Desalination is still a rather energy intensive process, and is also associated with the discharge of highly saline and chemically contaminated brine; both these factors detract from the sustainability of the desalination process. Fortunately, both these issues can be addressed by developing zero-liquid discharge (ZLD) processes that can be powered by low-grade (LG) heat sources.

The objective of the current work is to improve upon the world's first commercial forward osmosis ZLD system (developed by OASYS Water) by employing mainly LG heat. In the original system, the principal energy cost was associated with the regeneration of the thermo-responsive ammonia‑carbon dioxide draw solution, which was performed in a distillation column (DC). In this paper, a novel flow process is developed in which the same volatile draw solution is regenerated using a combined vacuum membrane distillation (VMD) and distillation column (DC) system.

The numerical results indicate that the standard DC draw solute regeneration system (DSR) outperforms the newly proposed VMD-DC DSR system when latent heat is available. However, when only sensible heat is available, the novel VMD-DC DSR system can reduce the overall energy consumption by more than 15% to 20% at source temperatures of 90 °C and 85 °C, respectively. Although these energy savings are substantial and allow for the efficient integration of various renewable and waste heat sources, the VMD-DC system still faces several drawbacks, such as high cooling loads and the regeneration of a more diluted draw solution. These difficulties originate from the non-selectivity of the VMD process and its difficult heat integration.

The numerical results presented here show the huge potential of membrane-based DSR systems for the recovery of volatile draw solutes. Nevertheless, the proposed DSR system will benefit from further optimisation via inclusion of more selective (e.g. pervaporation) or better heat integrated (e.g. multi-stage VMD) membrane processes to improve its technical and economical performance.

脱盐仍然是一个相当耗能的过程，并且还与高盐分和化学污染的盐水的排放有关。这两个因素都不利于淡化过程的可持续性。幸运的是，这两个问题都可以通过开发零液体排放（ZLD）工艺来解决，该工艺可以由低品位（LG）热源提供动力。

当前工作的目标是通过主要利用LG热量来改进世界上第一个商业正渗透ZLD系统（由OASYS Water开发）。在原始系统中，主要能源成本与热响应性氨-二氧化碳汲取溶液的再生有关，该再生过程在蒸馏塔（DC）中进行。在本文中，开发了一种新颖的流程，其中使用真空膜蒸馏（VMD）和蒸馏塔（DC）组合系统来再生相同的挥发性汲取溶液。

数值结果表明，当有潜热时，标准的直流汲取溶质再生系统（DSR）优于新提出的VMD-DC DSR系统。但是，当只有显热时，新颖的VMD-DC DSR系统在源温度为90°C和85°C时可以分别将总能耗降低15％到20％以上。尽管这些节能措施可观，并且可以有效集成各种可再生能源和废热资源，但VMD-DC系统仍然面临一些缺陷，例如高冷却负荷和稀释后的稀释溶液的再生。这些困难源于VMD工艺的非选择性及其难以进行的热整合。

此处提供的数值结果表明，基于膜的DSR系统具有回收挥发性吸引溶质的巨大潜力。尽管如此，通过包含更多选择性（例如全蒸发）或更好的热集成（例如多级VMD）膜工艺来改善其技术和经济性能，建议的DSR系统将受益于进一步的优化。