Leaching Of Contaminants Research Articles

Occurrence of per- and polyfluoroalkyl substances and unidentified organofluorine in leachate from waste-to-energy stockpile - A case study

Per- and polyfluoroalkyl substances (PFASs) are a diverse group of chemicals used in consumer products, which will inevitably end up in waste streams. Landfills are widely recognized secondary point sources of PFASs, but other types of waste management sites have received less attention. Therefore, in a case study presented here we investigated releases of PFASs from temporarily stored waste by determining quantities of 34 PFASs in leachate from a Waste-to-Energy stockpile (45 000 ± 2000 tonnes) during five months in 2019. We also measured extractable organofluorine (EOF) to account for PFASs not included in the target list. The mean total concentration of the 34 PFAS (Σ34PFAS) was 211 ± 31 ng/L, and short-chain (C4–C7) perfluorocarboxylic acids (PFCAs) accounted for 56–60% of the total. Moreover, we found that Σ34PFAS only accounted for 12% ± 4% of EOF detected in the leachate. Our results demonstrate that waste stockpiles are previously unexplored sources of PFASs in the environment, and the dominance of short-chain PFCAs is consistent with observed profiles of contaminants in landfill leachates.

Long-term effect of magnesium and iron nanoparticles on solute transport in saturated condition

ABSTRACT The aim of this study was to investigate the long-term effect of magnesium and iron nanoparticles on solute transport and its parameters, which has not been investigated to date. Different concentrations of two types of nanoparticle metal oxides, MgO and Fe3O4, were mixed with a loamy soil and their effects on solute transport and its parameters after three years were investigated. Nanoparticles improved soil structure through increased macro pores compared to the control, by 2.3% in the 3% concentration of MgO to 15.3% in the 3% concentration of Fe3O4. Immobile water content of the soil decreased from 0.42 in the control to 0.05–0.24 cm3 cm−3 in the treatments. The mass transfer coefficient was decreased from 0.48 in the control to 0.005–0.37 in the nanoparticle treatments. Moreover, nanoparticles increased the breakthrough curve peak concentration and decreased discharge time of chloride in the extract from 0.41 and 88.8 min in the control to 0.62–0.76 and 24.7–87.9 min in the treatments, respectively. The results of this study showed that the nanoparticles affected the solute transport and its parameters in the soil. Therefore, nanoparticles could be used to simplify the nutrients transport and leaching of salt and contaminants.

Geo-electrical modeling of leachate contamination at a major waste disposal site in south-eastern Nigeria

The contamination of aquifers due to the leaching of organic and inorganic waste materials deposited in landfills and open dumpsites leads to serious degradation of the environment. To determine the extent of leaching and to assess the migration of the leachate into the surrounding aquifer, vertical electrical sounding (VES) and electrical resistivity tomography (ERT) surveys were carried out along a heavily contaminated waste disposal site in South-eastern Nigeria. The results obtained from the vertical electrical soundings show that the area comprises three subsurface layers, and that the aquifer lies between the second and third layer. Computation of longitudinal conductance values shows that the overall protective capacity of the aquifer is weak; hence, the capacity for leachate contamination within the aquifer is higher. Models obtained from the electrical resistivity tomography surveys indicate the direction of the leachate plumes and also show the extent of leachate percolation into the aquifer. On the electrical resistivity tomography models, the locations of anomalous low resistivity zones indicate the presence of leachate. The results show that the leachate is moving rapidly towards the aquifer and this will create serious environmental degradation to valuable water resources in the area, thereby affecting health of humans and livestock within this heavily populated zone. Further, the results from the resistivity surveys confirm that the resistivity technique is a powerful tool for delineating the presence of leachate plumes and for indicating to what extent the leachate has infiltrated into the surrounding aquifer.

