G. Kostadinova*, D. Dermendzhieva, G. Petkov, I. Taneva

Department of Applied Ecology and Animal Hygiene, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Вulgaria

Abstract. The purpose of this study was to investigate and assess the wastewater quality in two monitoring points, at input and at output, of Municipal Wastewater Treatment Plant (MWWTP), Stara Zagora, Bulgaria, for a period 2011 – 2014, by physico-chemical parameters (temperature, pH, suspended solids, BOD5, COD, total N and total P), with a view to their discharge into the receiving water body (Bedechka river) and as a resource for irrigation of crops. For sampling and sample preparation of wastewater, international references of ISO and BSS were used. Sample analyses were made by equipment as follows: temperature and pH – BSS 17.1.4.27:1980, by рН-meter Multi HQ440d with integrated temperature sensor; suspended solids – BSS 17.1.4.04:1980; BOD5 – BSS EN 1899-1:2004 and BSS EN 1899-2:2004; COD – ISO 15705:2002 by Spectrophotometer – DR and Thermal reactor-DRB 200; total N and total P by UV/VIS Spectrophotometer and standard cuvette tests of “Hach-Lange” Company, Germany. It was found that: 1) Untreated wastewater (MWWTP input) is characterized by: temperature 7.8oC – 23.0oC, pH 7.47 – 8.41 pH units, suspended solids 46.0 – 167.5 mg/L, BOD 568.4 – 169.3 mg/L, COD 154.4 – 386.5 mg/L, total N 13.0 – 34.6 mg/L and total P 1.95 – 4.40 mg/L; 2) Treated waste water (MWWTP output) is characterized by: temperature 8.2 – 22.3oC, pH 7.24 – 7.40 pH units, suspended solids 1.90 – 35.7 mg/L, BOD5 1.30 – 13.3 mg/L, COD 15.0 mg/L – 34.9 mg/L, total N 2.80 11.6 mg/L and total P 0.60 – 3.67 mg/L; 3) Effectiveness of wastewater treatment by different indicators is as follows: suspended solids 80.5 – 93.6%, BOD5 95.7 – 96.4%, COD 89.0 – 90.8%, total N 64.3% – 74.0% and total P 28.0 – 70.5%; 4) Treated wastewater meets the regulatory requirements for discharge into the receiving water body – Bedechka river by indicators: suspended solids, BOD5, COD, total N and total P (in 2013 and 2014), and deviates from them by content of total N in January 2012 and total P in 2011 and 2012; 5) Treated wastewater meets the regulatory requirements for irrigation of crops by all investigated indices (temperature, pH, suspended solids, BOD5, COD, total N and total P); 6) Despite the high efficiency of the wastewater treatment in MWWTP the problem with nutrients (N, P) is not entirely resolved, which requires improving the technological operation of WWTP and use of suitable additives for their elimination.