A review of struvite crystallization for nutrient source recovery from wastewater

Application of physicochemical techniques to the removal of ammonia nitrogen from water: a systematic review

Ammonia nitrogen is a common pollutant in water and soil, known for its biological toxicity and complex removal process. Traditional biological methods for removing ammonia nitrogen are often inefficient, especially under varying temperature conditions. This study reviews physicochemical techniques for the treatment and recovery of ammonia nitrogen from water. Key methods analyzed include ion exchange, adsorption, membrane separation, struvite precipitation, and advanced oxidation processes (AOPs). Findings indicate that these methods not only remove ammonia nitrogen but also allow for nitrogen recovery. Ion exchange, adsorption, and membrane separation are effective in separating ammonia nitrogen, while AOPs generate reactive species for efficient degradation. Struvite precipitation offers dual benefits of removal and resource recovery. Despite their advantages, these methods face challenges such as secondary pollution and high energy consumption. This paper highlights the development principles, current challenges, and future prospects of physicochemical techniques, emphasizing the need for integrated approaches to enhance ammonia nitrogen removal efficiency.

Magnesium source with function of slowly releasing Mg and pH control for impurity-resistance synthesis ultra-large struvite from wastewater

Struvite (MgNH4PO4·6H2O, Magnesium ammonium phosphate, MAP), recovered from wastewater, has potential application as a slow-release fertilizer. However, crystal size distribution (CSD) of recovered MAP typically lied in the range of 50-300 μm, due to fast nucleation rate and notably narrow metastable zone width (MSZW) of MAP, with purity levels 40-90 %. In order to control the rate of nucleation, a novel magnesium source with the form of MgHPO4·3H2O wrapped with Mg(OH)2 was prepared, referred to as P-3. This compound gradually released Mg2+ and PO43-, regulating solution concentration kept in MSZW to promote crystal growth. The inherent Mg(OH)2 within P-3 also acted as a pH regulator in wastewater, eliminating the necessity for additional acid or alkali adjustments during crystallization process. The MAP precipitated by P-3 exhibited an impressive CSD of 5000-7000 μm, with a maximum size reaching 10,000 μm. This represented the largest CSD reported in literature for recovered MAP from wastewater. The significance of the ultra-large MAP precipitated by P-3 lied in its enhanced resistance to impurity adsorption, resulting in MAP with a remarkable purity 97 %, under conditions of low heavy metal ion concentration approximately 5 mg/L. Furthermore, the removal efficiency of ammonia nitrogen (NH4+) can reach 92 %. In comparison, two other magnesium sources, soluble salts (MgCl2 and Na2HPO4, P-1) and a combination of insoluble salts (Mg(OH)2 and MgHPO4, P-2) were evaluated alongside P-3. The CSD of MAP precipitated from P-1, P-2 was both <100 μm, with purity levels of 90 and 92 % and NH4+ removal efficiency of 92 and 90 %, respectively. Importantly, the strategy of obtaining ultra-large size MAP from wastewater in this study provided novel insights into the crystallization of other insoluble salts with large sizes.

Ca-Mg modified attapulgite for phosphate removal and its potential as phosphate-based fertilizer

The urgent concerns of controlling water body eutrophication and the alleviating phosphorus shortage have led to an urgent need for action. The removal of phosphate from polluted waters and its reuse are essential for the prevention of eutrophication and for the sustainable utilization of phosphate resources. In this study, modified attapulgite with different Ca:Mg molar ratios was synthesized to facilitate the recovery of phosphate, with subsequent use of soil fertilizer. Ca-Mg modified attapulgite with the optimal ratio (ACM-5:3) exhibited an exceptional adsorption quality, achieving a maximum adsorption capacity of 63.2 mg/g. The pseudo-second-order model and Langmuir model could well describe the adsorption kinetics and isotherms, respectively. The adsorption mechanism analyses suggested that the interaction between ACM-5:3 and phosphate depended mainly on ion exchange and electrostatic attraction. Moreover, phosphate-laden-ACM-5:3 demonstrated a significant potential as a phosphorus-releasing fertilizer. It could promote corn growth by ensuring a continuous supply of phosphorus and minimizing phosphorus runoff losses. The above results suggested that ACM-5:3 was a potential adsorbent for efficient phosphate removal and recovery.

