Hi dear Fungisai: The ...

Hi dear Fungisai:

The parameters of economic, level of pollution, land availability and most importantly the kind of consumption ( directly consumed by people or not) are the factors which determine the treatment approach.  But generally biological treatments (like aerated lagoons or wetlands) are preferred, because they are cheaper and enough efficient for decreasing the BOD5, COD and TSS. After that, with disinfection (preferably UV because of less byproducts) the grey water is ready to reuse. 

But if the level of TDS is high yet, you should use membrane technologies which increase the costs, but it is inevitable.