Wastewater Removal Research Articles

A Comparative Review on Low-Cost Adsorbent based Alkali-Activated Materials by Adsorption Study

The degradation of the condition of wastewater is becoming more and more serious due to the endless development. One of the main reasons is heavy metal contamination, which causes significant harm to the climate and humanity, such as bad health consequences, environmental degradation, and air pollution. Adsorption, which uses proven adsorbents such as activated carbon, is one of the most common methods for heavy metal removal in wastewater. However, since activated carbon is very expensive to build and repair due to complex production, most people choose another material to overcome this problem. Researchers have recently focused on finding low-cost adsorbents, which are typically industrial, agricultural and food wastes that can generate in large quantities. However, Alkali-Activated Materials (AAMs) have been recognized as a novel possible adsorbent because they are cheap, made from solid aluminosilicate and extremely alkaline activator solution, making them appropriate for usage in the civil engineering specialty. Moreover, they have become an option for various applications due to their unique geopolymer structure, which is highly mechanically, chemically and thermally stable. Hydroxyapatite (HAP) can be extremely useful in this application, as it is a promising biomaterial that has great potential for a low-cost AAMs adsorbent. The purpose of this study is to analyze the present development of a potential economic alternative adsorbent, particularly based on alkali-activated materials (known as geopolymers), for the elimination of heavy metal pollutants in wastewater using adsorption techniques.

Fe3O4@Fe2O3 carbon aerogel particle electrodes for three-dimensional electro-Fenton oxidation: A novel mechanism promoted by non-radical pathway

Three-dimensional electro-Fenton (3D-EF) has exhibited strengths over traditional electro-Fenton (EF) process for water decontamination, but recent researches on 3D-EF are focused on the decontamination mechanism driven by the radical pathway which was environmentally sensitive and poor in anti-interference capability. This study explored the non-radical mechanism in the 3D-EF process by preparing a novel Fe3O4@Fe2O3/carbon aerogel-700 (FFCA-700) particle electrode (PE) to construct a 3D-EF system promoted by non-radical pathway. The electrodes induced electric field spontaneously polarized FFCA-700 into PEs which led to higher active surface areas of electrodes and the enhancement of mass transfer. Numerous polarized FFCA-700 served as electron donor for dissolved O2 to obtain electron to form ·O2– while the increase in positive charge of the graphitized carbon, caused by the functional group containing electron-rich oxygen, was conducive for ·O2– to transform to 1O2 thus promoting the non-radical pathway. Tetracycline (TC) was selected as the model pollutant to evaluate and compare the remediation performance of different systems. The results suggested that FFCA-700-3D-EF system performed well for pollutant removal in real wastewater. Overall, this study provided a reference for the design and optimization of CPEs and the guidance for the mechanism studies on remediation of organically contaminated wastewater by 3D-EF process.

Fe3O4@APTES@CB[7] supramolecular cascade catalyst with tunable morphology for aniline removal in wastewater

Fe3O4@APTES@CB[7] supramolecular cascade catalyst with tunable morphology for aniline removal in wastewater

New trends of heavy elements removal in wastewater: A comprehensive review on inorganic membrane technology

New trends of heavy elements removal in wastewater: A comprehensive review on inorganic membrane technology

Synthesis of calcium phosphate nanomaterial from quail eggshell for cadmium removal from wastewater and its genotoxic/cytotoxic properties.

In recent years, pollutants released into the environment from various sources threaten environmental health. Rapid industrialization and the constantly increasing needs of people facilitate the release of more hazardous wastes into the ecosystem. The presence of pollutants in water resources causes a wide range of adverse effects. In this study, calcium phosphate nanomaterial (Ca3(PO4)2 NM) was synthesized from biological waste eggshells for the cadmium removal in synthetic domestic wastewater, and a treatment method was developed using these NMs. The Ca3(PO4)2 NMs were produced by using a biowaste which provides the synthesis procedure greener approach. The biogenic NMs were used to remove toxic cadmium ions from wastewater samples. Cytotoxicity and genotoxicity studies of the synthesized NMs were also carried out, and their possible effects on the health of living organisms and the ecology were examined. In the developed method, the parameters affecting the removal of cadmium from wastewater samples were optimized and the removal efficiency was calculated by determining cadmium in a flame atomic absorption spectrophotometer system (FAAS). Synthetic domestic wastewater samples were utilized for evaluating the applicability of the developed treatment strategy. In addition, the adsorption capacity of the material for Cd2+ ion was calculated and the values obtained were modeled by using Langmuir adsorption isotherm (LAI). The calculated LAI parameters were within the appropriate limits, which proved that the developed NM can be used as an effective material for cadmium removal. Moreover, a new, rapid, and feasible synthesis strategy for the synthesis of Ca3(PO4)2 NM was presented in the literature.

