Consecutive anaerobic-aerobic treatment of the organic fraction of municipal solid waste and lignocellulosic materials in laboratory-scale landfill-bioreactors

Surface emission determination of selected trace gases from an active municipal solid waste dumpsite under the surface physicochemical heterogeneity

Karadiyana municipal solid waste (MSW) dumpsite in Colombo, Sri Lanka, has been in operation for over 30 years and was evaluated for its surface Volatile Organic Compounds (VOCs), Ammonia (NH₃), and Hydrogen sulfide (H₂S) emissions. Based on the surface conditions and waste characters, the dump surface was divided into eight cells, and multiple samplings were done using static flux chamber methods. The study observed that the average flux rates of VOCs, H₂S, and NH₃ were 137.2 ± 243.8, 6.63 ± 15.9, and 14.2 ± 16.2 mg m^-2h^-1 throughout the dump site. The highest average VOCs and H₂S flux rates (828.6, 24.3 mg m^-2h^-1) were reported from new organic waste with a considerable fraction (62.5, 35.6 %) from the total emission (61.0, 3.1 Kg d^-1). Leachate-flowing trenches produced the highest NH₃ flux rate (36.0 mg m^-2h^-1), while the highest emission fraction (47.5 %) from the total (12.0 Kg d^-1) was reported on old mixed waste with vegetation. The moisture content of the organic waste layers is positively correlated with these trace gas flux rates, and the NH₃ flux rates depend on the pH of the surface. Results showed that the age of the waste determines the trace gas emission rate, and leachate provides an ideal pathway for landfill trace gas migration to the atmosphere. Gas collection and purification systems are essential for the initial waste dumping area and leachate treatment system. The arrangement of a proper drainage system on the dump would reduce trace gas emissions.

Dry tomb - bioreactor landfilling approach for enhanced biodegradation and biomethane generation from municipal solid waste Co-disposed with sugar mill pressmud

In this study, anaerobic co-landfilling of municipal solid waste (MSW) and sugar mill pressmud (PM) was performed in four different proportions [PM:MSW] viz. 0:1 (control: BR1), 1:3 (BR2), 1:1 (BR3) and 3:1 (BR4). Efficacy assessment of Dry tomb - Bioreactor landfill (DTLF - BRLF) operation was carried out through leachate characterization and biomethane production. Leachate recirculation as a part of bioreactor operation after 194th day onwards showed promising degradation of co-wastes. Moreover, leachate decontamination and methane production were reliant on co-disposal proportions of PM and MSW. Maximum biomethane generation of 46.355L was obtained in landfill lysimeter BR3 followed by BR4 (34.680L), BR2 (24.275L) and BR1 (12.850L). Both logistic function and Gompertz growth models showed efficient fitting (R² > 0.99) for observed methane production. This research could be a baseline study for selective operation of combined dry tomb and bioreactor landfilling at full scale in co-disposal scenarios.

Investigating leachate decontamination and biomethane augmentation through Co-disposal of paper mill sludge with municipal solid waste in simulated anaerobic landfill bioreactors

The study aims to investigate the feasibility of anaerobic co-landfilling of effluent treatment plant sludge (ETPS) from paper mill and municipal solid waste (MSW) in prismoidal shaped simulated anaerobic landfill bioreactors. Both ETPS and MSW were co-disposed in 0:100 (R1), 25:75 (R2), 50:50 (R3) and 75:25 (R4) ratios. Periodic assessments of leachate characteristics and biomethane production were carried out for 300 days. ETPS co-disposal with MSW showed considerable reduction in biochemical oxygen demand of leachate (R2: 95.9%, R3: 97.5% and R4: 93.2%). Moreover, cumulative methane gas generations were 2.974, 6.085 and 4.653 times more in R2, R3 and R4 bioreactors as compared to R1. Gompertz growth model was found in well-fitting for methane generation with the observed data. Correlogram plotted among leachate parameters exhibited exclusive relationships and justified leachate trends. This simulation of co-landfilling could be baseline study for the implementation of technology at pilot scale.

Improved Sugar Recovery from Orange Peel by Statistical Optimization of Thermo-Alkaline Pretreatment

Orange peel, which is a by-product of oranges, contains carbohydrates that can be converted into sugars and used in the fermentation process. In this study, the thermal alkaline pretreatment process was chosen because of its simplicity and lesser reaction time. In addition, the reaction factors were optimized using response surface methodology. The determined optimal conditions were as follows: 60.1 g/L orange peels loading, 3% KOH and 30 min. Under the optimal conditions, glucan content (GC) and enzymatic digestibility (ED) were found to be 32.8% and 87.8%, respectively. Enzymatic hydrolysis was performed with pretreated and non-pretreated orange peels using three types of enzyme complex (cellulase, cellobiase and xylanase). The minimum concentrations of enzyme complex required to obtain maximum ED were 30 FPU (filter paper unit), 15 CBU (cellobiase unit), and 30 XNU (xylanase unit) based on 1 g-biomass. Additionally, ED of the treated group was approximately 3.7-fold higher than that of the control group. In conclusion, the use of orange peel as a feedstock for biorefinery can be a strategic solution to reduce wastage of resources and produce sustainable bioproducts.

