of substrate as the limiting factor was used to perform the kinetic studies of batch anaerobic digestion system. The value of reaction rate constant, k, obtained was 0.0249 day-1. A laboratory bench scale reactor with a capacity of 36.8 litres was designed and fabricated to carry out the continuous anaerobic digestion of OFMSW in the third phase. The purpose of this study was to evaluate the performance of the digester at total solid concentration of 12% (semi-dry) under mesophlic condition (32°C). The digester was operated with different organic loading rates (OLRs) and constant retention time. The performance of the reactor was evaluated using parameters such as pH, volatile fatty acid (VFA), alkalinity, chemical oxygen demand (COD), TOC and ammonia-N as well as biogas yield. During the reactor’s start-up period, the process is stable and there is no inhibition occurred and the average biogas production was 14.7 L/day. The reactor was fed in continuous mode with different OLRs (3.1,4.2 and 5.65 kg VS/m3/d) at constant retention time of 30 days. The highest volatile solid degradation of 65.9%, with specific biogas production of 368 L/kg VS fed was achieved with OLR of 3.1 kg VS/m3/d. Modelling and simulation of anaerobic digestion of OFMSW in continuous operation is done using adapted Anaerobic Digestion Model No 1 (ADM1).The proposed model, which has 34 dynamic state variables, considers both biochemical and physicochemical processes and contains several inhibition factors including three gas components. The number of processes considered is 28. The model is implemented in Matlab® version 7.11.0.584(R2010b). The model based on adapted ADM1 was tested to simulate the behaviour of a bioreactor for the mesophilic anaerobic digestion of OFMSW at OLR of 3.1 kg VS/m3/d. ADM1 showed acceptable simulating results.

Bridging the Faraoni and Selli oceanic anoxic events: late Hauterivian to early Aptian dysaerobic to anaerobic phases in the Tethys.

A detailed geochemical analysis was performed on the upper part of the Maiolica Formation in the Breggia (southern Switzerland) and Capriolo sections (northern Italy). The analysed sediments consist of well-bedded, partly siliceous, pelagic carbonate, which lodges numerous thin, dark and organic-rich layers. Stable-isotope, phosphorus, organic-carbon and a suite of redox-sensitive trace-element contents (RSTE: Mo, U, Co, V and As) were measured. The RSTE pattern and Corg:Ptot ratios indicate that most organic-rich layers were deposited under dysaerobic rather than anaerobic conditions and that latter conditions were likely restricted to short intervals in the latest Hauterivian, the early Barremian and the pre-Selli early Aptian. Correlations are both possible with organic-rich intervals in central Italy (the Gorgo a Cerbara section) and the Boreal Lower Saxony Basin, as well as with the facies and drowning pattern in the Helvetic segment of the northern Tethyan carbonate platform. Our data and correlations suggest that the latest Hauterivian witnessed the progressive installation of dysaerobic conditions in the Tethys, which went along with the onset in sediment condensation, phosphogenesis and platform drowning on the northern Tethyan margin, and which culminated in the Faraoni anoxic episode. This episode is followed by further episodes of dysaerobic conditions in the Tethys and the Lower Saxony Basin, which became more frequent and progressively stronger in the late early Barremian. Platform drowning persisted and did not halt before the latest early Barremian. The late Barremian witnessed diminishing frequencies and intensities in dysaerobic conditions, which went along with the progressive installation of the Urgonian carbonate platform. Near the Barremian-Aptian boundary, the increasing density in dysaerobic episodes in the Tethyan and Lower Saxony Basins is paralleled by a change towards heterozoan carbonate production on the northern Tethyan shelf. The following return to more oxygenated conditions is correlated with the second phase of Urgonian platform growth and the period immediately preceding and corresponding to the Selli anoxic episode is characterised by renewed platform drowning and the change to heterozoan carbonate production. Changes towards more humid climate conditions were the likely cause for the repetitive installation of dys- to anaerobic conditions in the Tethyan and Boreal basins and the accompanying changes in the evolution of the carbonate platform towards heterozoan carbonate-producing ecosystems and platform drowning.