Electrocoagulation Treatment of Sanitary Landfill Leachate in Malaysia

The tropical climate condition and high moisture of solid waste characteristic in Malaysia led to the increase of leachate generation from landfill. Current leachate treatment showed less efficient to treat leachate due to various refractory pollutants in the leachate. This study employed electrocoagulation (EC) to investigate the effects of electrode material, current density and initial pH condition in reducing total suspended solid (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD5), ammonia-nitrogen and colour from the leachate. The result showed that aluminium electrode was able to remove all the parameters more effectively as compared to iron electrode. The optimum current density and pH condition were found to be 100 mA/cm2 and at pH 7, respectively. The COD in the leachate was predominantly exist as particulate matter and it was removed in the form of suspended solids. Although all the pollutant parameters still exceeded the standard discharge limit after the treatment, the electrocoagulation is proposed to act as pretreatment prior to biological treatment in sanitary landfill. The electrocoagulation also can treat leachate from open dumping landfill sites in order to reduce the leachate contamination into the environment.

A systematic approach for prioritizing landfill pollutants based on toxicity: Applications and opportunities

Landfills in the United States are a significant source of pollution to ground and surface water. Current environmental regulations require detection and/or monitoring assessments of landfill leachate for contaminants that have been deemed particularly harmful. However, the lists of contaminants to be monitored are not comprehensive. Further, landfill leachate composition varies over space and time, and thus the contaminants, and their corresponding toxicity, are not consistent across or within landfills. One of the main objectives of this study was to prioritize contaminants found in landfill leachate using a systematic, toxicity-based prioritization scheme. A literature review was conducted, and from it, 484 landfill leachate contaminants with available CAS numbers were identified. In vitro, in vivo, and predicted human toxicity data were collected from ToxCast, ECOTOX, and CTV Predictor, respectively. These data were integrated using the Toxicological Priority Index (ToxPi) for the 322 contaminants which had available toxicity data from at least two of the databases. Four modifications to this general prioritization scheme were developed to demonstrate the flexibility of this scheme for addressing varied research and applied objectives. The general scheme served as a basis for comparison of the results from the modified schemes, and allowed for identification of contaminants uniquely prioritized in each of the schemes. The schemes outlined here can be used to identify the most harmful contaminants in environmental media in order to design the most relevant mitigation strategies and monitoring plans. Finally, future research directions involving the combination of these prioritization schemes and non-target global metabolomic profiling are discussed.

Using advanced statistical tools to assess the impact of a small landfill site on the aquatic environment

The aim of the study was to assess the impact of a small municipal landfill on the aquatic environment over 9 years, using advanced statistical tools. The results of the study of surface, ground- and leachate waters from 2008 to 2016 were subjected to detailed statistical analysis based on 15 physicochemical indicators. Factor analysis accounted for the requirements of the WHO, the European Union and the nation of Poland using 8 statistical analytical methods. The analysis of leachate contamination from the landfill site with the use of advanced statistical tools revealed its interaction with groundwater. The assessment was based on increased and statistically significant values and correlations of temperature, Zn and N–NO3 between leachate and groundwater, factors demonstrating the negative impact of the landfill. In the case of Zn, there was also a correlation between the tested waters below the landfill. The increased PAH values in the examined surface and ground waters were not a consequence of waste disposal. However, the deterioration of the chemical state of groundwater in the vicinity of the landfill could result from a certain dysfunction of the facility’s infrastructure after operating for more than 20 years.

Food waste solution at home: conventional and rapid composting techniques

Food waste is a significant concern in waste management in recent years due to the inevitable outcome of human consumption in modern society. It has happened in almost every home daily. In Malaysia, 44.5% of organic waste (OW) consists of food waste (FW), this figure would increase with population growth. Therefore, without effective FW management, untreated FW dumping will cause environmental pollution, thus affecting human health as well as ecosystems. Conventional methods such as landfill and incineration have long been the most popular practice to address the FW issues, offering simple and cost-effective approach. Most of the time, these methods are not sustainable since they pose other environmental pollution such as greenhouse gas (GHG) emissions and leachate contamination leading to groundwater pollutions. Other issues with landfills are that self-composting at landfill site takes a long time and most landfills in Malaysia are almost at full capacity. The composting technique has recently gained more attraction as a cost-effective and sustainable method for the FW issue. This paper reviews techniques of composting food waste at home by using a conventional natural and rapid process. The performance of each technique in terms of cost, sustainability, user-friendly and time are measured in this review. Finally, the future direction of food waste solution by sustainable composting technique is briefly discussed in this paper.

