Andreja Žgajnar Gotvajn

Comparison of different physico-chemical methods for the removal of toxicants from landfill leachate.

Our work was focused on investigation of different treatment procedures for the removal of toxic fractions from a landfill leachate, because sometimes the existing treatment in biological sequencing batch reactor (SBR) is not efficient enough, leading to a hazardous environmental impact of the present persistent and toxic compounds. The efficiency of the procedures used was monitored by chemical analyses and two toxicity tests (activated sludge and Vibrio fischeri). The existing SBR (HRT=1.9 days) removed 46-78% of COD and 96-73% of NH(4)(+)-N. Experiments were conducted with three landfill leachate samples expressing significant difference in concentrations of pollutants and with low BOD(5)/COD ratio (0.06/0.01/0.03). The applied methods were air stripping, adsorption to activated carbon and zeolite clinoptilolite and Fenton oxidation. Air stripping at pH 11 was a viable treatment option for the removal of ammonia nitrogen (up to 94%) and reduction of toxicity to microorganisms. In the adsorption experiments in batch system with different concentration of PAC the most effective was the highest addition (50.0gL(-1)) where 63-92% of COD was removed followed by significant reduction in toxicity to V. fischeri. In the column experiments with clinoptilolite 45/93/100% of NH(4)(+)-N as well as 25/32/39% of COD removal was attained. The removal efficiency for metals followed the sequence Cr>Zn>Cd>Ni. The procedure with zeolite was the second most efficient one regarding reduction of toxicity to both organisms. Fenton oxidation at molar ratio Fe(2+):H(2)O(2)=1.0:10.0 assured 70-85% removal of COD but it only slightly reduced the toxicity.

Pretreatment of landfill leachate by chemical oxidation processes

Kinetics and efficiency of Fenton’s and ozonation processes for the pretreatment of two landfill leachates (fresh and mature) resulting from municipal waste disposal were studied. Both samples presented high organic load, high toxicity and low biodegradability. These were the reasons why oxidative treatment was proposed. Fresh and mature leachate showed different behaviors in the oxidation experiments. The final extents of removal were attained in comparable time intervals in both oxidation systems. Maximal removal of organics by the Fenton’s oxidation reached more than 50 % according to COD. Zero or first order kinetics were found the best to describe the organic components (in terms of COD and DOC) removal by the Fenton’s oxidation for both landfill leachates. Higher reaction rate values of the Fenton’s oxidation were achieved with fresh leachate samples. The efficiency of initial organics removal with ozone was about 70 % for mature leachate, while in case of the fresh one only 41 % of COD were removed. The best fits of COD and DOC experimental data from oxidation of fresh and mature leachates were obtained by a combined kinetic model. No significant improvement of the biodegradability of landfill leachates was achieved using these treatment procedures. Regarding toxicity, ozonation showed to be more effective than the Fenton’s oxidation. Advanced oxidation experiments confirmed that the Fenton’s oxidation and ozonation are comparable oxidative treatment techniques for the reduction of organic pollution in the investigated municipal landfill leachates. However, neither of them is effective enough to be used as a pretreatment method followed by biological treatment.

Seasonal variations in municipal landfill leachate quality

Purpose – The aim of this work is to compare quality of leachates from regional municipal landfill in different seasons (dry, snowy/rainy) during a three-year monitoring period due to the fact that quality of landfill leachate can rapidly change under different conditions. Design/methodology/approach – Raw leachates were sampled prior to biological treatment at different periods of the year (November 2007, March 2008, May 2008, March 2009, and January 2010) to detect the changes in their composition due to different physico-chemical conditions at the site (temperature, moisture, etc.). Leachates were physico-chemically characterized and the toxicity of chosen leachates was assessed by a battery of biotests. Findings – Most of the investigated raw leachates exceed Slovenian effluent limits. Samples from March 2008 and March 2009 generally showed higher concentration of measured parameters and also higher toxicity. It has been confirmed that the physico-chemical parameters of leachates usually decrease duri...

Fungal and enzymatic treatment of mature municipal landfill leachate.

