Mixed Landfill Research Articles

Stabilization of heavy metals in municipal solid waste incineration fly ash using organic chelating agents: Insight into risk assessment and function mechanism

Landfill treatment of municipal solid waste incineration fly ash (MSWI FA) after stabilization is the primary disposal technology. However, only few studies have assessed the stability of MSWI-FA-chelated products in different landfill scenarios. In this study, three commonly used dithiocarbamate (DTC)-based organic chelating agents (CAs) (TS-300, SDD, and PD) were selected to stabilize heavy metals (HMs) in MSWI FA. In addition, the leaching toxicity and environmental risks of the chelated products were assessed in different disposal environments. The results demonstrate that the HM leaching concentrations of the chelated products met the concentration limits of the sanitary landfill standard (GB16889–2008; mixed Landfill Scenario) for the three CAs at a low additive level (0.3 %). However, in the compartmentalized landfill scenario (the leaching agent was acid rain), the leaching of HMs from the chelated products met the standard when TS-300, SDD, and PD were added at 1.5 %, 6.0 %, and 8.0 %, respectively. Additionally, Pb, Zn, and Cd in the chelated products from the 1.5 %-TS-300 and 6.0 %-SDD groups met the leaching limits within the pH ranges 6–12 and 7–12, 6–12 and 7–12, and 8–12 and 8–12, respectively. This was primarily due of TS-300's multiple DTC groups forming stable chain-like macromolecular chelates with Pb. However, although the environmental risks associated with Pb, Zn, and Cd in the initial (0-d) chelated products of the 1.5 %-TS-300 and 6.0 %-SDD groups were minimized to low and negligible levels, there was a significant increase in the leaching of the three HMs after 28 d of storage. Therefore, with appropriate CA addition, although the leaching concentration of HMs in the chelated product may comply with the GB16889–2008 standards, it remains essential to consider its environmental risk, particularly in highly acidic or alkaline environments and during prolonged storage of the product.

Urbanity as a source of genotoxicity in the synanthropic Kelp Gull (Larus dominicanus)

Increases in human population lead to an increase in urban wastes, which could affect wildlife in several ways. Urban pollutants can affect erythrocytes of birds generating morphological membrane and nuclear anomalies. The Kelp Gull (Larus dominicanus) is an opportunistic species, which take advantage of urban environments, thus being highly exposed to environmental pollution. In northeastern Patagonia, the dynamic of the waste management was transformed in the last decade and consequently, gulls changed their movements in response to changes in waste management systems. The food available to the seagulls went from being a mixture of urban/fishing discards until 2015, when this landfill closures, to being domestic urban offerings. In order of evaluating genotoxicity and changes in pollutants exposition due to these changes, we analyzed the frequencies of erythrocytes nuclear abnormalities and micronuclei (ENAs and MN respectively) in 58 blood smears from adults extracted during the non-breeding season in two periods in landfills with different waste compositions: a mixed landfill (ML) in 2013 before closure (n = 24) versus an urban landfill (UL) (n = 34) in 2021. We found that the Kelp Gull showed high values of abnormalities with an average of 151.5 /10,000 RBC in comparison with other seabird species. The bud and notched types of ENAs were the most prevalent abnormalities in both sites. We did not find significate differences in the overall abnormality frequency between sites, however we found significant higher frequencies in displaced and tailed types of ENAs in ML. We also found poikilocytosis, as seen previously in other animals exposed experimentally to pollutants such as metals and crude oil. Cellular abnormalities found in the Kelp Gull suggest an exposition of individuals to pollutants in foraging areas. The hemispheric distribution and the synanthropic characteristics of the species denote its importance as a suitable global monitor of genotoxicity.

Land pollution by illegal dumps in the Tashkent region

The problem of the emergence of illegal dumps in rural areas is considered in the article on the example of the Tashkent region of the Republic of Uzbekistan. It was revealed that the sizes of illegal disposal fields vary from 1.0 to 18,895 m2, there are dumps for building materials from construction sites, agricultural, household waste, as well as mixed landfills. The continuity of the layer of illegal dumps ranges from 60 to 100%. The roadsides also present long stretched illegal dumps with a continuity of the waste layer from 10 to 42%. For a full-scale assessment of the location, size and composition of illegal dumps, it is recommended to develop a GIS monitoring system.