Ixora coccinea (jungle geranium): A dual-functioning agent for crystal violet removal from wastewater and dye production

ABSTRACT This study explores the red Ixora coccinea flower, also known as jungle geranium, as an effective adsorbent for removing crystal violet (CV) from synthetic and industrial effluents. Characterization techniques such as FESEM, BET surface area, FTIR, and pHZPC reveal the particle structure and characteristics. The adsorption performance is evaluated using various physicochemical parameters, including temperature, concentration, pH, and contact time. The results indicate rapid adsorption, with 93.73% removal within 15 min and 97.63% at equilibrium after 30 min at neutral pH. The maximum adsorption capacity is 129.23 mg/g. The pseudo-second-order kinetics model (R2 = 0.999) confirms the chemisorption process, while the Langmuir model (R2 = 0.999) describes the adsorption pathway. Thermodynamic analysis indicates an exothermic and spontaneous process, with ∆H values between −59.43 and −46.51 kJ/mol and ∆G values from −8.63 to −5.67 kJ/mol. The spent adsorbent can be regenerated in up to 75.26% of cases using a 1:1 MeOH/H2O solution. Practical applications demonstrate effective CV removal in industrial wastewater (54.21%). This work highlights the potential of Ixora coccinea flower extract for both wastewater treatment and as a source of natural dye.

Electrochemical Methods for Nutrient Removal in Wastewater: A Review of Advanced Electrode Materials, Processes, and Applications

In response to the increasing global water demand and the pressing environmental challenges posed by climate change, the development of advanced wastewater treatment processes has become essential. This study introduces novel electrochemical technologies and examines the scalability of industrial-scale electrooxidation (EO) methods for wastewater treatment, focusing on simplifying processes and reducing operational costs. Focusing on the effective removal of key nutrients, specifically nitrogen and phosphorus, from wastewater, this review highlights recent advancements in electrode materials and innovative designs, such as high-performance metal oxides and carbon-based electrodes, that enhance efficiency and sustainability. Additionally, a comprehensive discussion covers a range of electrochemical methods, including electrocoagulation and electrooxidation, each evaluated for their effectiveness in nutrient removal. Unlike previous studies, this review not only examines nutrient removal efficiency, but also assesses the industrial applicability of these technologies through case studies, demonstrating their potential in municipal and industrial wastewater contexts. By advancing durable and cost-effective electrode materials, this study emphasizes the potential of electrochemical wastewater treatment technologies to address global water quality issues and promote environmental sustainability. Future research directions are identified with a focus on overcoming current limitations, such as high operational costs and electrode degradation, and positioning electrochemical treatment as a promising solution for sustainable water resource management on a larger scale.

Development of pilot-scale plasma bubble reactors for efficient antibiotics removal in wastewater

Plasma bubble (PB) is a promising technology to control antibiotic wastewater pollution. However, the practical implementation of PB technology at the industrial-scale is still underdeveloped. In addition, the influence of different discharge modes for PB on wastewater treatment is largely unknown. This study designed pilot-scale PB reactors with different discharge modes to investigate the degradation effect of norfloxacin (NOR) and tetracycline (TC) in bulk tap water. Results indicate that the dielectric barrier discharge (DBD) mode with low average discharge power demonstrates superior degradation ability and higher production of O3(g) and .O2−(aq) compared to the spark mode which exhibits the high-intensity spark discharge in the tip area of the tube. After 40 min of treatment in a Double DBD reactor, 97.4% and 100% of NOR and TC are removed from 2 L tap water, attributed to the accumulation of antibiotic molecules by PBs and the in-situ generation of O3(g) and .O2−(aq) produced by plasma. Furthermore, a larger-scale PB reactor is developed by creating an array of four DBD reactors, effectively degrading 8 L mixed antibiotics solution. This study provides valuable insights for PB reactor design and the degradation performance of antibiotic wastewater, which will contribute to the further development of synergistic systems for plasma degradation.