Modelling the economics of farm-based anaerobic digestion in a UK whole-farm context

Anaerobic digestion (AD) technologies convert organic wastes and crops into methane-rich biogas for heating, electricity generation and vehicle fuel. Farm-based AD has proliferated in some EU countries, driven by favourable policies promoting sustainable energy generation and GHG mitigation. Despite increased state support there are still few AD plants on UK farms leading to a lack of normative data on viability of AD in the whole-farm context. Farmers and lenders are therefore reluctant to fund AD projects and policy makers are hampered in their attempts to design policies that adequately support the industry. Existing AD studies and modelling tools do not adequately capture the farm context within which AD interacts. This paper demonstrates a whole-farm, optimisation modelling approach to assess the viability of AD in a more holistic way, accounting for such issues as: AD scale, synergies and conflicts with other farm enterprises, choice of feedstocks, digestate use and impact on farm Net Margin. This modelling approach demonstrates, for example, that: AD is complementary to dairy enterprises, but competes with arable enterprises for farm resources. Reduced nutrient purchases significantly improve Net Margin on arable farms, but AD scale is constrained by the capacity of farmland to absorb nutrients in AD digestate.

Antipathogenic activity of probiotics against Salmonella Typhimurium and Clostridium difficile in anaerobic batch culture systems: is it due to synergies in probiotic mixtures or the specificity of single strains?

Probiotics are currently being investigated for prevention of infections caused by enteric pathogens. The aim of this in vitro study was to evaluate the influence of three single probiotics: Lactobacillus casei NCIMB 30185 (PXN 37), Lactobacillus acidophilus NCIMB 30184 (PXN 35), Bifidobacterium breve NCIMB 30180 (PXN 25) and a probiotic mixture containing the above strains plus twelve other strains belonging to the Lactobacillus, Bifidobacterium, Lactococcus, Streptococcus and Bacillus genera on the survival of Salmonella Typhimurium and Clostridium difficile using pH-controlled anaerobic batch cultures containing mixed fecal bacteria. Changes in relevant bacterial groups and effects of probiotic addition on survival of the two pathogens were assessed over 24 h. Quantitative analysis of bacterial populations revealed that there was a significant increase in lactobacilli and/or bifidobacteria numbers, depending on probiotic addition, compared with the control (no added probiotic). There was also a significant reduction in S. Typhimurium and C. difficile numbers in the presence of certain probiotics compared with controls. Of the probiotic treatments, two single strains namely L. casei NCIMB 30185 (PXN 37), and B. breve NCIMB 30180 (PXN 25) were the most potent in reducing the numbers of S. Typhimurium and C. difficile. In addition, the supplementation with probiotics into the systems influenced some fermentations parameters. Acetate was found in the largest concentrations in all vessels and lactate and formate were generally detected in higher amounts in vessels with probiotic addition compared to controls.

An assessment of the prebiotic potential of single and blended substrates in anaerobic in vitro batch culture fermentations using canine faecal samples as inocula

Previously, using an in vitro static batch culture system, it was found that rice bran (RB), inulin, fibersol, mannanoligosaccharides (MOS), larch arabinogalactan and citrus pectin elicited prebiotic effects (in terms of increased numbers of bifidobacteria and lactic acid bacteria) on the faecal microbiota of a dog. The aim of the present study was to confirm the prebiotic potential of each individual substrate using multiple faecal donors, as well as assessing the prebiotic potential of 15 substrate blends made from them. Anaerobic static and stirred, pH-controlled batch culture systems inoculated with faecal samples from healthy dogs were used for this purpose. Fluorescence in situ hybridization (FISH) analysis using seven oligonucleotide probes targeting selected bacterial groups and DAPI (total bacteria) was used to monitor bacterial populations during fermentation runs. High-performance liquid chromatography was used to measure butyrate produced as a result of bacterial fermentation of the substrates. RB and a MOS/RB blend (1:1, w/w) were shown to elicit prebiotic and butyrogenic effects on the canine microbiota in static batch culture fermentations. Further testing of these substrates in stirred, pH-controlled batch culture fermentation systems confirmed the prebiotic and butyrogenic effects of MOS/RB, with no enhancement of Clostridium clusters I and II and Escherichia coli populations.

