Joo-Yang Park

Effect of pH on Fenton and Fenton‐like oxidation

The lifetime of H2O2 is an important factor in the feasibility of Fenton’s reaction for soil and groundwater remediation. The lifetime of H2O2 was evaluated in Fenton’s reaction and Fenton‐like reactions with haematite and magnetite. H2O2 was more stable in the Fenton‐like reaction than in the Fenton’s reaction. The lifetime of H2O2 was also highly affected by the solution pH, and a pH buffered acidic condition was preferred. Fenton’s reaction and Fenton‐like reaction were tested for phenanthrene adsorbed on sand. Fenton‐like reaction and acidic condition showed better degradation rates in comparing with those of Fenton’s reaction and unbuffered systems. The dissolved iron species were measured in the Fenton’s reaction, and Fenton‐like reaction with haematite as a function of pH. In the presence of H2O2, ferric iron was the major dissolved iron species and the pH buffered to acidic condition maintained relatively high levels of dissolved iron in the aqueous solution. The higher iron concentration in the solution contributed to effective production of hydroxyl radical and degradation of organic contaminants.

A multi-component numerical leach model coupled with a general chemical speciation code

A multi-component numerical leach model (SBLEM) was developed by coupling a general chemical speciation code with a modified Crank-Nicolson algorithm to determine the leaching behavior of contaminants in stabillized/solidified (s/s) wastes. The thermodynamic database of the speciation code was modified using batch leaching data. SBLEM was evaluated by simulating a dynamic leaching test of cement-treated combined bottom and fly ash from a municipal solid waste (MSW) incinerator. Simulations used an input composition prepared from acid neutralization capacity (ANC) test data of the ash. The results show that SBLEM can reasonably predict the dynamic leaching behavior of metals from the cement-treated ash when the ANC of the ash and pH-solubility curves of metals are well described. This indicates SBLEM simulations may be able to augment or replace experimental leaching tests that can consume a substantial period of time (> 2 months) and in some cases, provide unreliable results.

Anaerobic treatment of palm oil mill effluent using combined high-rate anaerobic reactors.

Combined system of high-rate anaerobic reactors for treating palm oil mill effluent (POME) was developed and investigated in this study. The system composed of one common primary hybrid reactor which was shared by two different secondary filter reactors. An overall COD removal efficiency of 93.5% was achieved in both systems. The secondary reactors contributed not only in enhancing the COD removal efficiency, but also ensured the performance stability of the entire system. Biomass remained intact in the secondary reactor in contrast to the primary reactor in which occasional washout of biomass was observed. The pH of POME was adjusted at the beginning of the operation, as the process continued POME did not require the external pH adjustment as the pH was maintained in desired range. The biogas was produced up to 110 l/d with the yield of 0.171-0.269 l [CH₄]/g [COD removed] and 59.5-78.2% content of methane.

Electrochemical removal of nitrate using ZVI packed bed bipolar electrolytic cell

The present study investigates the performance of the zero valent iron (ZVI, Fe(0)) packed bed bipolar electrolytic cell for nitrate removal. The packing mixture consists of ZVI as electronically conducting material and silica sand as non-conducting material between main cathode and anode electrodes. In the continuous column experiments for the simulated groundwater (initial nitrate and electrical conductivity of about 30 mg L(-1) as N and 300 μS cm(-1), respectively), above 99% of nitrate was removed at the applied potential of 600 V with the main anode placed on the bottom of reactor. The influx nitrate was converted to ammonia (20% to maximum 60%) and nitrite (always less than 0.5 mg L(-1) as N in the effluent). The optimum packing ratio (v/v) of silica sand to ZVI was found to be 1:1-2:1. Magnetite was observed on the surface of the used ZVI as corrosion product. The reduction at the lower part of the reactor in acidic condition and adsorption at the upper part of the reactor in alkaline condition are the major mechanism of nitrate removal.

Prediction of chemical speciation in stabilized/solidified wastes using a general chemical equilibrium model II: Doped waste contaminants in cement porewaters

Abstract In the previous paper, SOLTEQ demonstrated its ability to represent chemical speciation in the pure s/s binder systems. The objective of this paper is to provide a method for representing doped waste contaminants in SOLTEQ so that their speciation can be determined. To evaluate this method, model predictions were compared with measured concentrations in the porewaters expressed from cement pastes doped with various metal salts. Among doped metals, only mercury showed concentrations that indicated primary control by precipitation. The other metals, such as Cr(VI), Cd, Pb, and Na, showed behaviors that imply sorption as a major immobilization mechanism. The Langmuir isotherm was found to be well suited to describe the sorption of Na + ions onto the effective surface of CSH. To support the sorption of metal anions onto presumably negatively charged silica surface in cement porewater, a hypothesis of “super-equivalent adsorption” is proposed.

Prediction of chemical speciation in stabilized/solidified wastes using a general chemical equilibrium model Part I. Chemical representation of cementitious binders

Abstract Chemical equilibrium models are useful to evaluate stabilized/solidified waste. A general equilibrium model, SOLTEQ, a modified version of MINTEQA2 for S/S, was applied to predict the chemical speciations in the stabilized/solidified waste form. A method was developed to prepare SOLTEQ input data that can chemically represent various stabilized/solidified binders. Taylor’s empirical model was used to describe partitioning of alkali ions. As a result, SOLTEQ could represent chemical speciation in pure binder systems such as ordinary Portland cement and ordinary Portland cement + fly ash. Moreover, SOLTEQ could reasonably describe the effects on the chemical speciation due to variations in water-to-cement, fly ash contents, and hydration times of various binder systems. However, this application of SOLTEQ was not accurate in predicting concentrations of Ca, Si, and SO 4 ions, due to uncertainties in the CSH solubility model and K sp values of cement hydrates at high pH values.

