VOCs emission from a final landfill cover system induced by ground surface air temperature and barometric pressure fluctuation.

Volatile organic compounds (VOCs) emission flux and their concentration profiles were measured at a final municipal solid waste (MSW) landfill cover in Hangzhou, China. The influencing parameters, especially ground surface air temperature and pressure were monitored concomitantly. Furthermore, a numerical model incorporating coupled thermo-hydro-chemical interaction to assess VOCs emission from this final landfill cover (LFC) system was developed and validated with the field test results. The tested total VOC emission flux from the final cover is 0.0124 µg/m2/s, which indicates that the total amount of VOCs emitted into the atmosphere is 391 mg/m2 annually. Among these, dichloromethane (DCM) dominated VOCs emission flux during May, comprising 51.8% of the total emission flux. The numerical simulation results indicated that the diffusive emission flux of VOCs varied consistently with the fluctuation of atmospheric temperature. Whereas, the advective flux varied inversely with the fluctuation of barometric pressure. The highest difference in diffusive emission flux induced by temperature variation is 183 µg/m2/day and occurred in spring. Moreover, the results demonstrated that the impact of atmospheric temperature and pressure fluctuation on the emission of VOC from final covers is non-negligible when reasonably assessing the risks of landfill and landfill gas emission budget.

Effect of ultrasonication conditions on polyethylene microplastics sourced from landfills: A precursor study to establish guidelines for their extraction from environmental matrices.

Establishing concentration of microplastics (MPs), designated as CMP, in aqueous, semi-solid and solid samples originating from unscientifically created landfills/dumpsites (UCLDs) and engineered landfills (ELFs) is of utmost importance to assess their impact on the geoenvironment. However, the accuracy of CMP will be guided by the extraction efficiency of MPs from these samples. The extraction of MPs from semi-solid and solid samples of UCLDs/ELFs would be cumbersome, mainly due to their trapping in solid aggregates (including organic matter). Such aggregates need to be dispersed to release the MPs, which can be achieved through the assistance of ultrasonication (US) in the presence of an appropriate dispersing agent. However, mere dispersion of solid aggregates during the US might not result in the complete release of MPs adhered (AMPs) to MPs native (NMPs) to these samples. This is because MPs would adhere to the surface of the adjacent ones due to various physical-mechanical-thermal-chemical processes that prevail in landfills. Hence, guidelines for US-assisted extraction of MPs should be developed by considering an approach that would ensure (i) cleaning of NMPs' surface and (ii) release of AMPs without damaging the former. This necessitates understanding the influence of US parameters such as energy applied (Eus), time (tus) and direct/indirect exposure of NMPs from landfills that would control CMP. In this context, the influence of above mentioned US parameters on the (i) surface cleaning of polyethylene NMPs and (ii) release of AMPs and their concentrations (CAMP) was investigated. It was observed that Eus equal to 500 kJ/L during the indirect method of US would result in surface cleaning of NMPs and complete release of AMPs without damaging the farmer's structure. The present work acts as a precursor study to establish the guidelines for the US-assisted extraction of MPs in environmental samples. Also, a generalized relationship between Eus and CAMP, which can be employed to study the impact of landfill type on the release of MPs during the US was developed.

Closing the loop: A case study on pathways for promoting sustainable waste management on university campuses.

The implementation of circular economy (CE) strategies has facilitated a comprehensive approach to waste management (WM) in university campuses. Composting food waste (FW) and biomass can mitigate negative environmental impacts and be part of a closed-loop economy. The compost can be used as a fertilizer, thereby closing the waste cycle. Implementing nudging strategies to promote effective waste segregation can help the campus move closer towards achieving neutrality and sustainability goals. The research was conducted at the Warsaw University of Life Sciences - WULS (SGGW). The University Campus is located in the south of Warsaw (Poland) and covers an area of 70 ha with 49 buildings. The SGGW campus generates selectively collected (glass, paper, plastic and metals, and biowaste) and mixed waste. Data were collected through a year-long report from the university administration. For the survey, waste data from 2019 to 2022 were obtained. The CE efficiency indicators of CE were measured. The indicators of CE efficiency for compost (Ic,ce) and plastic (Ipb,ce) showed Ic,ce at 21.05 %, which means that 1/5th of the waste generated on the campus can be introduced into the CE paradigm through composting, and the resulting value Ipb,ce of 19.96 % indicates that this amount can be reintroduced into the CE paradigm through its reuse. The results of the seasonality study showed that there were no statistically significant differences in the generated biowaste between the separated periods of the year, and the Pearson correlation coefficient (r = 0.068) provided additional confirmation. The weak correlation between the amount of biowaste generated and the average for each year (r = 0.110) also indicates a stable biowaste generation system that does not require a reduction or increase in the efficiency of waste processing, such as composting. By implementing CE strategies, university campuses can improve WM practices and achieve sustainability goals.

