P.W.W. Kirk

A review of atmospheric polycyclic aromatic hydrocarbons: Sources, fate and behavior

A review has been written to assess the sources, fate and behavior of polycyclic aromatic hydrocarbons (PAH) in the atmosphere. PAH are formed mainly by anthropogenic processes, especially the combustion of organic fuels. PAH concentration in air will reflect the location of source emitters, with high concentrations corresponding with urban and industrial areas. PAH are however ubiquitous contaminants of the environment having been detected in remote areas of the world. This is thought to be due to long term transport in the atmosphere. PAH can also be subjected to chemical and/ or photochemical change whilst resident in the atmosphere prior to their removal by either wet or dry deposition.

Phase distribution and particle size dependency of polycyclic aromatic hydrocarbons in the urban atmosphere

Abstract Distributional characteristics of polycyclic aromatic hydrocarbons in urban air were investigated with respect to gas-particle partitioning and dependency on particle size. The relationship between the gas particle distributions of PAH and ambient temperature was described using the Langmuir adsorption concept, while the particle size dependency was demonstrated based on a Lundgren type mass distribution.

Significance and behaviour of heavy metals in waste water treatment processes II. Sludge treatment and disposal

Abstract The literature concerning the significance and behaviour of heavy metals in sewage sludge treatment and following sludge disposal is reviewed. Particular attention is given to metal form during anaerobic digestion and following sludge disposal to agricultural land and to sea, and the influence of metal form on toxicity. It is evident that anaerobic digestion results in a strong association between sludge particulates and heavy metals due to the formation of inorganic precipitates, organo-metallic interactions and by association with the biomass. Toxic inhibition of anaerobic digestion by metals is concluded to be a direct result of the free metal ion concentration and thus mechanisms designed to reduce metal toxicity are based on artificial modification of heavy metal speciation in the digester. Guidelines and legislation designed to limit the application of sludge to agricultural land and the disposal of sludge to sea are reviewed and discussed. Following the application of sludge to agricultural land significant changes occur in heavy metal speciation, which ultimately determine metal availability to plants and potential contamination of groundwaters. Guidelines for application to land currently take limited account of metal form, although the importance of metal speciation is being recognised. Sludge disposal to sea has received relatively little attention with efforts being directed towards monitoring rather than more fundamental research. However, it is apparent that significant heavy metal solubilisation may occur following sludge discharge to the marine environment. It is concluded that sludge disposal to agricultural land and sea, which are increasingly becoming subject to more stringent international pressures, should take account of the ultimate forms of heavy metals in the receiving environment and that a more unified approach should be adopted in the formulation of standards for all forms of sludge disposal.

Characterisation of metal forms in sewage sludge by chemical extraction and progressive acidification

Sequential chemical extraction, acidification to pH 4, 2 and 0.5, and repetitive CaCl2 (0.05 M) extractions were used to evaluate the forms of Cd, Cu, Ni, Pb and Zn in seven sewage sludges. There was more variation in the fractionation profiles of different metals in the same sludge than of the same metal in different sludges. Speciation in air-dried and liquid forms of sludges differed slightly, but the former gave more reproducible results. The sequential extraction scheme indicated that the predominant fractions of Pb and Zn were extractable in 0.1 M Na4P2O7, corresponding to organic and some insoluble inorganic forms. The largest Cd and Ni fractions were extractable in 0.1 M sodium ethylenediaminetetraacetate (pH 6.5), corresponding to the carbonates. The major forms of Cu were probably the sulphide and organic phases, both extractable in 6 MHNO3. Progressive acidification of liquid sludges mobilised significant quantities of Zn at pH 4, of Cd and Pb at pH 2 and of Ni at all pH values investigated. Copper was relatively immobile throughout. Application of the sequential extraction scheme to the residues obtained following acidification indicated that Cu, Cd and Pb forms were relatively stable, but that Ni and Zn speciation was likely to change with decreasing pH. Repeated CaCl2 extractions resulted in a low degree of metal mobilisation and had little effect on the speciation of the metals remaining in the sludge.

Concentrations of particulate and gaseous polycyclic aromatic hydrocarbons in London air following a reduction in the lead content of petrol in the United Kingdom.

The environmental importance of tropospheric polycyclic aromatic hydrocarbons (PAH) is reviewed. The impact of reducing lead on airborne PAH is indicated and the importance of monitoring both particulate and gaseous-phase PAH is demonstrated. A Brief description of a sampling regime performed from 1985 to 1987 is given. Sampling of 18 PAH was performed and particulate lead concentrations at the kerbside were measured concurrently. Measurements indicate that there is a pronounced seasonality in PAH concentrations and in the distribution of PAH between particulate and gaseous phases. On average, 47% of the PAH measured were in the gaseous phase, indicating the importance of measuring the volatile fraction. The dominance of the common variation of each PAH was also investigated using principal components analysis. An uneven spread of data prior to and following the reduction in lead content, hindered a thorough examination of the effect of this change on PAH concentrations. However, they appeared to indicate only a small change in PAH concentration and this was linked to an increase in aromatic content of the petrol, which was much less than expected.

