BMP estimation of landfilled municipal solid waste by multivariate statistical methods using specific waste parameters: case study of a sanitary landfill in Turkey

The main objective of this study was to determine whether methane potential of waste could be estimated more easily by a limited number of waste characterization variables. 36 samples were collected from 12 locations and 3 waste depths in order to represent almost all waste ages at the landfill. Actual remaining methane potential of all samples was determined by the biochemical methane potential (BMP) tests. The cumulative methane production of closed landfill (cLF) samples reached 75–125 mL at the end of experiment duration, while the samples from active landfill (aLF) produced in average 216–266 mL methane. The average experimental k and L ₀ values of cLF and aLF were determined by non-linear regression using BMP data with first-order kinetic equation as 0.0269 day^?1–30.38 mL/g dry MSW and 0.0125 day^?1–102.1 mL/g dry MSW, respectively. The principal component analysis (PCA) was applied to analyze the results for cLF and aLF along with BMP results. Three PCs for the data set were extracted explaining 72.34 % variability. The best MLR model for BMP prediction was determined for seven variables (pH–Cl–TKN–NH4–TOC–LOI–Ca). R ² and Adj. R ² values of this best model were determined as 80.4 and 75.3 %, respectively.     

Effect of long chain fatty acids removal as a pretreatment on the anaerobic digestion of food waste

This study investigated the effect of long chain fatty acids (LCFAs) removal as a pretreatment prior to anaerobic digestion on the production of methane from food waste. The results showed that the anaerobic digestion of food waste containing 1.6 g COD/L of LCFAs was not inhibited (4 days lag-time, 78.3 % methane recovery in 35 days) compared to that of lipid free food waste (3 days lag time, 72.5 % methane recovery in 35 days); however, some unsaturated LCFAs, which are toxic to microorganism, were accumulated in the batch anaerobic digestion reactor. Meanwhile, in a methanogenic activity study, the activity of methanogens was observed to be linearly inhibited by the presence of more than 1 g COD/L of LCFAs. The possibility of the accumulation of unsaturated LCFAs in the reactor should be considered when operating a large-scale continuous system.     

The impact of pretreatment and inoculum to substrate ratio on methane potential of organic wastes from various origins

Biochemical methane potentials (BMP) of two different substrates from macroalgae (MA) and market place wastes (MPW) were investigated using anaerobic granulated sludge from food industry with different ratios of substrate to inoculum (S/X). The substrates were used as MA only, MPW only, MA–MPW mixture, pretreated MA, and pretreated MA–MPW mixture. Research involved investigation of the effects of parameters such as temperature (35, 45, and 55 °C), substrate to inoculum ratio (S/X = 0.5, 2.0, 4.0, and 6.0 as g VS_substrate/g VS_inoculum), and the type of pretreatment (by microwave, thermal, and ultrasonic) on BMP. BMP assays were performed for all substrates. The highest cumulative biogas production (and BMP) were obtained for MA only at an S/X ratio of 4.0 g VS/g VS as 357 L_biogas/kg VS (197 L CH₄/kg VS) and 33 L_biogas/kg VS (17 L CH₄/kg VS), respectively, at 35 and 55 °C. For pretreated substrates, the highest cumulative biogas production and BMP were observed as 287 L_biogas/kg VS and 146 L CH₄/kg VS using pretreated macroalgae at 35 °C. Results suggested that MA only and MA–MPW mixtures are suitable substrates for biogas production. It is also concluded that any type of pretreatment has adverse effects on biogas and methane productions.     

Assessment of the aerobic preparation and bottom ash addition as pretreatment steps before landfilling: Impact on methanogenesis kinetics and leachate parameters

