Omer Apaydin

Ultrasound-assisted activation of zero-valent magnesium for nitrate denitrification: identification of reaction by-products and pathways.

Zero-valent magnesium (Mg(0)) was activated by ultrasound (US) in an aim to promote its potential use in water treatment without pH control. In this context, nitrate reduction was studied at batch conditions using various doses of magnesium powder and ultrasound power. While neither ultrasound nor zero-valent magnesium alone was effective for reducing nitrate in water, their combination removed up to 90% of 50 mg/L NO3-N within 60 min. The rate of nitrate reduction by US/Mg(0) enhanced with increasing ultrasonic power and magnesium dose. Nitrogen gas (N2) and nitrite (NO2(-)) were detected as the major reduction by-products, while magnesium hydroxide Mg(OH)2 and hydroxide ions (OH(-)) were identified as the main oxidation products. The results from SEM-EDS measurements revealed that the surface oxide level decreased significantly when the samples of Mg(0) particles were exposed to ultrasonic treatment. The surface passivation of magnesium particles was successfully minimized by mechanical forces of ultrasound, which in turn paved the way to sustain the catalyst activity toward nitrate reduction.

Fuzzy-logic modeling of Fenton’s strong chemical oxidation process treating three types of landfill leachates

Three multiple input and multiple output-type fuzzy-logic-based models were developed as an artificial intelligence-based approach to model a novel integrated process (UF–IER–EDBM–FO) consisted of ultrafiltration (UF), ion exchange resins (IER), electrodialysis with bipolar membrane (EDBM), and Fenton’s oxidation (FO) units treating young, middle-aged, and stabilized landfill leachates. The FO unit was considered as the key process for implementation of the proposed modeling scheme. Four input components such as H2O2/chemical oxygen demand ratio, H2O2/Fe2+ ratio, reaction pH, and reaction time were fuzzified in a Mamdani-type fuzzy inference system to predict the removal efficiencies of chemical oxygen demand, total organic carbon, color, and ammonia nitrogen. A total of 200 rules in the IF–THEN format were established within the framework of a graphical user interface for each fuzzy-logic model. The product (prod) and the center of gravity (centroid) methods were performed as the inference operator and defuzzification methods, respectively, for the proposed prognostic models. Fuzzy-logic predicted results were compared to the outputs of multiple regression models by means of various descriptive statistical indicators, and the proposed methodology was tested against the experimental data. The testing results clearly revealed that the proposed prognostic models showed a superior predictive performance with very high determination coefficients (R2) between 0.930 and 0.991. This study indicated a simple means of modeling and potential of a knowledge-based approach for capturing complicated inter-relationships in a highly non-linear problem. Clearly, it was shown that the proposed prognostic models provided a well-suited and cost-effective method to predict removal efficiencies of wastewater parameters prior to discharge to receiving streams.

Final treatment of young, middle-aged, and stabilized leachates by Fenton process: optimization by response surface methodology

AbstractIn this study, Fenton’s oxidation process was applied after electrodialysis (ED) with bipolar membrane system for the final treatment of the ED-treated young, middle-aged, and stabilized leachates. Response surface methodology (RSM) was applied to evaluate and optimize physical and oxidative performances of Fenton process on treatability of leachate. The interactive effects of four operating variables: H2O2/COD rate, H2O2/Fe2+ rate, initial pH, and reaction time were evaluated by RSM. Three dependent parameters such as COD, TOC, and color removal were measured as responses. The Fenton process was found to be successful to treat all ED-treated young, middle-aged, and stabilized landfill leachate. In terms of COD and TOC removals, the efficiency of Fenton’s oxidation increased with increasing leachate age while color removal was found to be higher than 89% in all treated leachate samples. Fenton oxidation treatment enhanced the biodegradability of landfill leachates by 400, 100, and 44% for old, mid...