Microbial removal of phenol and ammonium from acidic wastewater using recycled polyurethane: Performance and mechanism

Using solid waste as fortifying agent can improve the efficiency of biological treatment of wastewater and solve the problem of difficult treatment of solid waste. In this study, the waste polyurethane was used as the immobilized carrier of strain, and the repair effect of the immobilized system on acidic phenol-containing wastewater was investigated under different conditions and the mechanism of microbial degradation and acid resistance enhanced by the carrier was discussed. The results showed that polyurethane immobilization improved microorganisms' resistance to harsh environments, strain growth, and pollutant removal efficiency in wastewater. Optimizing the culture conditions of the immobilized system increased the average removal efficiency of phenol and NH4+ by 68.77 % and 135.12 %, respectively, compared to the free strain. Additionally, immobilization enhanced the strain's tolerance to phenol, achieving efficient removal of high-concentration phenol-containing wastewater (2200 mg L−1) that free bacteria could not handle. In the MBBR reactor, the immobilized polyurethane-strain Hly3 system operated stably for 20 cycles, removing 95 % of 2000 mg L−1 phenol and 65 % of 100 mg L−1 NH4+. The mechanism by which the carrier improved microbial degradation and acid resistance was studied. It was found that carrier protection, accelerated material transfer, enhanced strain resistance, and increased activity of the acid-resistant reaction system were the main reasons for the improved acid resistance and degradation ability of strain Hly3. From an environmental and economic perspective, recycling polyurethane buffer materials as carriers to immobilize microorganisms offers a cost-effective wastewater treatment solution, also addressing the challenge of difficult solid plastic waste treatment.

Synthesis of cubic mesoporous silica SBA16 functionalized with carboxylic acid in a one-pot process for efficient removal of wastewater containing Cu2+: Adsorption isotherms, kinetics, and thermodynamics

Wastewater containing heavy metal ions, such as Cu2+, that are released into the environment will cause irreparable damage to the nature and human health of living. It is, therefore, absolutely crucial to remove these toxic ions from water. Herein, this paper utilizes the cyano group as a functional reagent to prepare carboxyl-functionalized SBA16 for adsorbing Cu2+ in water. In this paper, 2-cyanoethyltriethoxysilane is employed as a functionalizing reagent to prepare carboxyl-functionalized SBA16 through a one-pot method. The prepared material was characterized using various techniques, such as WXRD, TEM, FT-IR, and XPS. The results indicated that the introduction of the functionalizing reagent did not disrupt the original cage-like cubic mesoporous structure (Im3m symmetry) of SBA16. Crucial adsorption factors, namely pH, adsorbent dosage, Cu2+ initial concentration, and contact time, affecting the removal of Cu2+ were monitored and the optimum adsorption conditions were determined. Isotherm and kinetic investigations were conducted and a non-linear fitting method of experimental data was used to obtain isotherm and kinetic parameters. Maximum adsorption capacity reaches 181.3 mg g−1 was achieved in 60 min at pH = 3. Adsorption kinetics and adsorption isotherm followed the pseudo-second-order (R2 = 0.999) and Langmuir (R2 = 0.999) models, respectively. This suggests that the adsorption process primarily involves chemisorption and monolayer coverage. Thermodynamic parameters showed the spontaneous and endothermic nature of the adsorption process. After 5 cycles, the adsorbent still maintains a good adsorption capacity for Cu2+. This suggests promising applications for the adsorbent in treating wastewater containing Cu2+.

Effects of Temperature and Light on Microalgal Growth and Nutrient Removal in Turtle Aquaculture Wastewater.

The aim of this study was to explore the effects of temperature and light on microalgal growth and nutrient removal in turtle aquaculture wastewater using a single-factor experiment method. Results showed that the growth process of Desmodesmus sp. CHX1 in turtle aquaculture wastewater exhibited three stages, namely adaptation, logarithmic, and stable periods. Temperature and light significantly influenced the growth and protein and lipid accumulation of Desmodesmus sp. CHX1. The optimal conditions for the growth and biomass accumulation of Desmodesmus sp. CHX1 included a temperature of 30 °C, a photoperiod of 24L:0D, and a light intensity of 180 μmol photon/(m2·s). Increased temperature, photoperiod, and light intensity enhanced nutrient removal efficiency. Maximum nitrogen removal was achieved at a temperature of 30 °C, a photoperiod of 24L:0D, and a light intensity of 180 μmol photon/(m2·s), with the removal efficiency of 86.53%, 97.94%, 99.57%, and 99.15% for ammonia, nitrate, nitrite, and total phosphorus (TP), respectively. Temperature did not significantly affect TP removal, but increased photoperiod and light intensity improved the removal efficiency of TP. The development of microalgae biomass as a feed rich in protein and lipids could address feed shortages and meet the nutritional needs of turtles, offering a feasible solution for large-scale production.