The aim of our study was to evaluate biotreatability of mature municipal landfill leachate by using white rot fungus and its extracellular enzymes. Leachates were collected in one active and one closed regional municipal landfill. Both chosen landfills were operating for many years and the leachates generated there were polluted by organic and inorganic compounds. The white rot fungus Dichomitus squalens was able to grow in the mature leachate from the closed landfill and as it utilizes present organic matter as a source of carbon, the results were showing 60% of DOC and COD removal and decreased toxicity to the bacterium Aliivibrio fischeri. On the other hand, growth of the fungus was inhibited in the presence of the leachate from the active landfill. However, when the leachate was introduced to a crude enzyme filtrate containing extracellular ligninolytic enzymes, removal levels of COD and DOC reached 61% and 44%, respectively. Furthermore, the treatment led to detoxification of the leachate to the bacterium Aliivibrio fischeri and to reduction of toxicity (42%) to the plant Sinapis alba. Fungal and enzymatic treatment seems to be a promising biological approach for treatment of mature landfill leachates and their application should be further investigated.

Hydrodynamic cavitation in combination with the ozone, hydrogen peroxide and the UV-based advanced oxidation processes for the removal of natural organic matter from drinking water

Natural organic matter in drinking water is causing concern especially due to the formation of disinfection by-products (DBPs) by chlorine, as these are proven to have adverse health effects on consumers. In this research, humic acid was used as a source of dissolved organic carbon (DOC) in drinking water (up to 3mgL-1). The efficiency of DOC removal was studied by applying O3, H2O2/O3, H2O2/UV and O3/UV advanced oxidation processes (AOPs) alone and combined with hybrid hydrodynamic cavitation (HC), generated by an orifice plate, as this technology recently shows promising potential for the treatment of water, containing recalcitrant organic substances. It was observed that the combined treatment by HC could significantly affect the performance of the applied AOPs, with as little as 3-9 passes through the cavitation generators. For O3 and H2O2 dosages up to 2 and 4mgL-1, respectively, and UV dosage up to 300mJcm-2, HC enhanced DOC removal by 5-15% in all combinations, except for O3/UV AOPs. Overall, the potential benefits of HC for DOC removal were emphasized for low ratio between applied oxidants to DOC and high UV absorbance of the sample. Investigated DBPs formation potentials require special attention for H2O2/UV AOPs and combinations with HC.

Artemia salina acute immobilization test: a possible tool for aquatic ecotoxicity assessment

Despite the fact that the marine crustacean Artemia salina is extensively used in ecotoxicology, there is still a lack of information about its sensitivity to commonly used chemicals. In the presented study, acute toxicity of 18 commonly used chemicals - including organic solvents, industrial chemicals, metals and inorganic compounds - to A. salina was evaluated. A. salina showed a range of sensitivities to tested chemicals. Regarding all of the investigated organics, phenolic compounds expressed the highest toxicity to A. salina. Nitrite and mercury were the most toxic inorganic substances applied in the study. On the other hand, dimethyl sulfoxide, nitrate and ammonium were the least toxic. The possibility to use A. salina for interspecies correlation was assessed by comparison of sensitivities of different organisms (bacteria, fish, crustacean) to organic compounds. Correlation between various species was observed, especially between A. salina and fish. Due to the strong relation between toxicity and the logarithm of the octanol/water partition coefficient logP(OW,) lipophilicity was found to be the main factor influencing toxicity of the chosen organic compounds. No significant correlation between toxicity to A. salina and physico-chemical parameters of metals was observed.

Laboratory simulation of biodegradation of chemicals in surface waters : Closed bottle and respirometric test

Microbial degradation is the most dominant elimination mechanism of organics from the environment. For evaluation of biodegradability of pure chemicals many standardized tests are available, but no standardized procedure for assessment of biodegradability of chemicals in surface water is agreed upon. Rates of in-situ biodegradation are usually estimated in laboratory simulation where environmental factors are reproduced to some extent. The aim of our study was to compare standardised ready biodegradability assessment, test (Closed bottle test) and its modifications employing the basic agreements on test conditions to simulate biodegradation in surface water. Standard test was modified using various natural river waters to simulate the natural environment in a simplified way. The impact of different types and amounts of nutrients and microorganisms on biodegradation was confirmed. The conditions in the recipient should be examined to extrapolate the results from ready biodegradability tests to real surface water.