Bio-process performance, evaluation of enzyme and non-enzyme mediated composting of vegetable market complex waste

Vegetable Market have become major sources of organic waste. Some of such waste when being diverted to landfills not only increase the landfill loading but also contribute to increase greenhouse gas emission. Of the many technologies available in handling such hugely generated waste, composting has proven very effective for decades. Enzyme and non-enzyme mediated aerobic composting of vegetable market complex waste (VMCW) have been investigated. Conventional composting technique though being capable of handling large quantum of waste are found to consume more time. Proven to be disadvantages factor. In the present investigation, the pre-cultured seed inoculums used for vegetable market complex waste, shortened the typical composting period from 45 to 9 days for the first time. Also, rapid size and volume reduction of VMCW was witnessed. The organic degradation of VMCW was observed as 42% (82 ± 2.83% to 40.82 ± 0.61%), with a volume reduction from 0.012m³ to 0.003 m³ within 9 days. An enriched nutrients NPK level of compost bio-fertilizer was recorded as 0.91% w/w, 0.5% w/w and 1.029% w/w respectively. Compost maturity observed through the X-ray diffraction (XRD) analysis of the manure confirmed the conversion of the crystal structure of the compost particle to amorphous form and the mineralization of organic matter during the composting. Thus, the fermented pre-cultured seed inoculums favored an enhanced nutrients level with shortened composting time.

Effect of waste compaction density on stabilization of aerobic bioreactor landfills

Landfill stabilization contributes to the safe operation and maintenance of landfills. This study used a simulated aerobic bioreactor landfill to investigate the impact of different compaction densities on its stabilization to provide a basis for optimal parameter selection during landfill design. Samples of municipal solid waste were tested with compaction densities of 450, 500, 550, 600, and 650 kg/m³ during the experiment. The optimum compaction density was obtained by periodically monitoring the temperature of the waste pile, the water quality of leachate, and the composition of the waste. The impacts of waste compaction density on waste pile temperature and leachate were investigated and coupled with the analysis of waste composition to discuss the possible reaction mechanism. Results showed that the most complete waste degradation occurred at 550 kg/m³ compaction density, which was effective at accelerating stabilization of the simulated aerobic bioreactor landfill. Limitations of the experiment are given to lay foundations for further study.

Ex situ simultaneous nitrification-denitrification and in situ denitrification process for the treatment of landfill leachates

The objective of this research was to investigate the ex situ simultaneous nitrification-denitrification (SND) and in situ denitrification process and to evaluate its application for treating landfill leachates at long-term operations. Based on the predicted contaminant concentrations, two sets of laboratory-scale bioreactor landfill systems (an ex situ nitrification and in situ denitrification bioreactor as well as an ex situ SND and in situ denitrification bioreactor) were operated continuously for about 48 weeks. The recirculated leachate quantity and effluent characteristics of leachates were regularly monitored and analyzed by using the standard method. The ex situ SND and in situ denitrification process obtained a better leachate removal performance compared with the ex situ nitrification and in situ denitrification process, while the ex situ SND process can reduce the energy costs. However, the leachate treatment performance of this process was generally unsatisfactory as the contaminant concentrations do not meet the discharge standard within the forecasted time. These results further proved that the effectiveness of the treatment decreases along with an increasing landfill age. Therefore, further research must be performed to optimize the treatment efficiency of the bioreactor.

Effective use of iron-aluminum rich laterite based soil mixture for treatment of landfill leachate

