Investigation on trommeled legacy waste from full-scale mining of old dumpsites: Suitable for valorization or scientific disposal?

The burgeoning interest in resource recovery from old dumpsites has significantly propelled the adoption of Landfill Mining (LFM) in recent years. This study is centred around evaluating the quality of materials recovered from the full-scale LFM activities at two major dumpsites in India, focusing on the valorization potential of the segregated legacy waste. A detailed analysis was conducted on the segregated waste fractions based on particle size (-30 mm, 30 to 6 mm, and -6 mm, as sourced from the sites), employing both batch and column leaching methods across a range of liquid-to-solid (L/S) ratios (0.1-10.0 L/kg). The findings reveal a pronounced concentration of contaminants within the -6 mm fraction compared to the 30 to 6 mm and -30 mm fractions. Column leaching tests revealed a reduction in contaminant concentration, correlating with incremental changes in L/S ratio. Notably, this trend remained consistent across varying particle sizes and specific type of contaminants assessed. Notably, color intensity of leachate reduced significantly from 720 to 1640 Platinum Cobalt Units (PCU) at an L/S ratio of 0.1 L/kg to a minimal 94-225 PCU at an L/S of 10 L/kg. Dissolved salts emerged as a primary concern, marking them as significant contaminants in both leaching methods. The analysis confirmed that the segregated fractions comply with the USEPA Waste Acceptance Criteria (WAC), permitting their disposal in non-hazardous waste landfills. However, the elevated presence of dissolved salts, exceeding reuse limits by 5-35 times, limits their open or unrestricted reuse. Despite this, isolated reuse aligns with regulations from the Netherlands and Germany, suggesting viable pathways for compliant utilization. Geotechnical assessments indicate the potential for repurposing the -30 mm fraction as alternative earthfill and construction material. While heavy metal leaching does not pose significant concerns, the prevalent unscientific disposal practices near urban settlements highlight potential human health risks. This investigation enriches the understanding of the physicochemical properties, leaching behaviour, and reuse potential of segregated legacy waste, offering crucial insights for civic authorities in determining appropriate reuse and disposal strategies for such materials.

Identification and assessment of appropriate remediation management techniques for the recovery of soil-like material produced in landfill mining.

Landfill mining has received major attention in recent years for the reclamation of waste disposal sites, including in developing countries such as India where significant efforts are being made to manage sites in this way. The bulk of the material obtained from landfill mining consists of fine-grained soil-like material (SLM) but its direct reuse in off-site applications is restricted due to the presence of harmful heavy metals, soluble salts and other pollutants. In this study, appropriate techniques for managing SLM to permit recovery and reuse are assessed. As a result, experimental investigation explores the efficacy of two remediation techniques considered appropriate for SLM management: electrokinetic remediation and phytoremediation. These were applied to SLM from a recently mined landfill and their ability to reduce heavy metal and other soluble salt burdens assessed. Electrokinetic remediation has shown considerable potential to mobilise and transport heavy metals and soluble salts through and from the SLM over an eight-week period. Phytoremediation experiments also demonstrated mobilisation and uptake of metals from the SLM over a similar duration although relatively low amounts were recovered as a result of the low biomass produced over this period. Both technologies have demonstrated potential for recovery of metals from SLM, as well as recovering the SLM itself as a potential resource.

Investigations on fine fraction of aged municipal solid waste recovered through landfill mining: Case study of three dumpsites from India.