Comparison of hematite/Fe(II) systems with cement/Fe(II) systems in reductively dechlorinating trichloroethylene

Reactive reductants of cement/Fe(II) systems in dechlorinating chlorinated hydrocarbons are unknown. This study initially evaluated reactivities of potential reactive agents of cement/Fe(II) systems such as hematite (alpha-Fe(2)O(3)), goethite (alpha-FeOOH), lepidocrocite (gamma-FeOOH), akaganeite (beta-FeOOH), ettringite (Ca(6)Al(2)(SO(4))(3)(OH)(12)), Friedels salt (Ca(4)Al(2)Cl(2)(OH)(12)), and hydrocalumite (Ca(2)Al(OH)(6)(OH).3H(2)O) in reductively dechlorinating trichloroethylene (TCE) in the presence of Fe(II). It was found that a hematite/Fe(II) system shows TCE degradation characteristics similar to those of cement/Fe(II) systems in terms of degradation kinetics, Fe(II) dose dependence, and final products distribution. It was therefore suspected that Fe(III)-containing phases of cement hydrates in cement/Fe(II) systems behaved similarly to the hematite. CaO, which was initially introduced as a pH buffer, was observed to participate in or catalyze the formation of reactive reductants in the hematite/Fe(II) system, because its addition enhanced the reactivities of hematite/Fe(II) systems. From the SEM (scanning electron microscope) and XRD (X-ray diffraction) analyses that were carried out on the solids from hematite/Fe(II) suspensions, it was discovered that a sulfate green rust with a hexagonal-plate structure was probably a reactive reductant for TCE. However, SEM analyses conducted on a cement/Fe(II) system showed that hexagonal-plate crystals, which were presumed to be sulfate green rusts, were much less abundant in the cement/Fe(II) than in the hematite/Fe(II) systems. It was not possible to identify any crystalline minerals in the cement/Fe(II) system by using XRD analysis, probably because of the complexity of the cement hydrates. These observations suggest that major reactive reductants of cement/Fe(II) systems may differ from those of hematite/Fe(II) systems.

Stabilization of hydrogen peroxide using phthalic acids in the Fenton and Fenton-like oxidation.

The stabilization of hydrogen peroxide was evaluated in Fenton reaction with phthalic acid as a stabilizer. The stabilization effect was high at a low pH<pK(a1) and the effect was negligible at a high pH above pK(a2) in both Fenton and Fenton-like reactions. While the lifetime of hydrogen peroxide was prolonged by phthalic acid, the stabilization could not contribute on the increase of the reaction rate in the current Fenton and Fenton-like experimental systems because the systems were all well mixed systems. The interaction between dissolved iron and phthalic acid was spectroscopic monitored in variable pH over pK(a1) and pK(a2) of phthalic acid. Ferrous iron was well stabilized and the initial concentration was kept after mixing with phthalate while ferric iron was removed from the aqueous phase by the phthalic acid. It could be concluded that the stabilization by phthalic acid is due to inhibition of catalytic activity of dissolved iron and minimizes the self-decomposition of hydrogen peroxide. The stabilization is affected by ionization state of the organic acid.

The enhancement of ammonium removal from ethanolamine wastewater using air-cathode microbial fuel cells coupled to ferric reduction.

A microbial fuel cell (MFC) with biological Fe(III) reduction was implemented for simultaneous ethanolamine (ETA) degradation and electrical energy generation. In the feasibility experiment using acetate as a substrate in a single-chamber MFC with goethite and ammonium at a ratio of 3.0(mol/mol), up to 96.1% of the ammonium was removed through the novel process related to Fe(III). In addition, the highest voltage output (0.53V) and maximum power density (0.49Wm(-2)) were obtained. However, the ammonium removal and electrical performance decreased as acetate was replaced with ETA. In the long-term experiment, the electrical performance markedly decreased where the voltage loss increased due to Fe deposition on the membranes.

Performance comparison between mesophilic and thermophilic anaerobic reactors for treatment of palm oil mill effluent

The anaerobic digestion of palm oil mill effluent (POME) was carried out under mesophilic (37°C) and thermophilic (55°C) conditions without long-time POME storage in order to compare the performance of each condition in the field of Sumatra Island, Indonesia. The anaerobic treatment system was composed of anaerobic hybrid reactor and anaerobic baffled filter. Raw POME was pretreated by screw decanter to reduce suspended solids and residual oil. The total COD removal rate of 90-95% was achieved in both conditions at the OLR of 15kg[COD]/m(3)/d. The COD removal in thermophilic conditions was slightly better, however the biogas production was much higher than that in the mesophilic one at high OLR. The organic contents in pretreated POME were highly biodegradable in mesophilic under the lower OLRs. The biogas production was 13.5-20.0l/d at the 15kg[COD]/m(3)/d OLR, and the average content of carbon dioxide was 5-35% in both conditions.