Macrophyte Potential to Treat Leachate Contaminated with Wood Preservatives: Plant Tolerance and Bioaccumulation Capacity.

Pentachlorophenol and chromated copper arsenate (CCA) have been used worldwide as wood preservatives, but these compounds can toxify ecosystems when they leach into the soil and water. This study aimed to evaluate the capacity of four treatment wetland macrophytes, Phalaris arundinacea, Typha angustifolia, and two subspecies of Phragmites australis, to tolerate and treat leachates containing wood preservatives. The experiment was conducted using 96 plant pots in 12 tanks filled with three leachate concentrations compared to uncontaminated water. Biomass production and bioaccumulation were measured after 35 and 70 days of exposure. There were no significant effects of leachate contamination concentration on plant biomass for any species. No contaminants were detected in aboveground parts of the macrophytes, precluding their use for phytoextraction within the tested contamination levels. However, all species accumulated As and chlorinated phenols in belowground parts, and this accumulation was more prevalent under a more concentrated leachate. Up to 0.5 mg pentachlorophenol/kg (from 81 µg/L in the leachate) and 50 mg As/kg (from 330 µg/L in the leachate) were accumulated in the belowground biomass. Given their high productivity and tolerance to the contaminants, the tested macrophytes showed phytostabilization potential and could enhance the degradation of phenols from leachates contaminated with wood preservatives in treatment wetlands.

A novel method for the quantification of industrial and municipal waste materials for environmental hazard assessment

A novel methodological approach was developed to quantified the volume of industrial waste desposal (IWD) site, combined with municipal waste materials (MWM), through the integration of a non-invasive, fast, and less expenssive RES2-D Electrical Resistivity Technique (ERT), using Wenner-Schlumberger electrode array geophysical method with Oasis Montaj software. Underground water bearing structures, and the eco-system are being contaminated through seepage of the plumes emanating from the mixtures of the industrial waste materials (IWM), made of moist cemented soil with municipal solid wastes (MSW) dumped at the site. The distribution of the contiminant hazardous plumes emanating from the waste materials' mixtures within the subsurface structural lithological layers was clearly map and delineated within the near-surface structures, using the triplicate technique to collect samples of the soil with the waste mixtures, and the water analysis for the presence of dissolved ions. The deployed method helped to monitor the seepage of the contaminant leachate plumes to the groundwater aquifer units via the ground surface, through the subsurface stratum lithological layers, and hence, estimation of the waste materials' volume was possibly approximated to be 312,000 m3.In summary, the novel method adopted are as presented below:•The novel method is transferable, reproduce-able, and most importantly, it is unambiguous technique for the quantification of environmental, industrial and municipal waste materials.•It helps to map the distribution of the plumes emanating from the waste materials' mixtures within the subsurface structural lithological layers that was clearly delineated within the near-surface structures underlain the study site.•The procedure helped in the monitoring of leachate contaminants plumes seepages into the surface water bodies and the groundwater aquifer units, via the ground surface, through to the porous subsurface stratum lithological layers.

Delineation of leachate at a dumpsite using geo-electrical resistivity method: a case study of Abule Egba, Lagos, Nigeria

