Optimization of Algal–Bacterial Biomass for Sustainable Treatment of Textile Industry Wastewater

Textile wastewater represents a major environmental challenge due to its high organic load, salinity, suspended solids, and resistance to conventional physico-chemical treatment processes, which are often energy-intensive and generate excessive secondary sludge. Integrated algal–bacterial consortia offer a sustainable alternative by coupling bacterial biodegradation with algal nutrient uptake and photosynthetic oxygen production. In this study, the treatment performance of algal, bacterial, and integrated algal–bacterial sludge systems was evaluated using real textile wastewater collected from the inlet of the effluent treatment plant at Quetta Textile Mills, Pakistan. Indigenous microalgal strains (Chlorella vulgaris and Scenedesmus) and a bacterial strain (Bacillus subtilis) were cultivated and applied under controlled laboratory conditions. Treatment efficiency was assessed at hydraulic retention times of 2, 4, 6, and 8 h by monitoring pH, chemical oxygen demand (COD), biological oxygen demand (BOD), total dissolved solids (TDS), and total suspended solids (TSS). Among all tested systems, the Chlorella vulgaris–Bacillus subtilis consortium exhibited the highest treatment efficiency, achieving approximately 95% overall pollutant removal within 8 h. COD and BOD were reduced from 1486 to 90 mg L⁻¹ and 800 to 45 mg L⁻¹, respectively, while TDS and TSS decreased from 9000 to 1033 mg L⁻¹ and 720 to 60 mg L⁻¹. The integrated system also demonstrated excellent sludge settleability, with a sludge volume index (SVI) of 30–35 mL g⁻¹, indicating efficient solid–liquid separation. The superior performance of the algal–bacterial consortium was attributed to synergistic interactions, where algal oxygen production enhanced aerobic bacterial degradation, while bacterial metabolism supplied CO₂ and nutrients to support algal growth. These findings highlight the potential of algal–bacterial sludge systems as an eco-friendly, energy-efficient, and rapid treatment strategy for high-strength textile wastewater, with strong applicability for industrial-scale wastewater management, reuse, and integration into circular bioeconomy frameworks.