Effect of Pumice Particle Size on Organic Matter Removal (BOD5 and COD) from Slaughterhouse Wastewater

Abstract

This study evaluates the effect of pumice stone particle size on organic matter removal, expressed as Biochemical Oxygen Demand (BOD₅) and Chemical Oxygen Demand (COD) from highly polluted municipal slaughterhouse wastewater. A pilot-scale continuous flow filtration system was implemented using three different pumice stone diameters (5 mm, 10 mm, and 15 mm) under a constant hydraulic retention time of 1 h 03´ 39”. Raw wastewater exhibited extremely high average organic loads of 1,467.0 mg/L for BOD₅ and 2,935.1 mg/L for COD. Statistical analysis (ANOVA and Tukey’s test) demonstrated that the removal efficiency is influenced by the filter media's granulometry (p-value < 0.0001). The 5 mm diameter pumice stone recorded the highest removal rates, achieving average efficiencies of 49.3 % for BOD₅ and 44.1 % for COD, compared to 33.2 % and 32.0 % for the 15 mm media, respectively. The findings indicate that reducing the pumice particle size substantially increases the available surface area and pore multiplication, thereby maximizing organic matter retention. Although smaller granulometry optimizes the physical-chemical adsorption capacity of the volcanic rock, complementary treatments are required to fully meet environmental discharge standards for high-strength agro-industrial effluents.