Hasintha Wijesekara

Impact of wastewater derived dissolved organic carbon on reduction, mobility, and bioavailability of As(V) and Cr(VI) in contaminated soils.

In this work, the effects of various wastewater sources (storm water, sewage effluent, piggery effluent, and dairy effluent) on the reduction, and subsequent mobility and bioavailability of arsenate [As(V)] and chromate [Cr(VI)] were compared using both spiked and field contaminated soils. Wastewater addition to soil can increase the supply of carbon, nutrients, and stimulation of microorganisms which are considered to be important factors enhancing the reduction of metal(loid)s including As and Cr. The wastewater-induced mobility and bioavailability of As(V) and Cr(VI) were examined using leaching, earthworm, and soil microbial activity tests. The rate of reduction of As(V) was much less than that of Cr(VI) both in the presence and absence of wastewater addition. Wastewater addition increased the reduction of both As(V) and Cr(VI) compared to the control (Milli-Q water) and the effect was more pronounced in the case of Cr(VI). The leaching experiment indicated that Cr(VI) was more mobile than As(V). Wastewater addition increased the mobility and bioavailability of As(V), but had an opposite effect on Cr(VI). The difference in the mobility and bioavailability of Cr(VI) and As(V) between wastewater sources can be attributed to the difference in their dissolved organic carbon (DOC) content. The DOC provides carbon as an electron donor for the reduction of As(V) and Cr(VI) and also serves as a complexing agent thereby impacting their mobility and bioavailability. The DOC-induced reduction increased both the mobility and bioavailability of As, but it caused an opposite effect in the case of Cr.

Leachate plume delineation and lithologic profiling using surface resistivity in an open municipal solid waste dumpsite, Sri Lanka

This study presents the use of direct current resistivity techniques (DCRT) for investigation and characterization of leachate-contaminated subsurface environment of an open solid waste dumpsite at Kandy, Sri Lanka. The particular dumpsite has no liner and hence the leachate flows directly to the nearby river via subsurface and surface channels. For the identification of possible subsurface flow paths and the direction of the leachate, DCRT (two-dimensional, three-dimensional and vertical electrical sounding) have been applied. In addition, the physico-chemical parameters such as pH, electrical conductivity (EC), alkalinity, hardness, chloride, chemical oxygen demand (COD) and total organic carbon (TOC) of leachate collected from different points of the solid waste dumping area and leachate drainage channel were analysed. Resistivity data confirmed that the leachate flow is confined to the near surface and no separate plume is observed in the downstream area, which may be due to the contamination distribution in the shallow overburden thickness. The stratigraphy with leachate pockets and leachate plume movements was well demarcated inside the dumpsite via low resistivity zones (1–3 Ωm). The recorded EC, alkalinity, hardness and chloride contents in leachate were averaged as 14.13 mS cm−1, 3236, 2241 and 320 mg L−1, respectively, which confirmed the possible causes for low resistivity values. This study confirms that DCRT can be effectively utilized to assess the subsurface characteristics of the open dumpsites to decide on corridor placement and depth of permeable reactive barriers to reduce the groundwater contamination. GRAPHICAL ABSTRACT

The potential value of biochar in the mitigation of gaseous emission of nitrogen

Nitrogen (N) losses through gaseous emission of ammonia (NH3) and nitrous oxide (N2O) can contribute to both economic loss and environmental degradation. This study examined the effect of biochar and a chemical nitrification inhibitor, dicyandiamide (DCD), on N transformation and N losses via gaseous emission of NH3 and N2O from agricultural soils treated with a range of organic and inorganic N sources. The addition of DCD reduced N2O emission from both organic and inorganic N sources treated soils by 75%, but increased ammonium (NH4+) concentration and subsequently induced high NH3 emission from the soils. In contrast, the addition of biochar reduced both N2O and NH3 emissions from organic and inorganic N sources treated soils by 23% and 43%, respectively. The effectiveness of biochar and DCD in reducing NH3 volatilization and N2O emission depends on the nature of the N sources and their initial mineral N concentration. The study demonstrated that biochar can be used to mitigate N losses resulting from NH3 volatilization and N2O emission.

