Effects of capping on microbial populations and contaminants immobilization in an old unlined landfill

doi:10.21203/rs.3.rs-2207277/v1

Download PDF

Research Article

Effects of capping on microbial populations and contaminants immobilization in an old unlined landfill

https://doi.org/10.21203/rs.3.rs-2207277/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

This research aimed at evaluating the effects of capping on the mitigation of impacts generated by a closed unlined landfill in São Carlos, SP, Brazil. Physicochemical and microbiological analyses (16S rRNA sequencing) of buried solid waste samples were performed, in capped and uncapped areas. Even though leachate pockets could still be encountered in capped areas, the capping construction reduced oxygen availability and created more reducing conditions, propitiating the development of sulfate-reducing bacteria and possibly contributing to the precipitation of the metals Pb, Cd, Ni, Co, As, and Zn as metal sulfides, causing their immobilization. The microbial populations adapted to the anaerobic conditions created under capped zones belonged to the phyla Firmicutes, Chloroflexi and Euryarchaeota and the genera Methanosaeta, Hydrogenispora, Smithella,and Gelria. Differently, the phyla Acidobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria were more abundant in samples from the uncapped zones, in which the abundance of different genera varied homogeneously. Methanogenic activity was not impaired by the intervention measure, as assessed by the Specific Methanogenic Activity (SMA). Capping of old unlined landfills brings benefits to the immobilization of metals and does not impair microbial degradation, being effective for the mitigation of impacts on soils and water resources.

municipal solid waste

16S rRNA

environmental geochemistry

landfill cover

Considering the environmental and public health threat posed by inadequate waste disposal (Chakraborty et al., 2019; Idowu et al., 2019; Morita et al., 2021; Peter et al., 2019; Somani et al., 2019; Zolnikov et al., 2018), closing dumpsites has been the focus of many authorities and campaigns worldwide. In this regard, the International Solid Waste Association (ISWA) published a guide for closing dumpsites and setting up environmentally friendly systems for solid waste management, directed to governments and local authorities (Mavropoulos et al., 2016). In Brazil, the National Solid Waste Policy (Brasil, 2010) has already contributed to closing dumpsites (Matias et al., 2022), and this setup is expected to improve in the next years, with the approval of the new regulatory framework for sanitation (Brasil, 2020).

Such scenario shows that, on one hand, the closure of dumpsites will prevent further contamination of air, soil, and water resources. On the other hand, if no mitigation measures area adopted – which is common in developing countries (Cetrulo et al, 2018; Zolnikov et al., 2018) – long-term impacts are likely to persist (Morita et al., 2020a) and will probably receive less public and governmental attention. Thus, closing a dumpsite should not be limited to covering waste and fencing; it is also necessary to outline appropriate interventions (Mukherjee et al., 2014). Such interventions must be selected according to the performed environmental diagnosis, but should also consider the country’s socioeconomic context, guaranteeing their wide implementation and maintenance.

The most common approach for mitigating impacts from solid waste disposal sites is the combination of source control and monitored natural attenuation of the contaminant plume (Bjerg et al., 2013). Regarding source control, landfill capping is the most frequently applied, due to the lower cost and technological requirements (Bjerg et al., 2013; Koerner and Daniel, 1997).

Capping construction permits the maintenance of pH and ORP values quite invariable, avoiding their changes due to rainwater infiltration and the consequent remobilization of metals (Belevi and Baccini, 1989). Nevertheless, its adoption may affect microbial degradation and therefore, the landfill stabilization over time (Christensen et al., 1997; Qi et al.,2013). Thus, it is necessary to evaluate if microbial degradation would be indeed impaired by the adoption of cover in old landfills, considering that most organic degradation has already occurred 5 years after landfilling(Sandoval-Coboet al., 2020).

The present work aimed to evaluate the effectiveness of constructing capping layers over old unlined landfills, searching to answer: a) if intervention measures are still necessary at such sites, or, in other words, if they still pose risks to the environment and public health after decades of ceasing the activities; b) if a reduction in contaminants’ mobility can be inferred after capping; c) whether capping impairs microbial activity.

2.1. Study area

The study area is an old unlined landfill situated in the southeast of Brazil, São Carlos city (22.1° S, 47.8° W; Fig. 1). The site is located in a Guarani Aquifer outcrop zone, fundamentally constituted by sandstones and sandy soils, and the local climatic conditions are humid subtropical climate (Cfa by Koppen and Geiger), with annual rainfall of about 1440 mm and an average temperature of 19.7°C.

Domestic, industrial, construction and demolition, and health service wastes were disposed of at the site from 1980 to 1996, without the adoption of structures for collecting and treating leachate or gas. Consequently, contamination was found to be spreading to the surroundings (Morita et al., 2020b) and also to be persistent after a monitoring period of more than 20 years (Morita et al, 2020a). Currently, the site was included in the list of contaminated areas in São Paulo state, Brazil (CETESB, 2017).

2.2. Construction of capping layers

An area of about 900 m² (30 x 30 m), located in the center of the studied landfill, was covered with three capping layers: a) the first layer was applied over the landfill area, consisting of a 20 cm thick regularization soil; b) the second layer was applied over the first one and consisted of a geomembrane attached to a geotextile (0.80 cm thick); c) the third and last layer consisted of a 20cm thick regularization soil (Fig. 1_SM of Supplementary Material).

2.3. Sampling

After 16 months of the construction of the capping layers, solid waste samples were collected in 4 different sites and 2 different depths, totaling 8 samples: D11, D12, D21, and D22 were collected within the capped area, and F11, F12, F21, and F22 were collected outside the capped area, see Fig. 2. The depths considered for sampling at each site were 30cm deep (just after the landfill soil cover, where waste started to appear) and 1m deep (depth considered to be still affected by the capping, and where the first leachate pockets started to appear). Appropriate care was taken in order to clean the drill and avoid contamination. Samples (~ 500g of waste) were collected using the quartering method and were kept in sterilized containers in an icebox. In the laboratory, samples were kept at -20°C until the conduction of physicochemical and microbiological analysis.

