Ya Pang

This paper reviews the recent achievements in the enhanced production of volatile fatty acids (VFAs) from waste activated sludge (WAS). The enhanced strategies are divided into two approaches. The first strategy focuses on the regulation of carbon-to-nitrogen (C/N) ratio by co-digestion of WAS with carbon-rich substrates, including municipal solid wastes (MSW), marine algae, agricultural residues, and animal manures. The other strategy is to enhance the solubilization and hydrolysis of WAS or inhibit the methanogenesis by applying various pretreatments, such as mechanical, chemical, enzymatic, and thermal pretreatment. Finally, the applications of WAS-derived VFAs are discussed. The future researches in enhancing VFAs production and wide application of the VFAs from both technical and economic perspectives are proposed.

Landfill leachate was pretreated by chemical flocculation with polyaluminum chloride (PAC) as a flocculant, and subsequently purified by the microelectrolysis-Fenton (MEF) process. Response surface methodology was employed to optimize the MEF process, and the optimal conditions were initial pH 3.20, H₂O₂ concentration 3.57 g/L, and Fe-C dosage 104.52 g/L. The PAC coagulation combined with MEF processes obtained a superior decontamination performance, and the predicted chemical oxygen demand (COD) and humic acids (HA) removal were respectively 90.27% and 93.79%. The strong fluorescence peak at 425 nm and the trapping experiment showed that was generated during MEF, which had a strong oxidation ability to degrade organic recalcitrant pollutants. The ultraviolet–visible spectra and three-dimensional excitation–emission matrices spectra (3D-EEMs) indicated that PAC coagulation could preferentially remove protein-like substances, while the MEF process was effective in destructing organic recalcitrant pollutants, especially humic-like and fulvic-like substances.

Competitive adsorption of Pb²⁺, Cd²⁺ and Zn²⁺ ions on sodium dodecyl sulfate (SDS) in binary mixtures were investigated compared with non-competitive adsorption in the unitary metal solution in micellar-enhanced ultrafiltration at a temperature of 25 °C. Mutual interference effects were investigated based on the removal rate, the Langmuir Competitive Model (LCM) and equilibrium adsorption capacity ratios, q_e/q_m, which indicated the presence of other metal ions. The results indicated that the removal rate and adsorption capacity of Pb²⁺ were higher than that of the other metal ions in unitary and binary systems. The effects on SDS micelles for Cd-Pb and Zn-Pb combinations were found to be antagonistic. However, it was a favorable effect for the Cd-Zn combination, and the metal ions sorption followed the order: Pb²⁺ > Cd²⁺ > Zn²⁺. The behavior of non-competitive and competitive adsorption for Cd²⁺ and Zn²⁺ in a single system and in the presence of Pb²⁺ were well described by LCM. Moreover, the LCM showed poor fitting to non-competitive and competitive adsorption of Pb²⁺ in a single solution and in the presence of Cd²⁺ or Zn²⁺. In conclusion, the removal of Pb²⁺ in the presence of Zn²⁺ or Cd²⁺ showed greater efficacy than that of Cd²⁺ or Zn²⁺ in the presence of Pb²⁺.