This study presents the application of the dipole–dipole and the Schlumberger electrode arrays of electrical resistivity techniques to map the extent of leachate migration and its possible impact on groundwater at Abule Egba, dumpsite, Lagos. The uncontrolled mode of refuse disposal in Lagos over the years is worrisome because it reduces the potential sources of potable water for the growing population. This informed the evaluation of leachate migration to groundwater in the study area. To achieve this, 2-D resistivity imaging data was acquired along five traverses and was integrated with VES data acquired along the established traverses. The 2-D resistivity imaging and VES data were processed using DIPPRO and WINRESIST software respectively. The interpretation of the geo-electrical measurements was constrained by borehole data obtained within the study area. The results of the 2D and VES revealed five (5) geoelectric layers which correspond to the topsoil, clay, sandy clay, clayey sand and sand. The topsoil has layer thickness of 0.5–2.7 m and resistivity values within range of 9.8–133.3 Ωm. The clay has layer thicknesses between 1.7 m to 33.1 m and resistivity values ranging from 4.8 to 67.9 Ωm. The sandy clay layer has thickness of 1.0–14.5 m and resistivity values ranging from 13.5 to 128.8 Ωm. The clayey sand layer has thickness 1.9–44.4 m and resistivity values ranging from 16.3 to 129.0 Ωm. The sand delineated has thickness of 5.7–81.7 m and resistivity values ranging from 1.9 to 1230 Ωm. The fourth layer with low resistivity values of 1.9–2.4 Ωm at depth range 14.5–29 m is suggestive of leachate contamination when compared with the delineated sand of resistivity values of 419–916 Ωm in VES 19–24 which serve as control. The study revealed that some regions around the dumpsite have been contaminated by leachate which could infiltrate to the unconfined aquifers in the area if not properly monitored and regulated. Thus, this study shows the efficacy of electrical resistivity method in mapping leachate generated from solid wastes in the dumpsite.

Impact of dung beetle activity on the quality of water percolating through Allophanic soil

Dung beetles are described as key ecosystem service providers. Because of ecosystem benefits from their activity, approval has been granted to import dung-burying beetles for release into pasture systems in New Zealand. Concerns remain, however, about the impact of dung beetle tunnelling and burying activity on the leaching of contaminants through soil. To assess the quality of water leaching from soil cores containing dung beetles, a trial was conducted using 12 intact Allophanic soil core lysimeters under in situ soil moisture and temperature regimes. Four lysimeters received dung and beetles (Geotrupes spiniger and Onthophagus taurus), four received dung and no beetles and four (controls) received no dung and no beetles. The quality of water was assessed by monitoring leachate samples for Escherichia coli and total N and P for 6 months. Key findings of the study were that concentrations of E. coli, N and P leaching through the lysimeters treated with dung beetles were not significantly different from soils without dung beetles. In addition, where dung was buried there was a significant decrease in E. coli and total N and P in surface soil compared with the lysimeters receiving dung only. Results from this study suggest dung beetle tunnelling and burying activity does not negatively impact the quality of water leaching through Allophanic soil.

Assessment of the long-term leaching characteristics of cement-slag stabilized/solidified contaminated sediment

The use of stabilized/solidified (S/S) soils and sediments as sustainable construction materials is a global concern due to the potential risk of contaminant leaching including potentially toxic elements. The long-term leachability of four metals (Zn, Pb, Cd and As) in sediments mixed with OPC (Ordinary Portland Cement) and OPC/GGBS (Ground Granulated Blast Furnace Slag) binders were investigated through a combination of tank leaching tests and kinetic leaching models, with varying ranges of curing ages and ambient pH. The leaching data revealed that both binder compositions offer an excellent immobilization capacity for the four metals, while their releases are strongly pH-dependent and are a complex function of curing time. The partial replacement of OPC by GGBS is more effective for fixing Zn and As at pH of 1, Pb at pH of 7, Zn and Pb at pH of 10. Controlling leaching mechanisms and leachability indices were determined using nonlinear regression analysis and kinetic leaching models. The first-order diffusion model (FRDM) was the most applicable model for describing the leaching characteristics of these metals under the investigated cases, the leaching rate is controlled by surface wash-off initially and then by diffusion. The leachability indices indicate that the cement-slag S/S sediment can be regarded as an environmentally sustainable material with potential beneficial uses in construction.

