Phosphorus speciation in sewage sludge and their ashes after incineration as a function of treatment processes.

Phosphorus (P) is a key component in agricultural fertilizers, but it is also a scarce resource, why its recycling has been thoroughly investigated and one promising resources is sewage sludge. Because of stricter regulations in terms of sludge disposal, thermal treatment (e.g. incineration) has become an attractive option. The incineration process alters the chemical speciation of P in favour to calcium-associated (apatite, apatite phosphorus (AP)) species, which is preferred for P recovery. In order to achieve qualitatively transformation, it is important to identify limiting or promoting factors. This study reports on the impact of iron, aluminium and calcium on the transformation of iron- and aluminium-phosphate (NAIP) to AP species, assessed by studying sludge and ash from 10 municipal wastewater treatment plants in Sweden. The effect of iron and aluminium added in the treatment processes was also evaluated. The obtained results show that high calcium concentration favours formation of AP species in both sludge and ashes, whereas high concentration of iron and aluminium favours formation of NAIP species in the sludge. The transformation from NAIP to AP species is hampered by aluminium, irrespectively of its origin, whereas no such correlations could be seen for iron. Therefore, in order to enable efficient P recovery from sewage sludge ash, the amount of aluminium added in the treatment process, as well as its concentration in influent streams to the treatment plants, must be limited.

Phosphorus speciation in sewage sludge from three municipal wastewater treatment plants in Sweden and their ashes after incineration.

Given the high efficiency in phosphorus removal at municipal wastewater treatment plants (MMWWTP), sewage sludge constitutes a promising resource for phosphorus (P) recovery. Sewage sludge is, however, a complex matrix and its direct use as fertiliser is limited by its content of metals/metalloids and organic pollutants. In order to increase its usability as a potential resource of P, there is a need for increased knowledge on phosphorus speciation in these matrices. The sludge composition is highly influenced by local conditions (i.e. wastewater composition and treatment method), and it is therefore important to study sludge from several MMWWTPs. In this study, three different protocols for sequential extraction were utilised to investigate the chemical speciation of phosphorus in sludge from three different MMWWTP sludges in Sweden, as well as in corresponding ashes following incineration. The results showed that the total amounts of phosphorus ranged from 26 to 32 mg g-1 sludge (dry weight), of which 79-94% was inorganically bound (IP). In the sludge, 21-30% of the IP was associated with calcium (Ca-P), which is the preferred species for fertiliser production. Following incineration, this fraction increased to 54-56%, mainly due to transformation of iron-associated phosphorus (Fe-P), while aluminium-associated species of phosphorus (Al-P) remained unaltered. The results from this study confirm that incineration is a suitable treatment for sewage sludge in terms of potential phosphorus recovery.

Groundwater chemistry affected by trace elements (As, Mo, Ni, U and V) from a burning alum shale waste deposit, Kvarntorp, Sweden.

Worldwide, black shales and shale waste are known to be a potential source of metals to the environment. This project demonstrates ongoing weathering and evaluates leaching processes at a 100-m-high shale waste deposit closed in the 1960s. Some deep parts of the deposit are still burning with temperatures exceeding 500 °C. To demonstrate ongoing weathering and leaching, analyses of groundwater and solid samples of shale and shale waste have been undertaken. Largest impact on groundwater quality was observed downstream the deposit, where elevated temperatures also indicate a direct impact from the burning waste deposit. Groundwater quality is largely controlled by pH and redox conditions (e.g., for arsenic, nickel, molybdenum, uranium and vanadium), and the mixture of different waste materials, including pyrite (acidic leachates) and carbonates (neutralizing and buffering pH). Analyses of shale waste from the deposit confirm the expected pyrite weathering with high concentrations of iron, nickel and uranium in the leachates. No general time trends could be distinguished for the groundwater quality from the monitoring in 2004-2019. This study has shown that black shale waste deposits can have a complex long-term impact on the surrounding environment.

Microbiomes in a manganese oxide producing ecosystem in the Ytterby mine, Sweden: impact on metal mobility.

Microbe-mediated precipitation of Mn-oxides enriched in rare earth elements (REE) and other trace elements was discovered in tunnels leading to the main shaft of the Ytterby mine, Sweden. Defining the spatial distribution of microorganisms and elements in this ecosystem provide a better understanding of specific niches and parameters driving the emergence of these communities and associated mineral precipitates. Along with elemental analyses, high-throughput sequencing of the following four subsystems were conducted: (i) water seeping from a rock fracture into the tunnel, (ii) Mn-oxides and associated biofilm; referred to as the Ytterby Black Substance (YBS) biofilm (iii) biofilm forming bubbles on the Mn-oxides; referred to as the bubble biofilm and (iv) fracture water that has passed through the biofilms. Each subsystem hosts a specific collection of microorganisms. Differentially abundant bacteria in the YBS biofilm were identified within the Rhizobiales (e.g. Pedomicrobium), PLTA13 Gammaproteobacteria, Pirellulaceae, Hyphomonadaceae, Blastocatellia and Nitrospira. These taxa, likely driving the Mn-oxide production, were not detected in the fracture water. This biofilm binds Mn, REE and other trace elements in an efficient, dynamic process, as indicated by substantial depletion of these metals from the fracture water as it passes through the Mn deposit zone. Microbe-mediated oxidation of Mn(II) and formation of Mn(III/IV)-oxides can thus have considerable local environmental impact by removing metals from aquatic environments.

