Cladophora sp. and Ulva intestinalis are green macroalgae abundantly available in the Baltic Sea. Their low degradability could hamper the fully exploitation as resource for energy recovery through ...anaerobic digestion. For this reason, a co-digestion with lignocellulosic biomass represents a viable solution. This study aims to assess the potential effectiveness of the use of seaweed from Latvian nearshore co-digested with lignocellulosic biomass both in terms of increased BMP and kinetic constant of biodegradability. Specifically, biomethane potentials (BMP) in batch tests of 100 ml were assessed co-digesting Cladophora sp. and Ulva intestinalis from the Gulf of Riga with wheat straw and straw pellet from Brescia Region (Italy). The BMP tests were performed to evaluate the synergetic effect of co-digestion through a synergy index. A mechanical pre-treatment was also executed and its final effect assessed on the mono- and co-digestion experimental trials.
The co-digestion ratio (seaweed/lignocellulosic biomass) used based on the volatile solids content was 1:1. The used ratio substrate-to-inoculum was 1:3 on total solid base. The inoculum use was sewage sludge was collected waste water treatment plant in the Riga district. Two different rounds of experiments with duration of 30 days were performed in order to have a more consistent analysis of results. Results for mono-digestion show the lowest BMP for Ulva intestinalis (277.7 ± 8.6 mL CH4/gVS) and the highest for the Cladophora sp. 523.3 ± 23.24 mL CH4/gVS. The straw pellet and wheat straw present values in a range of 395.6 ± 25.07 mL CH4/gVS and 470.4 ± 7.40 respectively. The effect of the co-digestion results in a slight increase of the synergy index (i.e. from 1.9% to 4.7%) but not for all the co-digestion trials. The higher effect was detected for co-digesting of finely treated straw pellet and Ulva intestinalis. The kinetic degradation constant improvements are evident for all the tested trials with the most evident effect for finely treated Ulva intestinalis in the mono-digestion conditions (i.e. 53.8%). The experiments show that the co-digestion with seaweeds and lignocellulosic can be beneficial.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ
The impact of storage temperature (4, 22 and 37 °C) and storage time (7, 14 and 21 days) on anaerobic digestion inocula was investigated through specific methanogenic activity assays. Experimental ...results showed that methanogenic activity decreased over time with storage, regardless of storage temperature. However, the rate at which the methanogenic activity decreased was two and five times slower at 4 °C than at 22 and 37 °C, respectively. The inoculum stored at 4 °C and room temperature (22 °C) maintained methanogenic activity close to that of fresh inoculum for 14 days (<10% difference). However, a storage temperature of 4 °C is preferred because of the slower decrease in activity with lengthier storage time. From this research, it was concluded that inoculum storage time should generally be kept to a minimum, but that storage at 4 °C could help maintain methanogenic activity for longer.
This study aimed to give lights for establishing a psychrophilic BMP test by three approaches for inoculum acclimation under 25 °C. The first test was run using stabilized mesophilic (25 °C) and ...psychrophilic (15 °C) inoculums to digest cellulose. Second was based on temperature acclimatization of inoculum just by time, from 30 to 10 and 20 °C. The third was running a consecutive BMP under psychrophilic temperatures (23 °C). Cellulose psychrophilic BMP using stabilized psychrophilic inoculum achieve similar results to those obtained at mesophilic conditions with stabilized mesophilic inoculum. Time acclimatization of inoculum improve BMP results respect non-adapted (from 0.47 to 055 Nm3 CH4 kg−1 SV at 20 °C, from 0.31 to 0.44 Nm3 CH4 kg−1 SV at 10 °C). Consecutive BMP under psychrophilic conditions shows better results for inoculum acclimatization to run assays at low temperatures. There is a need to develop and standardize a procedure to run psychrophilic BMP.
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•Full scale psychrophilic digesters have better performance than laboratory research.•Psychrophilic BMP test is strongly affected by inoculum temperature adaptation.•Psychrophilic BMP (15 °C) of cellulose has similar results to BMP (35ªc).•The use of psychrophilic stabilized inoculum shows the better performance for BMP.•The is a need to standardize psychrophilic BMP test procedure.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The purpose of this research study is to examine the stock market’s response to terrorist attacks. The study uses data of terrorist attacks in different parts of the country (Pakistan) from June 1, ...2014 to May 31, 2017. The event window procedure applies to a 16-day window in which 5 days before and 10 days after the attack. In addition, several event windows have been built to test the response of the Pakistan Stock Exchange. KSE-100 index is taken as proxy of response. The total terrorist attacks are classified into four categories: attacks on law enforcement agencies, attacks on civilians, attacks on special places and attacks on politicians, government employees and bureaucrats. The standard market model is used to estimate the abnormal return of the Pakistan Stock Exchange, which takes 252 business days each year. Furthermore, BMP test is used to check statistical significance of cumulative abnormal rate of return (CAAR). The results of this study reveal that total number of terrorist attacks and attacks on law enforcement agencies show long-term effects on Pakistan stock exchange. However, attacks on civilians, attacks on special places and attacks on politicians, government employees and bureaucrats have little effect on the Pakistan Stock Exchange.
