An investigation into the role of treatment performance and soil characteristics of soil-based wastewater treatment systems

Soil-based onsite wastewater treatment systems (OWTS) are becoming more important for the treatment and disposal of wastewater in areas that do not have central wastewater collection and treatment systems. However, there are concerns that OWTS may have adverse effects on public health and environment. The purpose of this study is to treat wastewater using a natural soil column in order to evaluate treatment system performance. Wastewater was applied to two different natural soils at different flow rates of 9, 18 and 36 L/day. The treatment performances of wastewater and geotechnical properties of the natural soils were examined. As a result of this study, the percentage of COD and SS removal in wastewater after soil column filtration ranged from 36.2% to 80.5% and 84.4% to 97.9% respectively. pH values of wastewater after the filtration were measured at between 7.75 and 8.12. TP and TN removal rates were found in the range of 23.9-76.8% and 12.4-83.0%, respectively. The column effluent water was classified as both 'high hardness class' in terms of hardness and 'polluted water' in terms of conductivity. Column effluent water was found in 'low, medium, and high hazard' classes in terms of SAR. Whereas the PL values of the natural soils were found to increase by up to 4.8% in the filtration area, specific gravity decreased by nearly 1.1%. The values of LL, PI, maximum dry density, optimum water content, and permeability changed depending on the soil type. The UCS of the natural soils after wastewater filtration decreased by about 5.9%. It was concluded that natural soils have positive effects on treatment of wastewater in a short time.

NC-AFM imaging of the TiO(2)(110)-(1 x 1) surface at low temperature

The TiO(2)(110)-(1 x 1) surface is investigated using non-contact atomic force microscopy (nc-AFM) at 80 K. We successfully obtained a distinct type of image contrast mode which does not exhibit hydroxyl (OH) impurity defects that mostly appear in common nc-AFM images. We named the obtained distinct type of image contrast as the 'hidden mode'. The assignments of surface atomic rows in this contrast mode are not easy in the absence of defects. By recording different contrast modes in the same region of the surface, we identified the atomic rows obtained in the 'hidden mode' image contrast as bridging oxygen atoms (O(b)). The mechanism of contrast formation was attributed to tip-induced displacement of H atoms over oxygen atoms in the OH groups on the O(b) rows. This interpretation was supported by dissipation measurements. A possible candidate for the tip-generating hidden-mode image contrast was interpreted to be a positively terminated tip apex with a dimer-like structure, revealing an attractive interaction with oxygen and a repulsive force on H atom sites. In addition, with a different tip state at close tip-sample distances, we were able to successfully resolve a high resolution image of the in-plane oxygen atoms.