This work focuses on assessing the impact of two types of waste pretreatment: addition of bottom ashes and aerobic pretreatment on both the onset and kinetics of methanogenesis and the evolution of different parameters in the leachate. It also studies the correlation between methane production and the different parameters measured in the leachate produced. A total of six 68-L pilots were thus used with fresh municipal solid waste (MSW) shredded to a 40-mm size. After 14months of landfilling, the control has produced less than 10NLkg(-1)DM, which corresponds to around 7% of its biochemical methane potential (BMP). Nevertheless, on one hand for aerobically pretreated waste, the lag phase before the onset of methanogenesis is significantly reduced to 0.9month compared to more than 1year for the control. In addition to that, on average 110NLkg(-1)DM (90% of the BMP) is produced within around 6.5months. On the other hand, the waste with added bottom ash shows a slight improvement of the lag phase over the control for one of the duplicate: 6.1months of lag phase. At this stage, on average of 26NLkg(-1)DM waste are detected (22% of the BMP) no final conclusion concerning the impact of bottom ashes could be made. The data obtained for the leachate parameters agrees with the observations on methane production. Statistical correlation study shows that the two components of the corrected PCA interpret 76% of the variability of the data: SUVA (specific UV absorbance at 254nm) and HPI(*) (% of hydrophilic compounds) are identified as interesting parameters for following up the biodegradation in landfill conditions.     

Enhanced hydrolysis and methane yield by applying microaeration pretreatment to the anaerobic co-digestion of brown water and food waste

Microaeration has been used conventionally for the desulphurization of biogas, and recently it was shown to be an alternative pretreatment to enhance hydrolysis of the anaerobic digestion (AD) process. Previous studies on microaeration pretreatment were limited to the study of substrates with complex organic matter, while little has been reported on its effect on substrates with higher biodegradability such as brown water and food waste. Due to the lack of consistent microaeration intensities, previous studies were not comparable and thus inconclusive in proving the effectiveness of microaeration to the overall AD process. In this study, the role of microaeration pretreatment in the anaerobic co-digestion of brown water and food waste was evaluated in batch-tests. After a 4-day pretreatment with 37.5 mL-O₂/L_R-d added to the liquid phase of the reactor, the methane production of substrates were monitored in anaerobic conditions over the next 40 days. The added oxygen was consumed fully by facultative microorganisms and a reducing environment for organic matter degradation was maintained. Other than higher COD solubilization, microaeration pretreatment led to greater VFA accumulation and the conversion of other short chain fatty acids to acetate. This could be due to enhanced activities of hydrolytic and acidogenic bacteria and the degradation of slowly biodegradable compounds under microaerobic conditions. This study also found that the nature of inoculum influenced the effects of microaeration as a 21% and 10% increase in methane yield was observed when pretreatment was applied to inoculated substrates, and substrates without inoculum, respectively.     

Effect of pretreatment techniques on food waste solubilization and biogas production during thermophilic batch anaerobic digestion

The purpose of this study was to optimize the alkaline, ultrasonication, and thermal pretreatment in order to enhance the solubilization of food waste (FW) for the production of volatile fatty acids, hydrogen, and methane in thermophilic batch anaerobic digestion. Initially, the effect of pretreatment techniques in the acidogenic phase was studied, and the optimal combinations of different conditions were determined. It was found that each pretreatment technique affected food waste solubilization differently. Alkaline pretreatment increased hydrogen yield in the acidogenic sludge by four times over control. COD solubilization was increased by 47 % when FW pre-heated at 130 °C for 60 min. Ultrasonication at 20 kHz and 45 min reduced processing time to 38 h from the 60–80 h needed in normal operation. Response surface methodology (RSM) was used to optimize a combination of alkaline, ultrasonication, and thermal pretreatment. Optimized conditions were applied to methanogenic single-stage thermophilic AD process, and their impact on biogas production was monitored. Results showed that FW heated at 130 °C for 50 min geminates biogas production compared to control experiment. In conclusion, a short thermal pretreatment regime could significant affect biogas production in single-stage thermophilic AD.     

Enhancement of biogas production potential from <Emphasis Type="Italic">Acacia</Emphasis> leaf waste using alkaline pre-treatment and co-digestion

The objective of this research was to evaluate possibility of utilizing Acacia leaves (A. mangium and A. auriculiformis), which is an agro-industrial waste from the pulp and paper industry. The effects of alkaline pre-treatment and co-digestion with Napier grass for the enhancement of biogas production from Acacia leaf waste (ALW) were investigated. Six continuous stirred tank reactors with a working volume of 5 L were carried out at the laboratory scale. The results showed that pre-treatment of Acacia leaf waste (pretreated ALW) by soaking in 3 % NaOH for 48 h increased the biogas and methane productivity to 0.200 and 0.117 m³/kgVS_added compared to 0.098 and 0.048 m³/kgVS_added of raw ALW digestion, respectively. Meanwhile, the co-digestion of Acacia leaves with different proportions of Napier grass at ratios of 1:1–1:3 in volatile solid basis also increased the production of biogas and its productivity. The maximum gas production yields of 0.424 and 0.268 m³/kgVS_added for biogas and methane were obtained at 1:3 ratio. This finding affirms the potential of ALW and its possibility to use as biogas feedstock in both single and co-substrate with Napier grass.     