Long-term redox conditions in a landfill-leachate-contaminated groundwater

Indicators of redox conditions; oxygen, sulphate, nitrate, ammonium, iron and manganese, and in addition, bicarbonate and total organic carbon were studied in groundwater samples contaminated by leachate emanating from Revdalen Landfill (Norway). Based on these variables, the study aimed to deduce the redox conditions in the aquifer. Literature on landfill leachate contamination of confined aquifers is scarce and to the best of our knowledge, this study, which describes long-term analysis of redox chemistry, is the first of its kind in such an environment. Groundwater samples were monitored for a period of 24 years, enabling us to describe redox conditions on both short-term and long-term bases. Levels of measured parameters in the contaminated aquifer varied spatially and with time, but were generally elevated except oxygen; pH (4.9–8.8), oxygen (0–11.3 mg/L), sulphate (0–28 mg/L), nitrate (0–16 mg N/L), ammonium (0.02–40 mg/L), iron (0–99 mg/L), manganese (0.06–16 mg/L), bicarbonate (22–616 mg/L) and total organic carbon (1.3–47 mg/L). From the result, levels of iron, manganese, nitrate and ammonium violated the Norwegian drinking water norms. However, iron, ammonium, total organic carbon and bicarbonate showed strong attenuation along the groundwater flow path. By contrast, oxygen, nitrate and sulphate increased farther out in the plume. The redox conditions that developed in the aquifer were similar to those previously reported for phreatic aquifers, structuring by proximity to the landfill as sulphate-reducing, iron-reducing, manganese-reducing, nitrate-reducing, and finally aerobic condition. Eventually, there was an apparent breakdown of this system due to ecosystem shift in the landfill when leachable reduced ions were depleted and the landfill became aerobic. Overall, the redox framework provided remarkable attenuation to contaminants, and thus prevented potential degradation of ecological health due to the landfill leachate.

Valorization of MSWI Bottom Ash as a Function of Particle Size Distribution, Using Steam Washing

Treatments to reduce the leaching of contaminants (chloride, sulfate, heavy metals) into the environment from bottom ash (BA) are investigated, as a function of the ash’s particle size (s). The aim is to make BA suitable for reuse as secondary raw material, in accordance with the legal requirements. Such treatments must be economically feasible and, possibly, have to use by-products of the plant (in this case, steam in excess from the turbine). For the sake of completeness and comparison, carbonation is performed on those BA particle size classes that are not positively responsive to steam washing. BA is partitioned into four different particle size classes (s ≥ 4.75, 4.75 > s ≥ 2, 2 > s ≥ 1 and s < 1 mm, corresponding to 36, 24, 13 and 27 wt%, respectively). In the case of s ≥ 2 mm (60 wt%), steam washing is effective in reducing to under the legal limits the leaching of chlorides, sulfate and heavy metals (Zn, Cu, Cd, Pb). It has been observed that steam washing causes both removal and dissolution of thin dust adherent to the BA’s surface. BA with 2 > s ≥ 1 (~13 wt% of total BA) requires a combination of steam washing and carbonation to achieve a leaching below the legal limits. The finest BA fraction, s < 1 mm (~27 wt% of total BA), is treated by carbonation, which reduces heavy metals leaching by 85%, but it fails to sufficiently curb chlorides and sulfates.

Heavy metals in leachate, impacted soils and natural soils of different landfills in Malaysia: An alarming threat

Landfills are a potential threat to human health and the environment, especially from the detrimental and toxic heavy metals. This study focuses on the assessment of heavy metals contamination in leachate and surface soils from different landfills in Malaysia. Maximum quality rating scale (QRS) values of As (787) and Cr (552) denotes progressive deterioration of leachate contamination in landfill. The impacted soils showed high heavy metal concentrations especially at non-sanitary unlined landfills, as compared to background values, and natural soil nearby the landfills. In addition, to examine the environmental impacts of the landfill area (soil) in more detail, specific indexes; geo-accumulation index (Igeo), pollution index (PI) and integrated pollution index (IPI) were determined. Maximum As (3.122) and Cd (2.633) for Igeo and As (34.037) and Cd (20.881) for PI revealed that the soil samples in non-sanitary landfills were moderate to strongly polluted. The difference in range of IPI values for sanitary (0.294–0.322) and non-sanitary landfill soils (1.263–1.956) confirmed advanced decline of the soil quality in non-sanitary landfills. Arsenic concentrations were found to be statistically significant (ANOVA) for leachate and impacted soil in landfills investigated. It is also important to realize that rise in metal contents in landfill environments were not only caused by anthropogenic sources such as from the waste disposed, but also some other factors such as redox conditions, anoxic environments, pH, oxidation state of metals and microbial activities. Those conditions will actively promotes leaching of metals from waste and also natural soils in the landfill.

