RISK ASSESSMENT OF SURFACE WATER POLLUTION BY MUNICIPAL WASTEWATER EFFLUENT (THE CASE OF IKVA RIVER)

Abstract

The ecological assessment of Ikva River in the context of municipal wastewater effluent was done. The research area is surrounded by wastewater from sewage treatment plant in Mlyniv, Rivne oblast. BOD5, pH, turbidity, DO, temperature, COD, nitrates, nitrites, ammonia nitrogen, phosphates, sulphates, chlorides, TDS, total iron, manganese, copper, and zinc were measured in research. The water samples were collected from 3 points along Ikva River: (A) 0,5 km upstream and (C) 0,5 km downstream of the effluent discharge point, and (B) – effluent discharge point. Even at the point of sewage discharge, river water is strongly polluted. Four different assessment methods were used: (i) Water pollution index of Ukraine, (II) composite ecological index IE of Ukraine, (iii) WQI NSF USA, and (iv) author’s methodology based on the Harrington's desirability function applied for the fish farming. The results of the study showed several uncoordinated trends. However, on the whole, a paradoxical phenomenon: insufficiently purified sewage, according to all series of assessment was cleaner than river water. In WQI terms, upstream (A) was evaluated in 41 % (badly), waste effluent (B) – 47 % (badly), and downstream 41 % (badly); in terms of Harrington’s desirability function – 7 % (very badly), 22 % (badly), and 15 % (very badly) correspondently. Three of the four applied methods showed this positive dilution effect of wastewater effluent. In general, Ikva River is unfit for fish farming; its ecological state is described as an ecological disaster.