A modified BAF system configuring synergistic denitrification and chemical phosphorus precipitation: Examination on pollutants removal and clogging development

Manipulating electrochemical phosphate recovery from acidic wastewater for synthesizing LiFePO4/C cathode material

Phosphorus (P) recovery from wastewater offers a sustainable solution for mitigating pollution and securing resources for applications like lithium-ion batteries, where ferric phosphate is a valuable precursor. This study evaluates iron electrolysis for P removal and recovery from acidic wastewater with high phosphate concentrations and medium Ca²⁺ levels. The results suggested that effective P removal and high-purity iron phosphate production can be achieved by varying initial pH, current density, and oxidation conditions. Importantly, slow Fe release rates (0.02-0.04 mmol L⁻¹ min⁻¹) favored ferric phosphate formation (71%-77% removal), while faster rates (0.16-0.46 mmol L⁻¹ min⁻¹) predominantly produced vivianite (∼ 65% removal). In addition, air flush can enhance dissolved oxygen flux, achieving 89% P removal under rapid Fe release but with mixed products. H₂O₂ addition improved in situ Fe(II) oxidation, achieving 92% P removal and purer ferric phosphate. Compared to chemical precipitation, which required pH adjustment and suffered from Ca co-precipitation, iron electrolysis produced purer ferric phosphate directly, without pH pre-adjustment. The recovered ferric phosphate showed excellent potential as a precursor for high-performance LiFePO₄/C cathode material. These findings position iron electrolysis as a promising approach for sustainable P recovery and resource valorization from wastewater.

Clogging of reactive filters for phosphorus removal - A review

The objective of this paper is to present a comprehensive review of clogging that is associated with reactive filters applications aimed at phosphorus removal. Reviewed studies used various inlet design strategies: water flow direction (vertical or horizontal), influent pressurization (pressurized by pumps or gravity-fed by overflow) and feeding distribution types (point, water spraying, distribution pipes or coarse surface layers). They used operational strategies including prefilters, filters in series, regeneration of media, optimization of hydraulic retention time, concealment from the air, chemical additions and backwashing. Media mixes and different particle sizes in series were used as media selection strategies for clogging mitigation. Small reactive media size (0-10 mm) was used in most reviewed applications of reactive filters, while larger particle size was used to improve water distribution. While guidelines for particle size selection do exist, most authors did not systematically evaluate the suitability of the media for flow. Bicarbonate inputs from wastewater or from atmospheric CO2 were found to impact significantly the filter lifetime by chemical precipitation. However, most reviewed studies did not report the alkalinity or inorganic carbon concentration in the feeding wastewater and did not report the level of atmospheric concealment. The authors recommend to systematically report the following parameters in future studies on RFs: wastewater alkalinity; level of sealing from atmospheric CO2; complete description of operational parameters such as feeding pressure, presence of overflows, evolution of pressure over time, impact of maintenance events, feeding mode, wastewater distribution mode; and particle size stability.

Mathematical modeling and experimental validation of a novel Circulating Oxygenation Biofilm Equipment (COBE) for the management of decentralized wastewater treatment

The difficulties of management were the key barriers to the promotion of decentralized wastewater treatment in remote areas. In this study, a novel decentralized Circulating Oxygenation Biofilm Equipment (COBE) and its remote management potential based on mathematical modeling were investigated. The COBE is an integrated biofilm reactor that employs drippage aeration and enables oxygenation, filtration, and effluent processes to be controlled, thus providing convenience for controlling. The model for the COBE describing drippage aeration, comprehensive ammonia-related microbes, and corncob carbon source release process was studied to uncover the impacts of operational conditions on decentralized wastewater treatment in the COBE system. The equipment regulation parameter (circulating oxygenation ratio) was found to be linearly correlated with the oxygen mass transfer coefficient. This discovery enabled highly accurate prediction of COD, NH4-N, and TN concentrations in the equipment effluent at various scenarios. The comprehensive ammonia oxidation biological model indicated that the model could duplicate the actual situation of the succession of ammonia metabolizing related microorganisms. Comammox and ammonia-oxidizing archaea (AOA) dominated ammonia metabolism in this equipment rather than conventional ammonium-oxidizing bacteria (AOB). This study could contribute to the Internet of Things system construction of decentralized wastewater treatment equipment, and provide a solution for timely decentralized equipment management in remote areas.

