Settling pond

In case none of these methods apply, the subject material will be classified as unsuitable and will have to be disposed. The disposal can be done at offshore dumping grounds (often at large water depths) or at dedicated onshore disposal grounds. The settling ponds discussed in section 6.7.2 can be considered as such an onshore disposal ground. 

In case the fill contains too many fines and it is not allowed to return these fines with the discharge water into the surrounding environment, measures have to be taken. A common solution for hydraulic fills is to construct a settling pond adjacent to the 

Fine particles are extremely difficult to trap. The following measures can be taken to optimise the settling within the pond  

To reduce the settling of fines in the reclamation area the water level in this area should be kept as low as possible. This requires the installation of pumps between the reclamation area and the settling pond. 

The water level in the reclamation area and settling pond is controlled with weir 

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The remaining tailings left over from the clay fractionation step is either flocculated with alum, high molecular weight polymers, or a weak (pH 3.0) solution of sulfuric acid, and stored in settling ponds as waste, or may be filtered and sold to the brick industry as a coating material. It also may be dried and sold as a filler in plastics and textured paint (qv). 

Good housekeeping practices are key to minimizing losses and preventing fugitive emissions. Losses and emissions are minimized by enclosed buildings, covered conveyors and transfer points, and dust collection equipment. Yards should be paved and runoff water routed to settling ponds. 

Prevailing wind locate hazardous vents, burning flares, waste burning pits, waste settling ponds down-wind of plant proper. 

Chlorination plant Crane/lifting equipment Cooling tower (ID/FD/natural) Settling pond... 

Biological treatment Used in all sewage plants and many settling ponds. 

Settling ponds, a less sophisticated alternative to mechanical clarifiers, also remove suspended solids by sedimentation. Settling ponds may be clay-lined, synthetic-lined, or unlined and earthen, and have longer retention times than clarifiers. Settling ponds produce less constant solids loadings than mechanical clarifiers, but still provide sufficient solids removal prior to... 

In the titanium dioxide production plant where the chlorine process is employed, the wastewater from the kiln, the distillation column, bottom residue, and those from other parts of the plant first settle in a pond. The overflow from this pond is neutralized with ground calcium carbonate in a particular reactor, while the scrubber wastewater is neutralized with lime in another reactor. The two streams are sent to a settling pond before being discharged. 

Equipment that may spill inflammable materials Blowdown tanks Burning flares Settling ponds... 

This is a process for removal of suspended solids by settling. Typical examples are settling ponds and settling clarifiers. It requires 45 minutes to 2 hours retention time (RT), and can reduce TSS to 15 mg/L or below. 

Plant 3920 is a bituminous coal- and oil-fired plant with a generating capacity of 557 MW. This plant uses 1,220,000 Mg/year of coal. An ash settling pond was used to remove wastes from coal pile runoff, regeneration wastes, and fly ash. The influent data were obtained from the pond inlet whereas the effluent data were from the discharge stream to the river. The results of this treatment are shown in Table 9. 

Removal of sludge and sediment from treatment/settling ponds... 

Suspended matter down to bacterial size can best be removed by subsidence in settling ponds and by skimming off floating material such as grease, which may form a paste that coats heat-exchange surfaces. Filtration would, no doubt, do a better job (see later), but on a large scale it is not always cost-effective (besides, filters tend to clog). 

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