Study of aggregation in surface sludge deposits from 14 full-scale French constructed wetlands using particle size distribution and dynamic vapor sorption analyses

Abstract

French vertical flow constructed wetlands (French VFCWs) are widely used for the treatment of wastewaters from small communities. In the system, unsettled wastewater is percolated through two successive stages of filter-cells planted with reeds. This causes the formation of a surface sludge layer. This layer plays positive roles in the treatment performance, but also leads to clogging. The objective of this study was to contribute to the description of the sludge deposits characteristics and their dynamics of evolution, which may control the development of clogging. Representative samples of sludge deposits were taken from 14 French VFCWs full-scale plants and analyzed for particle size, dynamic vapor sorption and other parameters of composition to compare their structure and evaluate the factors of influence. Results showed that ageing of the surface deposits layer over the years of operation in each plant induced the formation and integration of microaggregates within the initial macrostructure of fresh organic matter (OM). The humification process of the OM was found to play a key role in the aggregation process. The injection of FeCl operated to precipitate phosphates before filtration was found to accelerate the aggregation process in the early phase (<1 year) of operation of the sludge.

Assessment of spatial representativity of X-ray tomography to study Vertical Flow Treatment wetlands

“…which depend on the molecule that is being adsorbed/desorbed (typically H2O(g) or N2(g)). In the work of Kania et al (2018), the studied samples were taken from the deposit layer of French VF treatment wetlands. Values with a similar order of magnitude of SS were found by Poots and McKay (1979) and…”

“…Biosolids are characterized by their high organic matter content which ranges from 50% to nearly 90% (Kania et al, 2018) and form a porous medium whose structure and consistency evolve with time due to water content changes, organic matter mineralization and internal erosion. Kania et al (2018) characterized the surface deposit of 14 French VF treatment wetlands and conclude that the deposit layer on mature wetlands (> 3 years of operation) has lower OM content, lower biodegradability, and higher humification than newly commissioned wetlands (≤ 3 years of operation). Structure of biosolids impacts water and oxygen transfer as well as biological activity (Molle, 2014).…”

Structural Changes in French VF Treatment Wetland Porous Media during the Rest Period: An Ex Situ Study Using X-ray Tomography

“…The biosolids contained in the gravel and deposit layers play an important role in wastewater treatment as a seat of the microorganisms and fauna responsible for organic matter degradation. Biosolids are characterized by their high organic matter content, which ranges from 50% to nearly 90% [6] and forms a porous medium in which its structure and consistency evolve over time due to water content changes, organic matter mineralization, erosion and bioturbation.…”

Leaching behavior of major and trace elements from sludge deposits of a French vertical flow constructed wetland

“…The selected plant was already extensively studied by Kim et al (2013Kim et al ( , 2015 and Kania et al (2018a andb, 2019). In this purpose, a methodology was developed based on waste management protocols (Chatain et al, 2013;Gonzalez et al, 2017).…”