IMPACT OF HIGH CHLORIDE WASTEWATER ON AN ANAEROBIC/ANOXIC/AEROBIC PROCESS WITH AND WITHOUT INOCULATION OF CHLORIDE ACCLIMATED SEEDS THONGCHAI PANSWAD* * M and CHADARUT ANAN Department of Environmental Engineering, Chulalongkorn University, Bangkok, 10330, Thailand (First received January 1998; accepted July 1998) AbstractÐThe performance of an anaerobic/anoxic/aerobic (2 + 2 + 12 h of hydraulic retention time) process with and without inoculation of sodium chloride acclimated seeds was investigated using a syn- thetic wastewater with COD, nitrogen, and phosphorus of 500, 25, and 15 mg/l, respectively. The sodium chloride in the fed wastewaters varied from 0 (control) to 30 g/l while maintaining the solids retention time at 10 d. The results indicated that the organic (in terms of COD) and nitrogen removal eciency of the non-acclimated system was reduced from 97 to 60% and 88 to 68% a the salt content increased from 0 to 30 g/l NaCl, respectively, whereas it decreased from 90 to 71% and from 85 to 70% as the salt content rose from 5 to 30 g/l NaCl, respectively, in the salt acclimated system. The phosphorus removal in this study was not as high as those reported elsewhere; probably due to the intense sensitivity of poly-P bacteria to high salt concentration. Time required to reach steady state was higher (10±20 d) for the non-acclimated system than that with acclimation (8±15 d). In addition, it is apparent that the system started up with high salt content and acclimated seed could better tolerate a shock of 70 g/l NaCl as well as required less recuperation period than that initially fed with low salinity and without acclimation. # 1999 Elsevier Science Ltd. All rights reserved Key wordsÐsalinity, biological nutrient removal, anaerobic/anoxic/aerobic, Phoredox INTRODUCTION At present, the problem of water supply shortage is getting worse in many countries, especially in arid and coastal areas. Using seawater in the situations which high quality water is not essential such as toi- let ¯ushing has been practised in Hong Kong and some certain areas for many years. The sewage resulting from such activities will hence contain a high salt content. Seawater in®ltration is also another cause of high salinity in the sewage in many regions. In addition, certain industries, e.g., tanning, pickling, seafood canning, etc., also dis- charge salty wastewater from their manufacturing processes. The high salt content in the wastewaters can pose certain problems in treatment systems par- ticularly on biological units. Eects of salt on the performance of some traditional aerobic- and an- aerobic-biological processes have been reported elsewhere (Lawton and Eggert, 1957; Stewart et al., 1962; Kincannon and Gaudy, 1966; Tokuz and Eckenfelder, 1979; Matsuo and Hosobora, 1988; Hamoda and Al-Attar, 1995; Mendez et al., 1995). This study was initiated to determine the salinity eects on the performance of a combined anaero- bic/anoxic/aerobic system. MATERIALS AND METHODS All experiments were done based on two lab-scale units run in parallel as shown in Fig. 1. Table 1 represents the unit details and operational criteria. The synthetic waste- water with the composition as shown in Table 2 was fed by diaphragm pumps to the systems while the excess sludge withdrawal was done manually and daily from the aerobic tanks in order to keep the solids retention time (SRT) of 10 d throughout the study. An equal volume of treated euent was added to the aerobic tanks so that the eect on hydraulic retention time (HRT) of the system was minimized. The fed wastewater was prepared such that it contained sodium chloride in the concentrations of 0 (control), 5, 10, 20, or 30 g/l. Units A and B were started up without and with the inoculation of the sodium chloride acclimated seeds (taken from a local salt-rich tannery wastewater treatment plant), respectively. Samples were taken and analyzed according to standard methods (APHA et al., 1995), except for the COD analysis in which a high dose of HgSO 4 (at the ratio of HgSO 4 :Cl À =10:1) was added to the samples to eradicate the chloride interference. After the system's performance at the steady state was evalu- ated, both units were shocked with 70 g/l of NaCl for four consecutive days before being allowed to return to the original conditions, i.e., the same NaCl doses as those at the steady state. The time period required for the systems Wat. Res. Vol. 33, No. 5, pp. 1165±1172, 1999 # 1999 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/99/$ - see front matter PII: S0043-1354(98)00314-5 *Author to whom all correspondence should be addressed. [Fax: +662-218-6666]. 1165