Bubble biofilm: Bacterial colonization of air-air interface.

Microbial mats or biofilms are known to colonize a wide range of substrates in aquatic environments. These dense benthic communities efficiently recycle nutrients and often exhibit high tolerance to environmental stressors, characteristics that enable them to inhabit harsh ecological niches. In some special cases, floating biofilms form at the air-water interface residing on top of a hydrophobic microlayer. Here, we describe biofilms that reside at the air-air interface by forming gas bubbles (bubble biofilms) in the former Ytterby mine, Sweden. The bubbles are built by micrometer thick membrane-like biofilm that holds enough water to sustain microbial activity. Molecular identification shows that the biofilm communities are dominated by the neuston bacterium Nevskia. Gas bubbles contain mostly air with a slightly elevated concentration of carbon dioxide. Biofilm formation and development was monitored in situ using a time-lapse camera over one year, taking one image every second hour. The bubbles were stable over long periods of time (weeks, even months) and gas build-up occurred in pulses as if the bedrock suddenly exhaled. The result was however not a passive inflation of a dying biofilm becoming more fragile with time (as a result of overstretching of the organic material). To the contrary, microbial growth lead to a more robust, hydrophobic bubble biofilm that kept the bubbles inflated for extended periods (several weeks, and in some cases even months).

Conditioning sulfidic mine waste for growth of Agrostis capillaris--impact on solution chemistry.

Contamination of the environment due to mining and mineral processing is an urgent problem worldwide. It is often desirable to establish a grass cover on old mine waste since it significantly decreases the production of leachates. To obtain sustainable growth, it is often necessary to improve several properties of the waste such as water-holding capacity, nutrient status, and toxicity. This can be done by addition of organic materials such as wood residues, e.g., compost. In this study, we focus on the solution chemistry of the leachates when a substrate containing historic sulfidic mine waste mixed with 30 % (volume) bark compost is overgrown by Agrostis capillaris. The pot experiments also included other growth-promoting additives (alkaline material, mycorrhiza, and metabolizable carbon) to examine whether a more sustainable growth could be obtained. Significant changes in the plant growth and in the leachates composition were observed during 8 weeks of growth. It was concluded that in this time span, the growth of A. capillaris did not affect the composition of the leachates from the pots. Instead, the composition of the leachates was determined by interactions between the bark compost and the mine waste. Best growth of A. capillaris was obtained when alkaline material and mycorrhiza or metabolizable carbon was added to the substrate.

Neutralisation of an acidic pit lake by alkaline waste products.

A former open pit where black shale (alum shale) was excavated during 1942-1965 has been water filled since 1966. The water chemistry was dominated by calcium and sulphate and had a pH of 3.2-3.4 until 1997-1998, when pH was gradually increasing. This was due to the intrusion of leachates from alkaline cement waste deposited close to the lake. A stable pH of around 7.5 was obtained after 6-7 years. The chemistry of the pit lake has changed due to the neutralisation. Concentrations of some dissolved metals, notably zinc and nickel, have gone down, as a result of adsorption/co-precipitation on solid phases (most likely iron and aluminium hydroxides), while other metals, notably uranium and molybdenum, are present at elevated levels. Uranium concentration is reaching a minimum of around pH 6.5 and is increasing at higher pH, which may indicate a formation of neutral and anionic uranyl carbonate species at high pH (and total carbonate levels around 1 mM). Weathering of the water-exposed shale is still in progress.

Remediation of heavy metal contaminated soil washing residues with amino polycarboxylic acids.

Removal of Cu, Pb, and Zn by the action of the two biodegradable chelating agents [S,S]-ethylenediaminedisuccinic acid (EDDS) and methylglycinediacetic acid (MGDA), as well as citric acid, was tested. Three soil samples, which had previously been treated by conventional soil washing (water), were utilized in the leaching tests. Experiments were performed in batches (0.3 kg-scale) and with a WTC-mixer system (Water Treatment Construction, 10 kg-scale). EDDS and MGDA were most often equally efficient in removing Cu, Pb, and Zn after 10-60 min. Nonetheless, after 10d, there were occasionally significant differences in extraction efficiencies. Extraction with citric acid was generally less efficient, however equal for Zn (mainly) after 10d. Metal removal was similar in batch and WTC-mixer systems, which indicates that a dynamic mixer system could be used in full-scale. Use of biodegradable amino polycarboxylic acids for metal removal, as a second step after soil washing, would release most remaining metals (Cu, Pb and Zn) from the present soils, however only after long leaching time. Thus, a full-scale procedure, based on enhanced metal leaching by amino polycarboxylic acids from soil of the present kind, would require a pre-leaching step lasting several days in order to be efficient.

