## 1 Introduction
There is a relatively small body of literature that is concerned with the fabrication or modification of membranes by native lignin. Ameliorating the performance of a membrane by using natural additives, such as lignin, which offers renewability, availability, and low cost advantages, is attentive due to environmental aspects in terms of biodegradability and of the reduction of membrane fabrication costs compared to synthetic additives [20]. In addition, it has been highlighted that polymeric hydrophilic additives like PEG might leach out from the membrane structure during membrane formation and filtration processes due to their affinity to water [20; 21; 22]. Leaching from the membrane structure can have detrimental health effects especially in the food separation industry, as it may interact with food materials. Moreover, such additives are not the ideal ones in the modification of thin-film composite membranes, as a remarkable part of the weight of the thin film can be removed, which in turn reduces the half-life of the membrane [20]. Cleaning operation is an inevitable part of membrane processes, playing a vital role in the aging of the membrane. Quick back flushing with a cleaning chemicals, such as chlorine and hypochlorite, is one of the most commonly used methods in membrane cleaning processes, which can affect the degradation of the membrane material by radical oxidation of polymer chains and thus shorten its life time and increase the operation costs [23]. Preparation and modification of the membrane with antioxidant characteristics can be an appropriate way to reduce the aging of the membrane causedby regular cleaning or in gas separation processes that are in contact with oxygen [24]. Furthermore, having an antioxidant membrane can reduce the possible changes that might happen during storage in different conditions. Above all, there is a great amount of published studies describing the antibacterial role of phenolic antioxidants [25; 26], and they can be used preferably as additives in membrane fabrication to reduce biofouling due to the formation of a biofilm on the surface of the membranes. So far, previous studies have demonstrated the potential of lignin as a natural plant-based polymer in improving the toughness of polymer composites [27; 28]. Lignin derivatives and alkaline lignin have been used as additives in membrane separation and fabrication. For example, [PERSON] and [PERSON] confirmed the effectiveness of sulphate lignin in the reduction of flux decline when separation of low molecular mass organic solutes was conducted by cellulose acetate membranes [29]. Lignosulfonates have been incorporated in the fabrication of polysulfone membrane to impart electrolyte transfer. This modification reduced the formation of macrovoids and facilitated the formation of larger surface pores [30]. In another work, [PERSON] et al. modified a cellulose triacetate membrane with three diffident propionated lignins (Kraft, Organosolv and Hydrolytic), and the membrane performance was examined by groundwater containing a high concentration of different ions. In general, they report that both wettability and flux were reduced as the propionation of lignin increased in the fabricated nanocomposites [31]. Alkali lignin (28 kDa; 0.125 and 0.5 wt %) has also been used as an additive in the synthesis of an ultrafiltration polysulfone membrane [20], and the membrane morphology and performance, as well as the tensile strength, porosity, glass transition temperature, thermal properties, and other mechanical properties of the fabricated membrane [16; 32], were studied and compared with PEG (10 kDa) and PVP (29 kDa) as the most two common additives used in membrane modification. It was found that alkali lignin improved the thermal stability and increased the bulk porosity and permeability of the prepared membranes. However, the alkali lignin-modified membranes revealed a high molecular cut-off value as the best separation factor (actual rejection of \(\sim 93\%\)) was obtained when PVP-360 kDa was utilized as a model compound [20].