Tunisia, like many other countries in the world, suffers from a shortage of conventional energy resources. Further, it exhibits large and increasing volumes of organic wastes that cause environmental ...and health problems. In this study, the considered wastes consist of the organic fraction of municipal solid wastes (OFMSW), the olive mill wastewater (OMWW), and the chicken wastes (CW). These bio-wastes can therefore be valorized by a biological process such as the anaerobic digestion to satisfy on the one hand the energy demands and on the other hand, to reduce the environmental problems. Accordingly, the first aim of this work is to investigate the biomethane potential of the mentioned bio-wastes and to assess the energetic content of the obtained biomethane production. Secondly, a theoretical analysis is conducted by using the Buswell equation to predict the biomethane generation and to determine the biodegradability of the studied substrates mixture. Finally, the experimental findings are used to carry out a kinetic study, by using four kinetic models to assess their suitability to fit the present anaerobic digestion process. To do this, the biomethane potential estimation of these biomasses, under mesophilic conditions, is carried out at a laboratory scale by using the biochemical methane potential (BMP) tests. These testes are performed under an optimal substrate-to-inoculums ratio and a controlled temperature during the testing period at a laboratory scale. The experimental results show that the net yield of the biomethane from the studied bio-wastes mixture is equal to 0.384 Nm
3
/kg VS, which is equivalent to 130.29 Nm
3
of biomethane, extracted from one ton of these bio-wastes mixture. The theoretical and the experimental results of the net produced biomethane show that the substrates mixture biodegradability is found equal to 66.89%. The studied kinetic models show good agreements with the experimental results, with a correlation coefficient R
2
≥ 95. It is found that the Gompertz model is the best one for predicting the anaerobic digestion process, due to the lowest root mean square prediction estimate (RMSPE) coefficient, as compared with the other studied kinetic models.
Graphical abstract
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
26.
Misspecification in event studies Marks, Joseph M.; Musumeci, Jim
Journal of corporate finance (Amsterdam, Netherlands),
08/2017, Volume:
45
Journal Article
Peer reviewed
We examine the statistical error and efficiency associated with two commonly used event-study techniques when applied to samples of various sizes. Previous research has established that the ...frequently used Patell (1976) test is not well specified when the event itself creates additional return variance. We find that even under ideal conditions when the event creates no additional variance, the Patell test rejects a true null hypothesis substantially more often than the stated significance level. In contrast, the alternate test of Boehmer et al. (1991) performs well in samples of all sizes and under all conditions we consider.
•Even absent event-induced variance, the default test in Eventus is misspecified.•The alternative BMP test is well specified, and is almost equally powerful.•With event-induced variance, the Patell test is severely misspecified.•In the presence of event-induced variance, the BMP test continues to work well.•Confidence null is false given it is rejected is higher with BMP than with Patell.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Microalgae may be a potential feedstock for biogas production through anaerobic digestion. However, this process is limited by the hydrolytic stage, due to the complex and resistant microalgae cell ...wall components. This fact hinders biomass conversion into biogas, demanding the application of pretreatment techniques for inducing cell damage and/or lysis and organic matter solubilisation. In this study, sonication, thermal, ultrasound, homogeneizer, hydrothermal and steam explosion pretreatments were evaluated in different conditions for comparing their effects on anaerobic digestion performance in batch reactors. The results showed that the highest biomass solubilisation values were reached for steam explosion (65–73%) and ultrasound (33–57%). In fact, only applied energies higher than 220 W or temperatures higher than 80 °C induced cell wall lysis in
C. sorokiniana
. Nonetheless, the highest methane yields were not correlated to biogas production. Thermal hydrolysis and steam explosion showed lower methane yields in respect to non-pretreated biomass, suggesting the presence of toxic compounds that inhibited the biological process. Accordingly, these pretreatment techniques led to a negative energy balance. The best pretreatment method among the ones evaluated was thermal pretreatment, with four times more energy produced that demanded.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Anaerobic digestion (AD) converts biomass to biogas. However, its performance is often affected by the nutrient condition of AD substrate. In this study, a few substrate supplements were selected to ...promote the biogas production; MgO, FeCl
3
, and cellulase were selected based on the result from elemental analyses of the biomass. The potential impact of the additives on AD process was evaluated by performing a series of biochemical methane potential (BMP) tests. BMP reactors with the substrate with one of the selected additives (i.e., MgO of 380 mg Mg L
−1
, FeCl
3
of 88 mg Fe L
−1
or cellulase of 25 mg L
−1
) exhibited higher microbial activity; 5–15% more biogas production was observed, compared to the blank. Microbial community analysis showed that different additives resulted in proliferation of different microbial species. Therefore, it was decided to add the mixture of the three additives to the biomass. Addition of the mixed additive resulted in 22% more gas production.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Application of anaerobic digestion (AD) has become common in treating palm oil mill effluent in Malaysia; however, employing AD in treating the organic fraction of municipal solid waste (OFMSW), ...especially food waste, is still scarce. This study aims to characterize the commercial Malaysian food waste (CMFW) and determine its potential as sustainable bioenergy feedstock through biogas production. The sample was digested
the biomethane potential (BMP) test with the variation of organic loading rates (OLRs), ranging from 0.38 to 3.83 gCOD/L. day, under mesophilic conditions. The digestion process was further evaluated in continuous operation using a 6-L continuous stirred-tank reactor (CSTR). The kinetic properties of the process were also determined. It was found that the CMFW had a significant amount of chemical oxygen demand of 230 g/L and an acidic pH of 4.5 with the carbon to nitrogen (C/N) ratio at 121:1. A maximum methane composition of 81% was obtained at 1.92 gCOD/L in the BMP test with specific methane production (SMP) at 0.952 L. CH
/L.COD fed. The biogas production was well-fitted with the modified Gompertz model with
at 0.9983 and the maximum biogas potential production rate at R
0.1573 L/day, whereas in the CSTR operation, a maximum methane composition of 85% was produced at OLR 6 gCOD/L. day with the SMP of 1.13 L. CH
/L.COD fed. The CSTR system was in high stability as the pH was maintained in a range of 6.6-6.7, with an alkalinity ratio of 0.28. This study indicates the CMFW is a sustainable feedstock for biogas production in Malaysia. Toward a circular economy approach, the authorities shall introduce commercial scale CMFW AD as part of managing municipal solid waste issues in Malaysia.
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