Optimizing the Use of Bitterns with Calcium Hydroxide as Coagulants for Textile Wastewater Treatment

Department of Environmental Engineering, Institut Teknologi Sepuluh Nopember, Surabaya 60111, Indonesia

^* Corresponding author: ervin@its.ac.id

Abstract

The rapid growth of Indonesia’s textile industry has intensified wastewater management challenges, particularly in meeting effluent quality standards. This study explores the feasibility of utilizing bittern, a magnesium-rich by-product of salt production, as a cost-effective and sustainable coagulant for textile wastewater treatment, in combination with calcium hydroxide (Ca(OH)₂), and evaluates its performance against polyaluminum chloride (PAC). Laboratory-scale coagulation–flocculation and optimization experiments were performed to assess the removal efficiencies of turbidity, BOD, COD, and chromium. The results showed that bittern + Ca(OH)₂ achieved the highest removal of turbidity (82%) and total chromium (77%), while PAC was more effective for organic pollutants (BOD 94%, COD 88%). Using Response Surface Methodology (RSM), the optimal mixing conditions were established at 192.43 rpm for rapid mixing and 25.86 rpm for slow mixing. Although some parameters remained above the national discharge standards (Regulation of the Minister of Environment and Forestry of the Republic of Indonesia No. P.16 of 2019), the use of bittern could substantially reduce chemical costs and sludge generation, contributing to greener industrial practices, and the circular economy goals of Indonesia’s wastewater management policies.