2.4. Physicochemical analysis

Solid waste samples were solubilized following the Brazilian norm NBR 10.006 (ABNT, 1984), after removing large particles (glass, stones, wood, and plastic). About 400g of each sample were weighed and dried at 42°C for 24 h. About 250g of the dried samples were weighted, placed in beakers and mixed with 1000 mL of distilled water. The solution was mixed for 5 minutes and then kept for 7 days at 25°C. Afterwards, pH and ORP (Oxidation-Reduction Potential) were immediately measured and samples were filtered through 0.45 -µm membranes in order to perform physicochemical analysis. The following physicochemical parameters were analyzed in all samples: alkalinity, nitrite (N-NO₂⁻), nitrate (N-NO₃⁻), ammoniacal nitrogen (N-NH₄⁺), total Kjeldahl nitrogen (TKN), sulfate (SO₄²⁻), phosphate (PO₄³⁻), fluoride (F⁻), chloride (Cl⁻), chemical oxygen demand (COD), total organic carbon (TOC), aluminum (Al), antimony (Sb), barium (Ba), cadmium (Cd), calcium (Ca), lead (Pb), cobalt (Co), copper (Cu), chromium (Cr), strontium (Sr), iron (Fe), magnesium (Mg), manganese (Mn), nickel (Ni), potassium (K), silver (Ag), selenium (Se), sodium (Na), and zinc (Zn). All the analyses were performed according to the Standard Methods for the Examination of Water and Wastewater (APHA 2012).

2.5. 16 S rRNA sequencing

DNA extraction from the collected solid waste samples was performed using the FastDNA™ SPIN Kit for Soil DNA Extraction (MP Biomedicals), using 0.5-g subsamples. It was also necessary to perform DNA purification, using the Geneclean ® Turbo Kit (MP Biomedicals). After DNA extraction, the 16S rRNA genes of distinct regions (V3–V4 466 bp) were amplified using the domain bacteria (341F CCTAYGGGRBGCASCAG; 806R GGACTACNNGGGTATCTAAT)with the barcode.

Sequencing libraries were generated using TruSeq® DNA PCR-Free Sample Preparation Kit (Illumina, USA) following manufacturer's recommendations and index codes were added. The library quality was assessed on the Qubit@ 2.0 Fluorometer (ThermoScientific) and Agilent Bioanalyzer 2100 system. At last, the library was sequenced on an IlluminaHiSeq2500 platform and 250 bp paired-end reads were generated.

Quality filtering on the raw tags were performed under specific filtering conditions to obtain the high-quality clean tags (Bukulich et al., 2013) according to the QIIME quality controlled process (Caporaso et al., 2010). Sequences analysis were performed by Uparse software (Edgar, 2013). Sequences with ≥ 97% similarity were assigned to the same OTUs. For each representative sequence, the Green Gene Database (http://greengenes.lbl.gov/cgi-bin/nph-index.cgi)was used based on RDP3 classifier (Version 2.2, http://sourceforge.net/projects/rdp-classifier/).

The 16S rRNA sequencing and bioinformatics were performed by GenOne Biotechnologies, situated in Rio de Janeiro, Brazil. These data have been uploaded to the National Center for Biotechnology Information Database (NCBI), under Bioproject number PRJNA837104 and BioSample Accession SAMN28189806, experiments SRX15263369, SRX15263370, SRX15263371, SRX15263372, SRX15263373, SRX15263374. SRX15263375, SRX15263376.

All this indices in our samples were calculated with QIIME(Version 1.7.0) and displayed with R software(Version 2.15.3).

2.6. Specific Methanogenic Activity (SMA)

Aiming to complement the microbiological analysis and assay the activity of methanogenic microorganisms, the Specific Methanogenic Activity test (SMA) was performed, using composite samples from inside the covered area (mixture of samples D11, D12, D21, and D22 to compose one single sample, D) and outside it (mixture of samples F11, F12, F21, and F22 to compose one single sample, F). The mixture and subsamples collection was performed using the quartering method, and the initial total volatile solids (TVS) concentration in each subsample was kept in 5 g TVS/L. The tests were performed using the Oxitop © system, and a mixture of acetic, propionic and butyric acids was used as carbon source.

3.1. Physicochemical analysis

The results of the solubilization tests are shown in Figs. 3 and 4. Superficial samples presented less humidity values, whereas D12 and F12 presented the highest values, possibly due to their close location and the accumulation of water/leachate in the region. Thus, a clear influence of the capping was not observed, being other factors such as location and landform promoting water accumulation more important. Moreover, the capping was not able to avoid accumulation of leachate in some regions (especially D12). Such leachate accumulation may have been produced before the capping construction, and remained immobilized by soil layers or non-degraded material, as observed by Pelinson et al. (2020).

Regarding pH values, no significant variability was observed at capped and uncapped areas, being all values close to neutrality, which is typical of the methanogenic phase in landfills. Thus, pH shifts causing contaminants remobilization was not observed.

EC and ORP values showed different behavior at capped and uncapped areas; at capped areas, the first layers presented higher EC and lower ORP values, whereas in uncapped areas the second layers were more conductive and reducing. This can be explained by the more intense leaching in uncapped areas, transporting ions and pluvial water from superficial to deeper zones, where oxidoreduction reactions are more intense and cause a decrease in ORP values.

However, it is important to highlight that in all samples the ORP values were negative or slightly positive, showing reducing conditions inside the landfill, independently of the capping construction. The construction of capping layers promoted lower ORP values in the first layers, enhancing metals immobilization and avoiding their in-depth transport. The lower ORP values can be attributed mainly to the absence of gaseous oxygen and the use of other electron acceptors in such conditions.

In this sense, N-NH₄ and N-NO₂ concentrations were higher in capped zones, which can be associated with lower oxygen availability preventing nitrification or with the use of nitrate as electron acceptor in anoxic conditions. N-NO₃ was generally lower in samples from capped areas, except for D22, which also presented higher ORP values, possibly associated with specific local conditions. In the case of SO₄, no clear pattern was observed in the evaluated samples, but its detection in all samples is relevant to promote its use as electron acceptor during anaerobic respiration, contributing to metals precipitation as metals sulfides, as already reported in biological reactors (Costa et al., 2021; Kousi et al., 2011, 2018).

Regarding organic matter, samples from uncapped areas generally presented higher COD and TOC values. This was not expected, as more oxygenation is associated with higher degradation rates and consequently lower remaining organic matter (Campanaro et al., 2020; Qi et al., 2013). Thus, it is supposed that COD and TOC values responded to the specific characteristics of the buried waste in each location, not being affected by the cover.

In this regard, most physicochemical parameters were not influenced by the shifts in environmental conditions after the capping construction, being more strongly associated with specific buried content; this agrees with several studies which assessed microbial communities in landfills (Morita et al., 2020c; Xu et al., 2017; Wang et al., 2017; Zainun and Simarani, 2018). Nonetheless, the parameters related to oxidation-reduction reactions, specifically ORP and electron acceptors, presented clear shifts in the first layers.