The role of subsidy in ensuring the sustainability of small-scale anaerobic digesters in Odisha, India

Small-scale anaerobic digester installation has been a development objective of the Indian government to provide rural households clean fuel. Anaerobic digester installation is heavily subsidised. Depending on caste, the rate of subsidy offered for the smallest system available (1m3) varies between 32.35% and 41.18% of the total installation price. Yet, there are gaps in knowledge regarding the usefulness of such subsidies from a sustainability perspective. A cost-benefit analysis was conducted to evaluate the circumstances required for digester sustainability. The analysis used household data collected from 115 cattle owning households in Odisha, India to evaluate profitability at three levels of subsidy (none, General caste subsidy, and Schedule Caste/Schedule Tribe subsidy). Additional analyses considered the effect of; taking a loan, replacing electric lighting with biogas lighting, and the wealth level of the household. The results indicated that access to subsidy improved profitability. Yet, profitability could be achieved without the use of subsidy. The level of benefit accrued by households was similar independent of wealth. However, the provision of subsidy was essential for ensuring profitability for those households required to take a loan to meet the expense of installation. Such findings highlight the importance of subsidy as a means of including the poor.

Assessment of antimicrobial effect of Biosilicate (R) against anaerobic, microaerophilic and facultative anaerobic microorganisms

This study assessed the antimicrobial activity of a new bioactive glass-ceramic (Biosilicate (R)) against anaerobic, microaerophilic, and facultative anaerobic microorganisms. Evaluation of the antimicrobial activity was carried out by three methods, namely agar diffusion, direct contact, and minimal inhibitory concentration (MIC). For the agar diffusion technique, bio glass-ceramic activity was observed against various microorganisms, with inhibition haloes ranging from 9.0 +/- 1.0 to 22.3 +/- 2.1 mm. For the direct contact technique, Biosilicate (R) displayed activity against all the microorganisms, except for S. aureus. In the first 10 min of contact between the microorganisms and Biosilicate (R), there was a drastic reduction in the number of viable cells. Confirming the latter results, MIC showed that the Biosilicate (R) inhibited the growth of microorganisms, with variations between <= 2.5 and 20 mg/ml. The lowest MIC values (7.5 to <= 2.5 mg/ml) were obtained for oral microorganisms. In conclusion, Biosilicate (R) exhibits a wide spectrum of antimicrobial properties, including anaerobic bacteria.

Effect of agitation on the performance of an anaerobic sequencing batch biofilm reactor in the treatment of dairy effluents

Agitation rate is an important parameter in the operation of Anaerobic Sequencing Biofilm Batch Reactors (ASBBRs), and a proper agitation rate guarantees good mixing, improves mass transfer, and enhances the solubility of the particulate organic matter. Dairy effluents have a high amount of particulate organic matter, and their anaerobic digestion presents inhibitory intermediates (e. g., long-chain fatty acids). The importance of studying agitation in such batch systems is clear. The present study aimed to evaluate how agitation frequency influences the anaerobic treatment of dairy effluents. The ASBBR was fed with wastewater from milk pasteurisation process and cheese manufacture with no whey segregation. The organic matter concentration, measured as chemical oxygen demand (COD), was maintained at approximately 8,000 mg/L. The reactor was operated with four agitation frequencies: 500 rpm, 350 rpm, 200 rpm, and no agitation. In terms of COD removal efficiency, similar results were observed for 500 rpm and 350 rpm (around 90%) and for 200 rpm and no agitation (around 80%). Increasing the system`s agitation thus not only improved the global efficiency of organic matter removal but also influenced volatile acid production and consumption and clearly modified this balance in each experimental condition.

A comparison of two bench-scale anaerobic systems used for the treatment of dairy effluents

The objective of this work was to compare two anaerobic reactor conflgurations, a hybrid upflow anaerobic sludge blanket (UASBh) reactor and an anaerobic sequencing batch reactor with immobilised biomass (ASBBR) treating dairy effluents. The reactors were fed with effluent from the milk pasteurisation process (effluent 1-E1) and later with effluent from the same process combined with the one from the cheese manufacturing (effluent 2-E2). The ASBBR reactor showed average organic matter removal efficiency of 95.2% for E1 and 93.5% for E2, while the hybrid UASB reactor showed removal efficiencies of 90.3% and 80.1% respectively.

