The paper presents the results of investigations on wastewater formation and its treatment in constructed wetlands (CW) with horizontal flow. The investigations were carried out on a dairy farm in the period of 1995-2004. On farmsteads containing cattle sheds, the pollution of wastewater is 2-3 times higher compared with domestic wastewater. The largest amount of slowly decomposing organic pollutants is retained during wastewater filtration via a septic tank (62.7% according to CODCr). During wastewater filtration through a horizontal CW, the amount of retained organic pollutants biochemical oxygen demand (BOD5) and chemical oxygen demand (CODCr) is 93.6%. During wastewater filtration through CW, nutrients (Ntotal and Ptotal) treatment efficiency on the dairy farms, where Ntotal concentration is 101.0 mg lE-1, is one the average 61.4% of nutrient load, and 41.4% of P where Ptotal concentration is 21.5 mg lE-1. The analyzed wastewater treatment facilities (septic tank + CW) are distinct for their buffering capabilities. They are affective enough, however due to limited P removal processes in sustainable natural environment, additional P-removal means are to be used in wastewater treatment facilities arranged on dairy farms.

The processing of milk in dairy companies produces a certain amount of wastewater and liquid wastes. During the treatment process of such wastes sludge is accumulated in treatment facilities. The sludge is a rather valuable soil fertilizer; however, apart from plant available nutrients, it also contains large amounts of pollutants. The paper analyzes the quality of wastewater treatment process performed in treatment facilities of dairy companies, and specifies the amounts of plant available nutrients contained in sludge accumulated during the treatment process of wastewater and liquid wastes. The amounts of heavy metals contained in sludge are compared with their maximum allowable concentrations determined in the environmental requirements for soil fertilization (Aplinkosaugos reikalavimai..., 2001). On the basis of the study results and normative documents of environment protection, the article presents optimal rates and regime for sludge fertilization as well as analyzes the agro-technical and qualitative characteristics of sludge spreaders made at the Water management Institute of Lithuanian University of Agriculture and used during the technological process of fertilization.