A case study to optimise and validate the brine shrimp Artemia franciscana immobilisation assay with silver nanoparticles: The role of harmonisation☆

Brine shrimp Artemia sp. has been recognised as an important ecotoxicity and nanotoxicity test model organism for salt-rich aquatic environments, but currently there is still no harmonised testing protocol which would ensure the comparable results for hazard identification. In this paper we aimed to design the harmonised protocol for nanomaterial toxicity testing using Artemia franciscana and present a case study to validate the protocol with silver nanoparticles (AgNPs). We (i) revised the existing nanotoxicity test protocols with Artemia sp. (ii) optimised certain methodological steps based on the experiments with AgNPs and potassium dichromate (K2Cr2O7) as a soluble reference chemical and (iii) tested the optimised protocol in an international inter-laboratory exercise conducted within the EU FP7 NanoValid project. The intra- and inter-laboratory reproducibility of the proposed protocol with a soluble reference chemical K2Cr2O7 was good, which confirms the suitability of this assay for conventional chemicals. However, the variability of AgNPs toxicity results was very high showing again that nanomaterials are inherently challenging for toxicity studies, especially those which toxic effect is linked to shed metal ions. Among the identified sources for this variability were: the hatching conditions, the type of test plate incubation and the illumination regime. The latter induced variations assumingly due to the changes in bioavailable silver species concentrations. Up to our knowledge this is the first inter-laboratory comparison of the Artemia sp. toxicity study involving nanomaterials. Although the inter-laboratory exercise revealed poor repeatability of AgNPs toxicity results, this study provides valuable information regarding the importance of harmonisation of all steps in the test procedure. Also, the presented AgNPs toxicity case study may serve as a platform for further validation steps with other types of NMs.

The impact of humic acid on chromium phytoextraction by aquatic macrophyte Lemna minor.

Studies assessing chromium phytoextration from natural waters rarely consider potential implications of chromium speciation in the presence of ubiquitous humic substances. Therefore, the present study investigated the influence of environmentally relevant concentration of humic acid (TOC = 10 mg L(-1)) on chromium speciation (Cr = 0.15 mg L(-1)) and consequently on phytoextraction by aquatic macrophyte duckweed Lemna minor. In absence of humic acid, only hexavalent chromium was present in water samples and easily taken up by L. minor. Chromium uptake resulted in a significant reduction of growth rate by 22% and decrease of chlorophyll a and chlorophyll b contents by 48% and 43%, respectively. On the other hand, presence of humic acid significantly reduced chromium bioavailability (57% Cr uptake decrease) and consequently it did not cause any measurable effect to duckweed. Such effect was related to abiotic reduction of hexavalent chromium species to trivalent. Hence, findings of our study suggest that presence of humic acid and chromium speciation cannot be neglected during phytoextraction studies.

Application of multiple toxicity tests in monitoring of landfill leachate treatment efficiency

Leachate from a closed landfill used for co-disposal of municipal and tannery waste was submitted to coagulation treatment, air stripping, adsorption on granular activated carbon, and Fenton oxidation with the aim to reduce toxicity of the leachate. Optimal operational conditions for each process were identified. The performance of the treatment was monitored by determination of organic matter (COD, DOC, BOD5), inorganic components (N-NH4+, Cl−, alkalinity, metals), organic compounds (BTEX, PAHs, PCBs, OCPs) while changes in toxicity were followed by multiple toxicity tests. Among the applied treatment techniques, adsorption on granular activated carbon was the most efficient method for removal of organic matter and metals while air stripping was the most efficient for removal of N-NH4+ and reduction of toxicity. Lower reduction of organic matter content and toxicity was obtained during coagulation treatment. Fenton oxidation was effective for removal of COD; however, it negatively affected toxicity reduction. The combination of adsorption on granular activated carbon and air stripping led to an appreciable reduction of organic and inorganic pollutants and to leachate detoxification. Application of bioassays was helpful for assessing suitability of treatment methods and demonstrated that they are, together with physicochemical parameters, an indispensable part for monitoring of treatment efficiency.