Environmental aspects of the use of NTA as a detergent builder

Abstract The behaviour, fate and significance of the detergent builder nitrilotriacetic acid (NTA) has been reviewed with particular reference to the removal of NTA during wastewater treatment and the effects of NTA on heavy metal solubility both during treatment and in the receiving environment. It is concluded that NTA removal during secondary biological treatment is subject to considerable variation, both temporal and between works as a result of changes in NTA load, temperature, water hardness and treatment process parameters. As a result of such variability, effluent NTA concentrations may be sufficient to mobilise heavy metals resulting in metal contamination of receiving waters and potable waters, particularly in areas of low effluent dilution and high water re-use. Removal of NTA during primary sedimentation and septic tank treatment is concluded to be predominantly due to adsorption to the sludge solids while removal in anaerobic sludge digestion is subject to operational characteristics of the treatment works. Disposal of NTA contaminated sludge to land may contaminate groundwaters and affect heavy metal speciation, while the disposal of contaminated sludge or sewage to sea may result in toxic algal blooms, in addition to effects on metal speciation.

The behaviour of heavy metals during wastewater treatment. I. Cadmium, chromium and copper.

Abstract Mechanisms of metal removal during sewage treatment are reviewed and the application of these mechanisms to cadmium, chromium and copper removals are discussed. Sampling was performed at Whitlingham sewage treatment works (Anglian Water), Norwich, to assess the removal mechanisms of these metals, with reference to partitioning between particulate and soluble phases. Mass balances were performed as a means of quality control. It was concluded that the metals were primarily associated with suspended solids. However, considerable solubilization of cadmium and copper occurred during activated sludge treatment, possibly due to the addition of anaerobic solids in the overflow from a waste activated sludge consolidation tank. Chromium was not affected in a similar manner, possibly due to a change in its valency state.

The behaviour of nitrilotriacetic acid during the anaerobic digestion of sewage sludge

Abstract In laboratory simulations of the anaerobic sludge digestion process, the impact of the detergent builder nitrilotriacetic acid (NTA) on digester efficiency has been studied. It was concluded that NTA at concentrations up to 30 mg l −1 had no adverse effect on anaerobic digestion. However, analysis of the digested sludge indicated that only 29–45% of the influent NTA was removed during treatment. To differentiate between biological and physical processes of removal, biological activity in the digesters was arrested by the addition of sodium azide. Effluent NTA concentration did not increase indicating that biological activity was not responsible for the removal observed. Batch experiments undertaken to evaluate NTA solubility in digested sludge (containing azide) at two solids concentrations indicated a decrease in soluble NTA with increasing solids concentration. It is concluded that the removal of NTA observed during anaerobic digestion was not biological and in part was the result of adsorption onto the solid phase.

The behaviour of heavy metals during wastewater treatment. III, Mercury and arsenic

Abstract The removal mechanisms of mercury and arsenic during sewage treatment are reviewed and possible biotransformations of mercury are discussed. Sampling was performed at Whitlingham sewage treatment works (Anglian Water), Norwich. Removal mechanisms were assessed with reference to partitioning between particulate and soluble phases. Further sampling and analysis was performed to determine the importance of mercury methylation. It was concluded that mercury behaved differently in the two studies, possibly due to a change in crude sewage speciation and the introduction of a picket fence thickener in the waste activated sludge consolidation tank. In situ methylation of mercury was found, especially in the presence of bacterial solids. Arsenic removals during primary sedimentation were very high, with soluble and particulate removals on a similar level. Paradoxically arsenic removals during activated sludge treatment were extremely low.

Methodological aspects of measuring polycyclic aromatic hydrocarbons in the urban atmosphere

Abstract The environmental importance of atmospheric polycyclic aromatic hydrocarbons (PAH) is briefly discussed. A sampling regime, using filters and Tenax TA adsorbent, is outlined which enables the collection of 18 PAH in air, from both the particulate and gaseous phases. An extraction and clean up process is described, which prepares the sample for reversed phase high performance liquid chromatography (HPLC) by transferring the analyte to acetonitrile. Tests on the overall methodology indicate that the procedure provides a sensitive and accurate method for assessing levels of atmospheric PAH. An examination of the differing sampling efficiency between impaction and filtration was undertaken, which indicated the effect of sampling duration and temperature on sample integrity. Evidence of the impact of other gaseous pollutants on measured PAH concentrations was highlighted by stepwise multiple regression.