Study of the Presence of Pesticides in Treated Urban Wastewaters

The increase of the industrial activity and the consequent economic and social development have produced, at least until some years ago, a growth of big cities which leads and complicates the supply of one of the most important elements to the life, “water”. Nowadays, faced with the growing water demand and the hydric resources shortage, the reuse of treated water is considered as a possible solution in order to increase existing resources. However, all effluents can`t be reused since environmental minimum flows have to be guaranteed downstream of the dumping (Ormad, 2011). The water reuse is the application, before its return to the public water resources and the terrestrial maritime one to a new exclusive use of waters that, having been used by who derived them, they have been subjected to a process or processes of treatment established in the corresponding authorization of dumping and to the necessary in order to get the quality required in function of uses to which it goes to be destined. As well, reuse waters are treated wastewaters that have been subjected to an additional or complementary process which is capable to adapt its quality to the destined use. All this is carried out in reclamation plants, group of installations where treated wastewaters are subjected to additional treatments which can be needed in order to adapt the water quality to the destined use (Royal Decree 1620/2007). Waters which go to be reclaimed, it is, treated wastewaters, are waters that must obey the specifications of Directive 91/271/EEC (Directive 91/271/EEC). However, in these waters can exist some substances which can be pollutants. In general, the composition of these waters mainly depends on two factors: the industrial contribution to the urban dumping and the type of water treatment in the wastewater treatment plant (WWTP). In spite of this, in general, these waters are characterized by: The presence of a great variety of pathogenic germs The presence of organic matter, with a Biologycal Oxygen Demand 5-day (BOD5) up to 25 mg L-1 and a Chemical Oxygen Demand (COD) up to 125 mg L-1 (according to the current legislation). In this generic group, there are two types of organic matter: • Non Hazardous Organic Matter: This organic matter is mayoritary composed by compunds which haven’t degraded in the WWTP. This is because they are refractary compounds or the achieved yields aren’t of 100%; they are organic substances non toxic like carboxilic acids, esters, proteins, carbon hydrates, aminoacids, polihydroxilated alcohols, etc.