Efficiency of Various Granular Activated Carbon Adsorbents in the Treatment of Waste Water Generated from Research and Development Laboratories: A Case Study

A host of chemicals/biochemicals is used in many research laboratories (RL) for R&D activities for various purposes. Such diverse R&D activities generate comparatively small quantities of waste streams with widely varying compositions. These waste streams may include aqueous solutions, organic solvents, heavy metals, and hazardous chemicals. As a result, the effluents generated in RL are highly toxic in nature, necessitating prior treatment before its discharge into the sewerage system.

In the present study, one of the RL effluents was characterized by the volume generated and chemical composition. Then a physicochemical treatment (PCT) sequence was evaluated with the objective of verifying the discharge standards in conformity with the Indian Standards.

In the PCT sequence, first the RL effluent was treated with lime and cationic polyelectrolyte sufloc-SN1 at a dosage of 400 and 2 mg L⁻¹ respectively. After chemical treatment, the residual COD is 120.72 ± 13.97 mg L⁻¹. The other analyzed parameters are within the prescribed Norms. However, sometimes pollution load exceeds the prescribed Norms (IS: 2490-1982) due to the quantitative and qualitative variability of the analyses carried out in the RL, which results in different effluent compositions. So to reduce the residual COD and to overcome the future pollution load problems further treatment is necessary. The methods commonly employed for the destruction of residual COD are oxidation by means of ozone, hydrogen peroxide or adsorption by porous solids such as activated carbon, fly ash, and natural clays. Among these, Sorption on granular activated carbon (GAC) is one of the most widely used methods in water and wastewater treatments. GAC is considered one of the most effective adsorbents, especially for those substances containing refractory organic compounds that persist in the environment and resist biodegradation. In the adsorption process, the choice of GAC is justified by its good adsorbing capacity, due to the high surface area, resulting from the high porosity.

The objective of this study is to compare the adsorption efficiencies of two different GAC adsorbents with respect to the removal of residual TOC/COD from RL effluent. The adsorption efficiency for the two sets of GAC was determined by Freundlich adsorption model and breakthrough curve studies. Then the adsorbent with higher adsorption efficiency was chosen, and used in Bed depth service time model experiments to find the carbon bed efficiency. Further studies on chemical regeneration of chosen GAC was carried out to restore the maximum adsorption capacity and to retain as much as possible, the original pore structure of the adsorbent. Based on the experimental results, a full-scale adsorber design and treatment cost evaluation was done for both GAC adsorbents.