Critical analysis of wastewater treatment using vermifilters: Operating parameters, wastewater quality, and greenhouse gas emissions

Abstract

Vermifiltration is a biooxidative process in which detritivorous worms interact intensely with microorganisms to eliminate contaminants present in the water. Although these systems have been presented as a plausible solution for the treatment of wastewater in rural areas, there are different parameters that can affect the removal efficiency and at a scientific level, there is no consensus on how to operate and design these systems, which It results in different alternatives and not very standardized forms of operation. This article presents a critical review of vermifiltration wastewater treatment, beginning with an analysis of related articles, followed by an evaluation of the influence of design and operational parameters, efficiency, and greenhouse gas generation. The main results of this review indicate that vermifiltration systems should use worm densities (DE) between 3000 and 6000 worms/m3, tributaries with hydraulic loading rates (HLR) below 2.5 m3/dm2, loading rates organic matter (OLR) not higher than 0.4 kgCOD/m2.d, and filter material (FM) that includes wood chips to counteract the increase in NO3- and TP concentrations generated by nitrification and mineralization. Regarding the generation of greenhouse gases (GHG), more research is required in the area, since, although the HLR and OLR can affect the process, it has not been clearly defined whether the activity of the earthworms can generate carbon sinks or GHG sources. The results of this review article allowed us to define the most important operating parameters and the operating ranges to be considered in its application and operation in rural areas.