Bioleaching of metals from sewage sludge: Microorganisms and growth kinetics

Microbial leaching is one of the advantageous methods of removing heavy metals from sewage sludge, however, the microbiological aspects of this technology have not been studied. This study presents the characterization of the naturally occurring microorganisms, responsible for the metal leaching activity, in 21 different sewage sludges. The results obtained indicate that the bioleaching of metals is carried out by successive growth of less-acidophilic and acidophilic thiobacilli. Several species of less-acidophilic thiobacilli participate in the sludge acidification, but Thiobacillus thioparus is the most important species. In contrast, Thiobacillus thiooxidans seems to be the only species involved in the acidophilic group of thiobacilli. The growth kinetics of the two groups of thiobaciili was followed in five different sewage sludges. After 5 days of incubation in shake flasks, the pH of the sludge was decreased to about 2.0 and this pH decrease solubilized the toxic metals (Cd: 83–90%; Cr: 19–41%; Cu: 69–92%; Mn: 88–99%; Ni: 77–88%; Pb: 10–54%; Zn: 88–97%). The maximum specific growth rate (μ_max) for the less-acidophilic thiobacilli varied between 0.079 and 0.104 h⁻¹ and that for the acidophilic thiobacilli varied between 0.067 and 0.079 h⁻¹.     

Sources of Cd,Cu, Pb and Zn in biowaste

Biowaste, the separately collected organic fraction of municipal solid waste, can be reused for soil conditioning after composting. In this way, environmentally harmful waste management strategies, such as landfilling or incineration, can be reduced. However, frequent application of composts to soil systems may lead to the accumulation of heavy metals in soils, and therefore legal criteria were laid down in a decree to guarantee the safe use of composts. The heavy metal content of biowaste-composts frequently exceeds the legal standards, and thus raises a conflict between two governmental policies: the recycling of solid waste on the one hand, and the protection of natural ecosystems and public health on the other hand. In this study, the heavy metal content (Cd, Cu, Pb and Zn) of biowaste was compared with the natural background content of Cd, Cu, Pb and Zn in the different constituents of biowaste. For this, the physical entities of biowaste were physically fractionated by wet-sieving and subsequent water-elutriation. In this way, organic and inorganic fractions of different particle sizes were obtained and the content of Cd, Cu, Pb and Zn and the organic matter content of the different fractions were determined. On the basis of particle size, density and visual appearance, the particle-size fractions were assigned to various indoor and outdoor origins of the biowaste. It was found that a large amount of biowaste was not organic, but over 50% was made up of soil minerals due to the collection of biowaste constituents from gardens. The heavy metal content of the various fractions in biowaste was compared with the natural background contents of heavy metals in the constituents of biowaste, i.e. food products, plant material, soil organic matter and soil minerals, by collecting literature data. The heavy metal content in the fractionated physical entities of biowaste corresponded with the natural background concentration of its constituents and indicated that biowaste was not contaminated by other sources. However, the natural background content of biowaste constituents will result in heavy metal contents for biowaste-compost that will exceed the legal standards. It is advised that the legal standards for composts should be critically re-examined. The protection of soil systems could be better guaranteed if the input of heavy metals was evaluated for all inputs of fertilisers and soil conditioners, i.e. animal manures, various types of compost and artificial fertilisers.     

The chemistry of heavy metals in digested sewage sludge—II. Heavy metal complexation with soluble organic matter

Characterisitcs of copper-binding, in the soluble fraction of a digested sewage sludge, were determined using ion-selective electrodes. Results showed that ion exchange with protons is a principal component in copper binding and that the soluble organic matter has a cation exchange capacity of 8.86 m-equiv g⁻¹ at pH 6.5. A pH-dependent exchange constant, defined in terms of mole fractions of exchange components, describes the data in the pH range 2–8 and is independent of both pH and the extent of exchange in the range 5.5–8. Supplementary data include acid/base titration curves and simple kinetic measurements. Anion uptake is insignificant in the pH range 2.5–7. A model of the aqueous phase of a sewage sludge, containing soluble organic matter with only copper and protons as competing ions, predicts that at pH 7 over 99% of the copper present will be bound to the soluble organic matter.     

DYNAMICS OF SEDIMENT-ASSOCIATED METALS IN A HIGHLY URBANISED CATCHMENT: BRADFORD, WEST YORKSHIRE

Urban watercourses are potential hazards because of their rapid flow changes, poor water quality and contaminated sediments. This study is a preliminary field investigation into fine sediment-associated metal contamination and its transport dynamics in a highly urbanised catchment in West Yorkshire, UK. Spatial and temporal changes in the concentration of channel-bed sediment-associated metals are investigated, and the fluxes of selected suspended sediment-associated metals, during an extreme high flow event, are determined. Channel-bed sediments were more contaminated at the most heavily urbanised sites. Data suggest that contaminated bed sediments could accumulate and possibly become increasingly contaminated between high-flow events, prior to being flushed from the system. Fluxes of contaminated suspended sediments were very high at the peak of the high flow event. The spatial and temporal dynamics of contaminated fine sediment which were identified in this study could inform planners with regard to future monitoring strategies.     

