Clogging processes caused by biofilm growth and organic particle accumulation in lab-scale vertical flow constructed wetlands

The accumulation of organic matter in substratum pores is regarded as an important factor causing clogging separately in the subsurface flow constructed wetlands.In this study,the developing process of clogging caused by biofilm growth or organic particle accumulation instead of total organic matter accumulation was investigated in two groups of lab-scale vertical flow constructed wetlands（VFCWs）,which were fed with glucose（dissolved organic matter） and starch（particulate organic matter） influent.Results showed that the growth of biofilms within the substratum pores certainly caused remarkable reduction of effective porosity,especially for the strong organic wastewater,whereas its influence on infiltration rate was negligible.It was implied that the most important contribution of biofilm growth to clogging was accelerating the occurrence of clogging.In comparison with biofilm growth,particles accumulation within pores could rapidly reduce infiltration rate besides effective porosity and the clogging occurred in the upper 0-15 cm layer.With approximately equal amount of accumulated organic matter,the effective porosity of the clogged layer in starch-fed systems was far less than that of glucose-fed systems,which indicated that composition and accumulation mode in addition to the amount of the accumulated organic matter played an important role in causing clogging.

Clogging Process Caused by Organic Particle Accumulation and Biofilm Growth in Subsurface Wastewater Infiltration System

Substrate clogging is the worst operational problem for subsurface wastewater infiltration system （ SWIS ）, nevertheless quantitative understanding of the clogging process is currently very limited. In this study, the developing process of clogging caused by organic particle accumulation and biofilm growth was investigated in two groups of lab-scale SWIS, which were fed with glucose （dissolved organic matter） and starch （particulate organic matter） influent and filled with the same substrate made of 50% brown soil and cinder at a weight of 50%. Results showed that in glucose-fed systems the growth of biofilm in the substrate pores certainly caused remarkable reduction of effective porosity, especially for the high concentration organic wastewater, whereas its influence on infiltration rate was negligible. In comparison with biofllm growth, organic particles accumulation could rapidly reduce infiltration rate and the clogging occurred in the upper layer in starch-fed systems and the most important contribution of biofilm growth to clogging was accelerating the occurrence of clogging.

An Investigation into the Behavior of Non-Isodense Particles in Chaotic Thermovibrational Flow

The ability to control the distribution of particles in a fluid is generally regarded as a factor of great importance in a variety of fields(manufacturing processes,biomedical applications,materials engineering and various particle separation processes,to cite a few).The present study considers the hitherto not yet addressed situation in which solid spherical particles are dispersed in a non-isothermal fluid undergoing turbulent vibrationally-induced convection(chaotic thermovibrational flow in a square cavity due to vibrations perpendicular to the imposed temperature difference).Although the possibility to use laminar thermovibrational flows(in microgravity)and turbulent flows of various types(in normal gravity conditions)to induce the accumulation of solid mass dispersed in a non-isodense fluid is already known,the interplay of finite-size finite-mass particles with chaotic flow in weightlessness conditions has never been considered.In the present study this subject is tackled through direct numerical solution of the fluid and particle tracking equations in the framework of a one-way coupling approach.Results are presented for relatively wide ranges of vibrational amplitude,particle size and density.