Low-Concentration Phosphate Removal Using Microwave-Assisted Granular Activated Carbon Modified by Magnesium

Objectives In this study, we propose a new method for preparing magnesium-modified granular activated carbon (Mg-GAC) using microwave irradiation. The objective is to identify the optimal factors for efficiently removing low-concentration phosphate using the Mg-GAC. Methods We impregnated Mg on activated carbon and modified Mg-GAC using microwave irradiation. Experiments were conducted with modification parameters such as impregnation time (1-12 hours), impregnation solution concentration (0.5-3 M), and microwave irradiation time (0-20 minutes). Factors affecting phosphate removal were set as pH (2-10) and reaction time (0-240 minutes), and were applied to kinetic models and isothermal adsorption models. Results and Discussion After modification, particle distribution on the adsorbent's surface and 40-time increase in percent composition of Mg showed that Mg effectively coated to the GAC surface. At initial concentration of 2 mg P/L, the optimal modification conditions were 1-M Mg impregnation solution concentration, 2-hr impregnation time, and 10-min microwave irradiation time. The optimal experimental conditions for low phosphate removal efficiency were pH 4 and 180-min adsorption time. The difference of maximum removal efficiency between Mg-GAC (91.9%) and GAC (63.6%) was 28.3%. Mg-GAC is suitable for both Langmuir and Freundlich isotherm models, and the reaction kinetics followed a pseudo-second-order model. The microwave irradiation time for Mg-GAC preparation was 10 min, and the energy consumption was 0.55 kWh/g, which showed that microwave irradiation is one of promising methods for modification of GAC by metal. Conclusion The Mg-GAC modified by magnesium and microwave irradiation enhanced removal efficiency for low-concentration phosphate compared with GAC

Use of order-specific primers to investigate the methanogenic diversity in acetate enrichment system

The applicability of order-specific primers in minimizing the possible underestimation of microbial diversity was evaluated via denaturing gradient gel electrophoresis (DGGE) analysis of a lab-scale anaerobic digester. Initially, a population analysis with real-time quantitative PCR demonstrated the existence of three methanogenic orders-Methanobacteriales, Methanomicrobiales, and Methanosarcinales-throughout the reaction period. DGGE analyses with three pairs of order-specific primers yielded eight operational taxonomic units (OTUs), whereas DGGE analysis with two independent Archaea-specific primers identified only five. Moreover, the order-specific primers amplified at least one OTU affiliated with each order, whereas no members of Methanobacteriales or Methanomicrobiales were identified with Archaea-specific primers in most samples. These findings provide evidence that order-specific analysis can detect the diversity of methanogens in greater detail than conventional Archaea-specific analysis.close121