Metal fractionation in sludge from sewage UASB treatment

Abstract

This study evaluates the trace metal composition and fractionation in sludge samples from anaerobic sewage treatment plants from six cities in Brazil. Ten metals were evaluated: Ni, Mn, Se, Co, Fe, Zn, K, Cu, Pb and Cr. Specific methanogenic activity of the sludge was also evaluated using acetic acid as the substrate. Among the essential trace metals for anaerobic digestion, Se, Zn, Ni and Fe were found at a high percentage in the organic matter/sulfide fraction in all sludge samples analyzed. These metals are less available for microorganisms than other metals, i.e., Co and K, which were present in significant amounts in the exchangeable and carbonate fractions. Cu is not typically reported as an essential metal but as a possible inhibitor. One of the samples showed a total Cu concentration close to the maximal amount allowed for reuse as fertilizer. Among the non-essential trace metals, Pb was present in all sludge samples at similar low concentrations and was primarily present in the residual fraction, demonstrating very low availability. Cr was found at low concentrations in all sludge samples, except for the sludge from STP5; interestingly, this sludge presented the lowest specific methanogenic activity, indicating possible Cr toxicity.

Assessment of the DGT technique in digestate to fraction twelve trace elements

“…Few studies [2][3][4] attempted to fractionate trace elements in digested sewage sludge by chemical 38 sequential extraction procedures to determine the degree of leachability of different trace 39 elements' species. Zhu et al [4] underlined that sequential extraction methods could be used for 40 environmental risk assessment of digestate as a soil fertilizer.…”

“…At the beginning and at the end of each experiment, an aliquot of digested sewage sludge was 178 sampled to measure the total and dissolved elements' content. About 5 g of raw sample (total 179 content) or 2 mL of supernatant (dissolved content), recovered after centrifugation at 3.000 g for 180 20 min, were digested with 6 mL of 69% HNO 3 Moreover, quality controls at 5 and 10 µg/L were added to check the performance of the analysis. 187…”

A simultaneous assessment of organic matter and trace elements bio-accessibility in substrate and digestate from an anaerobic digestion plant

“…Due to a complex network of reactions, controlling the chemical speciation of TE, a small fraction of TE in the digesters environment is often available for microbial activities, while the majority of TE occur as precipitates, adsorbed or complexed species (Aquino and Stuckey, 2007;Maharaj et al, 2019Maharaj et al, , 2018. Several studies attempted to determine the fraction of TE available for uptake by microorganisms with sequential extraction procedures, such as the modified Tessier method (van Hullebusch et al, 2005) and the Community Bureau of Reference (BCR) method (Rauret et al, 1991) to guarantee an adequate supply of TE in digesters (Braga et al, 2017;Cao et al, 2018;Ortner et al, 2014). The procedure involves sequential treatment of the samples by chemical reagents such as neutral salts, weak and strong acids or reducing and oxidizing agents to selectively extract TE.…”

“…Moreover, sequential extraction methods are useful tools to assess mobility, accessibility, and potential bio-availability of TE (Harmsen, 2007). Braga et al (2017) observed that micronutrient TE, including Se, Zn, Ni and Fe were mainly found in the organic matter (OM)/sulfide fraction of the modified Tessier method applied on sewage sludge samples. Similar results were also found by Zufiaurre et al (1998) in sewage sludge samples.…”

Avaliação da presença de elementos potencialmente tóxicos decorrentes da produção informal e domiciliar de joias e bijuterias na rede de esgoto sanitário de Limeira-SP

“…Este produto secundário do tratamento pode estar contaminado por EPTs o que gera uma preocupação sobre a sua disposição final (Ahluwalia e Goyal, 2007;Yang et al, 2017). Os principais elementos encontrados no lodo de estações de tratamento de esgotos em regiões industrializadas do mundo são: o cádmio, chumbo, cobre, níquel e zinco (Chen et al, 2008;Shamuyarira e Gumbo, 2014;Braga et al, 2017;Östman et al, 2017;Yang et al, 2017 (Cai et al, 2007;Yang et al, 2017). O lodo de esgoto pode ser usado para recuperação energética, como fonte de extração de compostos, como por exemplo, a recuperação de fósforo ou pode ser tratado e usado em terra como fertilizante e condicionador de solo (Fijalkowski et al, 2017).…”