Prasanna Kumarathilaka

Equilibrium and kinetic mechanisms of woody biochar on aqueous glyphosate removal.

We investigated the removal of aqueous glyphosate using woody (dendro) biochar obtained as a waste by product from bioenergy industry. Equilibrium isotherms and kinetics data were obtained by adsorption experiments. Glyphosate adsorption was strongly pH dependent occurring maximum in the pH range of 5-6. The protonated amino moiety of the glyphosate molecule at this pH may interact with π electron rich biochar surface via π-π electron donor-acceptor interactions. Isotherm data were best fitted to the Freundlich and Temkin models indicating multilayer sorption of glyphosate. The maximum adsorption capacity of dendro biochar for glyphosate was determined by the isotherm modeling to be as 44 mg/g. Adsorption seemed to be quite fast, reaching the equilibrium <1 h. Pseudo-second order model was found to be the most effective in describing kinetics whereas the rate limiting step possibly be chemical adsorption involving valence forces through sharing or exchanging electrons between the adsorbent and sorbate. The FTIR spectral analysis indicated the involvement of functional groups such as phenolic, amine, carboxylic and phosphate in adsorption. Hence, a heterogeneous chemisorption process between adsorbate molecules and functional groups on biochar surface can be suggested as the mechanisms involved in glyphosate removal.

Perchlorate as an emerging contaminant in soil, water and food.

Perchlorate ( [Formula: see text] ) is a strong oxidizer and has gained significant attention due to its reactivity, occurrence, and persistence in surface water, groundwater, soil and food. Stable isotope techniques (i.e., ((18)O/(16)O and (17)O/(16)O) and (37)Cl/(35)Cl) facilitate the differentiation of naturally occurring perchlorate from anthropogenic perchlorate. At high enough concentrations, perchlorate can inhibit proper function of the thyroid gland. Dietary reference dose (RfD) for perchlorate exposure from both food and water is set at 0.7 μg kg(-1) body weight/day which translates to a drinking water level of 24.5 μg L(-1). Chromatographic techniques (i.e., ion chromatography and liquid chromatography mass spectrometry) can be successfully used to detect trace level of perchlorate in environmental samples. Perchlorate can be effectively removed by wide variety of remediation techniques such as bio-reduction, chemical reduction, adsorption, membrane filtration, ion exchange and electro-reduction. Bio-reduction is appropriate for large scale treatment plants whereas ion exchange is suitable for removing trace level of perchlorate in aqueous medium. The environmental occurrence of perchlorate, toxicity, analytical techniques, removal technologies are presented.

Influence of Gliricidia sepium Biochar on Attenuate Perchlorate-Induced Heavy Metal Release in Serpentine Soil

Perchlorate ( ) is a strong oxidizer, capable of accelerating heavy metal release into regolith/soil. Here, we assessed interactions between and serpentine soil to simulate and understand the fate of Ni and Mn and their immobilization with the presence of biochar (BC). A soil incubation study (6 months) was performed using serpentine soil in combination with different concentrations (0.25, 0.5, 0.75, and 1 wt.%) and three different amendment rates (1, 2.5, and 5 wt.%) of Gliricidia sepium BC. Bioavailable fraction of Ni and Mn was analyzed using CaCl2 extraction method. An increase of concentrations enhanced bioavailability fraction of Ni and Mn. However, BC amendments reduced the bioavailability of Ni and Mn. In comparison, 5% BC amendment significantly immobilized the bioavailability of Ni (68–92%) and Mn (76–93%) compared to other BC amendment rates. Electrostatic attractions and surface diffusion could be postulated for Ni and Mn immobilization by BC. In addition, may have adsorbed to BC via hydrogen bonding which may reduce the influence of on Ni and Mn mobility. Overall, it is obvious that BC could be utilized as an effective amendment to immobilize Ni and Mn in heavy metal and contaminated soil.

