Recovery of struvite via coagulation and flocculation using natural compounds

Abstract

One of the major setbacks of struvite recovery processes is the difficulty in harvesting struvite crystals. This study evaluates the use of different coagulants to improve precipitation of struvite (MgNH4PO4.6H20) crystals. Chitosan and poly(diallyldimethyl ammonium chloride) (Poly-DADMAC) as a coagulant-flocculent and alginate and bentonite as a coagulant aid have been examined in jar tests. Also, a continuous three-phase process, i.e., struvite crystallization, coagulation/flocculation and precipitation process, was set up for real wastewater. Addition of chitosan as the coagulant and bentonite as the coagulant aid was significantly more efficient in forming struvite flocs in comparison to Poly-DADMAC alone or with coagulant aid, which did not show any positive effect. The calculated average settling velocity of struvite with chitosan-bentonite addition in synthetic and in real wastewater increased by approximately 5.3 and 2.8 folds, respectively, compared with that of no coagulant/flocculent addition. Phosphorus recovery of over 70% was achieved by the continuous process. Findings in this study clearly confirmed the possibility of using chitosan and bentonite as an efficient coagulant-flocculent to enhance the recovery of struvite crystals.

Biopolymer Flocculants and Oat Hull Biomass To Aid the Removal of Orthophosphate in Wastewater Treatment

“…By comparison, there are sparse reports where chitosan is used for the removal of particulate matter and dissolved substances in homogeneous solution. − Chitosan has unique properties as a coagulant and/or flocculant due to its pH-dependent charge density and variable molecular weight, along with its chelation and aggregation behavior at pH conditions above its p K a value . The unique physicochemical properties of chitosan along with biodegradability, biocompatibility, metal chelation, and low toxicity favor its use as a biopolymer flocculant. , Chitosan has been used for the removal of P i in wastewater using different techniques or processes besides coagulation and flocculation. − Teh and Wu have also shown that the amount of sludge produced using chitosan was significantly lesser as compared to alum…”

Struvite recovery efficiency using flocculation in batch and continuous settling systems for ammonia removal of mining wastewater

“…Latifian et al (2014) measured at 7.4 cm deep an average settling velocity of 14 cm.min −1 in synthetic wastewater and of 8 cm.min −1 in real wastewater. Average velocities greater than 14 cm.min −1 are here measured for depths below 0.74 and 0.34 m in the 45 and 90 ppm solutions, respectively.…”

“…Few studies have been conducted about flocculant addition on struvite recovery: Le Corre et al (2007) evaluated the agglomerative property of different coagulant/flocculant over struvite and identified polyDADMAC as a good option; Etter et al (2011) investigated the potential of Moringa Oleifera , as flocculants on struvite, but no improvement in terms of settling rates were shown; and Latifian et al (2014) studied different coagulant/flocculant (chitosan and polyDADMAC) and coagulant aid (bentonite and sodium alginate). Chitosan–bentonite used as the coagulant and coagulant aid significantly increased the average settling velocity of struvite crystals; however, smaller flocs formed in the continuous system (compared with jar tests).…”

“…Settling rates of struvite flocs have so far been studied at constant depth and constant concentration (Etter et al, 2011; Latifian et al, 2014; Peeva et al, 2022) whereas, because of their flocculent properties, these two parameters can affect their settling rate.…”

“…To the best of the authors' knowledge, only one study has been conducted on struvite flocs in a continuous process: Latifian et al (2014) studied the coagulation/ flocculation and precipitation of struvite in a continuous system, with chitosan as the coagulant and bentonite as the coagulant aid. The settling column used had a diameter of 6.5 cm and a height of 30 cm.…”