Development of a low-cost alternative for metal removal from textile wastewater

Industrial wastewater contains many pollutants in general. Our interest is focusing on heavy metals found in textile effluents because of their known toxicity effect in the environment. Wastewater from a textile industry (UTEXRWA) in Rwanda has been screened for the occurrence of Cd, Cr, Cu, Pb and Zn. Batch and pilot experiments on adsorption equilibrium, kinetics and sulfide precipitation using volcanic rock as adsorbent and packing material have been investigated. A low cost and integrated system for treatment has been developed; combining an anaerobic bioreactor as main treatment step followed by a polishing step composed by a polishing pond containing algae, duckweed and water hyacinth. More than 90 % of metal removal was achieved in the bioreactor, with metal sulfide precipitation as long term removal mechanism. The use of algae and duckweed as alternative for water hyacinth plants showed no differences between algae and duckweed ponds based on abiotic differences. Overall, both systems' performance was close and these systems are well suited as polishing step for wastewater containing low metal concentrations. The integrated system for heavy metal removal showed how two complementary systems for heavy metal removal can work in combination and good removal performance can therefore be achieved.