Bai Zhihui

Biofilm structure and its influence on clogging in drip irrigation emitters distributing reclaimed wastewater.

Using reclaimed wastewater for crop irrigation is a practical alternative to discharge wastewater treatment plant effluents into surface waters. However, biofouling has been identified as a major contributor to emitter clogging in drip irrigation systems distributing reclaimed wastewater. Little is known about the biofilm structure and its influence on clogging in the drip emitter flow path. This study was first to investigate the microbial characteristics of mature biofilms present in the emitters and the effect of flow path structures on the biofilm microbial communities. The analysis of biofilm matrix structure using a scanning electron microscopy (SEM) revealed that particles in the matrix of the biofilm coupled extracellular polysaccharides (EPS) and formed sediment in the emitter flow path. Analysis of biofilm mass including protein, polysaccharide, and phospholipid fatty acids (PLFAs) showed that emitter flow path style influenced biofilm community structure and diversity. The correlations of biofilm biomass and discharge reduction after 360 h irrigation were computed and suggest that PFLAs provide the best correlation coefficient. Comparatively, the emitter with the unsymmetrical dentate structure and shorter flow path (Emitter C) had the best anti-clogging capability. By optimizing the dentate structure, the internal flow pattern within the flow path could be enhanced as an important method to control the biofilm within emitter flow path. This study established electron microscope techniques and biochemical microbial analysis methods that may provide a framework for future emitter biofilm studies.

Comparison of soil microbial communities between high and low yield organically managed orchards

TM and phospholipid fatty acids (PLFAs) analysis were used to evaluate soil microbial communities for eight typical organic orchards in Beijing, China. These included high- and low-yield agricultural sites for four types of fruit orchards: pear, peach, apple and grape. The soil properties including soil organic matter (OM), soil pH, soil total nitrogen (TN), soil available phosphorus (AP), soil available K (AK), cation exchange capacity (CEC), soil bulk density, soil porosity, microbial biomass and microbial activities were investigated. There were significant higher microbial biomass and lower bulk density in the soils of high-yield orchards than that in low-yield orchards. Differences between the paired soils of high- and low-yield orchards were highly associated with the average well colour development and total PLFAs.