Vermiproductivity, maturation and microbiological changes derived from the use of liquid anaerobic digestate during the vermicomposting of market waste.

Dafne Crutchik,Claudia Pabón-Pereira,Gustavo Rodríguez-Valdecantos,Javier Bravo,Gabriela Bustos,Bernardo González

doi:10.2166/wst.2020.427

Abstract

Recently, it has been suggested that the liquid fraction of anaerobic digestate, derived from the treatment of wastewater and solid wastes, could be used in vermicomposting as a solution to its disposal, and even for its valorization. Nevertheless, the literature does not provide enough information about its impact on the process of vermicomposting itself and on the final quality of the end-product. In this study, the effect of different doses of digestate in the vermicomposting process treating market waste is assessed measuring earthworm population dynamics, the bacterial community succession present in the vermibeds, as well as maturation and the end-quality of the vermicompost. Our results show that the addition of liquid digestate to the vermibeds increased the earthworms biomass, i.e. 71%, 94% and 168% in control, and vermibeds with 30% and 60% digestate, respectively. Further, the increase in the amount of N in the vermicompost decreased as the digestate addition increased, i.e. 75%, 8%, 3%. The maturity achieved was high in all treatments as shown by the C/N ratio, 7.98, 7.40 and 10.20, and the high seed germination rate, above 90%. Finally, the succession of the microbial community was not disturbed and compositional stabilization was reached after 92 days.

Highlights

Anaerobic digestion is a mature and valuable technology to treat wastewater and solid wastes due to its capacity for energy and nutrient recovery
The evolution of vermicomposting temperature for the three treatments was followed during vermicomposting process (Figure 1)
Afterwards, it increased to 22 C at day 28, when the vermibeds were fed with fresh market waste, and subsequently decreased to around 18.5 C, keeping this temperature until day 65

Summary

Introduction

Anaerobic digestion is a mature and valuable technology to treat wastewater and solid wastes due to its capacity for energy and nutrient recovery. While the carbon is mostly recovered in the form of methane and carbon dioxide in the biogas, most of the nutrients present in the raw waste are still present in the digestate, which provides a high value as fertilizer and soil conditioner (Arthurson ). The management of digestate presents serious challenges related to its composition and large volumes (Golkowska et al ; Dahlin et al ; Zeng et al ). Costs of its handling can be quite high, when dealing with raw digestate with high water content; 1.94 €/m3 have been reported for direct application (Drosg et al ), and they can go as high as 13–32 €/ton input without including transport costs (Golkowska et al ). Options that reduce the volume and increase the transportability and fertilizing value of the digestate are desired. Ion exchange, and struvite precipitation can recover nutrients, and evaporation and membrane processes allow for nutrient concentration and water purification; costs in this case go from 5.45 up to 10 € per cubic meter (Dahlin et al ; Drosg et al )

Methods

Results

Conclusion