Laboratory and pilot scale soil washing of PAH and arsenic from a wood preservation site: changes in concentration and toxicity.

Soil washing of a soil with a mixture of both polycyclic aromatic hydrocarbons (PAH) and As was evaluated in laboratory and pilot scale, utilizing both single and mixtures of different additives. The highest level of decontamination was achieved with a combination of 0.213 M of the chelating agent MGDA and 3.2 x CMC* of a non-ionic, alkyl glucoside surfactant at pH 12 (Ca(OH)(2)). This combination managed to reach Swedish threshold values within 1 0 min of treatment when performed at elevated temperature (50 degrees C), with initial contaminant concentrations of As=105+/-4 mg/kg and US-EPA PAH(16)=46.0+/-2.3mg/kg. The main mechanisms behind the removal were the pH effect for As and a combination of SOM ionization as a result of high pH and micellar solubilization for PAHs. Implementation of the laboratory results utilizing a pilot scale equipment did not improve the performance, which may be due to the shorter contact time between the washing solution and the particles, or changes in physical characteristics of the leaching solution due to the elevated pressure utilized. The ecotoxicological evaluation, Microtox, demonstrated that all soil washing treatments increased the toxicity of soil leachates, possibly due to increased availability of contaminants and toxicity of soil washing solutions to the test organism.

Leaching of mercury-containing cement monoliths aged for one year.

A directive from the Swedish Government states that waste containing more than 1% of mercury shall be permanently deposited. The stabilization of mercury by conversion to a sparingly soluble compound like the sulphide is crucial to ensure long-term immobilization in a permanent storage. Immobilization by the solidification/stabilization (S/S) method and possible formation of HgS from mercury oxide or elemental mercury by reaction with a sulphur source (S or FeS) is investigated by a modified version of the NEN 7345 Dutch tank-leaching test. The diffusion of mercury during 11 months from 1-year-old mercury containing monoliths of Portland and slag cement is demonstrated. In a geologic repository under conditions representative of deep granitic bedrock (bicarbonate buffered to pH 8.6), a favourable monolith combination is slag cement with addition of the iron sulphide troilite. The apparent diffusion coefficient of mercury is estimated.

Diffusion tests of mercury through concrete, bentonite-enhanced sand and sand.

The transport by diffusion of Hg(II) and Hg(0) through a barrier of concrete or bentonite-enhanced sand was examined under aerobic conditions. Sand was used as a reference system parallel to the two systems. Speciation of mercury was performed with a purge and trap method, where dissolved Hg(0) was purged with nitrogen gas from the sample, through a trap for volatile oxidized mercury species and finally trapped in an oxidative solution. The apparent diffusion coefficient (from Fick's second law of diffusion) for oxidized mercury was 1 x 10(-14)m(2)/s in Standard Portland concrete and 4 x 10(-13)m(2)/s in quartz sand. The diffusion of Hg(0) seemed to be faster than for Hg(II), Hg(0) was however oxidized to Hg(II) under aerobic conditions, and after 45 months only 1-10% of the total mercury concentration was Hg(0).

Formation of cinnabar--estimation of favourable conditions in a proposed Swedish repository.

A deep repository for permanent storage of mercury will be designed and built in Sweden. The preferred chemical state for mercury in such a repository would be the sulphide HgS (cinnabar), which is a highly insoluble and the dominating natural mercury mineral. The possible formation of HgS from HgO or Hg(0) by reaction with a sulphur source (S, FeS or FeS(2)) is discussed from thermodynamic considerations, and pe-pH-diagrams are constructed by using the computer code MEDUSA to illustrate under which conditions HgS would dominate. Calculations of the speciation (PHREEQE) under varying conditions (S/Hg-ratios, presence of chloride) are given. Long-term laboratory experiments are performed, where the formation of HgS from the basic components is demonstrated (after mixing under various conditions and storage at room temperature for up to 3 years). The feasibility of HgS-formation with time in a geologic repository under conditions representative of deep granitic bedrock (calcium-bicarbonate buffered to pH 7-8.5) is discussed, as well as effects of alkaline conditions (concrete environment, pH 10.5-12.5). Formation of soluble polysulphides is not expected as long as the S/Hg mole ratio is within 1-1.3 and pH is below 10.5-11. Concrete should be used with caution. Suitable ballast materials could be introduced that would reduce porewater-pH that otherwise would be above 12.