Finally, it is important to highlight that high Pb and Cd concentrations were found in most samples (from capped and uncapped zones, see Supplementary Material), showing that the waste is not inert, and, therefore, the landfill still poses risks to the surroundings. Such high concentrations have already been discussed elsewhere (Pelinson et al., 2020).

3.2. 16S rRNA sequencing

3.2.1. Richness and diversity of microbial communities

The coverage ranged from 97 to 99%, showing significant representativeness of the microbial communities, and was generally higher for samples from capped areas. (Fig. 4_SM of the Supplementary Material). Differently, the number of OTUs was generally higher for samples collected in uncapped areas, except for F12, which shows the existence of more microbial populations developing in uncapped zones. Thus, it seems that the conditions generated by the capping construction caused a restriction in the development of microbial populations, especially for the first layers; this is feasibly associated with the anaerobic conditions created with the capping.

In respect of F12, specific physicochemical characteristics - higher values of EC, COD, TOC, Pb, Ca, and Mg, reducing conditions and phosphate below the detection limit, as shown in Figs. 3 and 4 and in the Supplementary Material - caused a decrease in the number of identified populations able to thrive in such environment.

Samples collected in uncapped areas seemed to propitiate conditions for more populations to thrive(higher Chao and ACE indices, except for F12). The communities seemed to have similar diversities, which means that no significant impact was observed with the capping construction.

3.2.2. Taxonomic analysis at the level of phyla

The analysis at the level of phyla permitted us to observe a clear difference of the samples from capped and uncapped zones (Fig. 5). The exceptions are samples D12 and F12, which may have suffered the same influence of water accumulation in a lower region of the studied area. Additionally, as they were collected in close sites, the specific buried content may have influenced the microbial communities more strongly than the environmental shifts caused by the capping construction.

Firstly, it is important to mention that the phylum Proteobacteria was more abundant in all samples(25–47%), followed by Acidobacteria (9–24%), Chloroflexi (4–14%), Actinobacteria (9–12%), and Firmicutes (3–9%). The phylum Proteobacteria comprehends a great diversity of organisms playing different roles in biochemical processes, both in cleaner and more polluted environments, in closed or active landfills (Morita et al., 2020c; Zainun and Simarani, 2018).

Thus, in the present study it is not possible to associate it with conditions found in capped or uncapped zones, and the phylum was abundant in both conditions. Nevertheless, its lower abundance in capped samples can be associated with its substitution by phyla more adapted to the conditions found in capped zones, such as Chloroflexi, Firmucutes, Euryarchaeota, and DHVEG-6. Those phyla were also abundant in F12, whose specific physicochemical conditions – lower ORP and higher COD and EC values (Figs. 3 and 4) – also may have caused the mentioned substitution.

The phylum Firmicutes has been associated with the hydrolysis of organic matter and correlated with biogas production (Campanaro et al., 2020), and playing important roles in anaerobic and methanogenic phases of organic matter decomposition in landfills (Liu et al., 2019; Song et al., 2015). This agrees with its great representativeness in capped zones, where methanogenesis is more relevant due to the absence of oxygen.

Similarly, representatives of the phylum Chloroflexi are hydrolytic anaerobic bacteria (Qin et al., 2019), being frequently reported in anoxic conditions, acting in the consumption of organic compounds generated by anammox bacteria (Anoxic Ammonia Oxidation) (Kindaichi et al., 2012) and in the degradation of carbohydrates and amino acids in biological reactors (Thiel et al., 2019). It was also dominant in the oxidation of fatty acids during acetogenesis, presenting syntrophy with methanogenic archaea (Saha et al., 2019). Such roles were relevant in the evaluated samples, considering that samples from capped zones presented higher ammonium concentrations and enhanced conditions for methanogenesis.

In this sense, the methanogenic archaea pertain to the phylum Euryarchaeota (Archaea Domain) being strict anaerobes that preserve energy with the production of methane (Madigan et al., 2016). Representatives of such phylum were found to be abundant at reservoir sediments with high metals concentrations (Guo et al., 2019), and at soils with lower pH values and higher water content and ammonium concentrations(Hu et al., 2013). Such phylum was more abundant in samples from capped zones and especially relevant in F12 and D12, where the accumulation of leachate led to higher water content creating anaerobic conditions. Therefore, the similarities found between samples from capped zones and F12 are feasibly associated with ORP conditions, i.e., anaerobic or anoxic conditions in such sites.

Finally, the phylum DHVEG-6 (Deep Sea Hydrothermal Vent Group 6), also abundant in capes areas, is also from the Archaea Domain, being reported in hydrothermal sediments, saline environments, and methanogenic biological reactors treating wastewater. It has been relevant in treatment systems applied to the removal of nitrogen and phosphorus, being favored by environments rich in organic matter and total phosphorus (Fan and Xing, 2016; Kuroda et al., 2014).

In respect of F12, the phyla Ignavibacteriae and Aminicenantes were also abundant in such site. Representatives of Ignavibacteriae are facultative anaerobes, using various electron acceptors, such as nitrite, iron (III), and arsenic (V) (Podosokorskaya et al., 2013). The phylum Aminicenantes, even also encountered in aerobic environments, was more abundant in anaerobic ones (Farag et al., 2014), performing the fermentation of carbohydrates, the anaerobic respiration using nitrite, and acting on the degradation of organic matter in deep aquifers, producing acetate and hydrogen (Kadnikov et al., 2019).

The canonical correlation analysis (CCA, Fig. 6) permitted to clearly observe the phyla Firmicutes, Chloroflexi, and DHVEG-6 in the second quadrant, being represented by samples from the capped zones and suffering influence of the parameters pH, ammonium, and sodium. In the third quadrant, there are the phyla Euryarchaeota, Ignavibacteriae and Aminicenantes, abundant in sample F12 and influenced by the parameters humidity, COD, Ca, and Mg, as well as negatively associated with ORP.

Finally, the phyla Acidobacteria, Proteobacteria, Bacteroidetes, and Actinobacteria abundanant in samples from the uncapped zones, were affected by ORP, phosphate, chloride, and manganese.

3.2.3. Taxonomic analysis at the level of genera

The most abundant genera in all the evaluated samples, independently of their location, were Methylocistis (2.9-5.0%), Anaeromyxobacter (0.9–3.3%), Candidatus Solibacter (0.5–3.5%), e Candidatus Koribacter (0.4–3.5%) (Fig. 7).

