Environmental Simulation and Pollution Control State Key Joint Laboratory, School of Environment, Tsinghua University, Beijing, 100084, PR China.
College of Water Resources and Civil Engineering, China Agricultural University, Beijing, 100083, China.
Sci Rep. 2020 Apr 24;10(1):6960. doi: 10.1038/s41598-020-63898-5.
The behavior of clogging has a close relationship with the biofilm attached on inner surface of the pipeline in a drip irrigation system using reclaimed water. Therefore, inhibiting biofilm growth is the key to completely addressing the clogging problem. Water shear forces play a vital role in the formation, development and detachment of biofilm. In order to find out the accumulation mechanism of biofilm under different water shear forces, this paper considered 8 different shear forces with a range of [0, 0.7]Pa on the inner surface of pipelines in drip irrigation systems using three kinds of reclaimed water. The results indicate that dry weight (DW), phospholipid fatty acids (PLFAs) and extracellular polymeric substance (EPS) of biofilms show a S-type trend, the maximum contents were observed when τ was 0.2 Pa or 0. 35 Pa. Besides, the influence of water shear forces on biofilms is dual. The formation of biofilm is a dynamic stabilization process. When there is a relatively large shear force, it is favorable to the transport and renewal of microorganisms and nutrients. Meantime, the renewal speed of biofilms is also relatively fast. It is easy to form the biofilms with large surface and small thickness due to relatively high possibility of detachment. When the shear force is small, the transport speed of microorganisms and nutrients are limited, and the ability of microorganisms to secrete polysaccharides is reduced, which makes the nutrients needed for microbial growth insufficient and the adhesion between particles is also reduced, resulting in loose, unstable and an easily removed biofilm structure. After a comprehensive consideration of the dual influence, the critical controlling threshold of internal water shear force was obtained as [0, 0.20] ∪ [0.35, +∞] Pa. In addition, the growth model established in this paper can well describe the growth kinetics of attached biofilms, and provide theoretical reference for monitoring the occurrence of bio-clogging process in drip irrigation systems.
堵塞行为与再生水滴灌系统中管道内表面附着的生物膜密切相关。因此，抑制生物膜的生长是彻底解决堵塞问题的关键。水剪切力在生物膜的形成、发展和脱落中起着至关重要的作用。为了找出不同水剪切力下生物膜的积累机制，本文在滴灌系统中考虑了 8 种不同的剪切力，范围为[0,0.7]Pa，使用三种再生水。结果表明，生物膜的干重（DW）、磷脂脂肪酸（PLFAs）和胞外聚合物（EPS）呈 S 型趋势，当 τ 为 0.2 Pa 或 0.35 Pa 时，最大含量。此外，水剪切力对生物膜的影响是双重的。生物膜的形成是一个动态稳定过程。当存在较大的剪切力时，有利于微生物和营养物质的输送和更新。同时，生物膜的更新速度也相对较快。由于脱落的可能性较高，很容易形成表面较大、厚度较小的生物膜。当剪切力较小时，微生物和营养物质的输送速度有限，微生物分泌多糖的能力降低，导致微生物生长所需的营养物质不足，颗粒之间的附着力也降低，从而导致生物膜结构松散、不稳定且易于去除。综合考虑这双重影响，得到内部水剪切力的临界控制阈值为[0,0.20]∪[0.35,+∞] Pa。此外，本文建立的生长模型可以很好地描述附着生物膜的生长动力学，为监测滴灌系统中生物堵塞过程的发生提供理论参考。