Survival strategies of ammonia-oxidizing archaea (AOA) in a full-scale WWTP treating mixed landfill leachate containing copper ions and operating at low-intensity of aeration

Recent studies indicate that ammonia-oxidizing archaea (AOA) may play an important role in nitrogen removal by wastewater treatment plants (WWTPs). However, our knowledge of the mechanisms employed by AOA for growth and survival in full-scale WWTPs is still limited. Here, metagenomic and metatranscriptomic analyses combined with a laboratory cultivation experiment revealed that three active AOAs (WS9, WS192, and WS208) belonging to family Nitrososphaeraceae were active in the deep oxidation ditch (DOD) of a full-scale WWTP treating landfill leachate, which is configured with three continuous aerobic-anoxic (OA) modules with low-intensity aeration (≤ 1.5 mg/L). AOA coexisted with AOB and complete ammonia oxidizers (Comammox), while the ammonia-oxidizing microbial (AOM) community was unexpectedly dominated by the novel AOA strain WS9. The low aeration, long retention time, and relatively high inputs of ammonium and copper might be responsible for the survival of AOA over AOB and Comammox, while the dominance of WS9, specifically may be enhanced by substrate preference and uniquely encoded retention strategies. The urease-negative WS9 is specifically adapted for ammonia acquisition as evidenced by the high expression of an ammonium transporter, whereas two metabolically versatile urease-positive AOA strains (WS192 and WS208) can likely supplement ammonia needs with urea. This study provides important information for the survival and application of the eutrophic Nitrososphaeraceae AOA and advances our understanding of archaea-dominated ammonia oxidation in a full-scale wastewater treatment system.

Unexpectedly higher soil organic carbon accumulation in the evapotranspiration cover of a coal bottom ash mixed landfill

Monolayer barriers, which are usually known as evapotranspiration (ET) covers, have long been used as alternative final cover systems in waste landfills. Coal bottom ash was evaluated as a good alternative to soil in landfill ET cover systems to increase the bottom ash (BA) recycling ratio in the past. In a previous study, applying BA promoted plant growth characteristics and improved the soil physicochemical properties, particularly the soil organic carbon (SOC) content. In this study, we investigated the effect of BA on the SOC increase by examining the chemical and physical characteristics of ET cover systems, and we compared BA mixed and pure soils. We collected two types of soil from the landfill cover, namely, BA mixed soil (BA 35% + soil 65%) and soil alone (100%), for treatments during the 5th year after installation. Bottom ash mixed soil has four times more SOC than the pure soil at the surface soil layer, but the SOC contents significantly decreased with the soil depth in BA mixed soil, and no differences were found between BA mixed soil and pure soil below a 25 cm soil depth. In addition, there was no significant difference in the chemical composition of the SOC according to a13C NMR. However, the allophane contents were significantly higher in BA mixed soil than pure soil, which physically protects the material from organic matter decomposition. Conclusively, the higher allophane content originating from BA might act as the primary factor in the high accumulation of soil organic carbon in the BA mixed soil layer by retarding the organic matter decomposition.

Energy Recovery from Waste Incineration—The Importance of Technology Data and System Boundaries on CO2 Emissions

Previous studies on waste incineration as part of the energy system show that waste management and energy supply are highly dependent on each other, and that the preconditions for the energy system setup affects the avoided emissions and thereby even sometimes the total outcome of an environmental assessment. However, it has not been previously shown explicitly which key parameters are most crucial, how much each parameter affects results and conclusions and how different aspects depend on each other. The interconnection between waste incineration and the energy system is elaborated by testing parameters potentially crucial to the result: design of the incineration plant, avoided energy generation, degree of efficiency, electricity efficiency in combined heat and power plants (CHP), avoided fuel, emission level of the avoided electricity generation and avoided waste management. CO2 emissions have been calculated for incineration of 1 kWh mixed combustible waste. The results indicate that one of the most important factors is the electricity efficiency in CHP plants in combination with the emission level of the avoided electricity generation. A novel aspect of this study is the plant by plant comparison showing how different electricity efficiencies associated with different types of fuels and plants influence results. Since waste incineration typically have lower power to fuel ratios, this has implications for further analyses of waste incineration compared to other waste management practises and heat and power production technologies. New incineration capacity should substitute mixed landfill disposal and recovered energy should replace energy from inefficient high polluting plants. Electricity generation must not be lost, as it has to be compensated for by electricity production affecting the overall results.

Landfill mining : potential source for maintenance-free construction materials?