Representatives of Methylocistis are methanotrophs, i.e., aerobic methane-oxidizing bacteria, which play important roles in the global cycle of methane, being able to attenuate methane emissions from major sources (Tveit et al., 2019). These organisms are widely distributed in diverse habitats, but most frequently in oxic-anoxic interfaces of methanogenic environments with counter gradients of oxygen, methane and hydrogen (Brune et al., 2000; Hakobyan et al., 2020). Thus, such genus plays an important role in the oxidation of methane and the consequent reduction in the landfill emissions.

Regarding the genus Anaeromyxobacter, it is facultative anaerobe with the ability to reduce various metals such as iron and uranium, dechlorinate aromatic compounds, and perform NO₃⁻ reduction (Masuda et al., 2020). Thus, the ability to use different electron acceptors for respiration permits its wide distribution in landfill environments.

Finally, Candidatus Solibacter (0.5–3.5%), e Candidatus Koribacter (0.4–3.5%) were found to be abundant in soil samples from forest and tilled land, showing their wide distribution in natural and disturbed soils (Wiryawan et al., 2022). It’s noticeable that these genera were more abundant in the first layers (samples D11, D21, F11, and F21), showing that their occurrence is feasibly associated with cover and intermediate soil layers.

Differently from those, some genera were found to be more abundant in specific landfill areas. For capped zones, as well as for F12, the most abundant genera were: Hydrogenispora (1.1–1.6% in capped samples and F12, and < 0.1% in other uncapped samples), Methanosaeta (0.3–1.1% in capped samples, 3.7% in F12, and ~ 0.1% in other uncapped samples), Gelria (0.1–0.4% in capped samples, 1.5% in F12, and < 0.04% in other uncapped samples), Smithella (0.1–0.3% in capped samples, 1.3% in F12, and < 0.1% in other uncapped samples), and Spirochaeta 2 (0.6–1.9% in capped samples and F12, < 0.4% in other uncapped samples).

Hydrogenispora (phylum Firmicutes) is composed of bacteria capable of producing butyric acid and H₂ (Huang et al., 2019), being abundant in sulfate-reducing environments, in anaerobic sludge (Fang et al., 2020), and in flooded soils, where they are able to survive, possibly due to their ability to produce endospores (Li et al., 2020). This shows that in capped zones and possibly in F12 there is no available oxygen and other electron acceptors, such as sulfate, are used for the degradation of organic matter.

This change in available electron acceptors appears to have been the main factor influencing microbial communities after the intervention measure. It is noteworthy that the use of sulfate with sulfide generation contributes to the precipitation and immobilization of several metals, such as Pb, Cu, Zn and Cd (Costa et al., 2021; Kousi et al, 2011, 2018). In this sense, the detection of high concentrations of sulfate in all samples (Fig. 4) and the microbial shift to anaerobic conditions contribute to the immobilization of such contaminants.

Regarding the genus Methanosaeta, it belongs to the group of methanogenic archaeas, especially to the order Methanosarcinales (Archaea domain) and uses acetate as a substrate for methanogenesis, which is the final step of anaerobic digestion (Madigan et al., 2016). It is an abundant genus not only in anaerobic reactors, but in a diversity of environments such as soils, sediments and contaminated aquifers, being considered the largest producer of methane available on Earth (Rotaru et al., 2014). This genus was found in greater proportion in samples from the capped zone and F12, indicating that appropriate conditions for methanogenesis are found in these environments, i.e., anaerobic environments with by-products of microbial degradation.

Additionally, the genera Methanobacterium, Methanoculleusand Methanosarcina, also belonging to the Archaea domain and frequently found in waste deposits (Campanaro et al., 2020; Song et al., 2015) were also more abundant in capped zones and in F12. Even not shown in Fig. 7 due to their abundance being less than 1%, this occurrence strengthens the influence of oxygen availability on microbial communities from capped zones.

Similarly, the genus Gelria has been reported as in the metabolism of fatty acids, in the final stages of fermentation (Fitzgerald et al., 2019) and in reducing landfill zones with higher organic matter and K content (Morita et al., 2020c). This genus was more abundant in samples located in capped zones and in F12, showing its greater relevance in methanogenic conditions. Since this genus has been associated with anaerobiosis and syntrophy mechanisms (Plugge et al, 2002), it is suggested that the products of its metabolism are substrates for methanogenic archaea.

Another genus commonly associated with syntrophy and which was found in samples from capped zones is Smithella, which has been related to the syntrophic degradation of alkanes, being frequently found in cultures of methanogenic degradation of crude oil (Ji et al., 2020; Wawrik et al., 2016). Oil degradation processes under anaerobic conditions seem to be relevant in the studied landfill, as reported by Pelinson et al. (2020).

Finally, the genus Spirochaeta can be obligate or facultative anaerobic, using carbohydrates as energy and carbon source and being found in aquatic environments and sediments (Paster, 2015). Thus, the anoxic conditions created with the capping construction seem to have favored its growth. Additionally, Pohlschroeder et al. (1994) reported their symbiotic activity with Clostridium species in the degradation of cellulose from leachate; the genus Clostridium is composed of obligatory anaerobic endospore-forming species (Madigan et al., 2016) and was also more abundant in capped zones (especially Clostridium sensu strictu 12, 1, 10, 13, 8, 3 and 1, which were not represented in Fig. 7 because they showed relative abundances lower than 1%).

Differently, the genera Haliangium and Candidatus Methylospira were more abundant in samples from uncapped zones. The genus Haliangium (0.8–1.1% in capped samples and F12, 1.1–2.8% in uncapped samples) is obligate aerobic (Fudou et al., 2002) and Candidatus Methylospira(0.4–0.5% in capped samples, 0.8–2.1% in uncapped samples)is obligate microaerophilic that uses methane as the only source of energy and carbon (Danilova et al., 2016). Thus, the greater availability of oxygen in uncapped zones provided a greater representation of these genera.

Finally, similarly to what was reported by Thakur et al. (2020), the genera not yet classified (“Other”) represented considerable percentages in the sampled points (between 48 and 63%), showing that there is still potential for the discovery of species of biotechnological application in urban solid waste deposits.

The CCA for the predominant genera (Fig. 8) presented an agglomeration of samples from capped zones in the first quadrant. Such aggrupation was represented by the genera Candidatus Koribacter, Candidatus Solibacter, Bacillus and Anaeromyxobacter and influenced by the parameters ORP, ammonium, nitrite, and zinc. Such genera, as previously described, were not distributed in capped areas only, but were located in such quadrant due to their higher relative abundance in such samples. Differently, in uncapped samples there were other locally specific genera with higher abundances, causing such samples to be more homogeneously distributed into the quadrants.

