# An Overview on Management and Valorisation of Winery Wastes
## 4 Winery Waste for Water Treatment  
The capitalization of the agri-food industrial wastes constitutes a good opportunity for developing other products in the frame of a circular economy and sustainable waste usage [83]. Table 5 presents the most relevant examples of water treatment using winery wastes. The high organic carbon content from wine processing sludge may lead to excellent adsorbents for heavy metals due to their large surface area and increased binding affinity. For example, an eco-friendly adsorbent was obtained from grape marc and tested for the removal of lead (heavy metal) from contaminated effluents [83]. It was proven that the adsorption was strongly affected by pH. Maximum lead adsorption capacities were around 40 mg/g for Merlot grape marc and 64 mg/g for Sauvignon Blanc grape marc, at pH = 5.5 and 22 \({}^{\circ}\)C [83]. However, further studies are needed to test the effectiveness of the heavy metal removal. Another study used wine processing waste sludge (WPWS) as an adsorbent for Ni removal [84]. WPWS proved to be effective due to its properties, such as the high organic matter contents, rough surface texture, and compounds with rich amino and carboxyl functional groups. The adsorption capacity was influenced by the pH, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Waste** & **Removed** & **Conditions** & **Adsorption Capacity** & **Ref.** \\ \hline Merlot grape marc & Pb & pH = 5.5 & 40.00 mg/g & [83] \\ Sauvignon Blanc grape marc & & T = 22 \({}^{\circ}\)C & 64.00 mg/g & \\ \hline Wine processing waste sludge & Ni & T = 50 \({}^{\circ}\)C & 66.55 \(\mu\)mol & [84] \\ \hline \multirow{4}{*}{Grape bagasse (GB)} & Cd & N/A & 54.00 mg/g & [85,86] \\  & Pb & & 42.00 mg/g & [85,86] \\ \cline{1-1} \cline{2-5}  & Basic blue 9, & & \\ Acid yellow 36 & & N/A & \textless{}417.00 mg/g & [87,88] \\ \cline{1-1} \cline{2-5}  & Hg & N/A & 46.00 mg/g & [89] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Relevant examples of water treatment using winery wastes. temperature, initial Ni concentration, and waste particle size. According to the Langmuir isotherm equation, the maximum sorption capacity was 66.55 umol at 50 \({}^{\circ}\)C [84]. Further investigation remains necessary to elucidate the interaction between Ni and functional groups from WPWS compounds. According to the literature, grape bagasse (GB) consisting of seeds and skins, has been used in its natural form for the removal of heavy metals such as Cd(II) and Pb(II) from water, exhibiting adsorption capacities of around 54 and 42 mg/g, respectively [85; 86]. It has also been used to obtain activated carbons, which were applied for the adsorption of dyes (basic blue 9 and acid yellow 36) and Cu(II), reaching adsorption capacities up to 417 mg/g [87; 88]. These results indicate that this type of adsorbent can be efficiently used for water treatment. A heavy metal found in water resources is mercury, a harmful chemical for humans and ecosystems due to its toxicological profile [90]. Its adsorption is essential, and adsorbents with specific surface functionalities are needed in order to reach a competitive removal performance [91]. In this respect, alternative adsorbents were prepared for mercury removal via the pyrolysis of grape bagasse [89]. Mercury adsorption capacities were evaluated through their heterogeneous surfaces containing carboxylic, lactonic, phenolic, and silicon functionalities. The maximum adsorption capacity reached 46 mg/g, with DFT calculations confirming that carboxylic functional groups and Si constituents were the primary active sites for adsorption [89]. Wine waste-based sorbents can be green and cost-effective alternatives to commercial ones in terms of pharmaceutical removal from water. Although conventional wastewater treatment systems are efficient in terms of organic matter or nutrient removal, they are still not equipped for the removal of complex micro-pollutants like pharmaceuticals [92]. Their release into the aquatic environment can lead to chronic toxicity [93].