Anaerobic digestion of organic fraction of municipal solid waste combining two pretreatment modalities, high temperature microwave and hydrogen peroxide

In order to enhance anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW), pretreatment combining two modalities, microwave (MW) heating in presence or absence of hydrogen peroxide (H₂O₂) were investigated. The main pretreatment variables affecting the characteristics of the OFMSW were temperature (T) via MW irradiation and supplemental water additions of 20% and 30% (SWA20 and SW30). Subsequently, the focus of this study was to evaluate mesophilic batch AD performance in terms of biogas production, as well as changes in the characteristics of the OFMSW post digestion. A high MW induced temperature range (115-175 °C) was applied, using sealed vessels and a bench scale MW unit equipped with temperature and pressure controls. Biochemical methane potential (BMP) tests were conducted on the whole OFMSW as well as the liquid fractions. The whole OFMSW pretreated at 115 °C and 145 °C showed 4-7% improvement in biogas production over untreated OFMSW (control). When pretreated at 175 °C, biogas production decreased due to formation of refractory compounds, inhibiting the digestion. For the liquid fraction of OFMSW, the effect of pretreatment on the cumulative biogas production (CBP) was more pronounced for SWA20 at 145 °C, with a 26% increase in biogas production after 8 days of digestion, compared to the control. When considering the increased substrate availability in the liquid fraction after MW pretreatment, a 78% improvement in biogas production vs. the control was achieved. Combining MW and H₂O₂ modalities did not have a positive impact on OFMSW stabilization and enhanced biogas production. In general, all samples pretreated with H₂O₂ displayed a long lag phase and the CBP was usually lower than MW irradiated only samples. First order rate constant was calculated.     

Investigating the performance of aerobic,semi-aerobic,and anaerobic bioreactor landfills for MSW management in developing countries

Three different laboratory bioreactors, each duplicated, with dimensions 0.5 × 0.5 × 1 m were set up and monitored for 160 days. Municipal Solid Wastes with an organic content of ~80 % and a density of 550 kg/m³ were placed in bioreactors. Fresh leachate collected from waste collection vehicles was used with a recirculation rate of 28 L/day. Aerobic bioreactors were aerated at a rate of 0.15–0.24 L/min/kg of waste. Almost the same level of treatment was observed in terms of chemical oxygen demand reduction of leachate, which was in the range of 91–93 %. However, for anaerobic bioreactor, it took almost twice the time, 160 vs. 76 days, to reach the same level of treatment and stabilization. The behavior of semi-aerobic bioreactor was somewhere between the aerobic and anaerobic ones. Total biogas production for anaerobic bioreactors was 90 L/kg of waste, which contained 57–63 % methane. Methane concentration measured in semi-aerobic bioreactor was below 5 %. The main advantage of aerobic bioreactor was the fast rate of the process, while for semi-aerobic bioreactor, it was the elimination of the need for energy to maintain aerobic conditions, and for anaerobic bioreactor it was the production of biogas and potential energy recovery.     

In-situ emission characteristics of odorous gases from two food waste processing plants

Odorous gas emission is the main environmental concern of food waste treatment. Two typical food waste processing plants, one for animal feed production by hydrothermal hydrolysis + aerobic fermentation (Plant A), and the other for biogas production by anaerobic digestion (Plant B), were selected to conduct in situ monitoring of fugitive odorous gas emission for five consecutive days, and the emission characteristics of NH₃ and total volatile organic compounds (TVOC) were compared in this paper. The results showed that the two processes had different emission characteristics of odorous gases. Closed-operated hydrothermal hydrolysis had positive effects on overall fugitive odor control in plant A. Meanwhile, more fugitive odor gases may be released into the environment during the pretreatment with high-temperature and seemingly-open facilities in plant B. The emission strength of odor gases at night was generally lower than that in the day since more fresh food waste was received in the day and the higher temperature and lower air pressure in the day were favorable to gas emission. In general, the process of hydrothermal hydrolysis + aerobic fermentation was more advantageous in controlling odor than the process of anaerobic digestion.     

