## 5 Conclusions  
Our mesocosms experiments set a suitable system to assess the performance of the tested BAP (Acti-zymeTM) as a remediation solution to treat OM-polluted river sediments. This represents an uncommon use of this biocatalyst product. As deduced from the study, an integrated treatment appears to be more convenient than the single use of the BAP, in such way that an optimization is possible with special focus on the syntrophic/methanogenic steps from acetate. Again, this is a novel capacity for the product. The consequences of treatments could already be found in a medium-short time frame, notwithstanding the fact that removal efficiencies could increase even more in a longer time frame. Outcomes indicate that the inoculum should be above threshold concentrations to trigger the degradation process of OM, preventing the occurrence of rate limiting steps. Furthermore, these concentrations appear to be higher than those usually used for conventional applications of the BAP for wastewater treatments, indicating that a stronger initial dose is likely required in natural ecosystems where the degradation of highly preserved OM is blocked. Our outcomes provide then new information on the applicability of Acti-zymeTM as a bioremediation product in natural environments, where research on this subject is still scarce. But beyond this application, our findings can also be useful for its more conventional uses. We claim for further studies incorporating molecular-based analyses to fully understand the role of the microbial populations involved.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/12/4308/s1](http://www.mdpi.com/2076-3417/10/12/4308/s1)]([http://www.mdpi.com/2076-3417/10/12/4308/s1](http://www.mdpi.com/2076-3417/10/12/4308/s1)). Figure S1: Microphotographs of the BAP cells stained with 4'-6-Diamidino-2-phenylindol (DAPI) after 18 h of rehydration. White bar indicates 5 um. Figure S2: Krona chart showing the relative abundance and diversity of Bacteria and Archaea in a sample of the studied fluvial sediment with a total number of 16,437 assigned reads. This html file consists in a multilevel pie chart that allows an interactive summary and visualization of the complete taxonomic annotation of the reads obtained.  
Conceptualization, A.C. and C.R.; methodology, A.C., C.R., A.P. and N.M.; software, C.R. and A.P.; validation, A.P. and A.C.; formal analysis, A.C., R., A.P. and N.M.; investigation, C.R., A.P., A.C. and N.M.; resources, A.C.; data curation, C.R.; writing--original draft preparation, C.R. and A.C.; writing--review and editing, A.C. and A.P.; visualization, C.R., N.M. and A.P.; supervision, A.C.; project administration, A.C.; funding acquisition, A.C. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Confederaion Hidrografica del Jucar (MITECO, Spanish Government) by means of the project \"Proyecto de regeneracion medioambiental del lecho del Rio Magro desde Caudete de las Fuentes hasta el Embas de Forata, (Valencia), Fase I\" (Research contract UVEGESPEC-20100699). Molecular analyses were supported by the project CLIMAWET (CGL2015-69557-R), funded by MINECO and FEDER-EU Funds. All projects were granted to A.C.  
Authors are indebted to the Water Quality and River Restoration Departments of the Confederaion Hidrografica del Jucar, which promoted the restoration of River Magro, as well as the corporations that were part of the consortium and undertook the study by providing either personnel or financial resources. [PERSON], [PERSON], and [PERSON] are specially acknowledged.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, nor in the decision to publish the results.