Molecular ecological insights into the synergistic response mechanism of nitrogen transformation, electron flow and antibiotic resistance genes in aerobic activated sludge systems driven by sulfamethoxazole and/or trimethoprim stresses

The prevalence of antibiotics poses a serious challenge to biological nitrogen removal in wastewater. In this study, the effects of sulfamethoxazole and/or trimethoprim (15 mg/L∼30 mg/L) on treatment performance, nitrogen transformation and antibiotic resistance genes (ARGs) were investigated in aerobic activated sludge systems to elucidate the metabolic mechanism under high antibiotic stress. 15 mg/L single antibiotic stress improved total nitrogen removal performance due to the persistence of nitrifiers and enrichment of denitrifiers, with an optimum removal efficiency of 96.5%. Up-regulation of all denitrifying genes, coupled with enhanced electron transfer of Complex II and III, contributed to the emergence of aerobic denitrification. The increased expression of antioxidant genes also alleviated intracellular pressure. Whereas combined antibiotic stress induced the significant down-regulation of denitrifying bacteria and genes (nirKS and nosZ), and suppressed the electron supply for denitrification by restraining genes related to Complex Ⅰ and energy supply by tricarboxylic acid cycle, driving the collapse of activated sludge system, with ammonia and total nitrogen removal efficiencies dropping to below 40% and 20%, respectively. The dominant genera in system changed from TM7a to Thiothrix and Sphaerotilus with increasing antibiotic concentration and type. Moreover, antibiotic stress promoted a slight enrichment of ARGs, especially those encoding efflux mechanisms. Cooperative relationships (> 93%) dominated among ARGs, and Klebsiella was identified as the crucial host. ARGs regulating antibiotic efflux were more likely to be co-expressed with functional genes. These results may provide a theoretical basis for establishing promising strategies to mitigate antibiotic-caused process deterioration.

Evaluation of large-scale poultry manure-derived biochar for efficient cadmium removal in zinc smelter wastewater

Cadmium (Cd), a carcinogen, is released from industrial activities like metal refineries and battery runoff, with significant contamination reported near zinc smelters in Korea. This study addresses the issue using an efficient, economical adsorption process with waste-derived biochar-based adsorbents known for high Cd removal. Poultry manure (PM), typically used as fertilizer, can lead to environmental pollution if mismanaged; therefore, it was pyrolyzed to produce biochar. The resulting poultry manure biochar (PMBC) was produced on a large scale (15 ton/day), demonstrating feasibility for large-scale implementation. The effectiveness of PMBC as an adsorbent for Cd was evaluated using wastewater discharged from a zinc smelter. The Cd adsorption capacity of PMBC (60.39 mg/g) was lower than that (302.0 mg/g) of hen manure biochar produced at a laboratory scale in our previous study but was comparable to other biochars reported in the literature. Response surface methodology analysis indicated that reaction time, dose, and agitation significantly influenced Cd removal by PMBC, whereas pH had a negligible impact. Notable contributions to Cd adsorption include the release of K+ from PMBC and the presence of O-containing functional groups. Under continuous flow conditions with real wastewater, Cd was not detected in the effluent for the initial 8 h, and PMBC sustained a removal efficiency of 40.77% until saturation was reached. The results from wastewater treatment and large-scale biochar production offer valuable insights into the potential of biochar as a medium for addressing environmental issues in real-world applications.