Evaluating the leachate contamination impact of landfills and open dumpsites from developing countries using the proposed Leachate Pollution Index for Developing Countries (LPIDC)

The Leachate Pollution Index (LPI) was formulated in 2005 to evaluate the pollution potential of landfill leachate, so that better strategies can be implemented to prevent continuous environmental degradation. As leachate characteristics are dependent on the waste composition, which is notably different between developed and developing countries, the LPI cannot be used to accurately evaluate leachate from all over the world. Hence, using the LPI as a benchmark would yield inaccurate conclusions on the severity of the pollution of these leachates. To address this, we developed an index that is more accurate in determining the pollution impact of leachate in developing countries; The Leachate Pollution Index for Developing Countries (LPIDC). LPIDC was developed after consulting various experts in waste management based in developing countries, who shared their expertise, knowledge and experience to identify parameters that needed to be assessed when evaluating the pollution potential of leachate. To determine the precision of LPIDC, we analysed leachate samples from Malaysian landfills and open dumpsites, and also reviewed leachate data from other developing countries. We then used the data to compare the precision of LPI and LPIDC. The data confirmed that LPIDC provided a more precise evaluation of the pollution impact of leachate in developing countries. This is due to the LPIDC taking into account several important parameters that were overlooked in the LPI, namely landfill liners and leachate volume.

Geophysical and hydrophysical evaluation of groundwater around the Igbenre Ekotedo dumpsite Ota, Southwest Nigeria, using correlation and regression analysis

A study involving geophysical survey and groundwater analysis was carried out at the Igbenre Ekotedo dumpsite in Ota, Southwest Nigeria. The aim was to monitor and track the depth of leachate contamination around the dumpsite. A proposed simple multiple linear regression (MLR) model of groundwater total dissolved solids (TDS) was also developed. This was achieved by correlating the observed TDS of groundwater samples collected within and around the vicinity of the dumpsites with multiple terrain conductivity data derived from a geophysical method. The results of the electrical resistivity tomography (ERT) obtained along four profile lines in August 2014, and a time-lapse survey in December 2015 delineated leachate plumes as low-resistivity zones ranging between 0.54 and 12.5 Ω m around the dumpsite, with good correlation between the wet and dry season models. The results also showed that leachate from the decomposed refuse materials has polluted the subsurface under the dumpsite from the surface to a depth of about 45 m, and by extension contaminating groundwater aquifer around the area. Results from the electromagnetic (EM-34) experiment and groundwater TDS parameters from seven (7) boreholes around the vicinity of the EM profiles showed a strong positive correlation. Therefore, a simple multiple linear regression (MLR) TDS model that relates the TDS data obtained from boreholes to the geophysical parameters obtained from the EM-34 data (HD 20, HD 40, and VD 40) was developed for the purpose of efficient groundwater resources monitoring and management around the dumpsite and their communities. The predictive power of the developed MLR TDS model was also apprised to determine the feasibility of using the TDS model to predict and estimate groundwater TDS around the study area. The developed TDS model can be reliably deployed for groundwater TDS estimation and monitoring around the study area where there are no boreholes, but with only terrain conductivity data. However, where there are borehole and hand-dug wells, terrain conductivity data around the area alone can be applied to the model to determine TDS concentration in groundwater, thus reducing the time and cost of determining and monitoring both parameters independently.