Landfill leachate poses environmental threats worldwide and causes severe issues on adjacent water bodies and soil by direct discharge. The primary objective of this study is to analyze the efficient use of compost and laterite mixtures (0, 10, 20, 30 and 40 wt% compost/laterite) on leachate treatment and to investigate the associated removal efficiencies under different sorption processes. Therefore, in the experimental design, laterite is used for providing adsorption characteristics, and compost for activating biological properties of the filter. The filtering process is continued until major physical changes occur in the filter at approximately 100 days. The raw leachate used for the experiment shows higher average values for many analyzed parameters. Parameters for the experiment are selected based on their availability in raw leachate in the Sri Lanka. During filtering, removal efficiencies of BOD (>90%), COD (>85%), phosphate (>90%) and nitrate (75-95%) show higher values for all filters. These removals are mainly associated with biodegradation, which is activated by the added compost. Perhaps the removal of nitrate steadily increases with time, which indicates in denitrification by the added excess carbon from the leachate. The removal of total suspended solids (TSS) is moderate to high, but conversely, the electric conductivity (EC) is unsteady, indicating an association between iron exchange and carbonate degradation. A very high removal efficiency is reported in Fe (90-100%), and wide ranges of efficiencies in Mn (30-90%), Cu (45-85%), Ni (30-93%), Cd (37-98%), Zn (15-98%), and Pb (35-98%) involve heterogeneous sorption processes. Furthermore, the normalization of raw leachate by the liquid filtrate has apparent improvements. The differences (p > .05) in removal efficiencies between the filters are significant. It can be concluded that the filter with laterite mixed with 20% of compost has the optimum conditions. Further, the Fourier-transforminfrared (FT-IR) models for filter media conclude multiple sorptions and reveal evidence on vacant sites. X-ray diffraction (XRD) analyses indicate secondary minerals gibbsite, hematite, goethite and kaolinite as the major minerals that involved on the sorption process.

Kinetics of biogas production and chemical oxygen demand removal from compost leachate in an anaerobic migrating blanket reactor

In this study, laboratory anaerobic migrating blanket reactor (AMBR) with four units was used to reduce and remove COD leachate of composting process; it was also used to determine the kinetic coefficients of COD removal and biogas and methane gas production in several different OLRs. The maximum concentration of organic matter entering the reactor was 100,000 mg/L and the reactor was under operation for 319 days. The results showed that the COD removal efficiency of AMBR in all concentrations of substrate entering the reactor was above 80%. First-order model and Stover-Kincannon were used to investigate the kinetics of COD removal via AMBR biological process; in addition, the two models of Modified Stover-Kincannon and Van der Meer and Heertjes were used to check the kinetic constants of biogas and methane gas production. The results obtained from the models showed that the experimental data on COD removal were more consistent with the results obtained from Stover-Kincannon model (R² = 0.999) rather than with the First-order model (R² = 0.926). Kinetic constants calculated via Stover-Kincannon model were as follows: saturation value constant (KB) and maximum utilization rate constants (U_max), respectively, were 208,600 mg/L d and 172,400 mg/L d. We investigated the linear relationship between the experimental data and the values predicted by the models; as compared with the values predicted by the First-order model, the values predicted by Stover-Kincannon model were closer to the values measured via experiments. Based on the results of the evaluation of kinetic coefficients of Stover-Kincannon model, with the migration of the leachate flow from unit 1 to unit 4, U_max value has fallen significantly. The values of maximum specific biogas production rate (G_max) and proportionality constant (GB) obtained from the Stover-Kincannon model, respectively, were 35,714 ml/L d and 42.85 (dimensionless) and value of kinetic constant of Van der Meer and Heertjes (ksg) was 0.0473 ml CH₄/mg COD.

N2O emissions from an intermittently aerated semi-aerobic aged refuse bioreactor: Combined effect of COD and NH4+-N in influent leachate

The carbon-nitrogen ratio (COD/NH₄⁺-N) is an important factor affecting nitrification and denitrification in wastewater treatment; this factor also influences nitrous oxide (N₂O) emissions. This study investigated two simulated intermittently aerated semi-aerobic aged refuse bioreactors (SAARB) filled with 8-year old aged refuse (AR). The research analyzed how differences in and the combination of influent COD and NH₄⁺-N impact N₂O emissions in leachate treatment. Experimental results showed that N₂O emissions increased as the influent COD/NH₄⁺-N decreased. The influent COD had a greater effect on N₂O emissions than NH₄⁺-N at the same influent ratios of COD/NH₄⁺-N (2.7 and 8.0, respectively). The maximum N₂O emission accounted for 8.82±2.65% of the total nitrogen removed from the influent leachate; the maximum level occurred when the COD was 2000mg/L. An analysis of differences in influent carbon sources at the same COD/NH₄⁺-N ratios concluded that the availability of biodegradable carbon substrates (i.e. glucose) is an important factor affecting N₂O emissions. At a low influent COD/NH₄⁺-N ratio (2.7), the N₂O conversion rate was greater when there were more biodegradable carbon substrates. Although the SAARB included the N₂O generation and reduction processes, N₂O reduction mainly occurred later in the process, after leachate recirculation. The maximum N₂O emission rate occurred in the first hour of single-period (24h) experiments, as leachate contacted the surface AR. In practical SAARB applications, N₂O emissions may be reduced by measures such as reducing the initial recirculation loading of NH₄⁺-N substrates, adding a later supplement of biodegradable carbon substrates, and/or prolonging hydraulic retention time (HRT) of influent leachate.