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Piotr Krawczyk

Abstract

Controlling low-temperature drying facilities which utilise nonprepared air is quite difficult, due to very large variability of ventilation air parameters - both in daily and seasonal cycles. The paper defines the concept of cumulative drying potential of ventilation air and presents experimental evidence that there is a relation between this parameter and condition of the dried matter (sewage sludge). Knowledge on current dry mass content in the dried matter (sewage sludge) provides new possibilities for controlling such systems. Experimental data analysed in the paper was collected in early 2012 during operation of a test solar drying facility in a sewage treatment plant in Błonie near Warsaw, Poland.

Open access

Piotr Krawczyk and Krzysztof Badyda

Two-dimensional CFD modeling of the heat and mass transfer process during sewage sludge drying in a solar dryer

The paper presents key assumptions of the mathematical model which describes heat and mass transfer phenomena in a solar sewage drying process, as well as techniques used for solving this model with the Fluent computational fluid dynamics (CFD) software. Special attention was paid to implementation of boundary conditions on the sludge surface, which is a physical boundary between the gaseous phase - air, and solid phase - dried matter. Those conditions allow to model heat and mass transfer between the media during first and second drying stages. Selection of the computational geometry is also discussed - it is a fragment of the entire drying facility. Selected modelling results are presented in the final part of the paper.

Open access

Sebastian Werle

Abstract

The Sewage Sludge Directive 86/278/EEC was adopted about 30 years ago with a view to encourage sewage sludge reuse in agriculture and to regulate its use. Meanwhile, some EU Member States have adopted stricter standards and management practices than those specified in the Directive. In particular, the majority of Member States has introduced more stringent standards for sludge quality, including stricter limits for most potentially toxic elements, organic contaminants and other elements. In general, untreated sludge is no longer applied and in several Member States it is prohibited. In some cases, stringent standards have resulted in an effective ban on use of sludge in agriculture. Moreover, the implementation of the Urban Wastewater Treatment Directive 91/271/EC should increase EU production of sewage sludge, thus enhancing problems related to sustainable sewage sludge management. Additionally, European legislation prohibits the landfill and water deposits of sewage sludge. The latest trends in the field of sludge management, ie combustion, pyrolysis, gasification and co-combustion, have generated significant scientific interest. This trend is specially strong visible in “new” EU Members countries which have to introduce strong EU Directive in their low system. Here the review the state of knowledge and technology in thermal methods for the utilization of municipal sewage sludge to obtain useful forms of energy such as pyrolysis, gasification, combustion, and co-combustion taking into consideration Poland situation is presented.