Effect of biosolid hydrochar on toxicity to earthworms and brine shrimp

Abstract

The hydrothermal carbonization of sewage sludge has been studied as an alternative technique for the conversion of sewage sludge into value-added products, such as soil amendments. We tested the toxicity of biosolid hydrochar (Sewchar) to earthworms. Additionally, the toxicity of Sewchar process water filtrate with and without pH adjustment was assessed, using brine shrimps as a model organism. For a Sewchar application of 40 Mg ha, the earthworms significantly preferred the side of the vessel with the reference soil (control) over side of the vessel with the Sewchar treatments. There was no acute toxicity of Sewchar to earthworms within the studied concentration range (up to 80 Mg ha). Regarding the Sewchar process water filtrate, the median lethal concentration (LC50) to the shrimps was 8.1% for the treatments in which the pH was not adjusted and 54.8% for the treatments in which the pH was adjusted to 8.5. The lethality to the shrimps significantly increased as the amount of Sewchar process water filtrate increased. In the future, specific toxic substances in Sewchar and its process water filtrate, as well as their interactions with soil properties and their impacts on organisms, should be elucidated. Additionally, it should be identified whether the amount of the toxic compounds satisfies the corresponding legal requirements for the safe application of Sewchar and its process water filtrate.

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization

“…So far, only one study has conducted a limited ecotoxicological assessment. With the application of biosolids-derived hydrochar (190 °C for 4 h) up to 80 Mg/ha or 4 wt%, no acute toxicity to earthworms was identified, although earthworms showed significant preference to control soil rather than hydrochar amended (Melo et al, 2017). Limited reports have shown that using MS-derived hydrochar may pose environmental and human health risks but probably depending on the hydrochar properties, soil properties, and soil biota.…”

Toxicity evaluation of process water from hydrothermal carbonization of sugarcane industry by-products

“…Previous studies to assess the toxic effect of hydrochar have focused on experiments with plants, in particular, evaluating the germination processes (Bargmann et al 2013;Fang et al 2015) and growth (Rillig et al 2010;Reibe et al 2015) as well as study the changes caused in the soil biota by hydrochar (George et al 2012;Salem et al 2013;Melo et al 2017c). Process water recirculation in the new HTC process has been reported in the literature as its main use (Lu et al 2014;Weiner et al 2014;Kabadayi Catalkopru et al 2017).…”

“…Process water recirculation in the new HTC process has been reported in the literature as its main use (Lu et al 2014;Weiner et al 2014;Kabadayi Catalkopru et al 2017). However, the process water also has been evaluated as a culture medium for algal growth (Biller et al 2012;Hognon et al 2015), in seed germination studies (Bargmann et al 2013;Vozhdayev et al 2015), and recently using Artemia salina to assess its toxic effects (Melo et al 2017c).…”

Hydrothermal Extraction of Microalgae Fatty Acid Influences Hydrochar Phytotoxicity

“…Furthermore, volatile compounds such as these may be associated with phytotoxic effects (Bargmann et al, 2013;Melo et al, 2017). There is no statistically significant difference in the relative germination number between the three conditions tested in the growth trials-all three hydrochar conditions do not affect the number of cress seeds germinating.…”