Investigation of the inhibitory effects of heavy metals on heterotrophic biomass activity and their mitigation through the use of natural minerals

Abstract

This study examined the inhibitory effects of lead, copper, nickel and zinc on heterotrophic biomass and their potential mitigation through the use of low-cost, natural minerals. Activated sludge was placed in batch reactors and specific heavy metal concentrations were added. Subsequently, the biomass specific oxygen uptake rate (sOUR) was determined to assess the level of biomass inhibition. Biomass inhibition by heavy metals followed the order Cu²⁺>Pb²⁺>Zn²⁺>Ni²⁺, with copper being the most toxic metal, causing high inhibition of heterotrophic biomass even at relatively low concentrations (i.e. 10 mg·L⁻¹). Zn had very small toxic effect at 10 mg·L⁻¹, while at 40 mg·L⁻¹ the level of biomass inhibition reached 80%. Nickel stimulated activated sludge activity at concentrations of the order of 10 mg·L⁻¹. The addition of 10 g·L⁻¹ bentonite and zeolite in activated sludge resulted in the decrease of the inhibitory effect of heavy metals on biomass respiratory activity. In some cases, mineral addition was very favorable as inhibition was reduced from 69–90% to less than 55% and even up to 12%. The beneficial action of minerals is attributed both to the adsorption of heavy metals on the mineral and on the potential aggregation between mineral and sludge particles.

Keywords:

• Toxicity
• heavy metals
• activated sludge
• minerals
• biomass inhibition

Acknowledgments

This research has been co-financed by the European Union (European Social Fund – ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) - Research Funding Program: Heraclitus II. Investing in knowledge society through the European Social Fund.