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Conventionally, a single Temperature Polarisation Coefficient (TPC) value is calculated to quantify Temperature Polarisation (TP). In this research, the extent of polarisation is investigated by capturing temperature profiles at specific points along a MD membrane using miniature thermocouples, eliminating the need for TPC calculations. The extent of polarisation at a point is affected by two contributory factors, namely the proximity of flow inlets and the difference in vapour pressure across the membrane at that point. Under this direction, this work examined the influence of permeate temperature, feed salinity, and flow direction on the development of the temperature profiles. Our analysis revealed an elevation in TP on both sides of the membrane when the permeate temperature was increased. In addition, changes in feed salinity had a very minute impact on the development of the temperature profiles. By comparing the cocurrent and counter-current flow, the influence of the two contributory factors was further proved, with counter-current flow working better for long membrane modules. Furthermore, an investigation on the symmetricity of polarisation across the membrane revealed asymmetricity depends on the operating conditions, especially direction of flow. The asymmetricity was infinitesimal at low inlet temperature differences for cocurrent flow.

Much of the research in the analysis of Temperature polarisation (TP) and the productivity of a membrane distillation (MD) system tends to concentrate on operational conditions. However, substantial enhancements in permeate flux can be realised through the incorporation of fundamental design modifications. This research showed that TP can be successfully mitigated almost to a level of non-existence, by manipulating the module orientation and flow channel height of an in-house designed direct contact membrane distillation (DCMD) system. Notably, at higher flow channel heights, changing the module orientation from the default horizontal position with the feed side on top (FST) to a sideway orientation led to a remarkable 90% increase in the permeate flux of the DCMD module. Permeate side on top (PST) and sideways orientations performed significantly better than FST for larger channel heights, while at low channel heights, the improvement was slight. Temperature measurements proved that thermal convective currents and secondary flows played a vital role in assisting or opposing TP and cannot be disregarded when investigating the hydrodynamics of a DCMD system. The impact of flow directions was insignificant with different channel heights, while the proximity of the flow inlets played a pivotal role in shaping the temperature profiles along the membrane.

Widespread contamination by heavy metals (HMs) and dyes poses a major health risk to people and ecosystems requiring effective treatment. In this work, rice husk (RH) and shrimp shells were extracted to obtain amorphous silica and chitosan, respectively, which were utilized to produce nano-chitosan-coated silica (NCCS). To ensure the stability of the nanoparticles, silica was freeze-dried after being coated with nano-chitosan. Functional groups (–NH2, –OH, P]O) from chitosan nanoparticles (CNPs) were introduced to the surface of silica during this process. Dyes such as brilliant green (BG), methylene blue (MB) and reactive brown (RB) as well as HMs (Cr6+, Pb2+, Cd2+, Ni2+) were removed by adsorbents. CNPs showed the highest adsorption capacity for RB (59.52 mg/g) among dyes and Cr6+ (42.55 mg/g) among HMs. CNPs showed the highest adsorption capacity for HMs among different adsorbents. Although NCCS and CNPs showed similar adsorption capabilities for HMs and dyes, NCCS showed the best stability. The adsorption performance decreased as RB > Cr6+ > MB > BG > Pb2+ > Cd2+ > Ni2+. The adsorption reactions followed both pseudo-first-order and second-order kinetics, and was spontaneous from thermodynamic analysis. In summary, the waste-derived adsorbents demonstrated excellent potential for removing HMs and dyes from water, while supporting effective management solid waste.