Arsenic speciation dynamics in paddy rice soil-water environment: sources, physico-chemical, and biological factors - A review

Rice is the main staple carbohydrate source for billions of people worldwide. Natural geogenic and anthropogenic sources has led to high arsenic (As) concentrations in rice grains. This is because As is highly bioavailable to rice roots under conditions in which rice is cultivated. A multifaceted and interdisciplinary understanding, both of short-term and long-term effects, are required to identify spatial and temporal changes in As contamination levels in paddy soil-water systems. During flooding, soil pore waters are elevated in inorganic As compared to dryland cultivation systems, as anaerobism results in poorly mobile As(V), being reduced to highly mobile As(III). The formation of iron (Fe) plaque on roots, availability of metal (hydro)oxides (Fe and Mn), organic matter, clay mineralogy and competing ions and compounds (PO43- and Si(OH)4) are all known to influence As(V) and As(III) mobility in paddy soil-water environments. Microorganisms play a key role in As transformation through oxidation/reduction, and methylation/volatilization reactions, but transformation kinetics are poorly understood. Scientific-based optimization of all biogeochemical parameters may help to significantly reduce the bioavailability of inorganic As.

Insights into Starch Coated Nanozero Valent Iron-Graphene Composite for CrVI Removal from Aqueous Medium

Embedding nanoparticles into an inert material like graphene is a viable option since hybrid materials are more capable than those based on pure nanoparticulates for the removal of toxic pollutants. This study reports for the first time on CrVI removal capacity of novel starch stabilized nanozero valent iron-graphene composite NZVI-Gn under different pHs, contact time, and initial concentrations. Starch coated NZVI-Gn composite was developed through borohydrate reduction method. The structure and surface of the composite were characterized by scanning electron microscopy SEM, X-ray diffraction spectroscopy XRD, Fourier transform infrared spectroscopy FTIR, Brunauer-Emmett-Teller BET, and point of zero charge pHpzc. The surface area and pHpzc of NZVI-Gn composite were reported as 525 m2 g−1 and 8.5, respectively. Highest CrVI removal was achieved at pH 3, whereas 67.3% was removed within first few minutes and reached its equilibrium within 20 min obeying pseudo-second-order kinetic model, suggesting chemisorption as the rate limiting process. The partitioning of CrVI at equilibrium is perfectly matched with Langmuir isotherm and maximum adsorption capacity of the NZVI-Gn composite is 143.28 mg g−1. Overall, these findings indicated that NZVI-Gn composite could be utilized as an efficient and magnetically separable adsorbent for removal of CrVI.

Arsenic accumulation in rice (Oryza sativa L.) is influenced by environment and genetic factors

Arsenic (As) elevation in paddy soils will have a negative impact on both the yield and grain quality of rice (Oryza sativa L.). The mechanistic understanding of As uptake, translocation, and grain filling is an important aspect to produce rice grains with low As concentrations through agronomical, physico-chemical, and breeding approaches. A range of factors (i.e. physico-chemical, biological, and environmental) govern the speciation and mobility of As in paddy soil-water systems. Major As uptake transporters in rice roots, such as phosphate and aquaglyceroporins, assimilate both inorganic (As(III) and As(V)) and organic As (DMA(V) and MMA(V)) species from the rice rhizosphere. A number of metabolic pathways (i.e. As (V) reduction, As(III) efflux, and As(III)-thiol complexation and subsequent sequestration) are likely to play a key role in determining the translocation and substantial accumulation of As species in rice tissues. The order of translocation efficiency (caryopsis-to-root) for different As species in rice plants is comprehensively evaluated as follows: DMA(V) > MMA(V) > inorganic As species. The loading patterns of both inorganic and organic As species into the rice grains are largely dependent on the genetic makeup and maturity stage of the rice plants together with environmental interactions. The knowledge of As metabolism in rice plants and how it is affected by plant genetics and environmental factors would pave the way to develop adaptive strategies to minimize the accumulation of As in rice grains.

Influence of bioenergy waste biochar on proton- and ligand-promoted release of Pb and Cu in a shooting range soil

Presence of organic and inorganic acids influences the release rates of trace metals (TMs) bound in contaminated soil systems. This study aimed to investigate the influence of bioenergy waste biochar, derived from Gliricidia sepium (GBC), on the proton and ligand-induced bioavailability of Pb and Cu in a shooting range soil (17,066mg Pb and 1134mg Cu per kg soil) in the presence of inorganic (sulfuric, nitric, and hydrochloric) and organic acids (acetic, citric, and oxalic). Release rates of Pb and Cu in the shooting range soil were determined under different acid concentrations (0.05, 0.1, 0.5, 1, 5, and 10mM) and in the presence/absence of GBC (10% by weight of soil). The dissolution rates of Pb and Cu increased with increasing acid concentrations. Lead was preferentially released (2.79×10-13 to 8.86×10-13molm-2s-1) than Cu (1.07×10-13 to 1.02×10-13molm-2s-1) which could be due to the excessive Pb concentrations in soil. However, the addition of GBC to soil reduced Pb and Cu dissolution rates to a greater extent of 10.0 to 99.5% and 15.6 to 99.5%, respectively, under various acid concentrations. The increased pH in the medium and different adsorption mechanisms, including electrostatic attractions, surface diffusion, ion exchange, precipitation, and complexation could immobilize Pb and Cu released by the proton and ligands in GBC amended soil. Overall, GBC could be utilized as an effective soil amendment to immobilize Pb and Cu in shooting range soil even under the influence of soil acidity.