Metal leachability and anthropogenic signal in roadside soils estimated from sequential extraction and stable lead isotopes.

Several roadside soil samples were collected at two field sites in Sweden. They were analysed for total elemental content (using both ICP-MS and XRF) and stable lead isotopes. Extraction with deicing salt solution and sequential extraction were performed in order to elucidate the potential mobility due to the use of deicing agents. The total concentrations of elements, especially lead, have decreased and lead is presently almost at background concentrations (15-51 ppm for surface samples). However, the isotopic signature indicates that old gasoline lead still is left at the site constructed prior to 1975. The field site constructed in 1992 showed, however, no 206Pb/207Pb ratio below 1.14. Only minor amounts were leached using deicing salt solutions; for lead only 0.29%, on average, was extracted indicating that the mobile fraction already was released. Sequential extraction indicated that lead mainly was associated with reducible (34.4%) and oxidisable (35.4%) fractions. Exchangable and acid soluble fractions contained 20.3% while 10.0% was found in the residual fraction. The salt extraction released, however, very low concentrations indicating that most in fraction 1 is acid soluble (e.g. carbonates). Tungsten was also found at high concentrations indicating a possible impact from studded tires. For tungsten the following composition was obtained: residual (48.0%) > oxidisable (47.6%) > reducible (3.3%) > exchangeable/acid soluble (1.1%). From the isotopic studies it was also suggested that the order for incorporating anthropogenic lead into soils is exchangeable/carbonates > (hydr)oxides > organic matter > residual. The multivariate technique principal component analysis (PCA) seems promising for evaluating large sequential extraction datasets.

Effects of a fulvic acid on the adsorption of mercury and cadmium on goethite.

The effects of an aquatic fulvic acid on the pH-dependent adsorption of Hg(II) and Cd(II) to particulate goethite (alpha-FeOOH) were studied in batch systems. The ionic medium consisted of 0.01 M HClO(4) and the total concentrations of mercury and cadmium were maintained at 10(-8) M with 203Hg and 109Cd as tracers. pH In the systems was varied in the range 3-10 by addition of HClO(4) and NaOH. All commercial chemicals were of analytical grade or better. An aquatic fulvic acid (20 ppm), previously isolated and characterised in detail, was used as a model for humic substances and its adsorption to goethite is included in this study. The adsorption of the fulvic acid (20 ppm) onto goethite decreased slowly from 90% at pH 3-7.5 to 10% at pH 10. In systems without fulvic acid the adsorption of mercury increased in a linear fashion from 10% at pH 3 to 70% at pH 10. In the presence of fulvic acid (20 ppm), the adsorption was almost quantitative in the intermediate pH range (pH 5-7), and exceeded 92% over the entire pH range. Thus, association between mercury and the fulvic acid enhanced adsorption in general although the largest impact was found at low pH. Adsorption of cadmium increased from nearly 0 to almost 100% at approximately pH 6. In the presence of fulvic acid, the adsorption increased below pH 7 and decreased above pH 7. The adsorption isotherm for mercury when the concentration was increased from 10(-8) to 1.8 x 10(-4) M showed a corresponding increase of K(d) (l/g) up to a total concentration at 10(-6) M. At higher mercury concentrations K(d) was lowered. In the presence of fulvic acid the corresponding relationship of K(d) was bi-modal, i.e. high values at low and intermediate concentrations of mercury. This behaviour suggests that in the absence of fulvic acid the adsorption follow the expected behaviour, i.e. adsorption sites with similar affinity for mercury. In the presence of fulvic acid, additional adsorption sites are available by the organic molecule (possibly sulfur groups) when it is associated to the goethite. The adsorption isotherm for cadmium indicates a lowering of K(d) at 10(-4) M. Cadmium had no competitive effect on mercury and vice versa. Zinc, however, affected the adsorption of cadmium but not the adsorption of mercury.

Speciation and transport of heavy metals and macroelements during electroremediation.

Electroremediation makes treatment of contaminated clay soils possible. The external electrical field causes several transport processes and changes in soil chemistry. This study concerns the leachability and transport of calcium, magnesium, copper, zinc, lead, nickel manganese, chromium, and iron during treatment with an electric field of soil from a chlor-alkali factory. As expected, most elements were removed from the acidic part of the soil and accumulated in the zone where pH changed from acidic to alkaline. However, acidic leaching of the soil in this zone did not mobilize the elements. Lead formed both an anionic complex which electromigration transported toward the anode as well as a cationic lead fraction which moved toward the cathode. The anionic complex could be lead sulfate. Lead from both fractions was strongly attached to the soil after treatment. The low availability of metals and macroelements after electrokinetic remediation could make electroremediation, excavation, and deposition of the accumulation zone an alternative for the treatment of contaminated soils.