Enhanced cationic/anionic dyes removal in wastewater by green nanocomposites synthesized from acid-modified biomass and CuFe2O4 nanoparticles: Mechanism, Taguchi optimization and toxicity evaluation

This article addresses the nanoadsorption mechanisms of rhodamine B (RB), crystal violet (CV), and Congo red (CR) using acid-treated C.edulis (ATCE)/CuFe2O4 (ATCE@CuFe2O4) from an aqueous solution. The physical and chemical characterizations of nanobiomass were studied using different techniques. The specific surface areas of the ATCE and ATCE@CuFe2O4 composites were 15.88 and 337.81 m2/g, respectively, indicating a significant specific surface area of ​​the ATCE@CuFe2O4 nanocomposite. A number of functional groups were determined, which promote the binding of the dye to the adsorbent. The SEM also shows that the adsorbent has a homogeneous texture with deep voids and significant porosity, which likely explains the retention and binding of dye ions on the surface of the adsorbent. In fact, the Langmuir isotherm with a correlation coefficient of 99 % for CV, RB and CR, respectively, represents the most suitable model to explain the adsorption mechanism. The maximum adsorption amount is 666.6 mg/g for CV, 645.16 mg/g for RB and 434.71 mg/g for CR at 308 °K. The adsorption kinetic processes were predicted by the pseudo-second order kinetic model. The thermodynamic properties showed that the adsorption on ATCE@CuFe2O4 was possible and spontaneous. The ATCE@CuFe2O4 recycling and elimination CV, RB, and CR were 74.23 %, 72.75 %, and 67.84 %, respectively, after seven cycles. The design, modeling and optimization of the adsorption parameters were carried out using the Taguchi experimental design. The maximum removal efficiency of CV, RB and CR dyes in optimal operating conditions were 99.96, 98.29 and 97.76 %, respectively. Which at the optimal conditions of 1 g/L, 90 min, 20 mg/L, 298 °K, pH 10 for CV and RB dyes and 1 g/L, 90 min, 20 mg/L, 308 °K, pH 4 for CR. This research demonstrated the performance of ATCE@CuFe2O4 in bean seed germination test and its effectiveness in removing dyes from wastewater.

Optimizing Synthesis of Anionic Surfactant‐Modified Carbon Black for Enhanced Ammonium Adsorption

The increasing levels of ammonium in wastewater pose serious environmental issues, highlighting the urgent need for effective adsorbents to facilitate its removal. Although conventional biological treatment methods have certain drawbacks, adsorption using carbonaceous materials, such as carbon black produced from waste tires, presents a promising alternative for ammonium removal. However, the use of these materials has not been thoroughly investigated. This study focuses on optimizing the synthesis of carbon black modified with anionic surfactants to improve its capacity for ammonium adsorption. Utilizing Response Surface Methodology (RSM) and a Box‐Behnken design, the optimization process examined key variables, including reaction time, surfactant concentration, carbon black dosage, and surfactant type. Comprehensive characterization of the adsorbent was conducted to analyze its surface properties, functional groups, morphology, and elemental composition. The regression models produced highly accurate results with an R2 value of 0.9437. The optimal synthesis conditions were identified as a 12.30‐hour reaction time, a surfactant concentration of 8 mmol/L of sodium dodecylbenzene sulfonate, and a carbon black dosage of 30 g, achieving an ammonium removal efficiency of 84.80%. This study offers a scalable solution for ammonium removal in wastewater, promising practical applications and future sustainable waste management research.

Photochemical Action of Far‐UVC Radiation (222 nm) in Wastewater Treatment and Indoor Air Disinfection

AbstractUltraviolet‐ C irradiation can effectively disinfect various pathogens present in air, surfaces, and water. Various recent research studies suggest use of KrCl* (krypton‐chloride) excimer lamps to disinfect high‐risk public spaces having pathogenic bateria and viruses, as they emit Far‐UVC radiation (222 nm) with lower health risks than germicidal UVC (254 nm). The purification of water and air having pollutants and pathogens is a critical challenge in environmental protection and public health assurance. Far‐UVC excimer lamps (222 nm) have shown potential in decontaminating various organic pollutants, however, their efficacy against inorganic pollutants present in wastewater and indoor air as well as associated chemistry requires further investigations for wider acceptance. This review examines various photochemical action of Far‐UVC radiation (222 nm) in wastewater treatment and indoor air disinfection, elaborating their potential for inorganic pollutant removal in wastewater as well as challenges associated with their application in disinfection of indoor air.