Gas transport in landfill cover system: A critical appraisal.

Landfill gas (LFG) emission is gaining more attention from the scientific fraternity and policymakers recently due to its threat to the atmosphere and human health of the populace living in surrounding premises. Though landfill cover (LFC) (viz., daily, intermittent and final cover) is widely used by landfill operators to mitigate or reduce these emissions, their overall performance is still under question. A critical analysis of available literature, primarily pertaining to (i) the composition of the landfill gases and their migration in the LFC system, (ii) experimental and mathematical investigations of the transport mechanism of gas and (iii) the impact of additives to cover soils on transport and fate of gas, has been conducted and presented in this manuscript. Investigation of the efficiency of modified soil was mainly focused on laboratory test. More field tests and application of amended cover soils should be conducted and promoted further. Studies on nitrous oxide and emerging pollutants, including poly-fluoroalkyl substances transport in landfill cover system are limited and need further research. The transport mechanisms of these unconventional contaminants should be considered regarding the selection of LFC materials including geomembrane and geosynthetic clay liners. The existing analytical and numerical models can provide a basic understanding of LFG transport mechanisms and are able to predict the migration behaviour of LFG; however, there are still knowledge gaps concerning the interaction between different species of the gas molecule when modeling multi-component gas transport. Gas transport through fractured cover should also be considered when evaluating LFG emission in the future. Simplified design method for landfill cover system regarding LFG emission based on analytical models should be proposed. Overall, mathematical models combined with experiments can facilitate more visualized and intensive insights, which would be instrumental in devising climate adaptive landfill covers.

A comprehensive methodology for determining buffering capacity of landfill-mined-soil-like-fractions.

The utilization of landfill-mined-soil-like-fractions (LFMSF), which is a major fraction resulting from landfill mining (LFM) activity, is being debated owing to a lack of comprehensive understanding of its characteristics. In this context, based on the physicochemical properties of LFMSF, several of the earlier researchers have opposed its utilization as compost, feedstock in waste-to-energy, and fill material in civil engineering applications. However, it has been noticed that LFMSF consists of required amount of organic matter (OM) and inorganic carbon (IC) to make it suitable as a buffering material that would help to modify/treat geomaterials exhibiting extreme pH values. In this context, determination of its buffering capacity (BC), a parameter that quantifies the buffering potential, becomes essential. However, determination of BC by resorting to the existing protocols is not suggestible mainly due to (i) an extremely narrow range of the pH (3-8) employed, (ii) lack of incorporation of the optimal time required for reaction/pH stabilization (tpHS), (iii) concern for decomposition of OM during the addition of H+/OH- while experimentation and (iv) heterogeneity associated with the LFMSF unlike the geomaterials that are commonly tested (viz., agricultural soils and compost). Hence, to overcome these limitations, a comprehensive methodology that can be employed for determining the ultimate buffering capacity (BCu) by establishing appropriate tpHS (i.e., 200 h) and liquid to solid ratio (i.e., 20), which would eliminate the decomposition of OM over a broad range of pH (i.e., 2-12) has been proposed. Based on the testing of several LFMSF samples collected from unscientifically created landfills/dumpsites and engineered landfills in India, easy-to-use relationships between the (i) reaction time (t) and (ii) physicochemical properties of the samples that influence BC and BCu, directly or indirectly, have also been proposed.

Leachate characteristics: Potential indicators for monitoring various phases of municipal solid waste decomposition in a bioreactor landfill.

Leachate is a contaminated liquid generated during the bio-chemical decomposition processes of municipal solid waste (MSW) that occurred at semi-solid or solid-state in a bioreactor landfill (BLF). Conceptually, leachate from a BLF is analogous to the urine generated in the 'human body', on which the medical practitioners rely to diagnose and remediate ailments. In line with this practice, to monitor the complex MSW decomposition processes, prolonged investigations were performed to establish the temporal variation of different chemical parameters (such as pH, electrical conductivity, chemical oxygen demand, organic- and inorganic carbon, nitrate- and ammonium-nitrogen, sugars and volatile fatty acids) of the leachate collected from different cells (age≈ 6-48 months) of a fully functional BLF in Mumbai, India. Furthermore, to understand the effect of the climate, MSW composition and landfill operating conditions on the rate of the decomposition process, chemical parameters of the leachate obtained from a landfill located in the central part of Poland were compared with the BLF. The study reveals that the chemical parameters, except for the pH, evince a rapid reduction with time and attain a constant value, which indicates the 'stabilized MSW'. Also, native microorganisms that are an integral part of MSW consume volatile fatty acids within a year in the BLF, which facilitate the rapid transformation of the decomposition process from acidogenesis and acetogenesis to the methanogenesis phase. It is worth iterating here that based on the long-term field study, a convenient and efficient methodology, which is currently missing from the literature, has been established to understand the kinetics of different phases of anaerobic decomposition. This study would be very helpful to the landfill operators, who are interested in accelerating MSW decomposition by augmenting leachate properties.

