Chemical Model for Thermal Treatment of Sewage Sludge

Abstract

Sewage sludge is here studied as a valuable source for processing or energy conversation thanks to its high nutrition and energy content. However, various origins of the wastewater, different water cleaning technologies, and seasonal and regional dependencies lead to the high variability of the sewage sludge properties. In thermal treatment units, that is, incineration, gasification and pyrolysis, sewage sludge serves as feedstock or fuel, hence a proper characterization and a mathematical description of the sewage sludge are required to estimate product streams and to formulate numerical simulations and optimization methods. The presented work introduces a surrogate concept that allows replication of sewage sludge’s ultimate composition, moisture, and ash content. The surrogate approach aims to model the decomposition of any sewage sludge sample, opposite to the established determination of kinetic rates for individual samples. Based on chemical solid surrogate species and corresponding reaction mechanisms, the thermal decomposition path is described. Sewage sludge is represented by a combination of lignocellulosic species, proteins, sugars, lipids, and representative inorganic species. The devolatilization and heterogeneous reactions are formulated such that they can be used together with a detailed gas-phase model, including tar oxidation and emission models for nitrogen and sulfur oxides, recently proposed by the authors. The developed chemical model is applied using a zero-dimensional gasification reactor in order to model weight loss within the thermogravimetric analysis, pyrolysis, gasification and combustion conditions. Weight loss, the composition of product gases, and emission release (nitrogen and sulfur oxides) are captured well by the model. The flexible surrogate approach allows us to represent various sewage sludge samples.

Significance and Challenges of Poultry Litter and Cattle Manure as Sustainable Fuels: A Review

“…In Europe, the most popular bedding materials are straw, wood carvings, or sawdust, but in the USA, the most recommended bedding material is sand, which unquestionably elevates the ash content, as Nam et al reported the ash content of dairy cattle manure with sand bedding to be 48.8 ± 3.1% [78]. High ash content positions animal manure closer to sewage sludge than plant-origin biomass [79][80][81][82].…”

Impact of temperature and residence time on sewage sludge pyrolysis for combined carbon sequestration and energy production

“…For instance, Wang et al [ 35 ] revealed that increasing retention time from 1hr to 2.5hrs resulted in biochar yield decline from 52% to 45%. Moreover, very few mathematical models are proposed to describe sewage sludge pyrolysis process due to complexity and variability of sludge characteristics [ 36 ]. Hence, further research is required to explore the influence of various parameters on sludge pyrolysis before it can be effectively modeled.…”

Environmentally Safe Method for Conditioning and Dewatering Sewage Sludge Using Iron Coagulant, Cellulose and Perlite

“…A frequently used natural reagent is lignocellulosic biomass. The use of lignocellulosic materials is particularly justified due to the calorific value and energetic processing of sludge, such as incineration, gasification, pyrolysis, as feedstock or fuel [26] and carbonisation [27]. Cellulose is also treated as a structure-forming material that reduces sludge compressibility.…”