Thermal Treatment of Municipal Sewage Sludge Aiming at Marketable P-Fertilisers

Abstract

Municipal sewage sludge is a carrier of nutrients -most important phosphorus (P) -but also contains organic pollutants and heavy metals. A two steps thermal treatment is suggested based on 1. mono-incineration of sewage sludge under destruction of organic pollutants and 2. thermochemical treatment of the resulting ashes to remove heavy metals and increase P-bioavailability. The targeted products are marketable Pfertilisers. The thermochemical treatment was investigated in a gas tight lab-scale rotary furnace. Seven sewage sludge ashes of different origin and composition and one residue from gasification of sewage sludge were mixed with a chlorine donor (e.g. MgCl 2 ) and thermochemically treated under systematic variation of operational parameters. The distributions of the heavy metals between solid and gas phase were determined. The heavy metals concentrations of the treated ashes met the legislative limits in most cases. The products from thermochemical treatment are suited raw materials for P-fertiliser production. Relevant process parameters such as temperature, type and concentration of Cldonor and retention time were optimised for the thermochemical treatment step.

Electrokinetic phosphorus recovery from packed beds of sewage sludge ash: yield and energy demand

“…The high phosphorus level mirrors the P-load of the waste water and its concentration in the SSA by water purification and incineration. The P-content of 48 g kg -1 agrees with published values [4,7,8]. According to powder XRD analyses amorphous matter accounts for approximately 40 wt% of the SSA.…”

“…During incineration, phosphorus (P) is enriched in the sewage sludge ash (SSA) yielding P-contents of up to 9% [7,8]. In recent years efforts have been made to recover high quality phosphate from SSA [9].…”

Comparison of two different electrodialytic cells for separation of phosphorus and heavy metals from sewage sludge ash

“…Secondary sources, such as municipal wastewater sludge, generally contain both organic and inorganic contaminants, limiting its direct application in agriculture. While many organic contaminants can be removed through biological (Parkin and Owen, 1986) or thermal treatment (Adam et al, 2007), inorganic contaminants remain generally in the ash (ICON, 2001). Furthermore, addition of iron-or aluminum salts during wastewater treatment, inducing the formation of insoluble phosphate complexes, results in a lower P fertilization value of both the sludge (Krogstad et al, 2005) and, upon incineration, the sewage sludge ash (SSA) (Franz, 2008).…”

Citric acid facilitated thermal treatment: An innovative method for the remediation of mercury contaminated soil

“…In thermochemical removal of heavy metals (Cu, Zn, Pb, Cd) from sewage sludge ash, MgCl 2 , CaCl 2 and gaseous HCl are often used as chloride donors [35][36][37][38][39], the removal mechanism involves forming volatile heavy metal chlorides. In this study, the chloride concentration was 17.4 mg/kg in untreated soil, the corresponding molar ratio of chloride to mercury in soil was 0.73:1.…”