A case study on establishing the state of decomposition of municipal solid waste in a bioreactor landfill in India.

Estimation of temporal changes undergone by municipal solid waste (MSW) in its physico-chemico-geomechanical properties in a bioreactor landfill (BLF) is essential for: (i) efficient landfilling, (ii) establishing the state of decomposition of MSW with time and (iii) deciding upon the appropriate time to initiate landfill mining. To achieve this, a series of destructive (DTs) and non-destructive tests (NDTs) can be conducted on the MSW samples in the BLF. With this in view, several DTs were conducted on these samples retrieved from different depths of the two cells of a fully operational BLF in Mumbai, India. Subsequently, the physical and chemical properties of these samples such as composition, moisture content, volatile solids (VS), elemental content, lignocellulosic content (i.e. cellulose, hemicellulose and lignin content) and bio-methanation potential, were determined by following the laboratory testing, as a function of time. Also, NDTs such as cone penetration test and multichannel analysis of surface waves were conducted on these cells of BLF to obtain geomechanical parameters (viz. cone resistance, sleeve resistance, friction ratio and shear wave velocity) of the MSW. Based on the data obtained from these tests, and reported in the literature, it has been observed that the VS, elemental content, lignocellulosic content and bio-methanation potential of MSW exhibits very well-defined trends, as compared to the geomechanical parameters, with time. Furthermore, it has been observed that the VS, hydrogen-, carbon- and nitrogen-content reduce significantly (≈62%, 70%, 50% and 30%, respectively), following an exponential decay, until the critical time (tcr) (≈4 years) has been achieved. As, beyond tcr these parameters remain practically unchanged, which corresponds to the 'stabilized MSW', mining of the BLF can be initiated without further delay.

Photocatalytic Mechanisms for Peroxymonosulfate Activation through the Removal of Methylene Blue: A Case Study.

Industrial activity is one of the most important sources of water pollution. Yearly, tons of non-biodegradable organic pollutants are discharged, at the least, to wastewater treatment plants. However, biological conventional treatments are unable to degrade them. This research assesses the efficiency of photocatalytic activation of peroxymonosulfate (PMS) by two different iron species (FeSO4 and Fe3+-citrate) and TiO2. These substances accelerate methylene blue removal by the generation of hydroxyl and sulfate radicals. The required pH and molar ratios PMS:Fe are crucial variables in treatment optimization. The kinetic removal is reduced by the appearance of scavenger reactions in acidic and basic conditions, as well as by the excess of PMS or iron. The best performance is achieved using an Fe3+-citrate as an iron catalyst, reaching the total removal of methylene blue after 15 min of reaction, with a molar ratio of 3.25:1 (1.62 mM of PMS and 0.5 mM Fe3+-citrate). Fe3+-citrate reached higher methylene blue removal than Fe2+ as a consequence of the photolysis of Fe3+-citrate. This photolysis generates H2O2 and a superoxide radical, which together with hydroxyl and sulfate radicals from PMS activation attack methylene blue, degrading it twice as fast as Fe2+ (0.092 min-1 with Fe2+ and 0.188 min-1 with Fe3+-citrate). On the other hand, a synergistic effect between PMS and titanium dioxide (TiO2) was observed (SPMS/TiO2/UV-A = 1.79). This synergistic effect is a consequence of PMS activation by reaction with the free electron on the surface of TiO2. No differences were observed by changing the molar ratio (1.04:1; 0.26:1 and 0.064:1 PMS:TiO2), reaching total removal of methylene blue after 80 min of reaction.

Simulation of municipal solid waste degradation in aerobic and anaerobic bioreactor landfills.

Municipal solid waste generation is huge in growing cities of developing nations such as India, owing to the rapid industrial and population growth. In addition to various methods for treatment and disposal of municipal solid waste (landfills, composting, bio-methanation, incineration and pyrolysis), aerobic/anaerobic bioreactor landfills are gaining popularity for economical and effective disposal of municipal solid waste. However, efficiency of municipal solid waste bioreactor landfills primarily depends on the municipal solid waste decomposition rate, which can be accelerated through monitoring moisture content and temperature by using the frequency domain reflectometry probe and thermocouples, respectively. The present study demonstrates that these landfill physical properties of the heterogeneous municipal solid waste mass can be monitored using these instruments, which facilitates proper scheduling of the leachate recirculation for accelerating the decomposition rate of municipal solid waste.