Robert Sidełko

Two composting phases running in different process conditions timing relationship.

This research work pertained to establishment of timing relationship for two sludge composting phases proceeding in different conditions. The first phase was performed in a dynamical reactor and the second - in periodically turned windrows. The research was carried out in three independent repetitions with five test series cycles in each varying in the hot phase timing. The compost windrows ripening phase was monitored for 5 months. The determined physical and chemical indicators (independent variables) made a basis for calculation of compost ripeness indices. To perform the numerical analysis an artificial neural network performing the generalised regression task was used. Using specific values of particular indices, as the ripeness criterion, a t(d)=f(t(p)) model was created, in form of decreasing linear function, interpreting the relationship between time of compost keeping in the reactor and the time of compost windrow ripening. The obtained results suggest that keeping the batch in reactor for a period in excess of 18 days is groundless, therefore, ineffective as it does not shorten significantly the compost ripening phase.

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.

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

ABSTRACT 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 13.1 mg kg−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. HighlightsComposting of sewage sludge was conducted in batch mode.Changes of mercury fractions and organic matter were investigated.The relationship between Hg fractions and these parameters were discussed.

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.

Fractionation of Chromium and Lead in Anaerobic Co-digestion

Anaerobic digestion is a common method of waste treatment various kinds of organic waste. The most commonly used substrates for the co-fermentation process are sewage sludge and organic fraction of municipal waste. The solid residue that is produced by fermentation can be used as an organic fertilizer. Restrictions on the use of fermented organic waste may be the content of heavy metals. Fractionation of heavy metals, based on sequential extraction, allows the assessment of the degree of hazard to the environment at the time of application to the soil of digested sludge. Two anaerobic digestion process cycles were performed, using different sewage sludge and municipal waste organic fraction mixing ratios. In the first cycle M70, the materials used in the bioreactor contained 70% municipal organic waste and 30% sewage sludge. The material used in the second cycle M30 contained 30% municipal organic waste and 70% sewage sludge. The volume of each batch was 50 dm3. The sequential extraction procedure developed by Tessier et al. was used in sludge anaerobic digestion to determine the heavy metal (Cr and Pb) fractionation. The paper presents the results of studies on changes in Cr and Pb concentrations in various fractions during the process of fermentation of substrates. During the process the immobilization of the tested metals was followed, which confirms the low values of mobility factor (Mf). The aim of this work was also to present the dependence of the composition of the mixture of organic waste, which were subjected to methane fermentation, to the distribution of metals in individual fractions. A mixture of organic waste, consisting of 70% organic fraction and 30% sewage sludge, was characterized by lower Mf values for Cr than in a 70% sludge mixture. On the other hand, the higher Mf values for Pb were recorded in waste in which 70% was organic fraction. Both studied elements were mainly found in the form of compounds difficult to access for living organisms, as evidenced by low values of mobility factor.