CARBON-SILICA COMPOSITE AS ADSORBENT FOR REMOVAL OF CATIONIC DYE (METHYLENE BLUE)

The aim of this research was to synthesize carbon-silica composite (CSC) as an adsorbent for cationic dye removal from wastewater. Molasses, a by-product of the sugar industry, was successfully utilized to prepare CSC by sol-gel method with tetraethoxylsilane (TEOS) as silica source. The physicochemical properties of the composites were studied by N2 adsorption, FTIR and TGA. The highest specific surface areas of CSC was 144 m2/g at a molasses/TEOS ratio of 0.8, with a mesopore volume of 83% and average pore width of 9.71 nm. This optimal CSC was evaluated for methylene blue (MB) adsorption using batch experiments under varying adsorption times and initial MB concentrations. Adsorption equilibrium was reached within 14 h and the pseudo-second order equation provided the adequate fit for the kinetic studies, suggesting that dye adsorption was limited by chemisorption. The equilibrium data were best described by the Sips model with a maximum adsorption capacity of 180.22 mg/g. The CSC derived from molasses is considered a potentially promising adsorbent for cationic dye removal in wastewater.

Sustainability Strategies in Municipal Wastewater Treatment

The European Parliament adopted a legislative resolution of 10 April 2024 on the proposal for a directive of the European Parliament and of the Council concerning urban wastewater treatment. The reduction in pollution in discharged treated wastewater in the parameters of BOD5, total nitrogen, and total phosphorus was emphasized. Based on these results, it stated that the impacts on the quality of lakes, rivers, and seas in the EU are visible and tangible. At the same time, it was emphasized that the sector of urban wastewater removal and treatment is responsible for 0.8% of total electricity consumption and about 0.86% of all greenhouse gas emissions in the entire EU. Almost a third of these emissions could be prevented by improving the treatment process, better use of sewage sludge, and increasing energy efficiency, as well as a higher rate of use of renewable resource technologies. It is also necessary to integrate treatment processes into the circular economy. Sludge management and water reuse are suboptimal as too many valuable resources are still being wasted. This article focuses on sustainable municipal wastewater treatment, innovative and new wastewater treatment processes and technologies (combined and hybrid processes, ANAMMOX, etc.) and their use in practice with the aim of increasing environmental and energy efficiency and reducing the carbon footprint. The research is focused on the possibilities of increasing the efficiency of energy processing of sludge, reuse of nitrogen and phosphorus, sludge, and reuse of treated wastewater.

Modification of steel slag and its application for phosphate and ammonia removal in aquatic products processing wastewater

ABSTRACT This study aims to modify different types of steel slag by heating, characterise the material and test its ability for adsorption of phosphate and ammonia from aquatic products processing wastewater. The materials were characterised by SEM, EDS, BET and FT-IR analyses. The effects of the type of steel slag, calcination temperature in steel slag modification, pH, contact time, adsorbent mass and initial pollutant concentration were investigated using the one-factor-at-a-time approach. The results show that the adsorption kinetic of the samples followed the pseudo-second-order model, whereas their adsorption isotherm fitted well with the monomolecular adsorptive Langmuir with a maximum phosphate adsorption capacity of 45.045 mgPO43-/g. Optimisation using Response Surface Methodology was conducted with the independent factors (adsorbent doses, contact time and calcination temperature of steel slag) and response (removal efficiency of phosphate). The temperature and dosage of the material significantly affected phosphate removal efficiency and optimisation conditions were suggested. Validation of one optimum condition at the calcination temperature of 801°C, the adsorbent dosage of 11.9 g/L and the contact time of 72 min using real aquatic products processing wastewater resulted in the removal efficiencies of 86.93, 87.59, 7.76 and 7.58% for phosphate, total phosphorus, ammonia and total nitrogen, respectively.

Enhanced nitrogen removal from secondary effluent of municipal wastewater using denitrification filter: Feasibility of refractory organics as a carbon source

Conventional advanced nitrogen removal in municipal wastewater is hindered by the limited availability of carbon sources in the secondary effluent. However, refractory organics present in it had the potential to serve as intrinsic carbon sources after hydrolysis for nitrogen removal via simultaneous denitrification and partial-denitrification anammox (PDA) processes. To assess this potential, a denitrification filter was set up in this study to evaluate its feasibility of concurrent processes. Results showed that increasing influent ammonium (NH4+-N) from 1.0 to 7.0 mg/L increased total nitrogen (TN) removal from 52.4 % to 89.9 %. Simultaneous occurrence of PDA and denitrification process were confirmed by the actual chemical oxygen demand (COD) consumption (0.8–1.2 mg/mg TN removal) from non-fluorescent organics. The presence of the anammox, hydrolytic and denitrifying bacteria further supported the achievement of nitrogen removal through PDA and denitrification processes by utilizing hydrolytic products biodegraded from refractory organics.