Resource recovery of high value-added products from wastewater: Current status and prospects

Wastewater resource recovery not only allows the extraction of value-added products and offsets the operational costs of wastewater treatment, but it is also conducive to alleviating adverse environmental issues due to energy and chemical inputs and associated emissions. A number of attractive compounds such as alginate-like polymers, struvite, polyhydroxyalkanoates, and sulfated polysaccharides, were found and successfully obtained from wastewater and have a wide range of application prospects. The aim of this work is to provide a comprehensive review of recent advances in recovery of these popular products from wastewater, and their physicochemical properties, main sources, and current recovery status are summarized. Various factors influencing the recovery performance of these materials are thoroughly discussed. Moreover, the research needs and future directions towards wastewater resource recovery are highlighted. This study can provide valuable insights for future research endeavors aiming to improve wastewater resource recovery through the retrieval of high value-added products.

Treatment and recovery of phosphate from submerged anaerobic membrane bioreactor effluent using thermally treated biowaste and powder activated carbon

This study presents a novel treatment system using a submerged anaerobic membrane bioreactor (SAnMBR) followed by adsorption onto thermally treated biowaste, and ending with a final treatment using powdered activated carbon (PAC). Despite limited phosphate and ammonium ion removal during SAnMBR operation, thermally treated eggshell (EGSL) and seagrass (SG) received SAnMBR effluent and enhanced phosphate recovery, achieving removal rates of 71.8-99.9% and 60.5-78.0%, respectively. The SAnMBR achieved an 85% COD removal, which was slightly reduced further by biowaste treatment. However, significant further reductions in COD to 20.2 ± 5.2 mg/L for EGSL effluent and 57.0 ± 13.3 mg/L for SG effluent were achieved with PAC. Phytotoxicity tests showed the SAnMBR effluent after PAC treatment notably improved seed growth compared to untreated wastewater. In addition, volatile organic compounds (VOCs) were significantly reduced in the system, including common wastewater contaminants such as dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol, nonanal, and decanal. Fractionation analysis of the solid fraction, post-adsorption from both synthetic and domestic wastewater, indicated that for SG, 77.3%-94% of the total phosphorus (TP) was inorganically bound, while for EGSL, it ranged from 94% to 95.3%. This study represents the first attempt at a proof-of-concept for simultaneous treatment of domestic wastewater and phosphorus recovery using this integrated system.

Simultaneous Wastewater Treatment and Resources Recovery by Forward Osmosis Coupled with Microbial Fuel Cell: A Review

Osmotic microbial fuel cells (OsMFCs) with the abilities to simultaneously treat wastewater, produce clean water, and electricity provided a novel approach for the application of microbial fuel cell (MFC) and forward osmosis (FO). This synergistic merging of functions significantly improved the performances of OsMFCs. Nonetheless, despite their promising potential, OsMFCs currently receive inadequate attention in wastewater treatment, water reclamation, and energy recovery. In this review, we delved into the cooperation mechanisms between the MFC and the FO. MFC facilitates the FO process by promoting water flux, reducing reverse solute flux (RSF), and degrading contaminants in the feed solution (FS). Moreover, the water flux based on the FO principle contributed to MFC's electricity generation capability. Furthermore, we summarized the potential roles of OsMFCs in resource recovery, including nutrient, energy, and water recovery, and identified the key factors, such as configurations, FO membranes, and draw solutions (DS). We prospected the practical applications of OsMFCs in the future, including their capabilities to remove emerging pollutants. Finally, we also highlighted the existing challenges in membrane fouling, system expansion, and RSF. We hope this review serves as a useful guide for the practical implementation of OsMFCs.