Land inputs of trace metals, major elements, particulate organic carbon and suspended solids to an industrial coastal bay of the NE Atlantic

Rivers, streams and municipal and industrial effluents flowing into the Ferrol Ria (NW Spain) were analyzed for dissolved and particulate trace elements (Cd, Cu, Pb, Zn), particulate major elements (Al, Fe, Si), particulate organic carbon and nitrogen (POC and PON), and total suspended solids. Trace metal clean techniques were applied. Mean annual fluxes of these components were calculated. Dissolved trace metal concentrations in the major freshwater inputs were found to be within typical values for uncontaminated rivers: Cd: 0.020-0.035 nM; Cu: 11.7-19.2 nM; Pb: 0.40-0.71 nM and Zn: 18-54 nM. Two sources of suspended particulate matter (SPM) were observed: (i) a detrital SPM, which becomes more important at high river discharges, with metal concentrations tending to lithogenic values; (ii) an organic- and metal-rich SPM, which becomes dominant at low discharges. Municipal and industrial effluents in the northern shore, despite of constitute a minor freshwater contribution to the bay, were responsible for more than 50% of total inputs of Cu, Cd, Pb, Zn, POC and PON. The fluxes of trace metals obtained for the Ferrol Ria are in the range of other inhabited world semi-enclosed embayments.     

The Development of Ion Chromatography for Metals Analysis in Saline Waters

Previous attempts to utilize ion chromatography for the analysis of sea water samples have failed through chronic interference by the major ions (na, Mg, Ca) during the preconcentration stage. As part of ongoing research into ion chromatography, a technique has been developed to overcome these interferences, using a two-stage preconcentration step, prior to separation on a cation-exchange column. This has made it possible to detect μg/l quantities of trace metals in samples containing g/l concentrations of sodium, magnesium and calcium. A modified commercially-available ion chromatographic system was used to analyse copper, nickel, zinc, cobalt and manganese in saline waters. Detection limits were typically less than 1 μg/l, with relative standard deviation of less than 10%. Hence this new method has the potential to provide an inexpensive multi-elemental sea water analysis with the minimum of handling. In addition, the simplicity and sensitivity of the technique may make it suitable for unattended use as a remote monitor of metals.     

Heavy metals in seawater: Effects on limpet pedal mucus production

Toxicological modification of molluscan mucus production has largely been ignored. This is probably due to an underestimation of the r le of mucus in molluscan physiology and its energetic cost. This paper reports that laboratory exposure to episodic doses of waterborne copper and zinc serve to reduce pedal mucus production by the common limpet Patella vulgata L. to about 60% of the unstressed rate. The metals are effective in this respect at concentrations as low as 10 μg l⁻¹, which in the case of zinc is below the current U.K. environmental quality standard. All metal doses reduced mucus production to the same level. This suggests a behavioural response of the limpet, limiting activity. The reduction in mucus production has important consequences both for limpet ecology and for the ways in which biological energy allocation and transformation are assessed.     

Adsorption character for removal Cu(II) by magnetic Cu(II) ion imprinted composite adsorbent

A novel magnetic Cu(II) ion imprinted composite adsorbent (Cu(II)-MICA) was synthesized, characterized and applied for the selective removal Cu(II) from aqueous solution in the batch system. The adsorption-desorption and selectivity characteristics were investigated. The maximum adsorption occurred at pH 5-6. The equilibrium time was 6.0h, and a pseudo-second-order model could best describe adsorption kinetics. The adsorption equilibrium data fit Langmuir isotherm equation well with a maximum adsorption capacity of 46.25mg/g and Langmuir adsorption equilibrium constant of 0.0956L/mg at 298K. Thermodynamic parameters analysis predicted an exothermic nature of adsorption and a spontaneous and favourable process that could be mainly governed by physisorption mechanism. The relative selectivity coefficients of Cu(II)-MICA for Cu(II)/Zn(II) and Cu(II)/Ni(II) were 2.31, 2.66 times greater than the magnetic non-imprinted composite adsorbent (MNICA). Results suggested that Cu(II)-MICA was a material of efficient, low-cost, convenient separation under magnetic field and could be reused five times with about 14% regeneration loss.     

Characteristics of industrial and laboratory meat and bone meal ashes and their potential applications

This paper reports the characterization of four meat and bone meal (MBM) ashes obtained from specific incineration (laboratory) and from co-incineration (industrial process). Three out of the four MBM ashes were mainly composed of calcium phosphates (hydroxyapatite and whitlockite). Their compositions (major and trace) were in the range for natural phosphate rocks. Trace element contents, including heavy metals, were below 0.6% and industrial ashes contained much more heavy metals than laboratory ash. The amounts of leached elements were low, especially for laboratory ash. According to the European classification of waste to be landfilled, the laboratory ash can be classified as an inert waste. Two industrial ashes are mostly inert. Only one ash is highly leachable and needs a stabilization treatment to be classified at least in the category of hazardous waste. It seems, from these results, that possibilities other than landfilling could be considered to give economic value to these ashes.