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.

Trace element dynamics of biosolids-derived microbeads

This study focused on quantifying and characterising microbeads in biosolids (i.e., treated sewage sludge), and in examining interactions of microbeads with trace elements when biosolids are added to soil. Under laboratory conditions, batch experiments were conducted to investigate the adsorption of Cu onto pure and surface modified microbeads suspended in soil. The ecotoxicity of microbead-metal complexes to soil microbial activities was also investigated by monitoring basal respiration and dehydrogenase activity. Concentrations of the microbeads were 352, 146, 324, and 174 particles kg-1 biosolids for ≤50, 50-100, 100-250, 250-1000 μm size fractions, respectively. The Scanning Electron Microscope (SEM) images illustrated wrinkled and fractured surfaces due to degradation. The adsorption of dissolved organic matter onto microbeads was confirmed through FT-IR microscopy, while using Inductively Coupled Plasma Mass Spectrometer (ICP-MS) the presence of trace metals including Cd (2.34 ng g-1), Cu (180.64 ng g-1), Ni (12.69 ng g-1), Pb (1.17 ng g-1), Sb (14.43 ng g-1), and Zn (178.03 ng g-1) was revealed. Surface modified microbeads were capable of adsorbing Cu compared to the pure microbeads, which may be attributed to the complexation of Cu with dissolved organic matter associated with the microbeads in the matrix. It was further revealed that the biosolids derived microbead-metal complexes decreased soil respiration (up to ∼ 26%) and dehydrogenase activity (up to ∼ 39%). Hence, microbeads reaching biosolids during wastewater treatment are likely to serve as a vector for trace element contamination, transportation, and toxicity when biosolids are applied to soil.

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.

Isolation, purification and analysis of dissolved organic carbon from Gohagoda uncontrolled open dumpsite leachate, Sri Lanka

ABSTRACT Extract and analysis of the Dissolved Organic Carbon (DOC) fractions were analyzed from the leachate of an uncontrolled dumpsite at Gohagoda, Sri Lanka. DOC fractions, humic acid (HA), fulvic acid (FA) and the hydrophilic (Hyd) fractions were isolated and purified with the resin techniques. Spectroscopic techniques and elemental analysis were performed to characterize DOCs. Maximum TOC and DOC values recorded were 56,955 and 28,493 mg/L, respectively. Based on the total amount of DOC fractionation, Hyd dominated accounting for ∼60%, and HA and FA constituted ∼22% and ∼17%, respectively, exhibiting the mature phase of the dumpsite. The elemental analysis of DOCs revealed carbon variation following HA > FA > Hyd, while hydrogen and nitrogen were similar in each fraction. The N/C ratio for HA was recorded as 0.18, following a similar trend in old dumpsite leachate elsewhere. The O/C ratios for HA and FA were recorded higher as much as 1.0 and 9.3, respectively, indicating high degree of carbon mineralization in the leachates. High content of carboxylic, phenolic and lactone groups in all DOCs was observed disclosing their potential for toxic substances transportation. The results strongly suggest the risk associated with DOCs in dumpsite leachate to the aquatic and terrestrial environment. GRAPHICAL ABSTRACT

Application of Biochar Produced From Biowaste Materials for Environmental Protection and Sustainable Agriculture Production

Abstract Biochar has created a lot of interest because of its unique properties of sustainable agricultural production and environmental protection. Biochar is known to reduce nitrogen loss from soil in terms of nitrous oxide emission and ammonia volatilization, improve the nutrient retention capacity and structural and chemical properties of soil, and increase plant growth and productivity. Biowaste materials such as biosolids, municipal waste, and paper mill sludge are effective raw materials for biochar production. These materials are rich in nutrient content, and biochar produced using these waste products is highly effective for agricultural production and environmental remediation.