Influence of Wastewater Treatment and The Method of Sludge Disposal on the Gasification Process

Abstract

Abstract:Municipal wastewater treatment results in the production of large quantities of sewage sludge, which requires proper environmentally accepted management before final disposal. Sewage sludge is a by-product of current wastewater treatment technologies. Sewage sludge disposal depends on the sludge treatment methods used in the wastewater treatment plant (anaerobic or aerobic digestion, drying, etc.). Taking into consideration presented given this information, a study concerning the effects of wastewater treatment processes and sewage sludge drying method on the sewage sludge gasification gas parameters was performed. Gasification is a prospective alternative method of sludge thermal treatment. For the purpose of experimental investigations, a laboratory fixed bed gasifier installation was designed and built. Two types of sewage sludge feedstock, SS1 and SS2, were analyzed. Sewage sludge SS1 came from a wastewater treatment plant operating in the mechanical and biological system while sewage sludge SS2 was collected in a mechanical, biological and chemical wastewater treatment plant with simultaneous phosphorus precipitation. The sludge produced at the plants was subject to fermentation and then, after being dehydrated, dried in a cylindrical drier on shelves heated up to 260ºC (sewage sludge SS1) and using hot air at a temperature of 150ºC in a belt drier (sewage SS2). The analysis shows that the sewage sludge properties strongly depend on the wastewater sources and the wastewater treatment processes. The gasification results, presented as a function of the amount of gasification agent, show that the greater oxygen content of SS1 caused a reduction in the reaction temperature. Paradoxically, this effect caused an increase in the quantity of combustible components in the gas. As expected, increasing the air flow rate caused a decrease in the heating value of the gas produced. A higher amount of oxidizer increases the amounts of noncombustible species and the volumetric fraction of nitrogen, thus reducing the heating value of the obtained gas. The higher hydrogen content in SS1 affects the gasification gas composition. As a result, combustible components are the majority of the syngas.

Temporal variability of sewage sludge heavy metal content from Greek wastewater treatment plants

“…As compared with heavy metal levels reported in literature for sludge collected from various WWTPs, our results (Table 1) are in good agreement with those found for Kavala by other authors [25,33], are comparable with findings for Kalamata [22], Komotini [23] and Crete [21] in Greece, for Spain [18,28,38], Poland [13,27] and Brasil [34,37], and are much lower than the values obtained for Greece at the largest WWTPs of Athens (Psyttalia and Metamorphosi) [33] and Thessaloniki [4], and also for China [35,36] and Thailand [7], probably due to the fact that the WWTPs in this study only receive domestic wastewater, while industrial wastes processed in other stations usually contain higher levels of heavy metals than residential wastes [39].…”

“…Population growth, urbanization, improvement of living conditions, and the increment of the number of inhabitants connected to WWTPs are responsible for the increase of the amount of sewage sludge produced daily (70-90 g of dry sludge/inhabitant equivalent) [10][11][12][13] and the proper disposal of sludge is a serious environmental issue worldwide [3,14]. Generally, the selection of the best disposal route for the sludge from a particular treatment plant requires the identification of the most secure and environmentally acceptable final destination taking into account the local, regional and/or national conditions (technical, economical, political, geographical) [11,15,16].…”

“…Generally, the selection of the best disposal route for the sludge from a particular treatment plant requires the identification of the most secure and environmentally acceptable final destination taking into account the local, regional and/or national conditions (technical, economical, political, geographical) [11,15,16]. Traditional disposal alternatives which have been widely tried include landfilling, soil application, incineration and sea dumping [10][11][12][13][14][17][18][19][20] and currently in Europe the most desirable use of treated sludge is in agriculture as a soil fertilizer [21]. Contrary to the European trends, in Greece sludge utilization in agriculture is very limited [3], the vast majority (> 90%) being landfilled, while the respective mean value in EU countries is only 27% [15,[21][22][23].…”

Metal Oxides in Heterogeneous Oxidation Catalysis: State of the Art and Challenges for a More Sustainable World

“…Catalysis forc lean air,w hich includes automotivee xhaust catalysis, desulfurization, wastewater treatment [51] and removal of volatile compounds (VOCs), is important application of heterogeneous catalysis ( Table 2). In the case of VOCs, such as formaldehyde, which is released from households and responsible for many health risks, noble metals such as Pt or Pd on different supports are appliedi ndustrially.…”

The assessment of sewage sludge gasification by-products toxicity by ecotoxicologial test

“…Sewage Sludge 1 originated from a wastewater treatment plant operated as a mechanical-biological system, and Sewage Sludge 2 originated from a mechanical-biological-chemical wastewater treatment system with simultaneous phosphorus precipitation. Analytical methods used in this analysis have been presented in earlier works (Werle and Dudziak, 2013, 2014b, 2014c. This high drying temperature caused the organic fraction present in the sludge to have a higher tendency to transform into the volatile organic compounds.…”