Evaluation of a novel integrated membrane biological aerated filter for water reclamation: A practical experience

The use of treated wastewater in addition to solving the problem of water shortage, can increase soil fertility and reduce the use of chemical fertilizers. We aim to provide a high-quality effluent to feed membrane system, reduce treatment costs and enhance the efficiency of wastewater recycling. All experiments were conducted on a novel integrated membrane biological aerated filter (IMBAF) consisting of a down flow cylindrical biological aerated filter (BAF) filled by silica and a novel sand-coated polystyrene granules (SCP), followed by ultrafiltration (UF) and reverse osmosis (RO) membranes. IMBAF reactor, with 73.6 L volume, was operated for 270 days (in three 90-day stages) with different conditions of returning backwash water. Accordingly, BAF generated high quality water for feeding UF membrane with 94.2%, 68%, 54.4%, 91.2%, and 99.95% of turbidity, 5-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), oil and grease (O&G), fecal coliform (FC) removal, respectively. At the end of stage 3, 99.88% of influent was recycled by UF and only 0.12% was disposed of as sludge. The BAF and UF module efficiently promote the quality of water entering RO system. After 75 days of continuous operation, the increase in trans-membrane pressure (TMP) and also decrease in RO membrane permeability were about 14% and 9.4%, respectively, indicating low clogging of the membrane. The use of BAF structure designed in this study increases the wastewater recycling rate, decreases membrane clogging and thereby reduces the costs of concentrate disposal and chemical cleaning.

Aeration Biofilter Filler Screening and Experimental Research on Nitrogen and Phosphorus Purification in Rural Black Water

In rural toilets, black water still remains polluted by nitrogen and phosphorus after being pre-treated by septic tanks. This study uses aerated biofilters to purify black water, screen the biofilter filler, and determine its effect on nitrogen and phosphorus purification in rural black water. This study introduced the concept of the “shape factor” into the Langmuir and Freundlich equations and optimized the isotherm adsorption model to better fit the actual dynamics of nitrogen and purification in black water. Combined with the first-order kinetic equation, the double constant equation, and the Elovich equation, the adsorption performance of seven kinds of biofilter fillers (i.e., zeolite, volcanic rock, sepiolite, ceramsite, anthracite, vermiculite, and peat) was studied. Then, the biofilter was constructed using a combination of fillers with better adsorption properties, and its ability to purify rural black water was studied. Results showed that vermiculite and zeolite had little effect on nitrogen and a high saturated adsorption of 654.50 and 300.89 mg·kg−1, respectively; peat and ceramsite had little effect on phosphorus and a high saturated adsorption of 282.41 mg·kg−1 and 233.89 mg·kg−1, respectively. The adsorption rate of nitrogen from fast to slow was vermiculite > peat > zeolite > volcanic rock > sepiolite > ceramsite > anthracite. The adsorption rate of phosphorus from fast to slow was peat > ceramsite > zeolite > sepiolite > vermiculite > volcanic rock > anthracite. Four combined biological filter fillers aided the removal of nitrogen and phosphorus from rural high-concentration black water. The combination of zeolite and ceramsite filler had a good nitrogen and phosphorus removal effect in high-concentration black water. After the system was stable, the nitrogen removal rate attained 71–73%, and the phosphorus removal rate attained 73–76% under the influent condition of total nitrogen and phosphorus concentrations of 150–162 and 10–14 mg·L−1, respectively. This study provides technical support and reference for the purification and treatment of rural black water.

Simulation and prediction of electrooxidation removal of ammonia and its application in industrial wastewater effluent

A FLUENT software able to predict and assess the electrooxidation of ammonia from the simulation of ammonia concentration and flow field distribution was developed in this study. The flow field-based models of ammonia removal were simulated and modified through the experimental results. The parameter of reaction constant k is corrected to 0.00195, and the modified model fitted well with experimental values, with the error less than 4%. The electrode depth of 4 cm was assessed to be optimal for ammonia removal based on the comparison of the simulation results on ammonia concentration and flow field distribution. The prediction result applied in the industrial wastewater treatment indicated that complete could be achieved at 0.27 Ah/L, and about 50% of total nitrogen was removed at 0.8 Ah/L. About 7% of chloride ions were converted into inorganic by-products, indicating low biological toxicity and risk on environment. The energy consumption increased with the promotion of removal efficiency of total nitrogen, requiring 5.4 kWh/m³ to remove 50% total nitrogen at 0.8 Ah/L. The results show the practicability and feasibility of this FLUENT software tool on the simulation and prediction of electrooxidation process, which can provide the simulation parameter settings for the subsequent application. PRACTITIONER POINTS: A FLUENT software based on the simulation of ammonia concentration and flow field distribution was able to predict and assess ammonia electrooxidation. A modified model is provided with a rate constant k of 0.00195 and the distinction of 4% with experimental results. The optimal electrode depth was predicted to be 4 cm via the obtained model. Complete ammonia and about 50% of total nitrogen could be at 0.27 Ah/L and 0.8 Ah/L, receptively. About 7% of chloride ions were converted into inorganic by-products in industrial wastewater with high chloride.

