Performance Analysis of Poly Aluminium Chloride (PAC) in Turbidity, COD, and Microbial Load Reduction from Domestic Washing Machine Effluent and Urban Lake Water

Abstract

This study evaluates Poly Aluminium Chloride (PAC) as a coagulant for improving water quality by removing turbidity, chemical oxygen demand (COD), and microbial contaminants. Samples were collected from domestic washing machine effluent and an urban lake in Mysuru, Karnataka. Initial laboratory tests involved creating controlled turbidity levels using Bentonite clay to evaluate the effectiveness of PAC at different concentrations, followed by application to Domestic Washing Machine (DWM) Effluent and Urban Lake (UL) water. PAC achieved substantial reductions in turbidity, COD, and microbial load even at low dosages, producing compact sludge. The results confirm PAC as an efficient, sustainable coagulant suitable for urban and semi-urban water treatment applications in India.

Introduction

Water is a crucial resource for life, but rapid urbanization and industrial growth have increased water demand and degraded quality, especially in urban lakes. These freshwater bodies now receive large volumes of untreated wastewater, including domestic laundry effluents, which are high in detergents, surfactants, and microbial contaminants.

Traditional coagulants like alum are commonly used for water treatment but have limitations such as high sludge production and residual aluminium. Poly Aluminium Chloride (PAC), a pre-polymerized coagulant, offers several advantages including:

• Greater turbidity and COD removal

• Lower dosage requirements

• Reduced sludge volume

• Better performance over a wider pH and temperature range

Despite international success, PAC use in India remains limited, especially for complex wastewater like domestic laundry effluent.

Study Objectives

1. Evaluate PAC's efficiency in removing turbidity, COD, and microbial contaminants

2. Assess how pH and dosage affect treatment

3. Identify optimal operational parameters for PAC application

Literature Review Highlights

• PAC generally outperforms alum in turbidity and COD removal, sludge reduction, and cost-efficiency.

• Advanced treatments like membranes and ozonation are effective but more expensive.

• PAC is confirmed effective across various effluents, including tofu wastewater and industrial laundry.

Materials & Methods

• Samples: Domestic washing machine wastewater and water from Kukkarahalli Lake in Mysuru.

• PAC and bentonite clay used for coagulation testing.

• Jar test method used to simulate real-world treatment and optimize PAC dosage and pH.

• Parameters measured include turbidity, pH, COD, bacterial count, and sludge volume.

• EDX analysis was performed on dried sludge to determine its elemental composition post-treatment.

Conclusion

The study successfully evaluated the effectiveness of Poly Aluminium Chloride (PAC) in treating various water types synthetic bentonite-induced turbid water, domestic washing machine (DWM) effluent, and urban lake (UL) water focusing on the removal of turbidity, chemical oxygen demand (COD), and microbial contaminants. The findings confirmed that PAC is a highly efficient coagulant, particularly in reducing turbidity and COD across all sample types. In synthetic turbid water up to 40NTU, PAC achieved near-complete turbidity removal at dosages ranging from 0.45 to 1.0 g/L, with final turbidity values dropping below 0 NTU due to enhanced clarity. Similarly, in DWM effluent, turbidity was reduced from an initial 52.2 NTU to a minimum of -0.75 NTU at an optimal dosage of 0.6 g/L, while COD was reduced from 2000 mg/L to 280 mg/L, reflecting an 86% reduction. For UL water, PAC reduced turbidity from 2.5 NTU to -0.16 NTU at an optimal dosage of 0.035 g/L and COD from 2800 mg/L to just 40 mg/L an impressive 98.57% reduction demonstrating its strong potential for treating polluted surface water. Microbial analysis revealed mixed outcomes. While DWM effluent showed no reduction in bacterial load (remaining at 6000 CFU/mL before and after treatment), the urban lake water showed a reduction from 6000 CFU/mL to 2000 CFU/mL. These results indicate that PAC alone may not be sufficient for effective bacterial removal in heavily contaminated greywater but can contribute to microbial reduction in less polluted water, likely due to enmeshment of microbial cells in flocs and their removal through sedimentation. Thus, for complete microbial control, especially in greywater treatment, PAC should be supplemented with a disinfection step. The influence of pH and coagulant dosage was critically observed throughout the study. Optimal performance occurred within the effective PAC pH range of 6–9. In DWM effluent, pH adjustment from 9.97 to 7.50 using 0.1 N H?SO? was necessary for efficient flocculation, with the final pH at optimal dosage recorded at 6.25. In contrast, urban lake water treatment did not require pH adjustment as the raw sample pH of 8.52 was already within the effective range. Overdosage beyond optimal PAC levels resulted in particle restabilization and higher residual turbidity, emphasizing the need for careful dosage control. Sludge generation trends were consistent across all samples, increasing with dosage but remaining within manageable limits, ranging from 7 mL in UL water to 28 mL in DWM effluent. Further insight into the treatment process was gained through Energy Dispersive X-ray (EDX) characterization of the sludge generated after PAC treatment. The elemental composition revealed high concentrations of aluminium (11.5%), confirming the presence of residual PAC, and significant amounts of carbon (27.3%) and oxygen (32.5%), indicating organic matter such as surfactants and microbial biomass. The detection of sodium (10.2%), sulphur (3.2%), and chlorine (12.2%) confirmed the presence of detergent-related compounds, while silicon and calcium suggested traces of soil particles and fabric residues. These findings validate the removal of both organic and inorganic pollutants during coagulation. In conclusion, the study demonstrates that PAC is a highly effective coagulant for turbidity and COD reduction, with partial efficacy in microbial removal. The success of treatment depends heavily on pH control and optimal coagulant dosage. The combination of performance data and EDX analysis provides strong evidence for PAC’s applicability in practical water treatment scenarios, particularly when integrated with complementary processes for complete contaminant removal. Beyond laboratory validation, the findings highlight the significance of PAC for decentralized wastewater treatment, especially in commercial establishments such as laundries, hostels, and residential complexes that discharge untreated effluent into drains and waterbodies. By adopting PAC-based treatment at the source, such facilities can substantially reduce the organic and particulate load entering municipal sewers, thereby easing the burden on centralized treatment plants and minimizing pollution of urban water bodies. This approach promotes sustainable water management while offering a cost-effective solution adaptable to both urban and semi-urban contexts.

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Copyright

Copyright © 2025 Vishwanath S Arakeri, Pallavi N. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.