Variations in Phosphorus Speciation in Response to Simulated Riparian Zone Enhancement with Red Mud to Treat Reclaimed Water

Abstract

Variations in phosphorus speciation in two sets of simulated riparian zones with and without Perennial ryegrass were compared. Each set consisted of four units, each measuring 700 mm  200 mm  200 mm, which were enhanced with 0, 2.5, 5, and 7.5% red mud (RM) by weight. The levels of total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP) in the effluent were analyzed, and phosphorus fractionation in the media were also determined after the systems had been operational for 3 months. The results showed that the unit received 2.5% RM had the highest rate of phosphorus removal, including TP, TDP, SRP, particulate phosphorus (PP), and dissolved organic phosphorus (DOP) were present at the average concentrations of 0.17, 0.10, 0.07, 0.08, and 0.03 mg/L in the effluent. Sequential phosphorus fractionation showed that calcium-bound phosphorus (Ca-P) was the major component, indicating that the addition of RM induced aluminum/iron-bound phosphorus (Al/Fe-P), which was intensely bioactive, to form intractable Ca-P, which further inhibited the release of phosphorus from the media. However, the presence of P. ryegrass had little effect on the removal of phosphorus. Therefore, RM, when used directly in riparian zones at a suitable concentration, is a novel and low cost additive material that can be used to remove phosphorus from reclaimed water. IntroductionRed mud (RM), which is generally classified as a solid waste, is generated from the production of alumina by the caustic digestion of bauxite ores [1]. RM, which has a large specific surface area and a homogeneous particle-size distribution, contains Ca, Fe, and Al oxides and other minor constituents [2,3]. It is usually directly disposed in deposit areas or dumped into the sea, which can result in not only the waste of this resource but also environmental pollution [1]. Recently, some studies have reported various applications for RM, including the removal of nitrates and phosphates, soil remediation at mines, metal recovery [4-6], etc. However, RM is still regarded as a hazardous environmental pollutant due to its highly alkaline properties and high concentrations of various chemical substances [3]. As a consequence, appropriate pretreatment of RM is necessary before practical use [2].Riparian zones have been widely used for reducing phosphorus pollution due to their low cost, convenient operation, and easy maintenance [7][8][9]. Adsorption and precipitation of the media is considered to be one of the most useful removal processes of phosphorus from a column of water in riparian zones [10,11]. Different forms of phosphorus in wastewater, such as soluble reactive phosphorus (SRP), organic-bound phosphorus (Org-P), and particulate phosphorus (PP), and their dynamics have been reported to affect the efficiency of phosphorus removal [12]. However, there are few reports on the use of riparian zones to remove phosphorus from reclaimed water, which generally has a lower phosphorus load. In addition, there are few studies that have focused o...

Species and Characteristics of Organic Phosphorus in Surface Sediments of Northwest Region of Taihu Lake, Eastern China

“…Though inorganic phosphorus occupied the largest proportion of TP, organic phosphorus accounting for 22-50% of TP played important roles in phosphorus circulation [14]. The northwest region of the lake had the highest TOP concentration which could partially convert into inorganic phosphorus form under the action of environmental biogeochemistry process and ingested by aquatic organism such as planktons [34]. Although organic phosphorus displayed the relatively stable trend and unobvious variation all over the research area, this process was important in phosphorus cycles and eutrophication of the lake because of remarkable proportion of TOP accounting for TP [3].…”

Dealkalization of Red Mud by Carbide Slag and Flue Gas

“…Much effort has been made to reuse red mud which is a caustic waste from bauxite ore processing in alumina extraction . Red mud can be used as an adsorbent to remove toxic heavy metals, arsenate, dyes, and phosphorus, an additive pigment for concrete, as well as sequestration of SO 2 and CO 2 . Red mud is also used as raw material in building materials on which a layer of “scum” is commonly formed.…”