Use of autoclaved aerated concrete particles for simultaneous removal of nitrogen and phosphorus as filter media from domestic wastewater

ABSTRACT In this study, autoclaved aerated concrete particles (AACPs) from construction waste were used to simultaneously remove phosphorus and nitrogen in biological aerated filters (BAFs). The effects of air/water (A/W) ratio on the removal performance of phosphorus (PO₄ ^3-), total organic carbon, total nitrogen (TN), and ammonia nitrogen were investigated. Results showed that AACP BAF was more efficient than commercially available ceramsite (CAC) BAF. For example, the removal rates of TN with AACP and CAC were 45.96% and 15.64%, respectively, and those of PO₄ ^3- with AACP and CAC were 72.45% and 33.97%, respectively, at the A/W ratio of 3:1. Different characterization methods were utilized to evaluate the surface shape, elemental compostion, and internal and surface structure of AACP. The interconnectivity and uniformity of pores and the rough surface of AACP were found to be suitable for the growth of microbial biofilm. In addition, the growth of internal pores in AACP promoted the removal of phosphorus and nitrogen. The surface of used AACP contained a small amount of irregular crystals and was covered with a layer of aggregates, which were characterized as hydroxyapatite [HAP, Ca₅(OH)(PO₄)₃]. The formation of HAP as a final byproduct confirmed the successful removal of phosphorus. Therefore, construction wastes, such as AACPs, could be recycled and utilized as a promising biofilter media for excellent wastewater treatment.

A novel membrane-aerated biofilter for the enhanced treatment of nitroaniline wastewater: Nitroaniline biodegradation performance and its influencing factors

Nitroaniline (NA) wastewater is known to be highly toxic and biodegradation-resistant. Based on the principles of molecular oxygen supply and biofilm formation, a novel membrane-aerated biofilter (MABF) combining membrane aeration with a biofilter was established for the first time to treat NA wastewater containing the same concentrations of p-nitroaniline (PNA) and o-nitroaniline (ONA). The NA wastewater treatment performance of the MABF was investigated, and the NA biodegradation characteristics were evaluated. When the influent NA concentration was 120 mg/L, the PNA and ONA removal rates reached 100% and 86.56%, respectively. The NA removal loading reached 111.62 g/m³·d, and the total nitrogen (TN) removal rate reached 82.97%. The synergistic effects of the diverse microorganisms in the membrane-aerated and nonaerated zones of the MABF enhanced the removal of NA and nitrogen. This MABF is an economically efficient and environmentally friendly technology for treating wastewater containing toxic and hazardous organic compounds.

A novel micro-ferrous dosing strategy for enhancing biological phosphorus removal from municipal wastewater

Ferrous salts have been widely used to enhance phosphorus removal in full-scale wastewater treatment plants, with an average dosage of 0.24-0.35 mM. However, such high dosage inevitably caused serious concerns on operation, potential biological toxicity and excessive sludge production. Thus, this study investigated the effect of micro-dosing of ferrous salt at the level of 0.02 mM on enhanced biological phosphorus removal (EBPR) in sequencing batch reactors. Results showed that micro-dosing of ferrous salt enhanced the overall performance, with average COD, TN and TP removal of more than 4.2%, 2.0% and 5.8%, respectively. In addition, the sequencing analysis further revealed that micro-ferrous dosing could significantly improve the diversity and richness of the microbial community (p < 0.05), whereas the regular dosing of ferrous salts (0.25 mM) negatively impacted on the EBPR performance. It was found that the abundances of phosphorus accumulating organisms (PAOs) in R2 (micro-dosing) were nearly 1.5-fold and 2-fold higher than those in R1 (control) and R3 (regular dosing). The contributions of biological and chemical pathways towards the observed phosphorus removal were also determined according to the phosphorus releasing rate. For micro-dosage and regular dosage of ferrous salts, phosphorus removal mainly relied on biological phosphorus removal and chemical phosphorus removal, respectively. It appears from this this study that the micro-ferrous dosing strategy is practically feasible and economically viable for enhanced phosphorus removal from municipal wastewater.