Thus, both the CCA at the level of phyla and genera permitted us to clear observe the differences of microbial populations from capped and uncapped areas. As previously discussed, the capped samples clearly responded to the anaerobic and anoxic conditions created with the capping construction, generating metabolic pathways and syntrophic relations for the degradation of the organic compounds. Consequently, the time lapse of 16 months was considered sufficient for the microbial community to adapt to the new environmental conditions, not being possible to infer that an impairment of the microbial activity occurred. In this regard, the SMA aimed to contribute to this analysis, especially focusing on the methanogenic activity.

3.3. Specific Methanogenic Activity (SMA)

As previously described, the collected samples were prepared in order to constitute composite samples from the capped (D) and uncapped (F) zones, in triplicates. The boxplot of the results is presented in the Supplementary Material.

Even though the median is mildly higher for uncapped samples, the t-test showed no statistical difference between the groups (t = 1,38 < t critical = 2,78), i.e., the samples from capped and uncapped zones belong to the same group. Nevertheless, it is important to highlight that the analysis using composite samples may have softened the negative effects possibly imposed to the first layers (i.e., D11 and D21), leading to similar results for both evaluated conditions. In this regard, Qi et al. (2013) found impairment in microbial activity in the portion just below the intermediate layer of soil, but attenuation of impacts with depth and distance from this layer.

Regarding the values for methane production, the results were compatible with sludge from UASB reactors - which range from 0.15 to 0.30 gCOD CH4/gSVT.d (Chernicharo, 2007; Lobato et al., 2018) - showing that the biomass from old landfills can be used as inoculum for biological reactors.

The results of the physicochemical, microbiological and SMA analysis indicate that the first layers (< 1m) of the landfill may be affected by the capping construction, but the impacts are not relevant for layers deeper than 1m. Additionally, the impacts on microbial populations did not seem to impair their methanogenic activity, but caused an adaptation to anaerobic conditions, enabled syntrophic relations and propitiated the use of different electron acceptors, including sulfate, which can be beneficial to metals immobilization as sulfide minerals.

This research aimed to integrate 16S rRNA sequencing with physicochemical analysis in order to evaluate the positive and negative impacts of the construction of capping layers over old unlined landfills.

Even though a clear reduction in leachate production was not observed - since some leachate pockets and high humidity values were still observed even in capped zones, possibly due to lateral influence -, it is possible to affirm that the creation of reducing conditions propitiated a shift in microbial populations, enabling the use of different electron acceptors, which was considered beneficial to metals precipitation into sulfide minerals. Additionally, no methanogenic activity impairment was observed, indicating that drawbacks of capping construction are not relevant in old landfills.

Therefore, considering that the buried solid waste was found not to be inert after decades of landfilling and that most organic matter have been already degraded after such periods of time, it is suggested that capping is adopted even in old landfills to prevent metals leaching along time, focusing on the creation of anaerobic conditions to promote the use of sulfate as electron acceptors. In this sense, it is suggested that controlled experiments are conducted to assay the feasibility of adding controlled sulfate sources under the covers, directing such metabolic pathways. Additionally, it is suggested that alternative and lower cost covers are studied, focusing on the creation of such environments and not necessarily on the landfills’ complete isolation. This approach would permit the development of new and more biotechnological landfill covers.

Funding

This study was financed by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Finance Code 001), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, grant number 168734/2018-4) and São Paulo Research Foundation (FAPESP, grant numbers 2015/ 03806-1 and 2018/24615-8).

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Alice Kimie Martins Morita and Isabel Kimiko Sakamoto. The first draft of the manuscript was written by Alice Kimie Martins Morita and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Ethical Approval

Not applicable

Consent to Participate

All authors agreed with the content and gave explicit consent to participate of the work that has been carried out.

Consent to Publish

All authors agreed with the content and gave explicit consent to submit and publish the present manuscript.

Availability of data and materials

The data that support the findings of this study are available from the corresponding author, A. K. M. Morita, upon reasonable request.