Reclamation of the dumps/landfills having huge quantities of decades-old garbage (aged waste or legacy waste) in an environmentally sound manner is one of the major challenges faced by the developing nations in general and in particular by urban local bodies in India. The article presents the feasibility of landfill mining operation specifically to recover soil-like material at old dumpsites of India for re-use in geotechnical applications. Aged municipal solid waste was collected from three dumpsites of India and initial tests were conducted on the soil-like material of the municipal solid waste. Initial tests results of grain size distribution, compositional analysis, organic content, total dissolved solids, elemental analysis, heavy metal analysis and colour of the leached water from finer fraction of aged municipal solid waste are presented. From the preliminary investigation, it was found that organic content in 15-20-year-old dumpsites varies between 5%-12%. The total dissolved solids ranges between 1.2%-1.5%. The dark coloured water leaching out from aged waste, with reference to local soil, is one of the objectionable parameters and depends on the organic content. The concentration of heavy metals of the finer fraction were compared with the standards. It was found that copper, chromium and cadmium are present at elevated levels in all the three dumpsites. The study concluded that the bulk of the soil-like material from aged municipal solid waste landfills can be used as cover material for landfills at the same site. However, some treatment in terms of washing, thermal treatment, blending with local soil, biological treatment, etc., is required before it can be re-used in other geotechnical applications.

Optimizing MSW incineration bottom ash reuse: A study on treated wastewater washing and leaching control.

The current study introduces an innovative methodology by utilizing treated wastewater (TWW) from an effluent treatment plant as a washing agent to enhance the characteristics of incineration bottom ash (IBA). This approach addresses sustainability concerns and promotes the circular economy by reusing wastewater generated in municipal solid waste incineration facilities. Previous research has underscored the challenges of open IBA reuse due to elevated leaching of chlorides, sulfates, and trace metal(loid)s. Thus, the experimental setup explores various combinations of washing, with or without screening, to optimize the properties of soil-like material (SLM < 4.75 mm) and overall material (OM < 31.5 mm) fractions of IBA for unrestricted applications. Batch leaching tests were conducted on treated samples, and leaching characteristics were evaluated in accordance with regulatory standards, primarily the Dutch standard for unrestricted IBA reuse. The findings reveal that washing in isolation proves insufficient to enhance IBA properties; however, washing followed by screening, specifically for removing fines (<0.15 mm), proves effective in reducing contamination. The study identifies that multiple steps of washing and screening (with recirculation) process render OM and SLM fractions suitable for unrestricted reuse with a cumulative liquid-to-solid ratio of 6 L/kg and a total washing time of 15 min. The multi-step treatment was found effective in reducing sulfate contamination by 65-74 % and chloride contamination by 83-89 % in IBA fractions. This approach offers a promising solution for overcoming the limitations associated with IBA leaching, thereby promoting sustainable waste reuse practices.

Sustainable utilization of incineration bottom ash in pavement construction: Environmental impacts and life cycle assessment.

The global drive towards sustainable development has prompted a notable shift in civil engineering practices towards utilizing secondary materials, such as incineration bottom ash (IBA). The literature review underscores the relevance of waste incineration and the crucial need for effective IBA management strategies. Existing studies, however, reveal a dearth of studies within the life cycle assessment (LCA) framework focusing on understanding IBA characteristics and field conditions. The study addresses this gap by proposing an LCA to assess the environmental implications of substituting natural aggregates with IBA in pavement layers. A comparative LCA was carried out, where different scenarios of reuse of IBA (as produced, treated, or with restrictions) were assessed against a baseline scenario that represents the conventional use of aggregates in roads and landfilling of IBA. The ReCiPe technique, incorporating a hierarchist perspective, was employed to assess impacts across different problem-oriented categories. Additionally, this study also explores the impact of data variability on LCA outcomes, considering changes in landfill height, pavement infiltration rate, time duration, and IBA transportation distance. The analysis indicates that incorporating IBA in road layers can significantly reduce impacts on non-toxic categories like global warming by over 35 %. However, the leaching properties of untreated IBA contribute to a more than 28 % increase in human carcinogenic toxicity, rendering it environmentally unsuitable for road layer reuse. The comparative study illustrated that reusing treated IBA is the most sustainable approach, remaining effective up to a distance of d + 15 km. In cases where treatment is not feasible, utilizing IBA with restrictions is recommended up to a distance of d + 5 km (d represents the transportation distance for natural materials). This research fills a critical gap in the literature by providing a framework to assess IBA reuse in road construction, thereby advancing the discourse on sustainable materials management in the construction industry.