Geophysical Investigation of the Impact of Solid Waste Dump on Subsurface Soil and Groundwater in Eneka, Rivers State Nigeria

The geophysical electrical method was used to investigate how the refuse dump in Eneka (Rivers State, Nigeria) affects the subsurface soil and groundwater within its environs. The research was carried out applying Wenner and Schlumberger array configurations of electrical resistivity techniques to image the subsurface resistivity within the area using ABEM SAS 300 Terrameter. A total of ten locations were investigated and the measured data across the profiles were processed using RES2DINV and ArcGIS 10.4 computer iterative software. The resulting inverse resistivity model isolated three resistivity zones (anomalously low, intermediate and high resistivity). The anomalously low resistivity zone was interpreted as contaminant leachate plumes and landfill gases from the dump area was observed to have travelled to depths of 14 m below the surface and over 30 m distance eastwards from the dump site, showing the tendency of farm land and crops pollution. However, the aquifer layer in the area estimated at the depth of 40 m may not have been contaminated. The spatial trend of almost all the resistivity values measured at equidistance reveals low value for lines 3 and 4 (which are farther away from the dump site) at the beginning and high value at the end and vice versa for lines 1 and 2. At the rate at which the leachate has infiltrated the subsurface the aquifer within the area is likely to be contaminated in the future if adequate measures are not taken. Keywords: Dump site; Electrical resistivity; Eneka; Groundwater; Leachate plume. DOI 10.35180/gse-2020-0037

Impact of sulfate ion addition on electrochemical oxidation of anaerobically treated landfill leachate using boron-doped diamond anode

Anaerobic biological process is commonly applied for treating leachate generated from solid waste landfill. However, it is often found less effective to degrade leachate contaminants with low biodegradability, high salinity, and rich nutrient constituents. High concentration of organic and nitrogen still remained in the effluent of landfill leachate treated by anaerobic processes. Therefore, further treatment is required to efficiently meet the effluent standard prior to release into water bodies. In this study, electrochemical oxidation process using boron-doped diamond anode was investigated as a post-treatment for the treatment of anaerobically treated leachate effluent. Boron-doped diamond anode is able to generate of active species, such as OH·, Cl·, Cl2·−, and SO4·− as well as other oxidative agents to promote more indirect oxidation processes of non-biodegradable organic contaminants. The effect of sulfate ion addition on the overall performance of the electrochemical oxidation was investigated in a lab-scale of three-compartment electrochemical reactor, consisting of anode, cathode, and central compartments. A 2-L of the pre-treated leachate was recirculated in a batch mode by applying constant current density of 25, 37.5, and 50 mA cm−2. The optimum removal of nitrogen and organic contaminants were obtained about 59% and 93%, respectively, at current density of 37.5 mA cm−2, molar ratio 1:1 of [SO42−]:[Cl−] sulfate ion addition based on specific energy estimation and removal efficiency. The implied removal of 2.28 g COD and 1.77 g total inorganic nitrogen with the total energy required was 5.7 Wh g−1 COD and 7.5 Wh g−1 N, respectively. The results also revealed that addition of sulfate ion enhances organic removal through indirect oxidation and leads to the formation of nitrate without affecting overall total nitrogen removal.

In vitro organogenesis and plant regeneration of Thymus serpyllum L.: an important aromatic medicinal plant

An efficient in vitro propagation system has been developed for the rapid micropropagation of Thymus serpyllum L. (Banajwain), an aromatic medicinal herb from nodal explant on MS medium. Phenolic leaching and high rate of contamination was the most significant problem in establishing in vitro culture of Thymus serpyllum which was overcome by preparing explants in an antioxidant ascorbic acid (1000 ppm) at 6°C for 45 min and addition of the same antioxidant (50 mgl−1) to the MS medium. The frequency of shoot production was influenced by different cytokinins (Kn, BAP, and Kn + BAP) and 95.56% shoot induction was observed when MS medium was supplemented with 1.0 + 2.0 mgl−1 (Kn + BAP). The maximum average number of shoots 16.93 ± 2.15 and average length (3.98 ± 0.55) was recorded when MS medium have 0.5 + 2.0 mgl−1 (Kn + BAP). The in vitro regenerated microshoots were rooted on MS and half strength MS medium and there was significant difference in root induction on both media under the influence of auxins (IAA, IBA, and NAA). The maximum average number (11.67 ± 3.03) and average root length (3.88 ± 0.71) was reported in half MS medium having 1.0 mgl−1 IBA. The complete regenerated plantlets were acclimatized under growth chamber before transferring to the earthen pots and showed 90% survival.