ABNT – Associação Brasileira de Normas Técnicas (1984) NBR 10.006. Procedimento para obtenção de extrato solubilizado de resíduos sólidos. Rio de Janeiro, 1984.
Belevi, H.; Baccini, P. (1989) Long-term behavior of municipal solid waste landfills. Waste Management and research, 7, 43-56.
Bjerg, P.L.; Albrechtsen, H.-J.; Kjeldsen, P., Christensen, T.H.; Cozzarelli, I. (2013) The Groundwater Geochemistry of Waste Disposal Facilities. In Holland, H.D.; Turekian, K.K. Environmental Geochemistry:Treatise on Geochemistry. Second edition, Elsevier Science.
Bokulich, N. A., et al. (2013) Quality-filtering vastly improves diversity estimates from
Illumina amplicon sequencing. Nature methods, 10.1, 57-59.
Brasil (2010). Lei no 12.305, de 2 de agosto de 2010. Institui a Política Nacional de Resíduos Sólidos; altera a Lei no 9.605, de 12 de fevereiro de 1998; e dá outras providências. Diário Oficial da União, Brasília, DF, 3 de agosto de 2010. Availableat: http://www2.mma.gov.br/port/conama/legiabre.cfm?codlegi=636. Accessedon May 15th, 2022.
Brasil (2020). Lei no 14.026, de 15 de julho de 2020. Atualiza o marco legal do saneamento básico. Diário Oficial da União, Brasília, DF, 16 de julho de 2020. Brasília, 2020. Available at: https://legislacao.presidencia.gov.br/atos/?tipo=LEI&numero=14026&ano=2020&ato=cfaATWE9EMZpWT417. Accessed on August 6^th, 2020).
Brune, A.; Frenzel, P.; Cypionka, H. (2000). Life at the oxic–anoxic interface: microbial activities and adaptations. FEMS Microbiology Reviews, 24(5), 691–710. https://doi.org/10.1111/j.1574-6976.2000.tb00567.x
Campanaro, S.; Raga, R.; Squartini, A. (2020) Intermittent aeration of landfill simulation bioreactors: Effects on emissions and microbial community. Waste Management, 117, 146-156.
Caporaso, J. G., et al. (2010) QIIME allows analysis of high-throughput community
sequencing data. Naturemethods 7.5, 335-336.
CETESB – Companhia Ambiental do Estado de São Paulo (Environmental Agencyof São Paulo State) (2022). Relação de áreas contaminadas, 2022. Availableat: http://areas.contaminadas.cetesb.sp.gov.br. AcessedonJune 2nd, 2022.
Cetrulo, T.B.; Marques, R.C.; Cetrulo, N.M.; Pinto, F.S.; Moreira, R.M.; Mendizábal-Cortés; A.D.; Malheiros, T.F. (2018). Effectiveness of solid waste policies in developing countries: A case study in Brazil. J. Clean. Prod. 205, 179-187. https://doi.org/10.1016/j.jclepro.2018.09.094.
Chakraborty, P.; Sampath, S.; Mukhopadhyay, M.; Selvaraj, S.; Bharat, G.K.; Nizzeto, L. (2019). Baseline investigation on plasticizers, bisphenol A, polycyclic aromatic hydrocarbons and heavy metals in the surface soil of the informal electronic waste recycling workshops and nearby open dumpsites in Indian metropolitan cities. Environ. Pollut., 248, 1036–1045. https://doi.org/10.1016/j.envpol.2018.11.010.
Chernicharo, C. A. L. (2007) Reatores anaeróbios. Princípios do Tratamento Biológico de Águas Residuárias, v.5, Belo Horizonte: DESA/UFMG.
Christensen, T.H.; Cossu, R.; Stegmann, R. (1997) Landfilling of waste: Leachate. London: Chapman and Hall.
Costa, R.B.; Godoi, L.A.G.; Braga, A.F.M.; Delforno, T.P.; Bevilaqua,D. (2021) Sulfate removal rate and metal recovery as settling precipitates in bioreactors: Influence of electron donors. Journal of Hazardous Materials, 403, 123622. https://doi.org/10.1016/j.jhazmat.2020.123622.
Danilova, O. et al. (2016) A new cell morphotype among methane oxidizers: a spiral-shaped obligately microaerophilic methanotroph from northern low-oxygen environments. ISME J 10, 2734–2743. https://doi.org/10.1038/ismej.2016.48
Edgar, Robert C. (2013) UPARSE: highly accurate OTU sequences from microbial amplicon reads. Nature methods 10.10, 996-998
Fan, X.; Xing, P. (2016) The Vertical Distribution of Sediment Archaeal Community in the “Black Bloom” Disturbing Zhushan Bay of Lake Taihu. Archaea (Vancouver, B.C.) 2016(9):1-8
Fang, Y.; Vanzin, G.; Cupples, A. M.; Strathmann, T. J. (2020) Influence of terminal electron-accepting conditions on the soil microbial community and degradation of organic contaminants of emerging concern. Science of The Total Environment, 706, 135327. https://doi.org/10.1016/j.scitotenv.2019.135327
Farag, I.F.; Davis, J.P.; Youssef, N.H.; Elshahed, M.S. (2014) Global Patterns of Abundance, Diversity and Community Structure of the Aminicenantes (Candidate Phylum OP8). PLoS ONE 9(3): e92139. https://doi.org/10.1371/journal.pone.0092139
Fitzgerald, J.A.; Wall, D.M.; Jackson, S.A.; Murphy, J.D.; Dobson, A.D.W. (2019) Trace element supplementation is associated with increases in fermenting bacteria in biogas mono-digestion of grass silage. Renew Energy 138:980–986.
Fudou, R.; Jojima, Y.; Iizuka, T.; Yamanaka, S. (2002) Haliangiumochraceum gen. nov., sp. nov. and Haliangiumtepidum sp. nov.: Novel moderately halophilic myxobacteria isolated from coastal saline environments. The Journal of General and Applied Microbiology, 48(2), 109–115. https://doi.org/10.2323/jgam.48.109
Guo, Q.; Li, N.; Chen, S.; Chen, Y.; Xie, S. (2019) Response of freshwater sediment archaeal community to metal spill. Chemosphere, 217, 584–590. https://doi.org/10.1016/j.chemosphere.2018.11.054
Hakobyan, A.; Zhu, J.; Glatter, T.; Paczia, N.; Liesack,W. (2020) Hydrogen utilization by Methylocystis sp. strain SC2 expands the known metabolic versatility of type IIamethanotrophs, Metabolic Engineering, Volume 61, 181-196. https://doi.org/10.1016/j.ymben.2020.05.003.
Hu, H.-W., Zhang, L.-M.; Yuan, C.-L.; He, J.-Z (2013) Contrasting Euryarchaeota communities between upland and paddy soils exhibited similar pH-impacted biogeographic patterns. Soil Biology and Biochemistry, 64, 18–27. https://doi.org/10.1016/j.soilbio.2013.04.003
Huang, W.; Yang, F.; Huang, W.; Lei, Z.; Zhang, Z. (2019) Enhancing hydrogenotrophic activities by zero-valent iron addition as an effective method to improve sulfadiazine removal during anaerobic 208 digestion of swine manure. Bioresource Technology, 294, 122178. https://doi.org/10.1016/j.biortech.2019.122178
