Aquatic worms (Tubificidae) facilitate productivity of macrophyte Azolla filiculoides in a wastewater biocascade system

Due to high waste sludge disposal at wastewater treatment plants and increasing phosphorus scarcity, there is a need to combine waste removal and nutrient recovery. One way to achieve this is by incorporating ecological processes intowastewater treatment. Positive species interactions, such as facilitation, are critical to increase productivity of biomass and nutrient recovery. In this study we showed the potential of using ecological principles including interspecific facilitation processes of aquatic plants (Azolla filiculoides) and worms (Oligochaeta, Tubificidae) in waste recovery and biomass production. This was investigated by developing a biocascade with monocultures of plants and aquatic worms that was fed on activated sludge. Tubificidae had an average relative growth rate of 0.02 g g(-1)DWd(-1) whereby sludge predation resulted in 45% sludge reduction. When Tubificidae were present in the biocascade, A. filiculoides biomass production significantly increased to a relative growth rate of 0.15 g g(-1)DWd(-1). The activity of Tubificidaemostly affected total suspended solids, chemical oxygen demand and ammonium concentration in the first compartment of the biocascade. Additionally, nitrification rates increased and the water acidified, leading to increased carbon dioxide concentrations and dissolved phosphorusbindingmetals (zinc, iron, aluminiumand manganese) that stimulated A. filiculoides growth. The high sludge reduction (45%) and phosphorus sequestration (133 mmol m(-3) d(-1)) showa strong potential of the biocascade for combined sludge waste reduction and phosphorus recovery from wastewater. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

This study demonstrated the potential of applying ecological principles in waste recovery and biomass production in wastewater treatment, utilizing positive species interactions between aquatic plants and worms. The use of a biocascade significantly increased biomass production of Azolla filiculoides and reduced waste sludge through interspecific facilitation processes.