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The byproducts of sewage sludge after wastewater treatment processes contain various contaminants and have arisen attention once they are introduced to natural environment through rainfall or runoff from land/monofill. These contaminants include organic micropollutants (OMPs) such as personal care products, pharmaceuticals and endocrine disrupting chemicals, and trace metals. They have adverse effects on human health and ecosystem. The leachability and bioavaibility of these contaminants depend greatly on the environmental and geotechnical properties of sewage sludge. Lime amendment is a popular approach to treat sewage sludge in New Zealand, and is expected to remove pathogens and enhance the sewage sludge shear strength. This work aims at understanding how lime amendment alters the environmental and geotechnical properties of sewage sludge and affects the fate and leachability of OMPs and trace metals. Parameters of pH, content and properties of dissolved organic matter (DOM) and calcium (Ca) concentration are considered as they are closely correlated with how OMPs and trace metals are distributed in solid and soluble phases. This study investigated sixteen OMPs with diverse physicochemical properties and five toxic trace metals. These 16 OMPs are diclofenac (DCF), erythromycin (ERY), fluoxetine (FLU), gemfibrozil (GFB), naproxen (NPX), sulfamethoxazole (SMX), 4-tert-octylphenol (4-OP), 4-para-nonyphenol (4-NP), 17-α-ethinyl estradiol (EE2), bisphenol A (BPA), estrone (E1), primidone (PMD), triclosan (TCS), carbamazepine (CBZ), progesterone (PGT) and testosterone (TST) and the five trace metals are Cd, Cu, Pb, Zn and Ni. The 16 OMPs represent ionised, variously ionised and non-ionised OMPs based on their acidity constant (pKa) at ambient pH. Extraction of the OMPs in sewage sludge/biosolids was achieved by the techniques of microwave digestion assisted extraction (MAE) combined with solid phase extraction. Liquid chromatography-mass spectrometry and high-performance liquid chromatography were employed to quantify the levels of the selected OMPs. Trace metal concentration in sewage sludge/biosolids were measured with inductively coupled plasma mass spectrometry after acid digestion with MAE. Attenuated total reflection Fourier transformed infrared spectroscopy and excitation and emission matrices combined with parallel factor (PARAFAC) analysis, successfully identified the prevalence of microbial byproducts and protein-like organics containing amide groups, carboxylic groups and polysaccharides in sewage sludge DOM. After lime amendment, the functional groups of DOM shifted from amide (I and II) and polysaccharide groups to carboxylic/carbonated and modified amide groups. DOM constituents were modified to be microbial byproducts and humic substances with higher excitations and emission wavenumbers. Lime amendment influenced OMPs’ leachability depending on their diversely physiochemical properties in biosolids. Specifically, lime addition increased the leachability of BPA, EE2, NPX, PMD, SMX and TCS, but reduced that for 4-OP, CBZ, E1, FLU, GFB and TST, and insignificantly modified the leachability of the other 4 selected OMPs. Increase in pH is of pivotal importance in relation to the effects of lime addition on the OMPs’ leachability, likely through affecting the hydrophobicity (logKow/logD) and speciation (pKa) of the OMPs (e.g. ERY and FLU), as well as hydrophobic interactions between DOM and OMPs (e.g. EE2, NPX, PMD, SMX and TCS) and/or their specific interactions such as hydrogen bonding, π-π interactions or van der Waals interactions. The increase in Ca levels was found to be another factor either increasing the DOM-OMP interaction by cation bridging the OMPs (e.g. BPA) and DOM, or reducing the DOM-OMP interactions by shielding the negative groups of DOM for some OMPs such as CBZ, GFB and TST. The affected leachability of the OMPs in lime-amended biosolids is a combined result from the modifications in physiochemical properties of the OMPs and DOM, as well as elevated pH and Ca levels. Microbial byproducts and protein-like organics, commonly present in biosolids, may have played an important role in interpreting the different leachability of CBZ in biosolids and soil. In addition to that in soluble phase, the fractions of the OMPs remained in solid phase, i.e. extractable fractions, contributed a large portion of their total quantity in sewage sludge. Lime amendment either reduced or increased the leachable and extractable forms of some OMPs. However, lime amendment did not essentially alter the overall fate of the OMPs in biosolids. The influence of lime amendment may be related to irreversible prevention of the microbial degradation of these OMPs, and modifications in the physicochemical properties of the OMPs and organic matters. The formation of CaCO3 is proposed to contribute to such effects, due to the important role of inorganic minerals in the strong binding between biosolids and OMPs. The investigation of five trace metals in biosolids showed that the leachability was significantly enhanced for Ni, but was less affected for Cd, Cu, Pb and Zn with 10% and 20% lime amendment. DOM and Ca, in combination with the speciation/precipitation mechanisms of metals, were involved in affecting metal leachability in the lime-amended biosolids at high pH. Specifically, the leachability of Cd is likely correlated with speciation/precipitation mechanisms due to pH changes in biosolids. DOM components containing carboxylic groups may also affect the leachability of Cd when the DOM content is high enough in lime-amended biosolid matrix. In the case of Cu and Ni, DOM plays an extremely important role in modifying leachability, in addition to the speciation/precipitation of the metals due to elevated pH. In particular, Cu more likely formed complex with DOM containing amide groups, such as protein-like organics, and the interaction was found to largely occur at pH above 8.5. Ni could complex with both amide groups and carboxylic groups contained in DOM over pH 5.5~11.5, which may have been responsible for the pronounced increase in its leachability in lime-amended biosolids at alkaline pH. High overburden pressure (225 kPa) increased leachate production in the first 21 days and after 28 days for lime-amended biosolids and sewage sludge, respectively. Such influences were observed to be much less significant in the late stage of curing. The content of DOM was similarly increased under higher overburden pressure in both sewage sludge and limeamended biosolids, which is likely related to the quantity of leachate production. However, no significant influences from overburden pressure on the fate of OMPs, metals and functional groups and constituents of DOM were observed. This may be related to their physically-based effects on sewage sludge/biosolids properties, as found in this thesis. The addition of 10% and 20% lime affected the OMPs’ fate and metals’ leachability, as well as DOM properties over 21 and 105 days, respectively. The shear strength of biosolids was increased by 79% with 20% lime addition, comparing to 51% of increase for 10% limeamended biosolids. This indicates that the effects on the environmental and geotechnical properties of biosolids are dependent on the amount of lime applied, and helps to determine the appropriate quantity of lime to be added to sewage sludge in wastewater treatment based on the desired duration of the effects. This thesis was therefore to show lime-amended biosolids could be more applicable for disposal in land/monofill, compared to sewage sludge, on the basis of the reduction in availability of the OMPs, modifications in DOM properties and increase in shear strength. However, given the significant increase in the leachability of some OMPs (e.g. variously ionised OMPs) and Ni, lime amendment is not always an appropriate choice to pre-treat sewage sludge, in particular, when sewage sludge/biosolids are used in an environment of high overburden pressures. The findings from this thesis have provided a better understanding of the fate and distribution of OMPs and trace metals in biosolids, and offered guideline information to biosolids industry during biosolids disposal. |
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