Idowu, I.A.; Atherton, W.; Hasim, K.; Kot, P.; Alkhaddar, R.; Alo, B.I.; Shaw, A (2019) An analyses of the status of landfill classification systems in developing countries: Sub Saharan Africa landfill experiences. Waste Manag. 87, 761–771. https://doi.org/10.1016/j.wasman.2019.03.011.
Ji, J.; Zhou, L.; Mbadinga, S.M. et al (2020) Methanogenic biodegradation of C9 to C12n-alkanes initiated by Smithella via fumarate addition mechanism. AMB Expr 10, 23. https://doi.org/10.1186/s13568-020-0956-5
Kadnikov, V.V.; Mardanov, A.V.; Beletsky, A.V. et al. (2019) Genome of the candidate phylum Aminicenantes bacterium from a deep subsurface thermal aquifer revealed its fermentative saccharolytic lifestyle. Extremophiles 23, 189–200. https://doi.org/10.1007/s00792-018- 01073-5
Kindaichi, T.; Yuri, S.; Ozaki, N.; Ohashi, A. (2012) Ecophysiological role and function of uncultured Chloroflexi in an anammox reactor. Water Science and Technology, 66(12), 2556–2561. https://doi.org/10.2166/wst.2012.479
Koerner, R.M.; Daniel, D.E (1997) Final covers for solid waste landfills and abandoned dumps. American society of civil engineers.
Kousi, P.; Remoundaki, E.; Hatzikioseyian, A.; Battaglia-Brunet, F.; Joulian, C.; Kousteni, V.; Tsezos, M (2011) Metal precipitation in an ethanol-fed, fixed-bed sulphate-reducing bioreactor. J. Hazard. Mater. 189, 677–684. https://doi.org/ 10.1016/j.jhazmat.2011.01.083.
Kousi, P.; Remoundaki, E.; Hatzikioseyian, A.; Korkovelou, V.; Tsezos, M. (2018) Fractionation and leachability of Fe, Zn, Cu and Ni in the sludge from a sulphate reducing bioreactor treating metal-bearing wastewater. Environ. Sci. Pollut. Res. 25, 35883–35894. https://doi.org/10.1007/s11356-018-1905-6.
Kuroda, K.; Hatamoto, M.; Nakahara, N.; Abe, K.; Takahashi, M.; Araki, N.; Yamaguchi, T (2014) Community Composition of Known and Uncultured Archaeal Lineages in Anaerobic or Anoxic Wastewater Treatment Sludge. Microbial Ecology, 69(3), 586–596, https://doi.org/10.1007/s00248- 014-0525-z
Li, L.; Jia, R.; Qu, Z.; Li, T.; Shen, W.; Qu, D (2020) Coupling between nitrogen-fixing and iron(III)- reducing bacteria as revealed by the metabolically active bacterial community in flooded paddy soils amended with glucose. Science of The Total Environment, 716, 137056. https:/doi.org/10.1016/j.scitotenv.2020.137056
Lobato, L. C. S.; Bressani-Ribeiro, T., Silva, B. S., Florez, C. A. D., Neves, P. N. P., Chernicharo, C. A. L. (2018) Contribuição para o aprimoramento de projeto, construção e operação de reatores UASB aplicados ao tratamento de esgoto sanitário – Parte 3: Gerenciamento de lodo e escuma. Revista DAE – edição especial, 66, 214, 30-55, 2018
Madigan, M.T.; Martinko, J.M.; Dunlap, P.V.; Clark, D.P (2016) Microbiologia de Brock. 14th Edition. Porto Alegre: Artmed.
Masuda, Y.; Yamanaka, H.; Xu, Z-X.; Shiratori, Y.; Aono, T.; Amachi, S.; Senoo, K.; Itoh, H (2020) DiazotrophicAnaeromyxobacterisolatesfromsoils. Appl Environ Microbiol86:e00956-20. https://doi.org/10.1128/AEM .00956-20.
Matias, M.; Pincelli, I.; Lange, L.; Fereira, J.A.; Castilhos Jr., A. (2022) Solid waste policy in Brazil: learnings and challenges after a decade of implementation. International Journal of Environment and Waste Management, https://doi.org/10.1504/ijewm.2022.10031433
Mavropoulos, A.; Cohen, P.; Greedy, D.; Plimakis, S.; Marinheiro, L.; Law, J.; Loureiro, A. (2016) A roadmap for closing waste dumpsites: The world’s most polluted places. International Solid Waste Association (ISWA) Report. Available at: https://www.iswa.org/home/news/news-detail/article/press-release-iswas-roadmap-report/109/. Accessed on August 14^th, 2020.
Morita, A.K.M.; Pelinson, N.S.; Wendland, E. (2020a) Persistent impacts of an abandoned non-sanitary landfill in its surroundings. Environ. Monit. Assess. 192 (7), 463. https://doi.org/10.1007/s10661-020-08451-7.
Morita, A.K.M.; Pelinson, N.S.; Elis, V.R.; Wendland, E. (2020b) Long-term geophysical monitoring of an abandoned dumpsite area in a Guarani Aquifer recharge zone. Journal of Contaminant Hydrology, 230, 103623. https://doi.org/10.1016/j.jconhyd.2020.103623
Morita, A.K.M.; Sakamoto, I. K.; Varesche, M. B. A.; Wendland, E. (2020c) Microbial structure and diversity in non-sanitary landfills and association with physicochemical parameters. Environmental Science and Pollution Research,27, 40690–40705. https://doi.org/10.1007/s11356-020-10097-4.
Morita, A.K.M.; Ibelli-Bianco, C.; Anache, J.A.A.; Coutinho, J.V.; Pelinson, N.S.; Nobrega, J.; Rosalem, L.M.P.; Leite, C.M.C.; Niviadonski, L.M.; Manastella, C. Wendland, E. (2021) Pollution threat to water and soil quality by dumpsites and non-sanitary landfills in Brazil: A review. Waste Management, 131, 163-176, https://doi.org/10.1016/j.wasman.2021.06.004
Mukherjee, S.; Mukhopadhyay, S.; Hashim, M.A.; Gupta, B. S. (2014) Contemporary environmental issues of landfill leachate: Assessment and remedies. Crit. Rev. Environ. Sci. Technol., 472–590. https://doi.org/10.1080/10643389.2013.876524
Paster, B. J. (2015) Spirochaetaceae. Bergey’s Manual of Systematics of Archaea and Bacteria, 1–2. https://doi.org/10.1002/9781118960608
Pelinson, N. S.; Shinzato, M.P.B.; Morita, A.K.M.; Martins, L.G.B.; Wendland, E. (2020) Innovative device to assay leachate production in non-sanitary landfills. J Mater Cycles Waste Manag, 22, 1985–1998. https://doi.org/10.1007/s10163-020-01084-5
Peter, A E.; Nagendra, S.M.S.; Nambi, I.M. (2019) Environmental burden by an open dumpsite in urban India. Waste Management, 85, 151–163. https://doi.org/10.1016/j.wasman.2018.12.022.
Plugge, C.M.; Balk, M; Zoetendal, E.G.; Stams, A.J. (2002) Gelriaglutamica gen. nov., sp. nov., a thermophilic, obligately syntrophic, glutamate-degrading anaerobe. Int J SystEvolMicrobiol, 52:401–407. https://doi.org/10.1099/00207713-52-2-401
