Removal of Organic Micro-Pollutants from Water Using Sewage Sludge Based Composite Adsorbents
Millions of tons of sewage sludge, waste oil sludge and fish waste are produced annually, and improper treatment/disposal of these wastes have resulted in numerous environmental issues. On the other hand, these wastes are rich in organic materials, metals, and inorganic minerals and could be sustainable resources if utilized properly. The main purpose of this dissertation study was, therefore, to convert these wastes into composite adsorbents, and then use these adsorbents to remove various types of organic pollutants, emerging organic contaminants in particular, from wastewater and drinking water sources. It is hypothesized that a hydrophobic carbon phase in the composite material would promote the physical adsorption of non-polar organic compounds, and an increase in the pores similar to the sizes of the non-polar adsorbates would further enhance physical adsorption on the carbon phase. It is further hypothesized that a polar mineral phase in the composite material would promote the chemical adsorption of polar organic compounds via specific interactions between the polar surface and functional groups of the adsorbates, and further diversifying the surface chemistry (e.g., introducing more elements especially catalytic metals to the mineral phase) would further enhance chemical adsorption of the polar compounds. To increase carbon content and diversify surface chemistry of the sewage sludge derived composite materials, two types of wastes were added to sewage sludge: 1) waste oil from a shipyard that is rich in organic carbon and metals, and 2) fish waste from a local food market that is rich in organic content as well as P and other elements. Different pyrolysis temperatures and acid wash procedures were employed in an effort to increase material surface area and porosity. The performances of these different composite materials for the adsorption of various types of organic contaminants were then evaluated, under batch, column, and in some cases field conditions. The metal leaching behavior of the sewage sludge/fish waste derived composite materials was thoroughly investigated to assure that these adsorbents would not yield secondary contamination when applied in water treatment. The impact of natural organic matter (NOM) on the analysis of selected organic contaminants (pharmaceutical compounds) via liquid chromatography-tandem mass spectrometry (LC/MS/MS) was also examined to make sure that such impact would not significantly alter the quality of the data collected. Adding waste oil or fish waste not only increased the C content by a few percent by weight in the hydrophobic carbon phase of the composite materials but also increased the content of some other elements such as Mg and P in the mineral phase. Increasing the pyrolysis temperature from 650 °C to 950 °C increased the surface area and total pore volume by as much as 100%, due to the decomposition of thermally unstable contents at high temperatures. Wash the sludge/fish waste derived composite materials with dilute acetic acid almost doubled the pore volume and surface area, due to the dissolution of some basic oxides such as CaO and also the removal of some tarry residues which may block the accesses to pores. When the performance of the sewage sludge/waste oil sludge derived composite materials was evaluated for antibiotic removal, it was found that these materials have maximum adsorption capacities ranging from 80 to 300 mg/g, comparable to activated carbons. A large volume of pores similar in size to the adsorbate molecules within the hydrophobic carbon phase was indicated as an important factor promoting the separation process. Moreover, the polar surface of an inorganic phase in the adsorbents attracted the functional groups of target molecules. The presence of reactive alkali metals promoted reaction with acidic groups, formation of salts and their precipitation in the pore system. When the adsorptive removal of 8 pharmaceuticals and endocrine disrupting compounds (EDCs) with the sewage sludge/fish waste based adsorbents was evaluated, it was found that the materials have the maximum adsorption capacities ranging from 16.9 to 38.6 mg/g, again comparable to activated carbons. Adsorption capacities obtained from rapid small scale column tests were about 50% of those obtained from batch equilibrium tests, demonstrating that the maximum adsorption capacities obtained from batch tests would be very relevant to the design of column experiments or the prediction of performance under rapid flow through conditions. During the field experiment, 14 pharmaceutical compounds were detected in the source water of the Little Falls Water Treatment Plant. The large size columns were able to consistently remove 85-90% of the input pharmaceutical compounds and did not show any degradation of performance after a month of operation (~3500 bed volumes). The sewage sludge/fish waste based adsorbents were also able to remove 6 nitrosamines from water under batch equilibrium and dynamic flow through conditions. The adsorption capacities determined from batch experiments ranged from 4.3 to 17 mg/g, comparable to those of many other materials such as modified zeolite, mesoporous silica, and metal impregnated activated carbons. The strong correlation between the adsorbed amounts and logKow values of the compounds suggests that hydrophobic interaction play a significant role on adsorption on the composite materials. When the metal leaching behavior of the raw and acid washed adsorbents (sewage sludge/fish waste based) was examined, it was found that dilute acetic acid wash significantly reduced metal leaching with only 5 metals exceeded their maximum contaminant levels (MCLs, or drinking water standards). When column leaching tests were conducted, the concentrations of all the 5 metals dropped to below their respective MCLs within 10 bed volumes. Acid wash also neutralized the materials and significantly increased their surface area and pore volumes, resulting in an enhancement on the adsorption of three organic compounds by 2-5 times. This result suggests that the acetic acid washed composite materials could be potentially used in packed filters to treat wastewater or even drinking water without the concern of metal leaching. As to the impact of NOM on the quantitative analysis of pharmaceutical by LC/MS/MS, it was found that NOM interacted with pharmaceuticals differently depending on the physicochemical properties of the analytes. The two anticonvulsants did not experience significant signal changes when mixed with NOM, whereas all 11 antibiotics experienced some signal supersession when mixed with one or more of the NOM. Possible mechanisms leading to the signal suppression include hydrogen bonds and electrostatic interaction between positively charged antibiotic species and negatively charged acidic groups of NOM, and π-interaction between the electron-withdrawing groups bonded to aromatic rings of the analytes and NOM. Overall the signal suppression was moderate (up to 24%), and the impact on quantitation by LC-ESI-MS could be mitigated by using a standard mixed with a typical NOM, at a concentration similar to that in the sample matrix.
Environmental Engineering, Environmental Sciences, sewage sludge, leaching, adsorbent, pyrolysis, NOM, pharmaceuticals
City University of New York - Graduate Center
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