Changes imposed by pyrolysis, thermal gasification and incineration on composition and phosphorus fertilizer quality of municipal sewage sludge

Abstract

Fertilizer quality of ash and char from incineration, gasification and pyrolysis of a single municipal sewage sludge sample were investigated by comparing composition and phosphorus (P) plant availability. A process for post oxidation of gasification ash and pyrolysis char was developed and the oxidized materials were investigated as well. Sequential extraction with full elemental balances of the extracted pools as well as scanning electron microscopy with energy dispersive X-ray spectroscopy were used to investigate the mechanisms driving the observed differences in composition and P plant availability in a short-term soil incubation study. The compositional changes related mainly to differences in the proximate composition as well as to the release of especially nitrogen, sulfur, cadmium and to some extent, phosphorus (P). The cadmium load per unit of P was reduced with 75-85% in gasification processes and 10-15% in pyrolysis whereas no reduction was observed in incineration processes. The influence on other heavy metals was less pronounced. The plant availability of P in the substrates varied from almost zero to almost 100% of the plant availability of P in the untreated sludge. Post-oxidized slow pyrolysis char was found to be the substrate with the highest P fertilizer value while ash from commercial fluid bed sludge incineration had the lowest P fertilizer quality. The high P fertilizer value in the best substrate is suggested to be a function of several different mechanisms including structural surface changes and improvements in the association of P to especially magnesium, calcium and aluminum.

Experimental Study of Moisture Content Effect on Geotechnical Properties of Solidified Municipal Sludge

“…Municipal sewage sludge is currently a major problem in China's urbanization process, and its improper disposal may result in high levels of environmental pollution [28,29]. Agricultural application, composting, and incineration cannot be widely adopted due to economic or technical reasons, which renders the existing problem of municipal sewage sludge di cult to solve [30,31].…”

Biomass gasification for bioenergy

“…Many other problematic issues may be overcome by fuel design, for example through proper mixing. Recent studies on these issues have indicated many potential benefits related to moisture content, ash melting-related issues and ash/char by-product quality (Skoglund et al, 2016;Thomsen et al, 2016;Thomsen et al, 2017b;Thomsen et al, 2017c).…”

“…Low-temperature circulating fluidized-bed schematic design and ash/char products. Adapted with permission fromThomsen et al (2017c).…”

Use of Penicillium bilaiae to improve phosphorus bioavailability of thermally treated sewage sludge – A potential novel type biofertiliser

“…Thermal conversion of sewage sludge by incineration, gasification or pyrolysis can be used to combine removal of organic contaminants with additional benefits such as high energy output [9,10]. Depending on the thermal conversion method used, a residual ash or biochar product that is free of pathogen contamination, reduced in weight and volume and high in P concentration compared with the raw sludge is obtained [10]. However, the P contained in these products is often poorly available to plants, resulting in rather low uptake efficiency when recycled back to agriculture [11][12][13][14].…”