Electrical conductivity profiling for rapid contamination assessment in unsaturated zones: A case study of an MSW landfill.

This study investigates the potential of using bulk soil electrical conductivity (ECbulk) to predict pore water conductivity (ECpw) for assessing the contamination in the unsaturated zone of an old municipal solid waste (MSW) landfill. ECbulk, ECpw, and water content were evaluated with depth at an old MSW landfill in Bhalswa, Delhi, using the Hydraulic Profiling Tool (HPT) and a dual tube soil sampling system. This data was also supplemented by a cone penetration test (CPTu) for high-resolution soil type identification. The correlation of ECbulk with ECpw was primarily influenced by volumetric water content and mineral conductivity with the latter being negligible at this site due to the high conductivity of the leachate. A reasonable linear correlation between normalized EC (ECbulk/ECpw) was observed with volumetric water content, except at low water contents. ECbulk and ECpw profiles with depth indicated attenuation of contaminants in clay layers, while sand layers exhibited constant profile with depth. ECpw was contributed by macro ions generally found in the leachate, including Na+, Mg2+, K+, Ca2+, NH4+, Cl-, SO42-, and HCO3-, as demonstrated by a strong correlation with their cumulative ionic strength. The results indicate that ECbulk profile can be used as a rapid semi-quantitative method for assessing contaminant migration in the unsaturated soil zone, supporting the remediation or control strategies at old landfills.

An investigation on mobility of heavy metals for assessing the reusability of soil-like material reclaimed from mining of municipal solid waste dumpsites.

Landfill mining, often referred to as "bio-mining", enables the recovery of resources, including combustible, compostable, and recyclable fractions from landfills. However, most of the materials mined from old landfills mainly consist of soil-like materials (SLM). The reuse of SLM depends on the concentration of contaminants, such as heavy metals, soluble salts, etc. A sound risk assessment requires sequential extraction to determine the bioavailability of heavy metals. This study focuses on the mobility and chemical speciation of heavy metals in SLM from four old municipal solid waste dumpsites in India by performing selective sequential extraction. Additionally, the study compares the results with those of four previous investigations to identify international similarities. It has been observed that Zn was mainly available in the reducible phase (average 41%), whereas Ni and Cr proved to have the highest distribution in the residual phase (64% and 71%, respectively). Pb analysis showed a large portion in the oxidizable phase (39%), while Cu was mainly present in the oxidizable (37%) and residual (39%) phases. Similarities with previous investigations were observed for Zn (primarily reducible 48%), Ni (residual 52%), and Cu (oxidizable 56%). Correlation analysis showed that Ni correlated with all heavy metals (ρ = 0.71-0.78), except with Cu. The present study suggested that Zn and Pb are associated with a high risk of pollution due to their maximum distribution in the bioavailable phase. The findings of the study can be used to assess the heavy metal contamination potential of SLM prior to its reuse in offsite applications.

Characterization of MSW incineration bottom ash for use as structural fill in reinforced soil structures: Geoenvironmental, geotechnical and economical assessment.

The study presents the geoenvironmental and geotechnical characterization of MSW incineration bottom ash (IBA) and examines its reuse as structural fill in reinforced soil structures (RSS).The suitability of reuse has been assessed with regard to international regulatory standards. The prime focus of the work remains on evaluating the pullout response of geosynthetic reinforcements through IBA fill to determine the interaction coefficient, which has never been addressed in the literature. The economic viability of using IBA instead of locally available river sand for a 12 m high MSE wall is also established. The column leaching test results confirm that IBA can be utilized in RSS with suitable design measures. The geotechnical investigation shows that IBA is a well-graded, non-plastic lightweight material with adequate drainage and high shear strength. The pullout test results demonstrate that the interaction coefficient of polymeric strips and geogrid in IBA (0.73-1.53 and 0.79-1.91, respectively) is comparable or higher to materials conventionally used as structural fill in RSS, indicating adequate bondage between IBA and geosynthetic reinforcement. Further, it is estimated that using IBA as a substitute for available river sand in the vicinity can potentially reduce the overall RSS project cost by 15-20%, even if IBA has to be transported 50 km away from the project site.

