Microplastic (MP) pollution is a matter of great concern attracting increasing attention due to its adverse effects on the environment. Different technologies and methodologies have been developed to remove these pollutants. Herein, we focus on a promising environmental solution that involves surface modification to change the wettability properties of MPs or solid materials by conferring superhydrophobicity and superoleophilicity to increase the selectivity for MP separation. Both processes can be used to selectively separate MPs because of the changes in the wettable properties of the MP or by changing the oil used in the case of superhydrophobic surfaces. We show two distinct methods based on changing the wettability properties of surfaces that could lead to innovative and environmental applications. We also discuss some of the challenges that need to be overcome.

Recent at sea surveys of floating macro-debris in the southeast Atlantic Ocean found that debris increases in size with distance from shore, suggesting that many smaller items, which dominate litter close to urban source areas, sink before dispersing far into the ocean. We test whether this pattern is evident in beach litter in the same region. Freshly stranded beach litter was collected at increasing distances (0km, 100km, 200km and 2800km) from Cape Town, a major urban litter source. Mean size and buoyancy of litter items increased significantly with distance from Cape Town. Size-specific sedimentation due to the ballasting effect of biofouling is a plausible explanation for the disappearance of smaller, less buoyant items. Our results provide further evidence that many low buoyancy items sink and support the hypothesis that size and buoyancy are strong predictors of dispersal distance for floating debris.

An engineering investigation and evaluation of vortex devices as bubble makers for use in the removal of suspended solids from wastewaters was conducted. Specific objectives included the development and test of bubble makers capable of generating bubbles having mean diameters of about 100 microns with vortex devices having minimum liquid passageways of 1/4 inch or greater. Bubbles having a mean diameter of 80 to 85 microns, with virtually no bubbles greater than 130 microns, were successfully produced. This mean size and size range are substantially the same as bubbles produced by pressurized water processes at similar operating pressures. Bubbles were produced both by aspirating atmospheric air directly into the vortex unit, and by aspirating atmospheric air at the suction side of the pump, dissolving it, and precipitating it or effervescing it at the vortex unit. Sufficient data now exist, however, to design vortex systems for direct functional tests in conventional air flotation systems.

The paper presents the results of laboratory research and application of continuous electro-coagulation and electro-flotation (ECEF) to remove natural organic matter (NOM) from groundwater in the treatment of drinking water. The highest NOM removal efficiency for current density of 5.78 mA/ cm square according to UV254 absorbance and dissolved organic matter (DOC) was 77% and 71% respectively. The specific energy and aluminum electrode consumption was 2.01 kWh/cubic m, 80 g Al/cubic m, respectively.

The report documents a study to develop a treatment system for combined sewer overflows. The processes of chemical oxidation, screening, dissolved-air flotation, and disinfection were evaluated in the laboratory. A 5 MGD demonstration system was designed, installed and evaluated. Suspended solids and volatile suspended solids removal in the range of 65-80% were consistently obtained at influent concentrations of 150 to 600 mg/l. BOD and COD removals were slightly lower at 55 to 65% for influent concentrations of 50 to 500 mg/l. Addition of chemical flocculents (ferric chloride and a cationic polyelectrolyte) was necessary to obtain these removals. Without the use of chemical flocculents, removal of BOD, COD, suspended solids, and volatile suspended solids were all in the range of 40-50%. The screening flotation system provided sufficient detention time (difference 15 minutes) for adequate disinfection with hypochlorite salts. Cost estimates are presented.