Landfill GHG reduction through different microbial methane oxidation biocovers

Emissions from daily and final covers of municipal solid waste (MSW) landfills can produce significant impacts on local and global environments. Simplifying, landfills can cause local impacts with odor emissions and global impacts with GHGs. This work focuses on hydrogen sulfide (H2S) and methane (CH4) emissions, with the aim of studying how it is possible to reduce their impacts by means of biofiltration systems. Both field and laboratory investigations have been carried out in Casa Rota Landfill (Tuscany, Italy). In the field trials, four pilot-scale biocovers made of compost from a source-selected organic fraction (SS compost), compost from a mechanical biological treatment plant-the residual fractions of the MSW, a mixed compost (SS-MSW compost) and sand were monitored in the daily cover area of the landfill, where high emissions were detected. Results showed that high CH4 and H2S emissions reductions occurred in the mixed SS-MSW compost plot, given a maximum methane oxidation efficiency of greater than 98% and an average oxidation efficiency of about 75%. To assess the specific oxidation rate, laboratory tests using SS-MSW compost sampled from the biocovers were done

In vitro digested milk proteins: Evaluation of angiotensin-1-converting enzyme inhibitory and antioxidant activities, peptidomic profile, and mucin gene expression in HT29-MTX cells

Over the past decades, several studies investigated the health-promoting functions of milk peptides. However, to date many hurdles still exist regarding the widespread use of milk-derived bioactive peptides, as they may be degraded during gastrointestinal digestion. Thus, the aim of our study was to in vitro digest intact whey protein isolate (WPI) and casein proteins (CNP), mimicking in vivo digestion, to investigate their bioactive effects and to identify the potential peptides involved. Whey protein isolate and CNP were digested using a pepsin-pancreatin protocol and ultra-filtered (3-kDa cutoff membrane). A permeate (3 kDa) were obtained. Soy protein was included as a control (CTR). Angiotensin-1-converting enzyme inhibitory (ACE1-I) and antioxidant activity (AOX) were assessed and compared with those observed in undigested proteins and CTR. Furthermore, the permeate was characterized by nano-liquid chromatography electrospray ionization tandem mass spectrometry (LC-nano ESI MS/MS) using a shotgun peptidomic approach, and retentate was further digested with trypsin and analyzed by MS using a shotgun proteomic approach to identify potentially bioactive peptides. Further, the effects of WPI, CNP, and CTR retentate on cell metabolic activity and on mucus production (MUC5AC and MUC2 gene expression) were assessed in intestinal goblet HT29-MTX-E12 cells. Results showed that WPI permeate induced a significant ACE1-I inhibitory effect [49.2 ± 0.64% (SEM)] compared with undigested WPI, CNP permeate, and retentate or CTR permeate (10.40 ± 1.07%). A significant increase in AOX (1.58 ± 0.04 and 1.61 ± 0.02 µmol of trolox AOX equivalents per mg of protein, respectively) upon digestion was found in WPI. Potentially bioactive peptides associated with ACE1-I and antihypertensive effects were identified in WPI permeate and CNP retentate. At specific concentrations, WPI, CNP, and CTR retentate were able to stimulate metabolic activity in HT29-MTX-E12 cells. Expression of MUC5AC was increased by CNP retentate and unaltered by WPI retentate; MUC2 expression was significantly increased by 0.33 mg/g of CNP and reduced by 1.33 mg/g of CNP. Our results confirm that milk proteins may be rich sources of bioactive compounds, with the greatest beneficial potential of CNP at the intestinal goblet cell level

Improvement of digestate stability using dark fermentation and anaerobic digestion processes

This paper assessed the effect of dark fermentation, the fermentative phase in a two-stage anaerobic digestion system, in terms of digestate biostabilization efficiency. The digestates analyzed in this study were obtained from a pilot-scale system in which two different substrates were used in order to simulate both the digestion and co-digestion process. Biostabilization performances were evaluated by measuring the specific oxygen uptake rate (SOUR) of the outgoing digestates. This index allowed us to define the degree of effectiveness in terms of stabilization of organic matter, between the traditional anaerobic digestion process and the two-stage configuration. Considering the traditional process as a reference scenario, the results highlighted an increase in biological stability for the two-stage co-digestion process, consisting of a dark fermentation stage, followed by an anaerobic digestion one. Digestates biostabilization efficiency increased up from 6.5% to 40.6% from the traditional one-stage configuration to the two-stage one by improving the anaerobic digestion process through a preliminary fermentative stage. The advantages of the two-stage process were due to the role of dark fermentation as a biological pre-treatment. Considering the partial stability results related to the second stage, biological stability was improved in comparison to a single-stage process, reaching an efficiency of 42.2% and 55.8% for the digestion and co-digestion scenario respectively. The dark fermentation phase allowed for a higher hydrolysis of the substrate, making it more easily degradable in the second phase. Results demonstrated better biostabilization performances of the outgoing digestates with the introduction of dark fermentation, resulting in more stable digestates for both the digestion and co-digestion process

Methane oxidation of residual landfill gas in a full-scale biofilter: human health risk assessment of volatile and malodours compound emissions