Municipal Solid Waste Biochar for Prevention of Pollution From Landfill Leachate

Municipal solid waste (MSW) is produced at an alarming rate, which may have a negative impact on the environment and on human health, if not properly managed. Open landfills are the most common way of disposing of MSW in the developing world. Landfill leachates generated from such open dump sites are directed to surface water bodies with no treatment in most places. Organic and inorganic compounds including organic acids, pesticides, volatile organic compounds, pharmaceuticals, heavy metals, and nutrients in the landfill leachates are extremely important substances to manage. Many different methods are currently in use to treat and fill leachates, such as aerobic biological treatment, anaerobic treatment, physiochemical treatment, coagulation, adsorption, and ion exchange. Among them, carbon adsorption is commonly used method for the remediation of organic and inorganic contaminants. Biochar (BC), a carbonaceous material produced by the pyrolysis of biomass under limited or no oxygen, is an efficient emerging substitute for activated carbon. Biochar from agricultural waste has exceptional capacity for the removal of many different pollutants. Similarly, BC can be potentially produced from the organic materials of the MSW itself, so that it may have a possibility for resource reuse. Hence, this chapter discusses the potential of BC from MSW and its applications to remediate different pollutants in MSW leachate as well as its ability to be used as a landfill cover and as a reactive barrier material.

Phytoremediation of Landfill Leachates

Municipal landfill leachate is a complex refractory wastewater which consists of extensive level of organic compounds, ammonia, and heavy metals. Contamination of water by landfill leachate has become a serious environmental concern worldwide due to its adverse impact on human health, aquatic organisms, and agricultural crop production. In recent years, constructed wetland (CW) has received promising attention in the treatment of landfill leachate, because of its cost-effective and eco-friendly nature and simplicity in operation, in addition to higher treatment efficiency. Hence, the present chapter is mainly focused on providing a concise discussion of the CWs and its phytoremediation attributes for the remediation of landfill leachate. Natural wetland plant species and short rotation coppice (SRC) have been introduced to remove contaminants from landfill leachate. Different processes such as phytoextraction, phytodegradation, phytovolatilization, rhizofiltration, phytostabilization, rhizo-redox reactions, sedimentation, adsorption, and complexation involve to remove nutrients (i.e., nitrogen and phosphate), heavy metal(loid)s, biological oxygen demand (BOD), and chemical oxygen demand (COD) to a great extent in CW systems. In addition, well-managed SRC systems save millions of dollars by eliminating the leachate transportation and treatment process which were earlier practiced. Further, there are a number of examples where phytoremediation has failed due to excessive leachate application and lack of management practices. Therefore, it is obvious that successful transfer of phytoremediation technologies from the laboratory to the field is a crucial step in terms of removal efficiency.

Bio-retention Systems for Storm Water Treatment and Management in Urban Systems

Among different anthropogenic activities, urbanization has greatly influenced the hydrological cycle. Due to increased impervious surfaces, the amount of infiltration has been reduced, thereby increasing the runoff volume leading to flood conditions even for low rainfall events. Storm water flow along these impermeable surfaces finally ends up in surface water reservoirs. Urban systems are fundamentally responsible for a lot of pollutants by different sources: vehicle, industries, atmospheric deposition, soil erosion, etc., which may release various types of pollutants such as metals, organics, nutrients, oil and grease, detergents, surfactants, etc., into the atmosphere. With the storm water runoff, these pollutants may end up in surface waters. This indicates the importance of storm water treatment. Although there are several storm water treatment methods available, low-cost environmental-friendly methods (e.g., bio-retention systems) will be more sustainable with urban systems. Bio-retention systems can manage storm water and improve water quality through containment and remediation of pollutants within the urban system. However, the limitation of these systems is its finite capacity to hold contaminants. Hence, suitable plants grown along the bio-retention systems will be an effective phytoremediation option to address the challenges encountered in these remedial systems.