Department of Environment & Energy, Sejong University, Seoul, 05006, South Korea.
Department of Civil and Environmental Engineering, University of South Carolina, Columbia, 300 Main Street, SC, 29208, USA.
Chemosphere. 2021 Sep;279:130524. doi: 10.1016/j.chemosphere.2021.130524. Epub 2021 Apr 9.
This paper deals with the membrane fouling issue in the Direct Contact Membrane Distillation (DCMD) process treating a wasted sludge from an anaerobic digestion process. The main objective is to define an optimal cleaning strategy to alleviate fouling. Using a lab scale DCMD process, a cleaning strategy based on DI water flushing followed by 0.2% sodium hypochlorite (NaOCl) and 3% citric acid (CHO) cleaning was tested with different cleaning frequencies and various chemical cleaning durations at different cross-flow velocities. To avoid severe fouling, the optimal cross-flow velocity was found at 0.18 m/s (0.8 L/min). Moreover, even if higher cross-flow velocity allows higher flux, it could increase fouling risks. For a better membrane regeneration and process productivity, a cleaning of 60 min duration for each chemical cleaning applied every two days was defined as the optimal cleaning strategy. Such conditions allowed the preservation of 75.5% of the initial flux after 96 h of operation. Furthermore, the effect on membrane flux regeneration of DI water flushing, sodium hypochlorite, and citric acid cleaning registered were, 31.52%, 11.95% and 20.65%, respectively. This study revealed that in the MD process treating real wastewater both external and internal fouling are responsible of permeate flux decline due to the accumulation of organic and inorganic matter on the membrane surface as well as within the pores.
本文针对膜污染问题，研究了直接接触式膜蒸馏（DCMD）工艺处理厌氧消化工艺废弃污泥的过程。主要目标是定义一种最佳的清洗策略，以减轻污染。采用实验室规模的 DCMD 工艺，对不同清洗频率和不同化学清洗时间在不同错流速度下，采用 DI 水冲洗后再用 0.2%次氯酸钠（NaOCl）和 3%柠檬酸（CHO）清洗的清洗策略进行了测试。为了避免严重的污染，发现最佳错流速度为 0.18 m/s（0.8 L/min）。此外，即使较高的错流速度可以提高通量，但也会增加污染的风险。为了更好地再生膜和提高过程生产力，定义了每两天应用一次每种化学清洗，每次清洗持续 60 分钟的清洗策略。在 96 小时的运行后，这种条件下可以保持初始通量的 75.5%。此外，DI 水冲洗、次氯酸钠和柠檬酸清洗对膜通量再生的影响分别为 31.52%、11.95%和 20.65%。本研究表明，在处理实际废水的 MD 过程中，由于有机和无机物质在膜表面和孔内的积累，外部和内部污染都会导致渗透通量下降。
