GLOBAL TOXICITY ASSESSMENT: CHEMICALS, ENVIRONMENTAL SAMPLES, AND ANALYTICAL METHODS Can we use Cd-contaminated macrophytes for biogas production? Katiúcia Dias Fernandes 1 & Susan Johana Benites Cañote 2 & Eruin Martusceli Ribeiro 3 & Geraldo Lúcio Thiago Filho 1 & Ana Lúcia Fonseca 1 Received: 14 November 2017 /Accepted: 13 May 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Aside from the ability of plants to remove domestic-industrial wastewater contaminants from various types of water, macrophytes can also serve as an alternative source of energy. The goal of the present study was to test the viability of biogas production using aquatic macrophyte species—Eichhornia crassipes and Pistia stratiotes—contaminated with cadmium (Cd) after the phytoremediation process. The plants were transferred to a nutrient solution contaminated with 0.8 mg L -1 of Cd. The experiment was set up in a 2 × 3 factorial scheme with the presence or absence of Cd and three phytoremediation times (20, 40, or 60 days) using P. stratiotes followed by an additional treatment consisting of P. stratiotes + E. crassipes for 20 days. The acute and chronic effects of bioassays with the microcrustacean Daphnia similis were used to evaluate the ability of the macrophytes to remove toxicity by phytoremediation. The viability test of biogas production after phytoremediation was evaluated using micro- biodigesters. According to the results, at least 60 days of phytoremediation are necessary to remove/remediate the Cd present in the contaminated solution. The metal did not influence the macrophytes’ methanogenic activity, showing that these macro- phytes can be used for biogas/methane production. The combination of Pistia stratiotes with Eichhornia crassipes is a good alternative to reduce phytoremediation time, but for 20 days of testing, the presence of Eichhornia crassipes reduces the biogas production/CH 4 . However, it is believed that if the digestion time is extended, this effect can be minimized. The phytoremediation time indicated that Pistia stratiotes must remain at least 60 days to remove/remediate the Cd present in the contaminated solution. Keywords Metane . Micro-biodigestion . Pistia stratiotes . Eichhornia crassipes Introduction Eutrophication and industrial contamination processes in trop- ical reservoirs are characterized by large assemblages of mac- rophytes. These species have adaptations that enable their rap- id spread and growth (Santamaría 2002). Invasive aquatic weeds are impossible to eradicate and are found in freshwater bodies, though its quest to grow in a nutrient-rich environment has provided an opportunity for its usage in phytoremediation (Mishra and Maiti 2017; Barua and Kalamdhad 2016). An example is the Itaipu Dam, which is a large hydroelectric dam on the Paraná River between Brazil and Paraguay with the presence, in the same local, species like Pistia stratiotes, Salvinia auricularia, Eichhornia crassipes, and Lemma sp. (Thomaz and Bini 1999). The phytoremediation process using aquatic macrophytes in contaminated environments has pre- sented promising results, mainly with heavy metals (Sharma et al. 2014; Pereira et al. 2014). Investigations carried out by several authors indicate the removal of 85 to 95% copper, zinc, cadmium, arsenic, mercury, and chromium using Eichhornia crassipes, Echinochloa crus-galli, Lemna minor, Pistia stratiotes, and other macrophytes (Qiong et al. 2017; Silva et al. 2013; Martelo and Lara-Borrero 2012; Sultana and Kobayashi 2011). However, the disposal of plant residues causes this process to be less attractive because all biomass produced is incinerated for volume reduction—provided that Responsible editor: Philippe Garrigues * Katiúcia Dias Fernandes katiuciadf@gmail.com 1 Natural Resources Institute (IRN), Federal University of Itajubá, Itajubá, MG 37500-903, Brazil 2 Natural Resources Institute (IRN) and Electrical Systems and Energy (ISEE), Federal University of Itajubá, Itajubá, MG, Brazil 3 Natural Resources Institute (IRN) and Energy Engineering (GEE), Federal University of Itajubá, Itajubá, MG, Brazil Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-2318-2