Preparation and Characterization of PVC Matrix Composites with Biochemical Sludge

Biochemical sludge (BS), generated in the waste water treatment of paper mills, was pretreated by enzyme hydrolysis. The effect and action mechanism of the enzymatic treatment on the properties of polyvinyl chloride (PVC) matrix composites with BS were discussed. Results showed that when the filler content was 30 wt%, the tensile strength of the PVC composites filled with BS and its modified products which were pretreated by laccase, cellulase and hemicellulase can be increased by 38.64, 67.4, 63.5 and 66.3% than the PVC composite filled with calcium carbonate. When the dosage of filler was 40 wt%, the elastic modulus of PVC composites filled with BS and its above three modified products decreased by 53.3, 52.3, 50.0 and 46.3%, respectively. Meanwhile, the thermal stability of PVC composites can also be improved at the temperature of over 340 °C. It can be concluded that the enzyme pretreatment can improve the application performance of BS usage in PVC matrix composites.     

Stable isotope signatures for characterising the biological stability of landfilled municipal solid waste

Stable isotopic signatures of landfill leachates are influenced by processes within municipal solid waste (MSW) landfills mainly depending on the aerobic/anaerobic phase of the landfill. We investigated the isotopic signatures of δ¹³C, δ²H and δ¹⁸O of different leachates from lab-scale experiments, lysimeter experiments and a landfill under in situ aeration. In the laboratory, columns filled with MSW of different age and reactivity were percolated under aerobic and anaerobic conditions. In landfill simulation reactors, waste of a 25 year old landfill was kept under aerobic and anaerobic conditions. The lysimeter facility was filled with mechanically shredded fresh waste. After starting of the methane production the waste in the lysimeter containments was aerated in situ. Leachate and gas composition were monitored continuously. In addition the seepage water of an old landfill was collected and analysed periodically before and during an in situ aeration.We found significant differences in the δ¹³C-value of the dissolved inorganic carbon (δ¹³C-DIC) of the leachate between aerobic and anaerobic waste material. During aerobic degradation, the signature of δ¹³C-DIC was mainly dependent on the isotopic composition of the organic matter in the waste, resulting in a δ¹³C-DIC of ?20‰ to ?25‰. The production of methane under anaerobic conditions caused an increase in δ¹³C-DIC up to values of +10‰ and higher depending on the actual reactivity of the MSW. During aeration of a landfill the aerobic degradation of the remaining organic matter caused a decrease to a δ¹³C-DIC of about ?20‰. Therefore carbon isotope analysis in leachates and groundwater can be used for tracing the oxidation–reduction status of MSW landfills.Our results indicate that monitoring of stable isotopic signatures of landfill leachates over a longer time period (e.g. during in situ aeration) is a powerful and cost-effective tool for characterising the biodegradability and stability of the organic matter in landfilled municipal solid waste and can be used for monitoring the progress of in situ aeration.     

Biodegradation characteristics of organic matters in swine carcasses under different initial operating conditions of simulated anaerobic lysimeter

This study was aimed to investigate the biodegradation characteristics of organic matters in swine carcasses. The lysimeters were simulated with different initial operating conditions: 30 % volumetric moisture content and no sludge addition for lysimeter A (control), 30 % volumetric moisture content and anaerobic sludge addition for lysimeter B, and 40 % volumetric moisture content and anaerobic sludge addition for lysimeter C. The degradation efficiency (18.4 %) of lysimeter B was higher than that (15.2 %) of lysimeter A due to anaerobic sludge addition. Lysimeter B showed higher CH₄ yield (15.6 L/kg VS) and CH₄ production rate (0.41 L/kg VS days) compared to lysimeter A by 31 % and 14 %, respectively. In addition, the degradation efficiency improved from 18.4 % (lysimeter B) to 26.3 % (lysimeter C) by increasing volumetric moisture content. The CH₄ yield (22.9 L/kg VS) and CH₄ production rate (0.68 L/kg VS days) of lysimeter C were higher than those of lysimeter B, respectively. Total organic carbon (TOC) removed in lysimeter C was converted to leachate (20.3 %) and gas (6.0 %), whose values were higher than those of lysimeter A and B. These results demonstrated that the proper control of initial operating conditions could accelerate the anaerobic degradation of organic matters in swine carcasses.     

