Removal of highly polar micropollutants from wastewater by powdered activated carbon

Due to concerns about ecotoxicological effects of pharmaceuticals and other micropollutants released from wastewater treatment plants, activated carbon adsorption is one of the few processes to effectively reduce the concentrations of micropollutants in wastewater. Although aimed mainly at apolar compounds, polar compounds are also simultaneously removed to a certain extent, which has rarely been studied before. In this study, adsorption isotherm and batch kinetic data were collected with two powdered activated carbons (PACs) to assess the removal of the polar pharmaceuticals 5-fluorouracil (5-Fu) and cytarabine (CytR) from ultrapure water and wastewater treatment plant effluent. At pH 7.8, single-solute adsorption isotherm data for the weak acid 5-Fu and the weak base CytR showed that their adsorption capacities were about 1 order of magnitude lower than those of the less polar endocrine disrupting chemicals bisphenol A (BPA) and 17-α-ethinylestradiol (EE2). To remove 90% of the adsorbate from a single-solute solution 14, 18, 70, and 87mg L−1 of HOK Super is required for EE2, BPA, CytR, and 5-Fu, respectively. Effects of solution pH, ionic strength, temperature, and effluent organic matter (EfOM) on 5-Fu and CytR adsorption were evaluated for one PAC. Among the studied factors, the presence of EfOM had the highest effect, due to a strong competition on 5-Fu and CytR adsorption. Adsorption isotherm and kinetic data and their modeling with a homogeneous surface diffusion model showed that removal percentage in the presence of EfOM was independent on the initial concentration of the ionizable compounds 5-Fu and CytR. These results are similar to neutral organic compounds in the presence of natural organic matter. Overall, results showed that PAC doses sufficient to remove >90% of apolar adsorbates were able to remove no more than 50% of the polar adsorbates 5-Fu and CytR and that the contact time is a critical paramete

Field Evaluation of Hardening Methods for Subsurface Utilities and Drainage Pipes

A new field monitoring approach in the form of metallic capsules is developed to evaluate Benzene and PCE diffusion through concrete pipe gaskets. The capsules are developed and tested with three gasket materials: Neoprene, Buna-N, and Viton. To validate the monitoring approach and develop field retrieval protocol, capsules were deployed in three contaminated sites: (i) Nash county maintenance depot in Nashville, NC (gasoline contaminated site), (ii) A maintenance facility yard in Newton, NC (gasoline contaminated site), and (iii) Triangle Laundromat in Durham, NC (chlorinated solvent contaminated site, PCE). The tensile strength of gasket materials, integrated with the deployed field capsules, is evaluated with time. In addition to testing under field conditions, tensile strength testing is also performed under controlled conditions in the laboratory to establish material degradation model. Computational modeling is used to simulate the site conditions of the installed capsules considering test sites\u2019 hydraulic gradient, soil properties and plume concentration and the influence of such parameters on the rate of breakthrough within the installed capsules. The hydraulic parameters of gaskets were calibrated using field measurements and data from a series of experimental studies under controlled condition. Results indicated nonlinear power relationship for the mass breakthrough of benzene and PCE with time. Compared to chlorinated solvent, benzene has higher diffusivity among gasket materials (Neoprene, Buna-N, Viton). Viton showed the highest resistance to the diffusion of benzene and PCE. Viton and Neoprene showed the lowest and highest tensile strength degradation, respectively, once exposed to gasoline or chlorinated solvent contamination. Based on modeling results, benzene concentration breaking through the Neoprene and Buna-N will reach more than 70% and 60% of the monitoring well concentration, respectively, after 4 months. Benzene breakthrough reaches 85% to 90% of monitoring well concentration after 6 months. Results from the experimental and modeling studies are synthesized and a protocol is proposed for installing/retrieval of capsules to monitor PCE and benzene breakthrough rates into pipe materials

Predicting the removal of atrazine by powdered and granular activated carbon

The general objective of this research was to develop and test bench scale procedures for the prediction of atrazine removal in full scale and pilot scale powdered activated carbon (PAC) and granular activated carbon (GAC) adsorption processes.To quantify the competitive effect of background organic matter (BOM) on the adsorption capacity of PAC for atrazine, the equivalent background compound (EBC) method was tested, in which the mixture of competing BOM compounds was represented by one hypothetical equivalent background compound (EBC). Using the Freundlich isotherm equation and the ideal adsorbed solution theory (IAST), a search routine was developed to determine the adsorption characteristics of the EBC. A comparison with experimental data showed that the EBC method successfully described adsorption equilibria of micropollutants over a wide range of initial concentrations. Furthermore, it was discovered that the capacity of activated carbon for a target compound that was present at trace levels in natural water was directly proportional to the initial target compound concentration as confirmed by experimental and mathematical modeling results for atrazine and other micropollutants.The pseudo single-solute homogeneous surface diffusion model (HSDM) was employed to describe the rate of atrazine adsorption on PAC. A combination of the EBC method and the pseudo single-solute HSDM successfully predicted atrazine removal in batch reactors over a large range of initial concentrations. Furthermore, reasonable agreement was obtained between the predicted and measured full scale removal of atrazine.Rapid small-scale column tests (RSSCTs) were judged to be most useful for predicting the initial performance of adsorbers that contained virgin GAC. However, results from the current study showed that RSSCTs could not predict atrazine removal after operating times that exceeded 3.5 to 7 months. Similarly, RSSCTs were not useful to predict the remaining life of GAC adsorbers after long preloading times.To predict the remaining life of operating GAC filters, the pseudo single-solute HSDM, which required the determination of equilibrium and kinetic parameters for preloaded GAC, proved to be the most promising technique.U of I OnlyETDs are only available to UIUC Users without author permissio

Characteristics of competitive adsorption between 2-methylisoborneol and natural organic matter on superfine and conventionally sized powdered activated carbons

When treating water with activated carbon, natural organic matter (NOM) is not only a target for adsorptive removal but also an inhibitory substance that reduces the removal efficiency of trace compounds, such as 2-methylisoborneol (MIB), through adsorption competition. Recently, superfine (submicron-sized) activated carbon (SPAC) was developed by wet-milling commercially available powdered activated carbon (PAC) to a smaller particle size. It was reported that SPAC has a larger NOM adsorption capacity than PAC because NOM mainly adsorbs close to the external adsorbent particle surface (shell adsorption mechanism). Thus, SPAC with its larger specific external surface area can adsorb more NOM than PAC. The effect of higher NOM uptake on the adsorptive removal of MIB has, however, not been investigated. Results of this study show that adsorption competition between NOM and MIB did not increase when NOM uptake increased due to carbon size reduction; i.e., the increased NOM uptake by SPAC did not result in a decrease in MIB adsorption capacity beyond that obtained as a result of NOM adsorption by PAC. A simple estimation method for determining the adsorbed amount of competing NOM (NOM that reduces MIB adsorption) is presented based on the simplified equivalent background compound (EBC) method. Furthermore, the mechanism of adsorption competition is discussed based on results obtained with the simplified EBC method and the shell adsorption mechanism. Competing NOM, which likely comprises a small portion of NOM, adsorbs in internal pores of activated carbon particles as MIB does, thereby reducing the MIB adsorption capacity to a similar extent regardless of adsorbent particle size. SPAC application can be advantageous because enhanced NOM removal does not translate into less effective removal of MIB. Molecular size distribution data of NOM suggest that the competing NOM has a molecular weight similar to that of the target compound