## 6 Sludge-Based Biochar (SDB) in Membrane Technologies  
The incorporation of SDB into membrane technologies represents a promising development in wastewater treatment. Particularly, membrane-based water treatment can benefit from SDB through fouling mitigation and contaminant adsorption. Recent studies show that dosing SDB into membrane bioreactors (MBRs) improves performance on multiple fronts. [PERSON] et al. [72] alleviated membrane fouling as well as improved nitrogen removal in a municipal wastewater MBR by adding 1 g/L of SDB. The SDB particles adsorbed soluble microbial products (SMPs), serving as nuclei for larger flocs that settle better and form a looser cake layer on membranes. Furthermore, the micro-scale anoxic niches within SDB-amended flocs could release labile carbon for biological nitrogen removal. Similarly,Huang et al. [87] found that the SDB addition significantly reduced membrane fouling, primarily due to the enlargement of floc size and the reduction in SMPs. These results suggest that biochar addition is a viable fouling control strategy in both aerobic and anaerobic MBR systems. However, the mechanical stability of SDB layers remains a concern under prolonged shear forces, as biochar particle detachment or compression could diminish performance over time. In addition to direct addition, SDB can be blended with membrane materials to form composite membranes or used as a pre-treatment or post-treatment component in membrane systems. Researchers have created biochar-based membranes by either blending biochar into polymeric membranes or using biochar as a coating layer [55,88]. Such membranes combine size-exclusion filtration with adsorption, aiming to remove micropollutants more effectively. SDB-based membranes, created by integrating SDB into a polymer matrix, have shown effectiveness in removing micropollutants like nitrobenzene from water [51,89]. These membranes enhance adsorption and filtration properties, positioning them as a promising technology for micropollutant removal in wastewater treatment. In such cases, the porous surface of SDB traps dissolved contaminants that pass through the membrane pores, enhancing effluent quality beyond the membrane's standalone performance. Furthermore, integrating SDB into the membrane matrix also improves both its thermal stability and mechanical strength [90,91]. Another emerging concept is the dynamic membrane or biofilm membrane where biochar is used as a filter aid. Powdered SDB can be added to the aqueous phase to form a pre-coat on a support screen, creating a \"biochar dynamic membrane\" that traps solids and contaminants. While still at the experimental stage, this approach could turn a conventional filter into a reactive adsorption barrier that is periodically renewable by replacing the biochar layer. In summary, SDB is increasingly utilized in membrane technology for various functions: as an MBR additive to mitigate fouling and enhance treatment efficiency, as a functional filler in membrane fabrication for improved pollutant removal, and as a potential dynamic membrane layer. These approaches harness biochar's adsorption capacity and surface reactivity to enhance membrane separation performance. While SDB has shown promise in membrane applications, its long-term durability and maintenance remain insufficiently studied. Most experiments report performance over short durations, with limited data on membrane integrity or fouling resistance over extended use. SDB-based dynamic membranes may require frequent replenishment due to surface abrasion or pressure drops, and binder-free composite membranes may face the detachment of biochar particles under high shear. A few studies indicate that biochar additions can delay membrane fouling and improve floc structure in MBRs [64,67], but detailed assessments of membrane reusability, cleaning protocols, and biochar degradation are lacking. Future research should address membrane longevity, structural reinforcement (e.g., polymer-biochar hybrids), and regeneration strategies to support sustainable operation.