Qualitative comparison of elemental concentration in soils and other geomaterials using FP-XRF.

Field portable X-ray fluorescence (FP-XRF) has tremendous potential in geoenvironmental engineering as a qualitative assessment tool. Identification of the elevated concentrations of the selected elements (Cr, Cu, Mn, Ni, Pb, and Zn) in various geomaterials like soil-like-material (SLM), incinerated bottom ash (IBA), construction and demolition waste (CDW), zinc tailings (ZT) and fly ash (FA) was performed by FP-XRF and compared with the local soil-Delhi silt. Comparably higher concentrations (mg/kg) of Cr (401.0), Cu (499.0), Pb (532.0), Zn (608.0) in SLM, Cr (195.0), Cu (419.0), Ni (93.0), Pb (931.0), Zn (771.0) in IBA and Cr (195.0), Cu (4000.0), Pb (671.0), Zn (7122.0) in ZT were observed. CDW and FA showed similar concentrations range as in local soils. FP-XRF was also used in-situ on local soil at 11 sites to examine its ability to identify the elements with significant variations in concentrations. The results showed high variability in Cl and S concentration values across the 11 sites attributed to the changing moisture content and dissolved salts. The concentration range for the remaining elements were similar at all sites. The verification of the detected elements through visual inspection of the spectrum was also carried out.

Contaminants of concern (CoCs) pivotal in assessing the fate of MSW incineration bottom ash (MIBA): First results from India and analogy between several countries.

Present study characterizes municipal solid waste incineration bottom ash (MIBA) from three incineration plants in Delhi with an intent to serve the dual objectives: a) assessing the disposal/reuse options for Delhi MIBA, b) evaluating variability in results across the countries (including India) and assessing if is significant enough to influence the fate of MIBA of varied origin. A review on leaching studies of MIBA (50 research papers) was conducted which aided in achieving both the objectives. Delhi MIBA samples were analysed for chemical composition. The two commonly adopted leaching tests i.e., TCLP and EN 12457-2, were conducted and the results were checked against regulatory threshold levels (RTLs) to achieve the first objective. Leaching concentration of the contaminants was compared with the compiled literature and RTLs to accomplish the second objective. The compendium of literature most importantly revealed the physicochemical parameters which are pivotal in determining the fate of MIBA but have been missing from many studies. Ten such parameters were identified: Cr, Cu, Mo, Sb, Cl-,SO42-, Cd, Pb, Ni and Zn and are referred as contaminants of concern (CoCs). Delhi MIBA was found suitable for disposal to non-hazardous waste landfills and unsuitable for unrestricted reuse. CoCs identified in Delhi MIBA were identical to those observed in literature (except Cd, Pb and Zn). The variability in leaching concentration of CoCs, observed from comparative assessment of results, spanned nearly 2 to 3 log10 magnitudes for Cu, Cr, Pb, Sb and Zn while 1 to 2 log10 magnitudes for Mo, Cl-andSO42-.

Review of groundwater contamination hazard rating systems for old landfills.

