Nthunya Lebea N, Mamba Bhekie B
Institute for Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa, Florida 1709, South Africa.
Membranes (Basel). 2025 Aug 4;15(8):235. doi: 10.3390/membranes15080235.
Though the pursuit of sustainable desalination processes with high water recovery has intensified the research interest in membrane distillation (MD), the influence of module connection configuration on performance stability remains poorly explored. The current study provided a comprehensive multiparameter assessment of hollow fibre membrane modules connected in parallel and series in direct contact membrane distillation (DCMD) for the first time. The configurations were evaluated under varying process parameters such as temperature (50-70 °C), flow rates (22.1-32.3 mL·s), magnesium concentration as scalant (1.0-4.0 g·L), and flow direction (co-current and counter-current), assessing their influence on temperature gradients (∆), flux and pH stability, salt rejection, and crystallisation. Interestingly, the parallel module configuration maintained high operational stability with uniform flux and temperature differences (∆) even at high recovery factors (>75%). On one hand, the serial configuration experienced fluctuating ∆ caused by thermal and concentration polarisation, causing an early crystallisation (abrupt drop in feed conductivity). Intensified polarisation effects with accelerated crystallisation increased the membrane risk of wetting, particularly at high recovery factors. Despite these changes, the salt rejection remained relatively high (99.9%) for both configurations across all tested conditions. The findings revealed that acidification trends caused by MgSO were configuration-dependent, where the parallel setup-controlled rate of pH collapse. This study presented a novel framework connecting membrane module architecture to mass and heat transfer phenomena, providing a transformative DCMD module configuration design in water desalination. These findings not only provide the critical knowledge gaps in DCMD module configurations but also inform optimisation of MD water desalination to achieve high recovery and stable operation conditions under realistic brine composition.
尽管对具有高水回收率的可持续海水淡化工艺的追求增强了人们对膜蒸馏（MD）的研究兴趣，但模块连接配置对性能稳定性的影响仍未得到充分探索。本研究首次对直接接触膜蒸馏（DCMD）中并联和串联连接的中空纤维膜组件进行了全面的多参数评估。在不同的工艺参数下对这些配置进行了评估，如温度（50 - 70°C）、流速（22.1 - 32.3 mL·s）、作为垢剂的镁浓度（1.0 - 4.0 g·L）以及流动方向（并流和逆流），评估它们对温度梯度（∆）、通量和pH稳定性、脱盐率以及结晶的影响。有趣的是，即使在高回收率（>75%）下，并联模块配置仍能保持高运行稳定性，通量和温差（∆）均匀。一方面，串联配置由于热极化和浓差极化而经历了波动的∆，导致早期结晶（进料电导率突然下降）。随着结晶加速，极化效应加剧，增加了膜湿润的风险，特别是在高回收率下。尽管有这些变化，但在所有测试条件下，两种配置的脱盐率都相对较高（99.9%）。研究结果表明，MgSO引起的酸化趋势取决于配置，其中并联设置控制了pH崩溃的速率。本研究提出了一个将膜组件结构与传质和传热现象联系起来的新框架，为海水淡化提供了一种变革性的DCMD模块配置设计。这些发现不仅揭示了DCMD模块配置中的关键知识空白，还为优化MD海水淡化提供了依据，以便在实际盐水组成下实现高回收率和稳定的运行条件。
