Modelling hydrodynamics of horizontal flow steel slag filters designed to upgrade phosphorus removal in small wastewater treatment plants

Abstract

Steel slag filters, if well designed and operated, may upgrade phosphorus removal in small wastewater treatment plants such as stabilization ponds and constructed wetlands. The main objective of this study was to develop a systemic modelling approach to describe changes in the hydraulic performances and internal hydrodynamics of steel slag filters under real dynamic operating conditions. The experimental retention time distribution curves (RTD curves) determined from tracer experiments performed at different times during the first year of operation of two field-scale steel slag filters were analyzed through a three stage process. First, a statistical analysis of the RTD curves was performed to determine statistical parameters of the retention time distribution. Second, classical tanks in series (TIS) and plug flow with dispersion (PFD) models were used to obtain a first evaluation of the dispersion and mixing regime. Finally, a multi-flow path TIS model, based on the assumption of several flow paths with different hydraulic properties, is proposed to accurately describe the internal hydrodynamics. Overall, the results of this study indicate that higher CaO content, round shape, and larger grain size distribution of steel slag may promote plug-like flow rather than dispersion. The results of the multi-flow path TIS model suggest that the internal hydrodynamics of steel slag filters can be primarily described by two main flow paths: (i) a faster main flow path showing higher plug flow, followed by (ii) a slower secondary flow path showing higher dispersion. The results also showed that internal hydrodynamics may change over time as a consequence of physical-chemical phenomena occurring in the filter, including accumulation of precipitates, slag hydration and carbonation, and particle segregation.

Phosphorus removal from wastewater by carbonated bauxite residue under aerobic and anoxic conditions

“…However, the lower particle size can also result in lower pore size between the grains, thus reducing the hydraulic conductivity of the filters [35]. In addition, various biological and physical-chemical phenomena, including biofilm growth, retention of suspended solids, particle segregation, precipitation and accumulation of precipitates, may further decrease the void volume and the pore size [36], thus affecting the long-term hydraulic and treatment performances of the filters and increasing the risk of clogging when treating real effluents. Therefore, Herron et al [34] recommended the < 6 mm as optimum particle-size in field scale applications.…”

Chemical Clogging and Evolution of Head Losses in Steel Slag Filters Used for Phosphorus Removal

“…Advantages inherent to these models include first, the possible calculation of the loss of effective porosity at each iteration of the simulation based on the mass precipitated. The TIS model, however, does not offer a mechanistic approach to calculate the evolution of hydraulic parameters, even if it was successfully used to calibrate tracer tests of full-scale AGFs [13]. Indeed, there is no direct mathematical relationship between the TIS hydraulic parameters (N, HRT Ve ) and the porosity reduction caused by the volume occupied by precipitates.…”

The potential utilization of slag generated from iron- and steelmaking industries: a review

“…The large amount production of iron-and steelmaking slag has proposed a great challenge to the environment as it has been considered as pollutant. In fact, the slag has showed impressive performance on removing contaminants from air, water, and soil (Barca et al 2014(Barca et al , 2018Jo et al 2015;Yu et al 2015;Zhou et al 2016;Zuo et al 2015). It indicates that the iron-and steelmaking slag has great potential in the application of environment treatment practice.…”

“…Studies using iron-and steelmaking slag as filtration media have shown that the slag had good performance in various types of wastewater treatment and revealed that the slag was capable of removing contaminants such as suspended solids, chemical oxygen demand (COD), biochemical oxygen demand (BOD), phosphate (P), and ammonium (N-NH 4 ? ) ( Barca et al 2014Barca et al , 2018Kadirova et al 2015;Zhou et al 2016;Zuo et al 2015). It was predicted that the porous structure of the slag would absorb the contaminants and free lime in the slag could react with the contaminants (Jha et al 2004(Jha et al , 2008Lu et al 2008).…”

“…CO 2 absorbents Global warming which is predicated to be caused due to the greenhouse gas Barca et al (2018) emission has become a serious environmental problem. The technology of carbon dioxide capture and storage, also called CO 2 sequestration, has been paid a great attention recently.…”