Podosokorskaya, O. A.; Kadnikov, V. V.; Gavrilov, S. N.; Mardanov, A. V.; Merkel, A. Y.; Karnachuk, O. V. et al. (2013) Characterization of Melioribacterroseusgen. nov., sp. nov., a novel facultatively anaerobic thermophilic cellulolytic bacterium from the class Ignavibacteria, and a proposal of a novel bacterial phylum Ignavibacteriae. Environmental Microbiology, 15(6), 1759– 1771. https://doi.org/10.1111/1462-2920.12067
Pohlschroeder, M.; Leschine, S.B.; Canale-Parola, E. (1994) Spirochaeta caldaria sp. nov., a thermophilic bacterium that enhances cellulose degradation by Clostridium thermocellum.Arch. Microbiol., 161:17-24.
Qi, G.; Yue, D.; Liu, J.; Li, R.; Shi, X.; He, L.; Guo, J.; Miao, H.; Nie, Y. (2013) Impact assessment of intermediate soil cover on landfill stabilization by characterizing landfilled municipal solid waste. Science of environmental management 128, 259-265. https://doi.org/10.1016/j.jenvman.2013.05.014
Qin, X.; Ji, M.; Wu, X.; Li, C.; Gao, Y.; Li, J. et al. (2019) Response of treatment performance and microbial community structure to the temporary suspension of an industrial anaerobic bioreactor. Science of The Total Environment, 646, 229–237. https://doi.org/10.1016/j.scitotenv.2018.07.309
Rotaru, A. E.; Shrestha, P.M.; Liu, F.; Shrestha, M.; Shrestha, D.; Embree, M.; Zengler, K. Wardman, C.; Nevin, K.P.; Lovley, D.R. (2014) A new model for electron flow during anaerobic digestion: direct interspecies electron transfer to Methanosaeta for the reduction of carbon dioxide to methane. Energy Environ. Sci., 7, 408-415. https://doi.org/10.1039/C3EE42189A
Saha, S.; Jeon, B.-H.; Kurade, M. B.; Govindwar, S. P.; Chatterjee, P. K.; Oh, S.-E.et al. (2019) Interspecies microbial nexus facilitated methanation of polysaccharidic wastes. BioresourceTechnology, 289, 121638, https://doi.org/10.1016/j.biortech.2019.121638
Sandoval-Cobo, J.J.; Casallas-Ojeda, M.R.; Carabalí-Orejuela, L. et al. (2020) Methane potential and degradation kinetics of fresh and excavated municipal solid waste from a tropical landfill in Colombia. Sustain Environ Res, 30, 7. https://doi.org/10.1186/s42834-020-00048-6
Somani, M.; Datta, M.; Gupta, S.K.; Sreekrishnan, T.R.; Ramana, G.V. (2019) Comprehensive assessment of the leachate quality and its pollution potential from six municipal waste dumpsites of India. Bioresour. Technol. Rep., 6, 198–206. https://doi.org/10.1016/j.biteb.2019.03.003.
Song, L.; Wang, Y.; Zhao, H.; Long, D. (2015) Composition of bacterial and archaeal communities during landfill refuse decomposition processes. Microbiol Res 181:105–111. https://doi.org/10.1016/j.micres.2015.04.009
Thakur, K.; Chownk, M.; Kumar, V.; Purohit, A.; Vashisht, A.; Kumar, V.; Yadav, S. K. (2020) Bioprospecting potential of microbial communities in solid waste landfills for novel enzymes through metagenomic approach. World Journal of Microbiology and Biotechnology, 36(3). https://doi.org/10.1007/s11274-020-02812-7
Tveit, A.T.; Hestnes, A.G.; Robinson, S.L.; Schintlmeister, A.; Dedysh, S.N.; Jehmlich, N.; von Bergen, M.; Herbold, C.; Wagner, M.; Richter, A.; Svenning, M.M. (2019) Widespread soil bacterium that oxidizes atmospheric methane. Proc. Natl. Acad. Sci. U.S.A. 116, 8515–8524. https://doi.org/10.1073/pnas.1817812116.
Thiel, V.; Fukushima, S.-I.; Kanno, N.; Hanada, S.(2019) Chloroflexi. Reference Module in Life Sciences. https://doi.org/10.1016/b978-0-12-809633-8.20771-1
Wang, X.; Cao, A.; Zhao, G.; Zhou, C.; Xu, R. (2017) Microbial community structure and diversity in a municipal solid waste landfill. Waste management, 66, 79-87. https://doi.org/10.1016/j.wasman.2017.04.023
Wawrik, B.; Marks, C. R.; Davidova, I. A.; McInerney, M. J.; Pruitt, S.; Duncan, K. E. et al. (2016) Methanogenic paraffin degradation proceeds via alkane addition to fumarate by “Smithella” spp. mediated by a syntrophic coupling with hydrogenotrophic methanogens. Environmental Microbiology, 18(8), 2604–2619. https://doi.org/10.1111/1462-2920.13374
Wiryawan, A.; Eginarta, W. S.; Hermanto, F. E.; Ustiatik, R.; Dinira, L.; Mustafa, I. (2022). Changes in Essential Soil Nutrients and Soil Disturbance Directly Affected Soil Microbial Community Structure – A Metagenomic Approach. Journal of Ecological Engineering, 23(7), 238-245. https://doi.org/10.12911/22998993/149972
Xu, S.; Lu, W.; Liu, Y.; Ming, Z.; Liu, Y.; Meng, R.; Wang, H. (2017) Structure and diversity of bacterial communities in two large sanitary landfills in China as revealed by high-throughput sequencing (MiSeq). Waste Management 63, 41–48. https://doi.org/10.1016/j.wasman.2016.07.047
Zainun, M.Y.; Simarani, K. (2018) Metagenomics profiling for assessing microbial diversity in both active and closed landfills. Science of the Total Environment 616–617, 269–278. https://doi.org/10.1016/j.scitotenv.2017.10.266
Zolnikov, T.R.; Silva, R.C.; Tuesta, A.A.; Marques, C.P.; Cruvinel, V.R.N. (2018). Ineffective waste site closures in Brazil: A systematic review on continuing health conditions and occupational hazards of waste collectors. Waste Manag., 80, 26-39. https://doi.org/10.1016/j.wasman.2018.08.047

SUPPLEMENTARYMATERIAL11.docx

Download PDF

Version 1

posted

You are reading this latest preprint version

Effects of capping on microbial populations and contaminants immobilization in an old unlined landfill

Status:

Version 1

Abstract

Figures

1. Introduction

2. Methodology

2.1. Study area

2.2. Construction of capping layers

2.3. Sampling

2.4. Physicochemical analysis

2.5. 16 S rRNA sequencing

2.6. Specific Methanogenic Activity (SMA)

3. Results And Discussion

3.1. Physicochemical analysis

3.2. 16S rRNA sequencing

3.2.1. Richness and diversity of microbial communities

3.2.2. Taxonomic analysis at the level of phyla

3.2.3. Taxonomic analysis at the level of genera

3.3. Specific Methanogenic Activity (SMA)

4. Conclusions

Declarations

References

Supplementary Files

Status:

Version 1