Phosphate removal from industrial wastewater through in-situ Fe2+ oxidation induced homogenous precipitation: Different oxidation approaches at wide-ranged pH

Phosphate removal through in-situ Fe²⁺ oxidation induced homogenous phosphate precipitation has shown its advantages in municipal wastewater treatment. Its feasibility and suitability for phosphate removal in industrial wastewater with wide-range pH variation like electro-plating wastewater were investigated in bench scale experiments using synthetic wastewater and continuous experiment using real wastewater. Bench scale experiments showed that different Fe²⁺ oxidation approaches worked well for phosphate removal at varied pH conditions. Sole dosing Fe²⁺ salt with aeration achieved sound phosphate removal at alkaline condition (pH ≥ 8). At neutral pH (6 < pH < 8), transition metallic ions catalytic oxidation is a suitable alternative. Cu²⁺ exhibited superior catalytic Fe²⁺ oxidization over Mn²⁺, Zn²⁺, and Ni²⁺. At acid pH (3.0 ＜ pH ≤ 6.0), Fenton reaction oxidation (H₂O₂ = 5 mg/L) showed its efficiency. At their corresponding optimal pH conditions and with Fe²⁺/P ratio of 1.8, dosing sole Fe²⁺ salt, Cu²⁺ catalyzed Fe²⁺ oxidation, and Fe²⁺/H₂O₂ treatments can achieve the TP discharge limit of 0.5 mg/L. In a 30-day continuous experiment using real electro-plating wastewater (pH 4.9-5.5), in both direct Fe²⁺/H₂O₂ treatment and Cu²⁺ catalyzed Fe²⁺ oxidation treatment after wastewater pH being adjusted to 7 effluent TP met China's discharge requirement 0.5 mg/L.

Simultaneous in situ nutrient recovery and sustainable wastewater purification based on metal anion- and cation-targeted selective adsorbents

The recovery of nitrogen (N) and phosphorus (P) from wastewater is of great importance in addressing the global nutrient crisis. The limitations of existing methods require the development of effective technology. Here, two different hydrogel adsorbents were fabricated with good separation ability for metal cation (M⁺) and metal anion (M^-) but showed little removal of nutrients. Based on the materials, a novel three-stage operation system combining adsorption and capacitive deionization (CDI) technology was presented for nutrient recovery and wastewater treatment. In the first two stages, mixed metals in wastewater were successfully separated (Cu²⁺: 144.6 mg/g; Cr₂O₇^2-: 167.0 mg/g), and nutrients were retained (N and P < 1 mg/g). In the third stage, the residual trace metal ions in the solution were removed (2.0 mg/L to N/A), and the nutrients were enriched through electroadsorption and desorption processes by CDI. Plants using recovered liquid fertilizers revealed similar values for height, root length, and chlorophyll compared with those obtained using actual fertilizers. The results indicated that this novel three-stage operation system (3S A-C system) combining adsorption and CDI is efficient in recovering liquid fertilizers from wastewater and is a promising technology for simultaneously addressing nutrient crises and environmental pollution.

Performance analysis and optimization of ammonium removal in a new biological folded non-aerated filter reactor

A new type of biological folded non-aerated filter (BFNAF) was found to be superior and feasible for the treatment of NH₄⁺-N wastewater. It was constructed with the folded structure suitable for the nylon biomass carrier. The advantages of the BFNAF included low energy consumption, long reaction path, large biofilm surface area and non-clogging compared to the traditional biological aerated filter. In this study, the effects of hydraulic retention time (HRT), and the influent NH₄⁺-N concentration on the performance of BFNAF were investigated and optimized by the response surface methodology. Under the optimal operating condition (HRT, 10 h; NH₄⁺-N concentration, 52 mg/L), the removal efficiency and removal rate were 94.62 ± 0.63% and 0.106 kg-NH₄⁺ m^-3 day^-1, respectively. The results showed that the BFNAF reactor could remove NH₄⁺-N from wastewater and realized the nitrification process effectively under natural ventilation conditions.

Impact of dissolved oxygen on the microbial community structure of an intermittent biological aerated filter (IBAF) and the removal efficiency of gasification wastewater

A novel IBAF system (altered conventional biological aerated filter (BAF) for intermittent aeration) was used to treat BDD anodes electrochemical oxidation gasification wastewater effluent, after which 454 pyrosequencing was applied to investigate the bacterial community of IBAF and demonstrate the relationship between dissolved oxygen (DO) and the bacterial community. The results showed that the concentration of COD, NH₄⁺-N and NO₃^--N reached 55.08, 7.64 and 7.76 mg/L, respectively, in IBAF effluent because of changes in the DO concentration at 30 days after system start-up. The bacterial community results revealed that the 40 cm sample had the highest bacterial diversity. The bacterial species were approximate in total samples at phylum and family level, but the relative abundance was significantly different because of change in DO concentration. In addition, sample distance analysis indicated that the similarity of different samples was related to the DO concentration at different heights.