what is ultrafiltration in wastewater treatment?

Answer 1

Ultrafiltration is is a technique where pressure is used to filter through filters that pass only molecules and species with molecular weights above 1500 through pores 0.005 – 0.1 micron in size. The pressures used are between 5-150 psig. Note that the actual species in water are bigger than the normal molecular weight you calculate in chemistry. This is because the actual species present may have multiple water molecules or ions actually attached. It is also dependent on the shape of the molecule and the presence of colloidal species.

UF is only used in specialized wastewater applications. The reason is that when the pore size gets smaller, the amount of water that passes becomes smaller. Say that in a 1MGD plant 99% of the water passes through, that still leaves 10000 gallons per day of highly concentrated waste that still must be treated. In few cases is there a way to do this. This limits UF to smaller wastewater operations where this waste can simply be landfilled or shipped to a waste site or operations where the contaminants are simple.

See the references for more info. A good web search will find hundreds of additional sources.

Answer 2

This is a process that is also called "reverse osmosis" or simply "RO". It is basically placing your waste water against a semipermiable membrane, and then applying a pressure to it, causing the water but not the waste to be forced through the membrane. It works fairly well in the right hands and this process can even be used to de-salinate sea water.