Dump
Our company prepares a study on the environmental risks of biogas production at the dump, and on the profitable utilization of the biogas. On the basis of our experiences, the most adequate long-term solution is the combined biogas utilization (electric energy and heat utilization) with the use of gas exploitation wells.
The production of biogas
During the miningbreakdown of waste, percolating water and biogas is produced. The breakdown process has five characteristic phases. (CHRISTIENSEN-KJELDSEN - 1989)
Phase I.: Immediately after the placement of the waste, an aerobic fermentation starts with the presence of micro-organisms. The process is nourished by air trapped by the waste in the lower regions, and in the subsurface regions by the oxygen of the atmosphere. The biogas produced is carbon-dioxide, and the leechate contains ammonium and the oxidation products of the other components. The process is exotherm, the temperature may reach 60-70 oC.
Phase II.: The reduction of oxygen results in anaerobic conditions, and in the dark, oxygen-free environment fungi and fermentation bacteria (lactic acid-, propionic acid-, coli-, butter-acid-, and buthyl bacteria) perform the fermentation-breakdown processes of carbohydrates, proteins and fats. The produced biogas consists of carbon-dioxide and hydrogen, and the nitrogen content decreases significantly. The pH of the leechate decreases (pH= 4-5), and it might contain calcium, iron, heavy metals and ammonium. At the end of the phase, the decreased redox potential reduces the initial high sulphate content, and the produced sulphide excretes in the iron, manganese and heavy metals.
Phase III.: The appearance and spread of methanogenic and sulphate-reducing bacteria start the process detailed in the previous point, and the methane concentration of the biogas increases, while the concentration of hydrogen and carbon-dioxide decreases. The pH of the leechate starts to increase, which results in the excretion of iron, manganese and other heavy metals. The quantity of ammonia produced and absorbed in the leechate is still significant.
Phase IV.: In the so-called methane phase, the methane production process started in the previous phase stabilizes, the methane concentration of the biogas stabilizes at 50-60 v/v %.
Phase V.: By the consummation of the degradable carbohydrates, proteins and fats only the resistant organic carbon remains in the waste. The methane production gradually reduces and because of the atmospheric diffusion nitrogen and oxygen appear in the biogas. The methane gas production ends in the aerobic zones close to the surface.
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Applied methods
Data procurement, revision of documentation
We collect the necessary topographical and geological maps and revise the data related to the territory found in literature and public databases (eg. Geological maps, data of geological drillings in the surrounding areas, wells of the territory or its surroundings, meteorological data), and the results of the previous environmental examinations.
On the spot review
During the visits on the spot we collect further information on the general environmental status of the territory, and we examine the local characteristics for drilling plans and the location of contaminating sources and other factors limiting the excavations.
Drilling, sampling planning and activities
We compile our sampling plan in order to execute the necessary examinations for the update of results and the accurate complementary survey.
During drilling planning we consider the information on activities of the site, our observations of site visits, the flow directions of the soil water, the physical-chemical characteristics of the contaminating materials and the nature of contaminations observed besides the previous examination results. When we appoint the drilling points, we consider the contaminating areas revealed by the results of the potential previous soil- and soil water examinations and the location of buildings and other surface and subsoil facilities and our results as well. During the drilling we continuously monitor the content modifications of the waste, soil and leechate, and take samples for laboratory examinations.
We examine the samples of waste, soil, leechate and biogas in accredited laboratories.
Waste sampling
During the drilling of biogas/leechate monitoring wells we continuously monitor the content modifications of the waste.
Soil water and leechate sampling
We take samples from the temporary soil water sampling points and biogas/leechate monitoring wells, which is anticipated by a thorough clearing pumping during which we continuously measure the pH value, the electric conductivity and temperature of the soil water. The general water chemical parameters, the concentration of toxic metals and the concentration of boron are determined from the soil water and leechate samples.
Biogas sampling
We sample biogas from the biogas/leechate monitoring wells. The sampling is performed from the atmosphere of the closed well, with the help of portable personal sampling gas-pump and vacuum trunks to hermetically closed, special, valve-equipped plastic sac. The gas samples are sent to the laboratory for detailed biogas evaluation (CH4, CO2, O2, N2, H2S gas components).