As the use of plastic products is very widespread, reuse of the plastic waste represents a huge challenge. Plastic packaging (e.g. thin plastic bags, foil, foodwrappings) and other plastic waste (pallets, garden furniture, buckets, sport and hobby equipment, car bumpers, canisters, pipes, bobbins, computer and TV cases, plastic refrigerator details, etc.) form the most problematic and continuously growing type of waste, that according to common solutions can be mainly landfilled, or incinerated.Initial sorting of waste and subsequent recycling of single-type plastics into uniform mass, granules or new products are the generally preferred solutions for recycling plastic. Recycling is normally performed based on one specific type of plastic, e.g. LDPE, HDPE, PS, PP or PET, in the course of which the sorted plastic waste is washed, shredded, dried and granulated. The biggest problem with mixed plastics is posed by the fact that polymers of different types are immiscible because of their different molecular weights and long polymer chains. Heating the polymers is not sufficient for decomposing polymer molecules; therefore, the polymers to be recovered must typically have identical compositions to achieve effective mixing. When plastics of different types are simultaneously melted together, they usually do not mix – like oil and water – and will form layers. Low-grade mixed dirty plastic is typically rejected from recycling. Rexest Grupp Ltd, however, has developed a technology for recycling mixed plastic waste.In this study it has been discovered that mixed plastic waste that was landfilled for over a decade did not differentiate from the fresh mixed plastic, neither had the landfilled plastic lost its polymeric properties. Landfilled plastic needs only to be separated from other materials (eg textile, paper) and soil. After mechanical separation, recycling technologies that are able to use of mixed plastic waste, were as also able to handle mixed landfill plastic.Experiments demonstrate that construction materials and products like decking boards, noise barriers, garden furniture etc. could therefore be produced also from landfilled plastic waste, turning this waste into the maintenance free products that are also recyclable after decades of use. Taking into account vast number of landfills that contain plastic waste it raises question whether turning these materials into recyclable construction materials could form a new challenge and possibility to support the environment, and lower the need for the usage of new resources.

Characteristics of landfill leachates in central Taiwan

Due to the complex nature of landfill leachates, the leachate treatment plants have difficulty to meet the current Taiwan EPA's effluent standards. Three typical types of landfills, closed landfill A, mixed landfill B (disposal of MSW with bottom ashes from MSW incinerators) and direct MSW landfill C, (disposal of MSW only), are investigated in this research in order to have a better understanding of characteristics of leachates. Factors investigated in this research include landfill age, pH, BOD, COD, TS, DS, VS, seasons, metals (Pb, Ca, Cd, Hg, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, and Zn), humic substances (humic acid, fulvic acid, and non-humic substance), aromaticity and toxicity. Results show that the active landfills B and C had the significant higher concentration of COD, VSS, TS, PtCo, TOC and conductivity. The mixed landfill B had the higher DS, TS, Na, Ca, Mg and conductivity than that of direct MSW landfill C. Direct MSW landfill C had the highest contents of Fe, Cr, Ni and acute toxicity among these landfills. A significant degree of variation was encountered and factors which may influence leachate quality were identified and discussed.

Environmental Isotopes as a Useful Tool for Studies at Mixed Uranium Mill Tailings Sites

Groundwaters in the area of a mixed landfill (domestic waste above uranium mill tailings) in Dresden (Saxony, Germany) were investigated for their isotope signatures to distinguish between different groundwater types. To determine between the two contamination sources (waste and uranium mill tailings) a multi parameter interpretation was done using both, the main hydrochemical parameters the radionuclides 234U, 238U, 226Ra and 222Rn as well as the environmental isotopes of the elements hydrogen, oxygen, sulphur and carbon. The seepage water from the landfill shows higher δ34S, δ18O and tritium values as the inflow. The tritium values give an idea about water movement in the dump and mean residence time of the groundwater. The water in the dump shows varying δ13C values which indicate different processes occurring in the dump.

Isotopic Composition of Groundwater from Mixed Uranium Mill Tailings in Saxony/Germany

Groundwaters in the area of a mixed landfill (domestic waste above uranium mill tailings) in the Erzgebirge (Saxony, Germany) were investigated for their isotope signatures to distinguish between different groundwater types. The seepage water from the landfill shows higher δ34S values as the inflow whereas the parameters tritium and δ18O do not significantly vary. Uranium values are lower than at other comparable sites, The maximum of 0.7 mg/l Unat was measured in the geological underground of the landfill. Significant radium concentrations occur in the geological background and are due to former mining activities. The landfill does not produce increased radium values in the water.