Evaluation of a liquid-phase plasma discharge process for ammonia oxidation in wastewater: Process optimization and kinetic modeling.

Removing ammonia-nitrogen (NH3N) from wastewater is of paramount importance for wastewater treatment. In this study, a novel continuous liquid plasma process (CLPD) was evaluated to remove NH3N from synthetic wastewater. The Box-Behnken experimental design was used to optimize the main process parameters, including the initial NH3N concentration (50-200 mg/L), power input (150-300 W), and gas-flow rate (1.5-2.5 L/min), for efficient NH3N removal from wastewater. The gas-flow rate and power input were found to be significant factors affecting the removal efficiency of NH3N, whereas the initial concentration of NH3N played a vital role in determining the energy efficiency of the process. Under the optimal conditions of an initial NH3N concentration of 200 mg/L, applied power of 223 W, and gas-flow rate of 2.4 L/min, 98.91% of NH3N could be removed with a N2 selectivity of 92.91%, and the corresponding energy efficiency was 0.527 g/kWh after 2 hrs of treatment. A small fraction of undesirable NO3--N (7.05 mg/L) and NO2--N (2.83 mg/L) were also produced. Kinetic modeling revealed that NH3N degradation by the CLPD followed a pseudo-first-order reaction model, with a rate constant (k) of 0.03522 min-1. Optical emission spectroscopy (OES) was used to gather information about the active chemical species produced during the plasma discharge. The obtained spectra revealed the presence of several highly oxidative radicals, including ‧OH, ‧O, and ‧O2+. These results demonstrate the potential of liquid phase plasma discharge as a highly efficient technology for removing ammonia from aqueous solutions.

Author Correction: Dairy Manure Wastewater Remediation Using Non-airtight Digestion Pretreatment Followed by Microalgae Cultivation.

The original version of this article unfortunately contained a mistake.

Dairy Manure Wastewater Remediation Using Non-airtight Digestion Pretreatment Followed by Microalgae Cultivation.

The non-airtight digestion technology is emerging to be applied in the acidogenic phase for two-stage methane production. However, in this study, it was used to pretreat screened dairy manure (SDM) in order to provide microalgae cultivation with a substrate that might be more suitable for nutrient reduction, especially phosphorus. SDM was firstly underwent non-airtight digestion applying different dilution folds, i.e., blank (no dilution), 5-fold, 10-fold, and 15-fold. Total solids (TS), total dissolved solids (TDS), and chemical oxygen demand (COD) of the SDM were mostly reduced when there was no dilution applied. Five-fold dilution is the most beneficial one for ammonia reduction. Total phosphorus (TP) was reduced the most efficiently in the blank SDM. After the non-airtight digestion, 5-fold diluted original SDM, 5-fold diluted digested original SDM, and digested 5-fold diluted SDM were used to grow microalgae for 8 days. Microalgae grown in 5-fold diluted digested original SDM and digested 5-fold diluted SDM had better removal efficiencies in COD and NH4-N. From the monitoring of pH and TP during the 8-day culture period, it is found that pHs were peaked on the 4th day for microalgae grown in 5-fold diluted digested original SDM and digested 5-fold diluted SDM, corresponding to the maximal TP removal. Non-airtight digestion of SDM could help achieve better nutrient removal by microalgal cultivation in a shorter time span.