A human health risk assessment was performed to evaluate if a biofilter for the biological methane oxidation reduces the risk from exposure to landfill gas emissions and improves the air quality mitigating odour emissions from an aftercare landfill. Accordingly, three different scenarios of landfill gas management were defined, 9 volatile organic compounds (VOCs) (cyclohexane, n-hexane, 2-methylpentane, 3-methylpentane, benzene, xylenes, toluene, dichlorodifluoromethane, vinyl chloride) were identified and using the CALPUFF dispersion model; the pollutant concentration at eleven sensitive receptors was determined. Consequently, the risk (for cancer and non-cancer compounds) was assessed applying the methodology proposed by USEPA 2009. From one hand, to determine concentration and emission rates of VOCs and hydrogen sulphide, a sample of raw landfill gas and three air samples from the biofilter surface were collected with dynamic flux chamber method and analysed in accordance with US EPA, 1986 and USEPA TO-15, 1999. To the other hand, odour emissions were assessed based both on chemical and dynamic olfactometric measurements (EN 13725:2003). The field surveys results showed a reduction of the cancer risk on average by 79% and of the hazard quotient on average by 92%. In contrast, the results of olfactometry measurements showed a lower efficiency on odour reduction than the target value of 70%. Nonetheless, the odour concentration was always far below 300 uoE m−3 at the biofilter surface and odour concentration never exceed 1 uoE m−3 at the sensitive receptors

Comparison of single-stage and two-stage anaerobic Co-Digestion of food waste and activated sludge for hydrogen and methane production

In this study, the co-digestion of food waste and activated sludge was evaluated in a two-stage anaerobic system and compared to the traditional single-stage process. The two-stage system was composed by two reactors connected in series able to perform the fermentative and the methanogenic phases separated. Experiments were carried out in semi-continuous mode under mesophilic conditions (37 °C). The two-stage technology achieved an overall improvement of the anaerobic performances. Results highlighted an increase in biogas production and volatile solids degradation of 26% and 9%, respectively. Considering the whole two-stage system, i.e. the sum of the biogas productions of the first and the second digester, these percentages increased up to 35.0%. Concerning gas quality, the two-stage system achieved a hydrogen rich biogas in the first fermentative reactor and an improvement of methane content in the second methanogenic digester. The average methane content shifted from 61.2% to 70.1%. The highest methane production of the two-stage process was due to improved substrate hydrolysis, with increased amounts of volatile fatty acids made readily available in the second stage

Energy recovery from biowaste: Influence of hydraulic retention time on biogas production in dry-anaerobic digestion

The hydraulic retention time (HRT) is a key parameter in dry-anaerobic digestion to set during the reactor configuration in order to achieve the optimal biogas production. For this reason, the study compared the results of two experimental tests operating with an HRT of 23 and 14 days. During the tests, the feedstock was organic fraction of municipal solid waste with a solid content of 33% and the digester was a pilot-scale plug-flow reactor operating in thermophilic condition. The highest specific biogas production of 311.91 Nlbiogas kg d was achieved when the HRT was set to 23 days. On the contrary, the highest methane production rate of 1.43 NlCH4 l d was achieved for an HRT of 14 days. In addition, the volatile solids removal (49.15% on average) and the energy content o(4.8 MJ kg on average) were higher for HRT 23 days than for HRT14 days. The results indicated that in dry-anaerobic digestion of organic fraction of municipal solid waste, 23 days is a suitable HRT for energy recovery

Bromatological, proximate and ultimate analysis of OFMSW for different seasons and collection systems

In order to study the quality of organic fractions of municipal solid waste (OFMSW), five different municipalities in Tuscany were chosen for sampling according to the peculiarities of their collection systems. The five collection systems selected were sampled four times: during March, June, September and December, for a total of 20 picking analyses. In addition, emphasis was also given to the study of the variability of OFMSW composition related to ultimate, proximate and bromatological analyses. Road container collection systems proved to have a higher content of non-compostable and undesirable fractions (22%±1%) when compared to door-to-door systems (6% ± 1%). During months with lower temperature (March and December), the garden waste content in the OFMSW was negligible, with kitchen waste prevailing. This altered the physical chemical composition of OFMSW, which had a lower lignin content and higher methane production in the months with lower temperatures (272 ± 23 NLCH4 kgTVS -1) compared to June and September (238 ± 14 NLCH4 kgTVS -1). In general, the Tuscan OFMSW had a higher dry matter content (42%) than observed in previous studies. In conclusion, the result could direct possible future operators of anaerobic digestion plants towards the choice of dry and semi-dry technologies

Risk assessment of a methane oxidizing biofilter for reducing landfill gas emissions from a post-closure landfill

This study focuses on the assessment of volatile organic compounds (VOCs) and odor compounds emissions from a post-closure landfill. A human health risk assessment and an air quality evaluation were performed to compare two different landfill gas management scenarios and to assess whether a methane oxidizing biofilter mitigates the risk from inhalation exposure to VOCs and odor emissions. Three specific monitoring campaigns were performed: one sample of raw biogas at the biofilter inlet and three air samples from the biofilter surface were collected and analyzed to determine the concentration levels of VOCs, H2S and odor compounds accordingly to US EPA, 1995 and US EPA TO-15, 1999, NIOSH 6013:1994, and dynamic olfactometry (EN 13725:2003), respectively. Concerning the raw biogas, five odor compounds were selected from the mixture and then the odor activity value (OAV) was evaluated. CALPUFF dispersion model was used to evaluate the VOCs concentration in air at eleven sensitive receptors. In the risk assessment, cyclohexane, n-hexane, 2-methylpentane, 3-methylpentane, benzene, xylenes, toluene, dichlorodifluoromethane, vinyl chloride were selected to evaluate the hazard index (HI) for non-carcinogenic compounds and the cancer risk (R) for carcinogenic compounds (benzene). The results showed that for both LFG management scenarios HI and R resulted negligible (HI≤1 and R<10-6) and the odor concentration resulted always below 1 UO m-3 at each sensitive receptor. Furthermore, emerged that the biofilter reduce HI and R on average by 93% and 17%