Coagulation of alkalized municipal wastewater using seawater bittern

Ayoub, G.M., Merhebi, F., Robinson, D. and El-Fadel, M. (1999) Coagulation of alkalized municipal wastewater using seawater bittern. Water Environment Research, 71 (4), 443-453.

Abstract

Laboratory studies were conducted to determine the efficacy of seawater bittern as a coagulant for the treatment of municipal wastewater. Freshly collected grab samples of municipal wastewater from two different discharge points were alkalinized to pH levels of 11.4 ± 0.1 by adding slaked lime or caustic soda. Serial dosages of liquid bittern were added and the jar test technique was used to determine the effect of the process on a number of determinant parameters.

Seawater, liquid bittern, and dried bittern were used as coagulating agents in one of the four test sets to determine the effect of the three magnesium ion (${\rm Mg}^{2+}$) sources on effluent characteristics. The extent of bacterial inactivation and the use of ${\rm CO}_{2}$ to control effluent pH were investigated as well. Seawater liquid bittern was found to be an effective and economic source of ${\rm Mg}^{2+}$ that may be used in the treatment of municipal wastewater. Turbidity and suspended solids removal exceeded 95%. Recorded chemical oxygen demand removals were in excess of 75%, while dissolved organic carbon removals averaged approximately 30%.

Very limited differences in efficiency of treatment were noted between the use of slaked lime and caustic soda as alkalinizing agents. Besides its reduced bulk when compared to seawater, liquid bittern demonstrated an added advantage (over seawater and dry bittern) in imparting the least increase in dissolved solids to treated effluent. The process is very effective in inactivating fecal bacteria. Carbonation by the addition of ${\rm CO}_{2}$ in concentrations ranging between 56 and 362 mL/L (depending on initial levels of pH, alkalinity, and the nature of the alkalinizing agent used) were needed to neutralize clarified supernatants to acceptable levels.

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