The demand for phosphorus (P) sources is increasing with the growing world population, while objections to direct agricultural use of waste P sources, such as sewage sludge, are being raised. Therefore, the need arises to employ safe and efficient secondary P fertilizer sources, originating from P-rich wastes. These recycling sources are commonly tested in accordance with the current fertilizer rules, designed originally for conventional apatite-based P fertilizers. The behavior of sewage sludge ash, an inorganic recycling secondary P source, was investigated under soil-like conditions. Standardized soil P tests, including the soil buffering capacity test and the Olsen, the Mehlich3, and water extraction methods, were employed together with standardized fertilizer P-solubility tests by neutral ammonium citrate and 2% citric acid extraction. In addition, total content and the overall soil mobility of selected metallic elements present in sewage sludge ash were investigated. The suitability of standardized soil tests for the evaluation of recycling P sources was shown. An apparent influence of Ca:Al content ratio on sewage sludge ash behavior under different soil-like conditions shows the inadequacy of the current fertilizer test and the necessity to understand soil-like behavior of secondary P sources, when considering these as possible agricultural P bearers (fertilizers).
Sewage sludge incineration in a fluidized bed is considered to be one of the most suitable ways of sewage sludge disposal. This process reduces the volume of the waste and causes the destruction of organic contaminants such as POPs, pharmaceuticals, and other compounds with endocrine-disrupting potential. Oxygen-enriched air combustion and oxy–fuel combustion can increase the combustion efficiency, reduce the amount of flue gas, and make possible CO2 capture more effective. However, the influence of incineration medium composition has not yet been thoroughly investigated in the case of sewage sludge incineration. In this paper, the incineration of sewage sludge in a bubbling fluidized bed reactor was studied at oxygen-enriched air conditions, oxy–fuel conditions, and oxy–fuel conditions with zero and nonzero concentrations of steam, CO, NO, N2O, and SO2 in the inlet combustion medium. Consequently, the effects of various operating parameters on pollutants formation were comprehensively described with emphasis on aforementioned sewage sludge incineration processes. An increase in combustion temperature resulted in an increase in NO x and SO2 emissions and in a decrease in N2O emissions. Increase in inlet oxygen concentration led to a decrease in NO x and N2O emissions. N2O and SO2 emissions were higher in CO2-rich atmosphere (oxy–fuel combustion conditions). The presence of water vapor in the inlet combustion medium resulted mainly in the reduction of NO x emissions. The presence of CO, NO, N2O, and SO2 in the dry inlet combustion medium reduced mainly overall nitrogen-to-NO x conversion, while the effect on SO2 removal efficiency was only marginal.
Prior to sewage sludge application to agricultural soil, the sludge should be treated appropriately to suppress its negative features like content of microorganic pollutants or leaching heavy metals. Pyrolysis has been investigated as one way of producing sewage sludge-derived biochar (solid pyrolysis residue) which is stable and less toxic than sewage sludge. A significant amount of heat must be provided to the pyrolysis process due to its endothermic character. To make the process economically and energy efficient, the necessary heat can be obtained by the combustion of primary pyrolysis products (pyrolysis oil and gas), however in the case of sewage sludge, attention must be paid to the resulting gaseous pollutants due to high nitrogen and sulphur content. Slow pyrolysis of stabilized sewage sludge in inert helium atmosphere was performed at temperatures 400-800°C in order to examine the influence of pyrolysis temperature on the properties of pyrolysis products and sulphur distribution amongst these products. Pyrolysis at higher temperatures resulted in lesser biochar yield and promoted gas yield. At temperatures of 500°C and higher, over 50% of energy bound in the input sewage sludge was transformed to liquid and gas products. Finally, the effect of pyrolysis temperature on sulphur distribution amongst pyrolysis products was only marginal.
With increasing demands for cleaning and purification of water, wastewater treatment plants (WWTP) require their most efficient operation. The operators are thus obliged to constantly review the efficiency of the processing units and technological equipment of WWTPs and seek opportunities for improvements. To increase the efficiency of particular equipment, the important parameters to be used for the intensification must be correctly selected. A common WWTP consists of different types of processing units, where the basic parameters can be changed to achieve the highest efficiency (i.e., maximum output with minimum energy consumption) in the WWTP. However, due to many possible technologies in the wastewater treatment process, the combinations of processing units can be complex. In such cases, the efficiency assessment can be misleading if only basic parameters were accessed. Moreover, single-unit intensification can potentially improve the efficiency of the unit itself but cannot guarantee full process improvement. This can be due to negative causal effects in the downstream due to that unit intensification. This work reviews of key parameters at five selected pieces of WWTP equipment (inlet pump station, airlift pump, primary sedimentation tank, aeration chamber, and mixing of anaerobic digester) to demonstrate the correct selection of all affected parameters for the efficiency assessment. In the context of the whole WWTP process, it is necessary to take into account several other parameters to evaluate the efficiency of the equipment. Finally, a methodology for assessing the significance of the identified parameters is proposed. This methodology is effectively applied and demonstrated in the WWTP case study.
Waste to energy is nowadays in many countries preferred to landfilling. In areas with low population density, small-scale waste to energy plants can help to avoid large collection areas. However, in small scale, flue gas treatment is very expensive and, therefore, has to be for these purposes simplified. One of the possibilities for flue gas treatment simplification is the use of one reactor for removal of multiple pollutants. In an extreme case, it is possible to realise the removal of solid particles, acidic gases, selective catalytic reduction of NOx, and catalytic oxidation of polychlorinated dibenzodioxins and furans. In case of suitable flue gas composition and suitable catalyst, it is possible to lower the operation temperature below 180°C, which could allow the use of activated carbon for mercury capture. However, finding the optimal conditions is a big challenge as they depend on flue gas composition, desired concentrations of pollutants in flue gas after cleaning, and used agents. These conditions can be, therefore, very different according to specific application. To be able to find good compromise conditions, the understanding of the influence of individual operation parameters on all considered processes is necessary. The experimental activity, conducted with real flue gas, was focused on dry sorption of acidic gases with emphasis on the possibility to use simultaneously other cleaning processes. The sorption was realised by sodium bicarbonate and sorbent particles were captured on ceramic filters forming a filter cake containing the sorbent. Different flue gas compositions, temperatures, and sorbent excesses were used. The flue gas composition was measured online and manually taken samples (absorption solutions) were analysed by ion chromatography. Particle size distribution was analysed by laser diffraction. The acquired data was used to assess the limits of simultaneous removal of various pollutants from flue gas in relation to flue gas composition.
The 2 nd International Conference on Technologies & Business Models for Circular Economy (TBMCE) was devoted to presentations of circular economy concepts, technologies and methodologies that contribute to the shift of business entities and society as a whole to a more responsible, circular management of resources. In the framework of TBMCE 2019, we presented the Strategic Research and Innovative Partnership-Network for the Transition to Circular Economy (SRIP-CE) as a platform for establishing a successful long-term public-private partnership. The conference program included panel discussions, plenary and keynote sessions, oral and poster presentations on the following topics: Sustainable energy, Biomass and alternative raw materials, Circular business models, Secondary raw materials and functional materials, ICT in Circular Economy, Processes and technologies. TBMCE 2019 was organized by Faculty of Chemistry and Chemical Engineering, University of Maribor and held in Portorož, Slovenia at the Grand Hotel Bernardin from October 24th to October 25th, 2019. The event was under the patronage of Ministry of Economic Development and Technology.
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