Effect of polyethylene addition to coal on hydrogasification enhancement

Hydrogasification of a coal/polyethylene mixture was carried out using a low concentration of polyethylene in the samples with the aim of industrial application. Coal/polyethylene mixtures in the ratio of 90:10 and 75:25 were used in this study. A hydrogasification experiment was conducted using a unique batch reactor at 1073 K under a 7.1 MPa hydrogen atmosphere. The reaction time varied from 1 to 80 s. The results revealed a methane yield from the mixtures that was noticeably greater than the values calculated from experimental results obtained from coal and polyethylene respectively, assuming no mutual influences. A significant synergistic effect was observed even when the polyethylene content was as low as 10 %. It is suggested that there might be an advantage in hydrogasification processes if waste plastics are mixed with coal, such content being practically assumed.     

Investigations on enhanced in situ bioxidation of methane from landfill gas (LFG) in a lab-scale model

The performance of an exogenous bacterium, Methylobacterium extorquens, in inducing bioxidation of methane from landfill gas (LFG) was assessed in a laboratory scale bioreactor. The study show that enhanced oxidation of methane is attained when the bacteria are introduced into the landfill soil. The maximum percentage reduction of methane fraction from LFG when the bioreactor was inoculated with the methanotrophic bacteria was 94.24 % in aerobic treatment process and 99.97 % in anaerobic process. In the experiments with only the indigenous microorganisms present in the landfill soil, the maximum percentage reduction of methane for the same flow rate of LFG was 59.67 % in aerobic treatment and 45 % in anaerobic treatment. The methane oxidation efficiency of this exogenous methanotrophic bacterium can be considered to be the optimum in anaerobic condition and at a flow rate of 0.6 L/m²/min when the removal percentage is 99.95 %. The results substantiate the use of exogenous microorganisms as potential remediation agents of methane in LFG.     

Estimation of methane emission rate changes using age-defined waste in a landfill site

Long term methane emissions from landfill sites are often predicted by first-order decay (FOD) models, in which the default coefficients of the methane generation potential and the methane generation rate given by the Intergovernmental Panel on Climate Change (IPCC) are usually used. However, previous studies have demonstrated the large uncertainty in these coefficients because they are derived from a calibration procedure under ideal steady-state conditions, not actual landfill site conditions. In this study, the coefficients in the FOD model were estimated by a new approach to predict more precise long term methane generation by considering region-specific conditions. In the new approach, age-defined waste samples, which had been under the actual landfill site conditions, were collected in Hokkaido, Japan (in cold region), and the time series data on the age-defined waste sample’s methane generation potential was used to estimate the coefficients in the FOD model. The degradation coefficients were 0.050 1/y and 0.062 1/y for paper and food waste, and the methane generation potentials were 214.4 mL/g-wet waste and 126.7 mL/g-wet waste for paper and food waste, respectively. These coefficients were compared with the default coefficients given by the IPCC. Although the degradation coefficient for food waste was smaller than the default value, the other coefficients were within the range of the default coefficients. With these new coefficients to calculate methane generation, the long term methane emissions from the landfill site was estimated at 1.35 × 10⁴ m³-CH₄, which corresponds to approximately 2.53% of the total carbon dioxide emissions in the city (5.34 × 10⁵ t-CO₂/y).     

Greenhouse gas emissions from biogenic waste treatment: options and uncertainty

A simplified life cycle assessment was conducted to estimate greenhouse gas (GHG) emissions and energy production from each component of biogenic waste treated in an open dumping site, and by composting, anaerobic digestion, and incineration employed with additional options. The impact of uncertainties and sensitivities of the parameters in the treatment methods were investigated. We conducted a sensitivity analysis to identify the most sensitive parameters, and we discussed the relationship between uncertainty and sensitivity. Our results revealed that the moisture content of food waste and the biomass-derived carbon and methane concentration of the landfill gas of biogenic waste subjected to open dumping are the most sensitive parameters across all the treatment methods. The net GHG emissions from food waste treated in an open dumping site ranged over ten times (0.30 ? 3.67 Gg CO₂ eq/Gg). In addition, by employing additional options for the open dumping site, including soil cover, a landfill gas collection system, shifting to a semi-aerobic condition, and energy conservation by using a gas engine, we found that the net GHG emissions could be reduced by 10, 27.9, 37.4 %, and up to 56.7 %, respectively. Shifting to a semi-aerobic system is the most effective method for reducing GHG emissions, followed by landfill gas collection.     

