Abstract
Landfill leachate is characterized by high toxicity and contains significant concentrations of organic and inorganic pollutants. This study evaluates the efficiency of a newly developed biological treatment system for landfill leachate using a combined vermifiltration approach that includes a sand filter, fresh vermicompost, wood charcoal, and contact with live earthworms.
The toxicity of landfill leachate before and after treatment was assessed using a phytotoxicity bioassay with garden cress seeds (Lepidium sativum L.). The results demonstrated that untreated leachate completely inhibited seed germination. In contrast, after treatment with the proposed vermifiltration system, a substantial recovery of seed germination was observed, indicating a significant reduction in toxicity.
The obtained results suggest that vermifiltration-based systems have promising potential for the biological detoxification of landfill leachate.
Introduction
Sewage sludge and landfill leachate represent complex waste streams containing numerous pollutants as well as pathogenic microorganisms. Landfill leachate from municipal solid waste sites contains high concentrations of organic matter, ammonium nitrogen, heavy metals, and various toxic compounds, posing a significant environmental threat.
Traditional treatment technologies for such waste streams are often energy-intensive and costly.
Currently, both in Ukraine and worldwide, alternative environmentally friendly biological treatment approaches are being developed that combine physical, chemical, and biological detoxification mechanisms using vermitechnologies [1–5].
Vermicomposting offers an environmentally safe solution for the management of sewage sludge and organic waste. This process involves the combined action of earthworms and microorganisms to modify and accelerate the decomposition process [6,7].
It should be noted that although such methods are highly promising, the specific composition of certain wastes requires the development of individual experimental approaches when designing vermitechnologies for particular applications.
Another advantage of vermicomposting is that various types of solid wastes, including food residues, agricultural wastes, sewage sludge, and industrial wastes, can serve as raw materials in this process [8–11].
Therefore, phytotoxicity assessment was selected as a key criterion for evaluating the reduction of toxicity in the proposed treatment technology.
The aim of this study was to develop an experimental vermifiltration system for landfill leachate treatment and to evaluate its efficiency using phytotoxicity testing.
Materials and Methods
Landfill leachate from a municipal solid waste disposal site was used as the object of the study. The composition of the waste and its leachate was analyzed. The phytotoxicity of leachate samples was determined using a biotesting method with seeds of garden cress (Lepidium sativum L.), which is widely used as a sensitive test organism for assessing the toxicity of aqueous environments. The assessment was carried out based on seed germination and root length indicators [12].
A multistage experimental treatment system was developed for the study, consisting of the following components performing different functions: mechanical filtration through a sand filter; aeration of the leachate (oxygen saturation); contact with a layer of fresh vermicompost containing active microbiota; filtration through a layer of charcoal for adsorption of organic toxicants; and contact with live earthworms for 2 hours.
Two controls were used to assess changes in toxicity. The first control was untreated landfill leachate, in which no germination of garden cress seeds was observed (0%). After passing through the multistage treatment system, the germination rate reached 70%, indicating a significant reduction in phytotoxicity compared to the untreated leachate. The second control consisted of water enriched with micronutrients, in which 100% seed germination was observed.
Results
Biotesting of the initial leachate revealed high toxicity levels. The use of untreated leachate resulted in complete inhibition of germination of the garden cress test culture, with seed mortality observed at the early stages of the experiment. In contrast, the leachate treated by the biofiltration system showed recovery of germination in 70% of the seeds: 30% germinated within the first 24 hours, and an additional 40% after 60 hours, with normally developed seedlings observed. This indicates a significant reduction in leachate phytotoxicity.
The obtained results can be explained by the combined effect of several treatment mechanisms: mechanical filtration in the sand layer, microbiological degradation of organic compounds by vermicompost microbiota, adsorption of toxic substances by charcoal, and biotransformation of pollutants in the digestive system of earthworms.
The combination of these factors ensures effective reduction of leachate toxicity and requires further detailed investigation.
Conclusions
Landfill leachate from municipal solid waste sites exhibits high phytotoxicity and significantly inhibits plant seed germination.
The application of a combined vermifiltration system significantly reduces leachate toxicity, as demonstrated by phytotoxicity bioassays showing a 70% recovery of seed germination after treatment.
Vermifiltration can therefore be considered a promising environmentally friendly method for the preliminary biological detoxification of landfill leachate.
References
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