Anaerobic bio-digestion of concentrate obtained in the process of ultra filtration of effluents from tilapia processing unit

The objective of the present study was to evaluate the efficiency of the process of biodigestion of the protein concentrate resulting from the ultrafiltration of the effluent from a slaughterhouse freezer of Nile tilapia. Bench digesters were used with excrements and water (control) in comparison with a mixture of cattle manure and effluent from the stages of filleting and bleeding of tilapias. The effluent obtained in the continuous process (bleeding + filleting) was the one with highest accumulated population from the 37th day, as well as greatest daily production. Gases composition did not differ between the protein concentrates, but the gas obtained with the use of the effluent from the filleting stage presented highest methane gas average (78.05%) in comparison with those obtained in the bleeding stage (69.95%) and in the continuous process (70.02%) or by the control method (68.59%).

Aminophylline affects glycemia control and increases anaerobic glycolysis in horses during incremental exercise

A study was conducted on the effects of acute administration of aminophylline on physiological variables in purebred Arabian horses submitted to incremental exercise test. Twelve horses were submitted to two physical tests separated by a 10-day interval in a crossover study. These horses were divided into two groups: control (C, n = 12) and aminophylline (AM, n = 12). The drug at 10 mg/kg body weight or saline was given intravenously, 30 minutes before the incremental exercise test. The treadmill exercise test consisted of an initial warmup followed by gradually increasing physical exigency. Blood samples were assayed for lactic acid, glucose, and insulin. Maximal lactic acidemia was greater (P = .0238) in the AM group. Both V-2 and V-4 (velocities at which lactate concentrations were 2 and 4 mmol/ L, respectively) were reduced in the AM group by 15.85% (P = .0402) and 17.76% (P = .0 109), respectively. At rest as well as at 4 minutes, insulinemia was greater in the AM group (P = .0417 and .0393), Glycemia group at times 8 was statistically lower in the Al (P = .0138) and 10 minutes (P = .0432). Use of ammophylline in horses during incremental exercise does not seem to be beneficial, because this drug has a tendency to cause hypoglycemia and to increase dependence on anaerobic glucose metabolism.

Anaerobic biodigestion of pigs feces in the initial, growing and finishing stages fed with diets formulated with corn or sorghum

Objetivou-se avaliar a produção e a qualidade do biogás e do biofertilizante obtidos em biodigestores abastecidos com dejetos de suínos, nas fases inicial, crescimento e terminação, alimentados com dietas formuladas à base de milho ou sorgo. Foram utilizados 20 biodigestores de bancada, com tempo de retenção hidráulica de 30 dias, e cargas diárias que continham 4,0 a 6,0% de sólidos totais (ST) e 3,6 a 5,2% de sólidos voláteis (SV). Nos efluentes dos biodigestores, foram verificados teores médios de ST variando de 1,6 a 2,0% e de SV entre 1,2 e 1,6%. As reduções médias de ST foram de 57,7 a 64,7% e de SV de 61,7 a 69,0%, sendo que houve diferença somente na fase de terminação, na qual as maiores reduções médias foram para biodigestores abastecidos com dejetos de animais alimentados com dietas à base de milho. Nos biodigestores abastecidos com dejetos de animais em fase inicial e de crescimento, alimentados com dietas formuladas à base de milho, foram verificadas maiores produções médias de biogás e os maiores potenciais médios de produção de biogás. Os potenciais médios obtidos foram 0,033; 0,181; 0,685; 0,788 e 1,132 m³ por kg de afluente, estrume, ST adicionados, SV adicionados e SV reduzidos, respectivamente. Não foram verificadas diferenças quanto ao teor médio de metano no biogás entre dietas e fases. As concentrações médias dos nutrientes N, P, K, Ca, Mg, Na, Fe, Mn, Zn e Cu no afluente e efluente dos biodigestores variaram entre as dietas e fases.