Managing habitat and microorganisms for degrading industrial effluents: a study case

Abstract

The efficiency of a treatment for industrial effluents based on a combination of habitat and microbial population management was tested in a metallurgic plant in Córdoba, Argentina. Effluents (between 30 - 40 m³ day) were originated from a) zinc process (20%), b) engine washing (70%), and c) sewage (10%). The treatment process included a combination of three managed habitats: aquatic (pond), wetland (flooding plots), and agricultural land (flooding and crop plots). The three habitats were managed to optimize the degrading activity of water, soil, and phyllosphere microorganisms. Management practices included introduction of terrestrial and aquatic vegetation, water aeration, sediment removal, and inoculation of selected native microorganisms. Efficiency was assessed through five years using the following parameters: a) monthly: water pH and abundance of degrading and coliform bacteria in the pond b) yearly: Zn, Cr and mineral oil content in the underground water (9 m deep), sediments in the ponds and organic matter in the subsoil (1 and 2 m deep). Water pH was permanently high (8.4 -10.9), whereas abundance of degrading microorganisms was very low at the beginning (log 1.2/ ml) increasing through the following years and with fluctuations of between log 3.6 and 8.9/ ml. No increase in bacterial abundance was detected after inoculation. Coliform bacteria were scarcely observed. High concentration of Zn (6.48 – 7.08 mg/kg) and Cr (0.19 – 0.50 mg/kg) and low mineral oil content (0.23 – 1.01 mg/kg) were detected in the pond’s sediments. None of these components were detected in underground water and subsoil. Habitat management allowed an efficient degradation of sewage and mineral oils. The system does not produce waste material such as sludge, water, nor underground water pollution.