Benefits and risks of agricultural reuse of digestates from plastic tubular digesters in Colombia

The aim of this study is to characterize the digestates from three plastic tubular digesters implemented in Colombia fed with: i) cattle manure; ii) cattle manure mixed with cheese whey; iii) pig manure. All the digesters worked under psychrophilic conditions. Physico-chemical characteristics, heavy metals, pathogens, and agronomic quality were investigated. All the digestates were characterized by physico-chemical characteristics and nutrients concentration suitable for their reuse as biofertilizer. However, these digestates may only partially replace a mineral fertilizer due to the high nutrients dilution. Heavy metals were under the detection limit of the analytical method (Pb, Hg, Ni, Mo, Cd, Chromium VI) or present at low concentration (Cu, Zn, As, Se) in all the digestates. Biodegradable organic matter and pathogens (coliform, helminths and Salmonella spp.) analysis proved that all the digestates should be post-treated before soil application in order to prevent environmental and health risks, and also to reduce residual phytotoxicity effects. The digestate from pig manure had a higher nutrient percentage (0.2, 0.6 and 0.05 % w/w of total N, P2O5 and K2O, respectively), but also higher residual phytotoxicity than the other digestates. Co digestion seemed not to significantly improve the digestate fertilizing potential. Finally, further studies should address how to improve fertilizing potential of digestates from plastic tubular digesters, avoiding environmental and health risks.

Automated summary

The study characterizes digestates from plastic tubular digesters in Colombia fed with cattle manure, cattle manure mixed with cheese whey, and pig manure. The digestates have suitable physico-chemical characteristics and nutrient concentrations for reuse as biofertilizers, but may require post-treatment for heavy metals and pathogens. Pig manure digestate has higher nutrient percentage and residual phytotoxicity compared to others. Further research is needed to improve the fertilizing potential of digestates and reduce environmental and health risks.