The current situation of the environment regarding climate change, pollution and raw material depletion is being aggravated due to the population growth and improved living standards. Hence, there is an imperative need to develop robust technologies which allow the exploitation of new renewable sources and satisfy the concept of process intensification and rationalisation of raw materials. In this regard, membrane contactors have been presented as an alternative over conventional separation units due to their attractive features, especially the higher achievable overall productivity and the potential cost savings during operation. For these reasons, membrane contactors at lab-scale for the valorisation of residual liquid effluents by means of the separation and recovery of dissolved methane (CH4) and phosphorus (P) were investigated in this thesis. Thus, this thesis aims to: i) elucidate the effects of the operational conditions and membrane properties in the CH4 recovery performance using flat-sheet membrane contactors under simulated and real conditions, ii) optimise the dissolved CH4 recovery process using a hollow fibre membrane contactor working in combination mode (simultaneous application of vacuum and sweep gas), and iii) integrate a membrane crystallisation process for the recovery of dissolved P as vivianite. On the one hand, the recovery of dissolved CH4 from anaerobic effluents were evaluated with a gas-liquid flat-sheet membrane contactor using different common membrane materials (PDMS, PP and PVDF). The use of a flat-sheet membrane module presented great advantages for investigation purposes such as versatility and easy membrane extraction, replacement, and analysis. The effects of the membrane properties in the CH4 removal efficiency and mass transport were investigated. Additionally, a membrane functionalisation method based on the grafting of fluoroalkylsilanes was evaluated for increasing the wetting resistance of PVDF membranes. Two membranes activation methods (alkali and plasma treatments) previous to the grafting were evaluated, and the modification conditions were optimised. Stability of the membranes and functionalisation layers were evaluated in long-term operation using deionised water and a real anaerobic effluent to determine their useful lifetime. The composition and mechanisms of the fouling developed on PVDF membranes when treating a real anaerobic effluent were characterised. Finally, the dissolved CH4 recovery process was optimised using a PP hollow fibre membrane contactor in combination mode to minimise the energy and sweep gas consumption. On the other hand, the recovery of dissolved P from liquid streams in vivianite form by means of a membrane-assisted reactive crystallisation was evaluated for the first time in the literature, as far as we know. The vivianite crystallisation was evaluated in a flat-sheet membrane contactor at lab-scale under different hydraulic conditions and membranes (PP, PVDF and PTFE) to elucidate how the boundary layer and membrane properties can be used to regulate the nucleation kinetic. Regarding the results of dissolved CH4 recovery with the polymeric flat-sheet membrane contactor, the dissolved CH4 removal efficiency was mainly influenced by the hydraulic conditions in the liquid phase. Moreover, the mass transfer resistance of the membrane and gas phase was negligible, except for PVDF membranes which suffered from wetting. Therefore, a surface functionalisation with alkali activation was applied to increase the antiwetting properties of PVDF, and the results showed an increase in the removal efficiency. However, all the membranes tended to suffer from a surface deterioration and/or deformation at moderate-high liquid velocities, affecting their properties and efficiency. In this regard, a new surface functionalisation with a vacuum oxygen plasma activation was investigated to obtain more stable PVDF membranes over time. As result, superhydrophobic membranes were obtained with a pillared-like surface and a higher surface porosity and roughness. In addition, superhydrophobic PVDF presented a more stable hydrophobicity in long-term operation than that of the functionalised PVDF with alkali activation. After evaluating operational conditions and membrane wetting mitigation methodologies for the dissolved CH4 recovery from synthetic effluents, PVDF membranes were tested under real operational conditions to evaluate another critical issue regarding membrane operations: membrane fouling. Despite the higher fouling experienced by the functionalised PVDF with alkali activation, this membrane showed a greater chemical and/or mechanical resistance and stability than the non-modified PVDF when treating a real anaerobic effluent during >800 h. The fouling developed on the membranes showed a stratified composition: a first layer mainly of proteins and polysaccharides, the fouling cake bulk composed of calcium, carbonate, and phosphate salts, and the cake top composed mainly of organic matter including biomass. This fouling characterisation will ease the selection of the appropriate cleaning protocols. The final step regarding the evaluation of the dissolved CH4 recovery was the optimisation of the energy and input consumption using hollow fibre membrane contactors as most representative configuration in industrial processes. In this regard, the use of the combination mode was evaluated, showing significantly greater removal efficiencies, mass transfer coefficients and net energy productions than independent operational modes (vacuum and sweep gas). Additionally, the combination mode mitigated the membrane wetting. In conclusion, setting the appropriate hydraulic conditions, grafting of fluoroalkylsilanes, and combination mode can enhance the performance of the membrane contactor to recover dissolved CH4 from anaerobic effluents, reducing the operational costs and carbon footprint of an anaerobic wastewater treatment plant. In the search of new applications for integrating membrane technology, a membrane crystallisation process was investigated for the P recovery as vivianite. As result, nanoparticles of ~35 nm with a relatively narrow distribution were always obtained. Crystal nucleation was strongly influenced by the boundary layer inside the membrane module, in which nucleation rate increased as the liquid velocity decreased. In addition, a porous membrane facilitated the micromixing of the reactants and lowered the energy barrier for nucleation. An ion-dependent collision mechanism for the nucleation kinetic was inferred, in which the higher supersaturation rates promote greater mixing and a higher ion collision probability for nucleation. Moreover, the previous surface functionalisation was elucidated as a useful methodology to increase nucleation rate as the hydrophobicity increases. Thus, the membrane-assisted reactive crystallisation offered a high control over nucleation compared to conventional crystallisers with a somewhat inefficient mixing of reactants.