Hello andrea

                 There are many basic pollutants in which already people have reported. U can go for specific pollutants of emerging contaminants which belong to family of  EDCs, PCB, PCPs, Pharmaceutical compounds etc for ur study through adsorption technique.

hello,

           You can work on  the persistent organic pollutants such as organochlorine compounds ( PCBs; DDTs; CHLs; HCHs; HCB) which cause a big  surface and groundwater pollution. 

Hello, emerging contaminants are a great challenge, among emerging contaminants in water include drugs, perfluorinated compounds, hormones, drugs of abuse and care products and personal care.

as the answers above show there is no most dangerous etc.

Regarding problematic to eliminate of course pollutants with high solubility low reactivity belong, e.g. sulfates, fluoride. In this respect associated costs are a problem.

Andrea, this depends very much on point of view and the ackground you are working in.

Around glasgow I would suspect the impact of heavy and coal industry being very important- PAH easy to sorb.

All wastewater related issues EDC etc are less relevant in the eyes of the british administrators as the major WWTPs discarge directly inot the sea - no drinking water issue. - this is different around the severn, were basically Severn water is used for drinking water production.

Viewpoint in Sweden or Germany is different as a lot of drinking water is produced from surface water of say dubious qualities.... and high wastewater fractions in....Israel will have another angle....I think irrigation water for agriculture in the desert contains 50-80% wastewater...

Hello Andrea,

It is depends on the type of wastewater, type of treatment and disposal and the cost of removal.

Usually, most pollutant in domestic wastewater is organic matter and it is easy to degrade on the contrary the industrial wastewater is more dangerous for the environment if it is disposed to water bodies or groundwater due to presence of industries by-products like heavy metals. Moreover, the most dangerous pollutants in agricultural wastewater are different types of pesticides.

Furthermore, if your question intended to the drinking water all chemical pollutants are dangerous + biological pollutant like fecal coliform, salmonella, …..    

You  must also consider the toxic  mineral pollutants such as lead, cadmium, mercury etc ..

Disinfection by-products and algal toxins

Its a tough question and all depends on if you are concerned with regional or global contaminants, plus the latitude plays a role. For example the SVOCs such as POPs are of greater concern in colder climates while for inland lakes and coastal locations algal toxins are of concern particularly as these have not been monitored and with increased nutrients and boats moving from lake to lake these algae can be widely distributed.

persistent and refractory pollutants (those cataloged by USEPA) are difficult to treat. Much of antibiotic residues and hormones that are excreted in water often pass unharmed in conventional treatments.

So ... if you want to work with procedures that promote the removal by adsorption or waste minimization employing catalysis and / or photocatalysis, you will have a series of articles and well established work in technical and scientific literature to guide you