Natural Low Cost Adsorbents for Dairy Wastewater Treatment

Abstract

Dairy industry is one of the major polluting industries in Palestine and elsewhere. Locally, dairy wastewater is discharged into sewer system or open spaces without any kind of treatment causing high organic loads and septic degradation. This project investigates the treatment of dairy wastewater by adsorption on stone cutting solid waste, marl and clay soil. Curves of percentage reduction in Chemical Oxygen Demand (COD) are obtained for stirred batch experiments.

The technical feasibility of the three adsorbents was confirmed. Then, the treatment efficiency is investigated as functions of operating parameters including: stirring rate, pH, solid to liquid ratio (dosage), organic load and contact time.

For the three adsorbents, increasing stirring rate increases the adsorption rate and thus reduces the time needed to reach equilibrium, with no effect on equilibrium efficiency. When wastewater is contacted with particles with no stirring, a time period of 9 to 12 days is required to reach equilibrium, compared to few hours with stirring at the same conditions. This indicates that the adsorption process is mass transfer controlled. Both the rate of adsorption and the final equilibrium adsorption increases with increasing particle dosage. The effect of pH is found to be unique using stone cutting particles; the adsorption occurs mainly at a pH value of around 6. Marl adsorption experiments favored alkaline conditions, while clay showed a trend toward acidic range. Natural soil is mainly alkaline and this means the adsorption probability is weak at normal conditions, but marl has a great probability for pollution. The equilibrium isotherm for both marl and clay was of none favored type. Stone cutting experiments have a linear isotherm.