Competitive removal of Cu-EDTA and Ni-EDTA via microwave-enhanced Fenton oxidation with hydroxide precipitation.

Ethylenediaminetetraacetic acid (EDTA) can form very stable complexes with heavy metal ions, greatly inhibiting conventional metal-removal technologies used in water treatment. Both the oxidation of EDTA and the reduction of metal ions in metal-EDTA systems via the microwave-enhanced Fenton reaction followed by hydroxide precipitation were investigated. The Cu(II)-Ni(II)-EDTA, Cu(II)-EDTA and Ni(II)-EDTA exhibited widely different decomplexation efficiencies under equivalent conditions. When the reaction reached equilibrium, the chemical oxygen demand was reduced by a microwave-enhanced Fenton reaction in different systems and the reduction order from high to low was Cu(II)-Ni(II)-EDTA ≈ Cu(II)-EDTA > Ni(II)-EDTA. The removal efficiencies of both Cu(2+) and Ni(2+) in Cu-Ni-EDTA wastewaters were much higher than those in a single heavy metal system. The degradation efficiency of EDTA in Cu-Ni-EDTA was lower than that in a single metal system. In the Cu-Ni-EDTA system, the microwave thermal degradation and the Fenton-like reaction created by Cu catalyzed H2O2 altered the EDTA degradation pathway and increased the pH of the wastewater system, conversely inhibiting residual EDTA degradation.

Development and validation of a cognitive model-based novel questionnaire for measuring potential unsafe behaviors of construction workers.

The accident death rate in the construction industry is one of the highest among all occupational accidents. In order to identify the most common and direct causes of accidents, the unsafe behaviors of construction workers must be investigated, which necessities a questionnaire. Considering that safety climate research and behavior safety research barely explained the causes of unsafe behavior, this research was conducted from a cognitive model-based perspective. A new questionnaire was designed to evaluate the potentially unsafe behaviors, and a cognitive model with 11 factors was adopted. After verification by exploratory factor analysis, confirmatory factor analysis and reliability analysis, the new questionnaire showed good validity (content validity index < 0.79 and content validity ratio aaaa 0.42, average variance extracted > 0.5) and reliability (Cronbach's α > 0.7, composite reliability > 0.7), and the cognitive model fitted well. Therefore, the new questionnaire is effective and reliable in assessing the causes of unsafe behaviors of construction workers.