Integration of coagulation-flocculation process for improved solid–liquid separation of anaerobically treated textile effluent

ABSTRACT

Anaerobic process is a promising technique for textile effluent treatment. However, poor solid–liquid separation and residual chemical oxygen demand (COD) in the treated effluent limit its scope for industrial applications. The study analyzed the nature of suspended microbial biomass in the anaerobically treated effluent and further targeted its feasible separation process. The size of the majority of suspended biomass (82%) particles ranged from 500 to 1000 nm. The suspended biomass showed 37.13% hydrophobicity and −15.4 mV zeta potential. The optimization of the coagulation-flocculation (CF) process showed 93% turbidity removal at 400 mg/L of alum, 8 mg/L of a cationic polymer and acidic pH 4, through one variable at a time approach. The optimized results using Central Composite Design (CCD) were experimentally validated, and 97% turbidity removal was recorded at 400 mg/L alum concentration, 12 mg/L of the cationic polymer, and pH 3.2. The results obtained were statistically significant, with a high regression coefficient (R² = 0.97) at 95% confidence limits. The final treated effluent after CF showed 67% COD removal (from 862 ± 40 to 280 ± 14 mg/L) with 83% color removal (from 740 to 124 Hazen). Hence, the integration of the CF process with the anaerobic process could be a promising approach for textile effluent treatment.

GRAPHICAL ABSTRACT

KEYWORDS:

• Coagulation
• flocculation
• cationic polymer
• alum
• effluent treatment

Acknowledgments

The authors gratefully acknowledge the industrial partner for providing effluent and material support. Anushree Malik is grateful to IIT Delhi for Institute Chair Professorship funding (IITD/E-1/U-3/2019/71543). Partial financial support from the Department of Biotechnology, Government of India is gratefully acknowledged.

Disclosure statement

The authors of the present study declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Statement of novelty

After anaerobic treatment, the treated effluent had yellow tinch with high turbidity and residual COD, making it unfit for direct discharge in the waterbodies. In this study, the improvement of solid–liquid separation of anaerobically treated effluent was achieved using CF method through RSM. This process could be more economical due to easy availability and cost-effectiveness of coagulants and flocculants.

Highlights

• Stable zeta potential (−15.4 mV) & hydrophobic nature hindered solid–liquid separation

• CF process was optimized via RSM to improve the treatment efficiency

• 97% turbidity removal at alum (400 mg/L), cationic polymer (12 mg/L) & pH 3.2

• 83% color removal & 67% COD reduction achieved

Additional information

Funding

The work was supported by the Institute Chair Professorship funding, IIT Delhi [IITD/E-1/U-3/2019/71543].