Inorganic profiles of chemical phosphorus removal sludge

Abstract

Iron dosing is commonly used to remove phosphorus from wastewater but little is known about how this changes the distribution of iron, phosphorus, calcium, magnesium and trace metals in activated and digested sludge. This research compared the inorganic profiles of sludge from full-scale processes (activated sludge and anaerobic digestion) with and without iron dosing, with the aim of identifying changes in inorganic distribution resulting from iron dosing. Sludge phosphorus and metals were fractionated using sequential chemical extraction. Bioavailable iron was lower in iron-dosed activated sludge, as was bioavailable phosphorus (6·5 g/kg compared with 1·8 g/kg), with most of the iron and phosphorus bound as iron-hydroxy-phosphates. Similar results were found for anaerobically digested sludge after iron dosing; iron and phosphorus in the sludge increased by 4 and 1·35 times, respectively, but bioavailability was decreased. The ratio of chemical oxygen demand to bioavailable phosphorus in the digester was 840 : 1 after iron dosing. By contrast, calcium, magnesium, copper and zinc were increasingly bioavailable in the digester after iron dosing. The reported changes were linked to the iron content of the sludge; hence the level of iron dosing is key to minimising changes in sludge inorganic profiles.

Using polyaluminum chloride and polyacrylamide to control membrane fouling in a cross-flow anaerobic membrane bioreactor

“…Therefore, a modified sequential chemical extraction method was used for the fractionation of phosphorous in flocculant-dosed sludge [23]. Deionized water, acetate buffer (0.1 M), NaOH (1 M), HCl (0.5 M) and Aqua regia were used in sequence to extract phosphorus.…”

“…5a shows the average P fractionation profiles. The fractions recovered by deionized water and acetate buffer were taken as the bioavailable P [23]. The P extracted by NaOH, which was the major proportion of P, was in the form of organic or iron/aluminum-associated P. The HCl plus residual P fraction represented calcium P. The ratio of bioavailable P decreased gradually as the dosage of PAC increased.…”

Chemical speciation of sulfur and metals in biogas reactors – Implications for cobalt and nickel bio-uptake processes

“…Furthermore, inorganic P and S in a substrate contribute to the presence of phosphate and sulfide ligands. For example, the anaerobic digestion of primary and activated sewage sludge, containing a large quantity of P in the form of Fe-phosphate precipitates, results in a high concentration of phosphate in the reactors (Carliell-Marquet et al 2010). An example of a sulfate-rich substrate is stillage, a by-product of bioethanol production, which is associated with extensive biogenic hydrogen sulfide production due to the microbial reduction of sulfate during anaerobic digestion (Gustavsson et al 2011).…”

Significance of Vivianite Precipitation on the Mobility of Iron in Anaerobically Digested Sludge

“…Metcalf & Eddy Inc. (2003) report that the median concentration of iron in wastewater sludge is 17 g/kg Dried Solid (DS), 10 times higher than the median concentration of the second highest heavy metal, zinc, at 1.7 g/kg DS. Moreover, the iron concentration in anaerobic sludge digesters at municipal wastewater treatment works (WWTW) is often increased further by iron dosing for chemical phosphorus removal (CPR) and/or hydrogen sulfide control (Carliell-Marquet et al, 2010;Zhang et al, 2010). The establishment of a phosphorus limit discharge by Urban Wastewater Treatment Directive encouraged the development of CPR in the main WWTW in the UK.…”