The down-flow hanging sponge (DHS) process has been rigorously studied as a significant post-treatment of anaerobically pretreated sewage and later for broader applications in industrial wastewater and pre-settled sewage treatment. The DHS has several advantages over conventional wastewater treatment technologies, i.e., simple process control, less workforce requirement, less footprint, low construction, operation, and maintenance costs due to simple design and less mechanical parts. DHS technology requires no external aeration, which saves energy use and minimizes the associated costs. Low excess sludge yield in the DHS process adds to economic efficiency. DHS achieved high organics removal efficiency up to 99% with considerable nutrient and pathogen removals at extremely short HRT. Up-to-date, six DHS configurations have been developed and extensively tested at pilot scale applications under different operational conditions, i.e., HRTs, OLRs, and SRTs. Accordingly, the DHS module has successfully been translated into full-scale demonstration plants in Japan, India, Egypt, and Thailand. This paper comprehensively reviews the mechanism and development history of the DHS system. The process performance for municipal and industrial wastewaters treatment covers a broad range of parameters, i.e., organics, nutrients, pathogens (bacteria, viruses, parasites) has been summarized. The unique feature of sludge reduction efficiency of DHS is comprehensively discussed. Moreover, the process microbiology, energy efficiency, emerging application of DHS for direct sewage treatment, pilot and full-scale experiences in the last 20 years are also reviewed. DHS technology has not yet being fully explored, mainly for nutrients removal, process modelling, optimization of wastewater and air flow configurations in DHS reactor, and biomass growth, which could help for further advancement in the process for better performance and wider applications.

严格研究了下流式悬挂海绵（DHS）工艺，将其作为厌氧预处理污水的重要后处理方法，后来广泛用于工业废水和预先结算的污水处理中。与传统的废水处理技术相比，DHS具有多个优势，例如，简单的设计和较少的机械零件，使过程控制简单，所需劳动力少，占地面积少，结构，操作和维护成本低。DHS技术不需要外部曝气，从而节省了能源并最大程度地降低了相关成本。在DHS过程中低的剩余污泥收率提高了经济效率。DHS在极短的HRT上实现了高达99％的高有机物去除效率以及相当多的营养和病原体去除。最新，已经开发了六种DHS配置，并在不同运行条件下的中试规模应用（即HRT，OLR和SRT）上进行了广泛的测试。因此，DHS模块已成功转换为日本，印度，埃及和泰国的全面示范工厂。本文全面回顾了DHS系统的机制和发展历史。城市和工业废水处理的过程性能涵盖了广泛的参数，即，有机物，营养物，病原体（细菌，病毒，寄生虫）已被总结。全面讨论了DHS减少污泥效率的独特特征。此外，过程微生物学，能源效率，DHS在直接污水处理中的新兴应用，还回顾了过去20年的试点和全面经验。DHS技术尚未得到充分探索，主要用于营养去除，过程建模，DHS反应器中废水和空气流配置的优化以及生物量的增长，这可能有助于该过程的进一步发展，以实现更好的性能和更广泛的应用。