Advanced methods to calculation of pressure drop during aeration in composting process

The objective of our research work was to develop a model that could be used to determine resistance of air flow through a bed of organic material processed in composting operation. The raw material used for testing was organic fraction below 80mm separated from municipal waste. The range of process parameters values treated as independent variables was: for hydraulic load 8.49÷50.96m³·m^-2·h^-1, thickening coefficient 0.69÷0.94 and airflow direction from the bottom upwards and vice versa. The research work lasting 19÷25days was performed in three independent series varying in the bed height. Material humidity was maintained at a constant level of approx. 45%. Analysis of simulation results allowed for selection of MLP/5-9-1 neural network. High quality of such obtained neural network was confirmed by statistical evaluation indicators represented by a coefficient of correlation between the forecast and real values (0.906) and the range of standardized rests of the forecast results (4.082÷5.453).

Method of evaluating the impact of landfill leachate on groundwater quality

Closed municipal and industrial waste landfill sites create potential hazard of ground water pollution. Pollutants that occur in leachate infiltrate to the soil substratum, where they are carried to in underground water. A municipal waste landfill substratum can be used for elimination of pollutants contained in leachates. Model research was performed with the use of a sand bed and artificially prepared leachates. Efficiency of filtration in a bed of defined thickness was assessed based on change of COD value. Results of the model tests have indicated that the mass of pollutants contained in leachate filtered through porous ground layer depends on the mass of supplied pollutants, intensity of supplied leachate, and layer thickness. Increase of the mass of pollutants supplied to a unit area of ground layer causes reduction of the relative value of COD mass. The method of evaluation of quality of water seeping through the aeration layer presented in this paper allows for estimation of the flowing out pollutants mass. Based on the test results obtained, efficiency of purification in the aeration zone can be assessed; likewise, safe thickness of the filtration layer under the landfill site can be designed.

Assessment of mobility and bioavailability of mercury compounds in sewage sludge and composts

Content of heavy metals, including mercury, determines the method of management and disposal of sewage sludge. Excessive concentration of mercury in composts used as organic fertilizer may lead to accumulation of this element in soil and plant material. Fractionation of mercury in sewage sludge and composts provides a better understanding of the extent of mobility and bioavailability of the different mercury species and helps in more informed decision making on the application of sludge for agricultural purposes. The experimental setup comprises the composing process of the sewage sludge containing 13.1mgkg^-1 of the total mercury, performed in static reactors with forced aeration. In order to evaluate the bioavailability of mercury, its fractionation was performed in sewage sludge and composts during the process. An analytical procedure based on four-stage sequential extraction was applied to determine the mercury content in the ion exchange (water soluble and exchangeable Hg), base soluble (Hg bound to humic and fulvic acid), acid soluble (Hg bound to Fe/Mn oxides and carbonates) and oxidizable (Hg bound to organic matter and sulphide) fractions. The results showed that from 50.09% to 64.55% of the total mercury was strongly bound to organo-sulphur and inorganic sulphide; that during composting, increase of concentrations of mercury compounds strongly bound with organic matter and sulphides; and that mercury content in the base soluble and oxidizable fractions was strongly correlated with concentration of dissolved organic carbon in those fractions.

Polychlorinated biphenyl concentration changes in sewage sludge and organic municipal waste mixtures during composting and anaerobic digestion

We determined the changes in polychlorinated biphenyl (PCB) concentrations in a mixture of sewage sludge and the organic fraction of municipal waste during composting and during anaerobic digestion. The processes were carried out on a laboratory scale. The PCBs were analyzed in the waste samples using gas chromatography-mass spectrometry. We evaluated the rates at which the PCB concentrations decreased during composting and during anaerobic digestion and compared the PCB degradation kinetics during these processes. The most important conclusion of this work is that anaerobic digestion is much more effective than composting at removing PCBs from a mixture of sewage sludge and the organic fraction of municipal waste.