Agua De Produccion

Process Biochemistry 38 (2002) 399 Á/403 www.elsevier.com/locate/procbio

Empirical models for biological treatment of saline wastewater in rotating biodisc contactor
Fikret Kargi *
Department of Environmental Engineering, Dokuz Eylul University, Buca, Izmir, Turkey ¨ Received 10 January 2002; received in revised form 15 March 2002; accepted 10 April 2002

Abstract Biological treatment ofsaline wastewater in a rotating bio-disc contactor (RBC) was investigated under different operating conditions, such as A /Q ratio, feed COD, COD loading and salt concentrations. COD removal efficiencies were determined and correlated with the aforementioned variables. The constants of the proposed empirical equation were determined using experimental data. Plots of COD removal efficiency asfunctions of these variables were established in order to estimate the performance of the system under different operating conditions. # 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Empirical modelling; Saline wastewater; RBC; Biological treatment

1. Introduction Chemical oxygen demand (COD) removal efficiencies in the biological treatment of saline wastewater are usually low because ofinhibitory effects of salt on microbial flora. Salt (NaCl) concentrations /1% cause plasmolysis of cells resulting in reduced biological activity. A number of studies have reported on adverse effects of salt on microorganisms. Early studies with Bacillus cereus indicated that the endogenous respiration rate of the culture increased with NaCl concentrations up to 1%, but decreased above thisconcentration [1]. In a study on adaptation of Escherichia coli to NaCl, cells exhibited the greatest degree of adaptability in the early stationary growth phase compared to other growth phases [2]. Reductions in salt concentration were reported to have more adverse effects on microbial flora than increases in NaCl content [3,4]. Rapid changes in salt concentration caused immediate release of cellularconstituents resulting in an increase in soluble COD [4]. Sludges grown in high salt concentrations exhibited low carbohydrate and protein, but high lipid and RNA content. In addition, rapid shifts in salt concentration
* Tel.: '/90-232-453-1143; fax: '/90-232-453-1153 E-mail address: fikret.kargi@deu.edu.tr (F. Kargi).

were reported to be more inhibitory than gradual shifts [3,4]. Biologicaltreatment of saline wastewater has been investigated in different systems by different researchers. In a study on biological treatment of saline wastewater in a trickling biological filter, low biological oxygen demand (BOD) removal efficiencies were observed when the salt concentration exceeded 20 g/l [5]. When saline wastewater was treated in an extended aeration process, low percent BODremovals were obtained with severe changes in salt concentrations along with high organic loading [6]. Ludzack and Noran [7] investigated the effects of salt concentrations up to 20 g/l on the activated sludge process. Salt concentrations /1% resulted in low BOD removal and flocculation efficiencies. The adverse effects of salt may be reduced to some extent by using fixed biofilm systems in thetreatment of saline wastewaters. When a rotating bio-disc contactor (RBC) unit was used for treatment of domestic wastewater containing seawater salinity (2%), up to 64% COD removal was obtained [8]. Wastewaters rich in halogenated organics were treated at different salt concentrations and BOD removal performance was found to decrease with increasing salt concentration [9]. Utilization of halophilicbacteria in biological treatment of saline wastewater may overcome the adverse

0032-9592/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 9 5 9 2 ( 0 2 ) 0 0 1 3 7 - 1

400

F. Kargi / Process Biochemistry 38 (2002) 399 Á/403

effects of salt and result in high COD removal efficiencies. Woolard and Irvine studied the treatment of hypersaline...