A large number of old uncontrolled landfills exist in developing countries. These are potentially harmful to the environment, especially with respect to groundwater contamination, and therefore, are in need of appropriate control and remedial measures. However, due to resource constraints, such measures are to be undertaken in a phased manner. An appropriate landfill hazard rating system that can evaluate relative groundwater contamination hazard of different sites is a useful tool for site ranking in order to set priorities. This paper reviews 18 existing hazard rating systems that follow the index function approach. Nine systems that are best representative of the existing systems, have been applied to six hazardous waste landfills as well as six municipal solid waste landfills. When used for ranking hazardous waste landfills, some systems such as HRS-1990, ERPHRS, WARM and RSS respond well whereas others like DRASTIC, NCS, NPC system and JENV system show a clustering effect. However, these rating systems do not perform well when applied to old municipal solid waste landfills. Even the HRS-1990, which is observed to be the most sensitive among all rating systems, exhibits some shortcomings. Improvements have been suggested in the waste quantity factor values of HRS-1990 to make it suitable for old municipal solid waste landfills. The improved system is observed to provide superior results in comparison with the existing systems, making it appropriate for use as a tool for ranking of old landfills in need of remediation and control measures.

A new system for groundwater contamination hazard rating of landfills.

In developing countries, several unregulated landfills exist adjacent to large cities, releasing harmful contaminants to the underlying aquifer. Normally, landfills are constructed to hold three types of waste, namely hazardous waste, municipal solid waste, and construction and demolition waste. Hazardous waste and municipal solid waste landfills are of greater importance as these pose greater hazard to groundwater, in comparison with landfills holding waste from construction and demolition. The polluting landfills need to be prioritized to undertake necessary control and remedial measures. This paper assesses existing site hazard rating systems and presents a new groundwater contamination hazard rating system for landfills, which can be used for site prioritization. The proposed system is based on source-pathway-receptor relationships and evaluates different sites relative to one another. The system parameters have been selected based on literature. The Delphi technique is used to derive the relative importance weights of the system parameters. The proposed system is compared with nine existing systems. The comparison shows that the site hazard scores produced by the existing systems for hazardous waste, municipal solid waste, and construction and demolition waste landfills are of the same order of magnitude and tend to overlap each other but the scores produced by the proposed system for the three types of landfills vary almost by an order of magnitude, which shows that the proposed system is more sensitive to the type of waste. The comparison further shows that the proposed system exhibits greater sensitivity also to varied site conditions. The application of different systems to six old municipal solid waste landfills shows that whereas the existing systems produce clustered scores, the proposed system produces significantly differing scores for all the six landfills, which improves decision making in site ranking. This demonstrates that the proposed system makes a better tool for prioritization of landfills for adopting control measures and remediation.

Mechanical characterization of municipal solid waste from two waste dumps at Delhi, India.

The article presents the physical and mechanical properties of the emplaced municipal solid waste (MSW) recovered from different locations of the Ghazipur and Okhla dumps both located at Delhi, India. Mechanical compressibility and shear strength of the collected MSW were evaluated using a 300×300mm direct shear (DS) shear box. Compression ratio (Cc') of MSW at these two dumps varied between 0.11 and 0.17 and is falling on the lower bound of the range (0.1-0.5) of the data reported in the literature for MSW. Low Cc' of MSW is attributed to the relatively low percentages of compressible elements such as textiles, plastics and paper, coupled with relatively high percentages of inert materials such as soil-like and gravel sized fractions. Shear strength of MSW tested is observed to be displacement dependent. The mobilized shear strength parameters i.e., the apparent cohesion intercept (c') and friction angle (ϕ') of MSW at these two dumps are best characterized by c'=13kPa and ϕ'=23° at 25mm displacement and c'=17kPa and ϕ'=34° at 55mm displacement and are in the range reported for MSW in the literature. A large database on the shear strength of MSW from 18 countries that includes: the experimental data from 277 large-scale DS tests (in-situ and laboratory) and the data from back analysis of 11 failed landfill slopes is statistically analyzed. Based on the analysis, a simple linear shear strength envelope, characterized by c'=17kPa and ϕ'=32°, is proposed for MSW for preliminary use in the absence of site-specific data for stability evaluation of the solid waste landfill under drained conditions.