Environmental risk assessment of heavy metal extractability in a biosludge from the biological wastewater treatment plant of a pulp and paper mill

Abstract

A five-stage sequential extraction procedure was used to fractionate heavy metals (Cd, Cu, Pb, Cr, Zn, Fe, Mn, Ni, Co, As, V and Ba) in a biosludge from the biological wastewater treatment plant of Stora Enso Oyj Veitsiluoto Mills at Kemi, Northern Finland, into the following fractions: (1) water-soluble fraction, (2) exchangeable fraction, (3) easily reduced fraction, (4) oxidizable fraction, and (5) residual fraction. The biosludge investigated in this study is a combination of sludge from the primary and secondary clarifiers at the biological wastewater treatment plant. Extraction stages (2)-(4) follow the protocol proposed by the Measurements and Testing Program (formerly BCR Programme) of the European Commission, which is based on acetic acid extraction (stage 2), hydroxylamine hydrochloride extraction (stage 3), and hydrogen peroxide digestion following the ammonium acetate extraction (stage 4). The residual fraction (stage 5) was based on digestion of the residue from stage 4 in a mixture of HF + HNO3 + HCl. Although metals were extractable in all fractions, the highest concentrations of most of the metals occurred in the residual fraction. From the environmental point of view, it was notable that the total heavy metal concentrations in the biosludge did not exceed the maximal allowable heavy metal concentrations for sewage sludge used in agriculture, set on the basis of environmental protection of soil by European Union Directive 86/278/EEC, and by the Finnish legislation. The Ca (98.6 g kg(-1); dry weight) and Mg (2.2 g kg(-1); dry weight) concentrations in the biosludge were 62 and 11 times higher than the typical values of 1.6 and of 0.2 g kg(-1) (dry weight), respectively, in arable land in Central Finland. The biosludge had a slightly alkaline pH ( approximately 8.30), a high loss-on-ignition value ( approximately 78%) and a liming effect of 10.3% expressed as Ca equivalents (dry weight). This indicates its potential as a soil conditioner and improvement agent, as well as a pH buffer.

Total and extractable heavy metal, phosphorous and sulfur concentrations in slaker grits from the causticizing process of a pulp mill for use as a soil amendment

“…aqueous sodium hydroxide, sodium sulfide, and sodium carbonate) in the slaker. Furthermore, calcium is also the most abundant nutrient in wood (Pöykiö et al, 2005(Pöykiö et al, , 2007. Copper and zinc are trace elements in wood chips, but they can also originate due to corrosion in the recovery process and from process chemicals.…”

“…Extraction studies are often applied in assessing the worst case environmental scenarios in which the individual elements of the sample become soluble and mobile (Lorenzen and Kingston, 1996). This study is part of a major project in which the sequential extraction procedure has been used for assessing the leachability of metals in solid industrial residues and by-products originating from pulp and paper mills (Pöykiö et al, 2005(Pöykiö et al, , 2007.…”

Repeated Annual Paper Mill and Alkaline Residuals Application Affects Soil Metal Fractions

“…This is one of first reports for soils amended with biosolids from paper mill wastewater treatment. Pöykiö et al (2007) found that a major portion of total Zn and Cd (>80%) is associated with the oxides of Fe and Mn and the organic matter in PB, whereas most of Cu is organically bound. Besides, Stietiya and Wang (2011) observed that soil organic matter oxidation and the intensity caused significant changes in the different pools of metals, in particular causing increases in the exchangeable fractions.…”

“…In many cases, fresh land application of municipal biosolids was reported to increase the most available soil fractions for Cd, the fraction bound to Fe‐Mn oxides for Zn, and the fraction bound to organic matter for Cu (Ippolito and Barbarick, 2008; Achiba et al, 2009; Stietiya and Wang, 2011). In a rare attempt to assess the environmental risk associated with biosolids and alkaline residuals generated by pulp and paper mills, Pöykiö et al (2006, 2007) and Nurmesniemi et al (2008) found that metals in these residues are mostly associated with fractions of low extractability. Based on this finding and on the total metal content present, those researchers concluded that these materials pose a low risk for agricultural use.…”

Extractability of heavy metals in cyclone ash

“…Extractants like electrolytes, weak acids, and chelating agents release metals from coordination sites, while strong acids and redox agents are capable of releasing additional quantities of metals as a result of the decomposition of the solid matrix [18]. Validation of the extraction procedure carried out using reference materials is presented in our previous studies [19,20]. The exchangeable fraction (F1), which is extractable with CH 3 COOH, gives an indication of the amount of metals bound on the surface of the particles, as well as of metals that are released as acid-soluble salts such as carbonates.…”