Ranking (Categorisation) of the Receiving Waters

1. IV. Wastewater Treatment TechnologiesTopic IV. 5. Ranking and Quality Standards of the Receiving Waters. Necessary Wastewater Treatment Efficiency Ranking (Categorisation) of the Receiving Waters I. According to the Regulation No 7 / 1986 (old, but still valid) - 3 categories (ranks) depending on the receiving water use • I category (rank) -surface waters used for potable water supply • II category (rank) -surface waters used for cattle water drinking, fishering, sports and recreation • III category (rank) -surface waters used for irrigation II. According to the EU standards (and Regulation No? at the new Bulgarian Water Act - 2000) - 5 categories (ranks)

2. Quality Standards of the Receiving Waters(Imission or Ecological Norms) According to the Regulation No 7 / 1986 (still valid) I. Main groups of water quality parameters • Group A - general physical and non-organic water quality parameters • Group B - general water quality parameters for organic pollutants • Group C - general water quality parameters for non-organic pollutants of industrial origin • Group D - general water quality parameters for organic pollutants of industrial origin • Group E - biological water quality indicators

3. Suspended solids - SS II rank - 50 mg/l III rank - 100 mg/l BOD5 II rank - 15 mg/l III rank - 25 mg/l COD II rank - 70 mg/l III rank - 100 mg/l Ammonium-N II rank - 2,0 mg/l III rank - 5,0 mg/l Nitrates-N II rank - 10 mg/l III rank - 20 mg/l Phosphates-PO4 II rank - 1,0 mg/l III rank - 2,0 mg/l Quality Standards of the Receiving Waters(Imission or Ecological Norms)According to the Regulation No 7 / 1986 (still valid)II. Standard values (upper limits) of some important water quality parameters (out of 87)

4. Quality Standards of the Wastewater Emissions(Emission Norms) According to the Regulation No 6 / 2000 (At the new Water Act - 2000) Particularities: • Establishing of upper limits for harmful substances and definite characteristic pollutants in wastewater emissions from municipal WWTP’s and in some kinds of industrial wastewater • Introducing additional types of surface waters ranking, depending of their sensitivity to eutrophycation • Sensitive zones - with restrictions for nutrients upper limit concentrations • Less sensitive zones - without restrictions for nutrients concentrations • Establishing of specific requirements for nutrients upper limit concentrations in the receiving waters depending on their sensitivity to eutrophycation

5. Necessary Wastewater Treatment Efficiency Receiving Waters Self Purification General information: • Two types of surface waters pollutants • Biodegradable - depleting both by dilution and degradation • Biorefractory - depleting only by dilution • Biodegradable pollutants concentrations decrease down the stream from the point of introduction, due to the processes of self purification and turbulent mixing in the receiving water • Pollutants standard concentration values are controlled at the point of water intake in a distance L, downstream from the point of wastewater emission introduction

6. Necessary Wastewater Treatment Efficiency General Pollutants Mass Balance Qwe- wastewater emission discharge, m3/s Qrw - receiving water discharge, m3/s Cwe - pollutant concentration in wastewater emission, g/m3 Crw - pollutant concentration in receiving water, g/m3 Clim - pollutant limit concentration in receiving water, g/m3 a - coefficient of mixing (of wastewater and receiving water) Fsp - factor (function) reflecting receiving water self purification Fsp= 1 for biorefractory pollutants and when applying Streeter-Phelps equations

7. Necessary Wastewater Treatment EfficiencyGeneral Pollutants Mass Balance For BOD depletion without considering reaeration: For oxygen balance according to the Streeter-Phelps equations: where Lo is obtained by solution of the Streeter-Phelps equations Necessary Wastewater Treatment Efficiency  - necessary wastewater treatment efficiency Ccw - pollutant concentration in the coarse wastewater at the inlet of the WWTP, g/m3