Bioassessments of anaerobically decomposing organic refuse in laboratory lysimeters with and without leachate recycling and pH adjustment

Effects of Monotypic and Binary Mixtures of Metal Oxide Nanoparticles on Microbial Growth in Sandy Soil Collected from Artificial Recharge Sites

The potential effects of monotypic and binary metal oxide nanoparticles (NPs, ZnO, NiO, Co₃O₄ and TiO₂) on microbial growth were evaluated in sandy soil collected from artificial recharge sites. Microbial growth was assessed based on adenosine triphosphate (ATP) content, dehydrogenase activity (DHA), and viable cell counts (VCC). Microbial growth based on ATP content and VCC showed considerable differences depending on NP type and concentration, whereas DHA did not significantly change. In general, ZnO NPs showed the strongest effect on microbial growth in all measurements, showing an EC50 value of 10.9 mg/L for ATP content. The ranking (EC50) of NPs based on their effect on microbial growth assessed by ATP content and VCC was ZnO > Co₃O₄ > NiO > TiO₂. Upon exposure to binary NP mixtures, synergistic and additive modes of action were observed for ATP content and VCC, respectively. The ranges of observed (P(O)) and expected (P(E)) activity were 83%-92% and 78%-82% of the control (p-value 0.0010) based on ATP content and 78%-95% and 72%-94% of the control (p-value 0.8813) based on VCC under the tested conditions, respectively. The results indicate that the effects of NP mixtures on microbial growth in the sandy soil matrix were as great, or greater, than those of single NPs. Therefore, understanding the effects of single NPs and NP mixtures is essential for proper ecological risk assessment. Additionally, these findings demonstrate that the evaluation of NP effects may be profoundly influenced by the method of microbial growth measurement.

Effects of spiked metals on the MSW anaerobic digestion

This study aimed to investigate the effects of eight metals on the anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) in bioreactors. Anaerobic bioreactors containing 200 mL MSW mixed completely with 200 m L sludge seeding. Ca and K (0, 1000, 2000 and 6,000 mg L(-1)) and Cr, Ni, Zn, Co, Mo and W (0, 5, 50 and 100 mg  L(-1)) of various dose were added to anaerobic bioreactors to examine their anaerobic digestion performance. Results showed that except K and Zn, Ca (~728 to ~1,461 mg  L(-1)), Cr (~0.0022 to ~0.0212 mg  L(-1)), Ni (~0.801 to ~5.362 mg  L(-1)), Co (~0.148 to ~0.580 mg  L(-1)), Mo (~0.044 to ~52.94 mg  L(-1)) and W (~0.658 to ~40.39 mg  L(-1)) had the potential to enhance the biogas production. On the other hand, except Mo and W, inhibitory concentrations IC(50) of Ca, K, Cr, Ni, Zn and Co were found to be ~3252, ~2097, ~0.124, ~7.239, ~0.482, ~8.625 mg  L(-1), respectively. Eight spiked metals showed that they were adsorbed by MSW to a different extent resulting in different liquid metals levels and potential stimulation and inhibition on MSW anaerobic digestion. These results were discussed and compared to results from literature.