Evaluating the biochemical methane potential (BMP) of low-organic waste at Danish landfills

The biochemical methane potential (BMP) is an essential parameter when using first order decay (FOD) landfill gas (LFG) generation models to estimate methane (CH₄) generation from landfills. Different categories of waste (mixed, shredder and sludge waste) with a low-organic content and temporarily stored combustible waste were sampled from four Danish landfills. The waste was characterized in terms of physical characteristics (TS, VS, TC and TOC) and the BMP was analyzed in batch tests. The experiment was set up in triplicate, including blank and control tests. Waste samples were incubated at 55 °C for more than 60 days, with continuous monitoring of the cumulative CH₄ generation. Results showed that samples of mixed waste and shredder waste had similar BMP results, which was in the range of 5.4–9.1 kg CH₄/ton waste (wet weight) on average. As a calculated consequence, their degradable organic carbon content (DOCC) was in the range of 0.44–0.70% of total weight (wet waste). Numeric values of both parameters were much lower than values of traditional municipal solid waste (MSW), as well as default numeric values in current FOD models. The sludge waste and temporarily stored combustible waste showed BMP values of 51.8–69.6 and 106.6–117.3 kg CH₄/ton waste on average, respectively, and DOCC values of 3.84–5.12% and 7.96–8.74% of total weight. The same category of waste from different Danish landfills did not show significant variation. This research studied the BMP of Danish low-organic waste for the first time, which is important and valuable for using current FOD LFG generation models to estimate realistic CH₄ emissions from modern landfills receiving low-organic waste.     

A New and Sound Technology for Biogas from Solid Waste and Biomass

Organic waste, as a main constituent of municipal solid waste, has as well as solid biomass a high potential for biogas generation. Despite the importance of biogas generation from these materials, the availability of large-scale biogas processes lacks behind the demand. A newly developed double-stage solid–liquid biogas process, consisting of an open hydrolysis stage and a fixed-bed methane reactor, allows the biogas production from almost all biodegradable solid waste and renewable resources like maize, grass, sugar cane, etc. Furthermore, residues from industrial processes, like the glycerine waste water from biodiesel production, can also be converted into biogas successfully. Due to the strong separation of hydrolysis and methanation, the process is extremely stable. No malfunction has been detected so far. The open hydrolysis releases CO₂ and allows oxidation of sulfur. Consequently, the biogas has a high methane (>72%) and low H₂S concentration (<100 ppm). Stirrers or other agitation equipment are not necessary; only liquids are pumped. The biogas generation becomes controllable for the first time; thus, the actual generation can be easily adapted to the consumption.     

Variability of nitrous oxide and carbon dioxide emissions continuously measured in solid waste incinerators

Nitrous oxide and carbon dioxide were continuously measured and variability of emission factors (EFs) was evaluated in five municipal waste incinerators (MWIs) and four industrial waste incinerators (IWIs) from 24 to 86 days between 2008 and 2011. N₂O EFs were calculated by Monte Carlo simulation and mean N₂O EFs were 7.1, 107, 127, 219 g N₂O/ton waste combusted in MWIs with selective catalytic reduction (SCR) for NOx control, MWIs with selective non-catalytic reduction (SNCR), IWIs with SNCR, and a MWI using fluidized bed with SNCR, respectively. Climate-relevant CO₂ EFs ranged from 0.45 to 0.72 ton CO₂/ton waste combusted in MWIs. Maximum values of upper limit for 95% confidence intervals (CIs) of N₂O EFs estimated in each MWIs with SCR, MWIs with SNCR, IWIs with SNCR were 185, 94, 101% of mean N₂O EFs, respectively. Meanwhile, maximum values of upper limit for 95% CIs of CO₂ EFs were much lower as between 18 and 36% in those facilities. 84% CIs of mean N₂O EFs in MWIs with SNCR and IWIs with SNCR were overlapped indicating those values are not significantly different.