Is digestate safe? A study on its ecotoxicity and environmental risk on a pig manure

Abstract

Abstract. Digestate represents a precious by-product in particular in agriculture, however its impact on the environment and human health is still unexplored. In this work, the toxicity of a pig slurry digestate was assessed through 7 ecotoxicity tests and considering 10 different endpoints. Besides, a synthetic index was applied to the outputs of the battery of tests for the environmental risk assessment, in order to evaluate the opportunity to use directly this kind of digestate in agriculture or to introduce an additional treatment. All the organisms were sensitive to digestate toxicity (EC 50 ranged from 14.22% for Cucumis sativum to 0.77% for Raphidocelis subcapitata). The physical-chemical features at the base of this toxicity seem to be the high content of ammonium, salinity, COD, phosphate and colour. The synthetic index showed that the digestate was very toxic and associated to an extremely high environmental risk. Thus a pre-treatment is needed to reduce its toxicity and environmental impact, whatever could 2 be its exploitation.

Microalgae treatment removes nutrients and reduces ecotoxicity of diluted piggery digestate

“…It has recently been characterized from a chemical and ecotoxicological point of view (Tigini et al, 2016 Chlorella vulgaris CCAP 211/11b (Culture Collection of Algae and Protozoa, Argyll, UK) was selected for this study in view of our previous experiences with digestates (Franchino et al, 2013). Firstly, C. vulgaris was pre-grown in 250 mL Erlenmeyer flasks containing 100 mL of Removal efficiency (RE) was estimated by dividing the difference between the initial nutrient concentration and that on day n (Ci-Cn) by Ci, and then multiplied by 100, while the Elimination Capacity (EC) by dividing the difference between the nutrient concentration of two subsequent samples (Cn-1 and Cn) by the time elapsed between them.…”

“…However, particularly high ammonia concentration like that found in pig manure remains a major challenge because it is often responsible for microalgal growth inhibition (Tigini et al, 2016). Moreover, it can pose a serious environmental issue as in Europe pig farming is a major agricultural industry and many large centralised pig farms have been established.…”

“…Indeed the same piggery digestate recently analyzed through a battery of bioassays (Tigini et al, 2016) resulted as highly toxic. A secondary aim is to find a cheap and easily available substrate for microalgae cultivation in order to exploit their biomass.…”

Innovative liquid formulation of digestates for producing a biofertilizer based on Bacillus siamensis: Field testing on sweet pepper

“…Such results are in accordance with those reported by other authors ( Alburquerque et al, ; Pivato et al, ; Stefaniuk et al, ; Tigini et al, ), who also observed that as a general trend, the application of low concentrations of AD acted as a stimulant giving higher values of GI and stimulating seedling growth. Such an improvement in germination could be related not only to the nutrients provided by the digestate solutions, but also to a phytohormone‐like effect ( Emino and Warman , ; Moldes et al, ).…”

Digestate and Fugate - Fertilizers with Ecotoxicological Risks

“…Research focused on the effects of digestate on soil microbial community structure and activity also proved that direct application of digestate on soil (in contrast to compost or manure) did not stimulate microbial activity with exception of nitrification (Gomez-Brandon et al 2016). The toxicity of digestate to bacteria was also proved in the comparative study of seven ecotoxicity tests (Tigini et al 2016), where bioassay with Vibrio fisheri was the most sensitive bioassay. This recent study as probably the first scientific paper in this field clearly concludes, that the digestate represents extremely high environmental risk and that is why a pre-treatment of digestate is needed to reduce toxicity and negative environmental impact.…”