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Ammonia monohydrate (NH3·H2O) is an important chemical widely used in industrial, agricultural, and pharmaceutical fields. Reject water is used as the raw material in self-built bipolar membrane electrodialysis (BMED) to produce NH3·H2O. The effects of electrode materials, membrane stack structure, and operating conditions (current density, initial concentrations of the reject water, and initial volume ratio) on the BMED process were investigated, and the economic costs were analyzed. The results showed that compared with graphite electrodes, ruthenium-iridium-titanium electrodes as electrode plates for BMED could increase current efficiency (25%) and reduce energy consumption (26%). Compared with two-compartment BMED, three-compartment BMED had a higher ammonia nitrogen conversion rate (86.6%) and lower energy consumption (3.5 kW· h/kg). Higher current density (15 mA/cm2) could achieve better current efficiency (79%). The BMED performances were improved when the initial ${\rm NH}_ 4^+$ NH 4 + concentrations of the reject water increased from 500 mg ${\rm NH}_ 4^+$ NH 4 + /L to 1000 mg ${\rm NH}_ 4^+$ NH 4 + /L, but the performance decreased as the concentration increased from 1000 mg ${\rm NH}_ 4^+$ NH 4 + /L to 1500 mg ${\rm NH}_ 4^+$ NH 4 + /L. High initial volume ratio of the salt compartment and product compartment was beneficial for reducing energy consumption. Under the optimal operating conditions, only 0.13 $/kg reject water was needed to eliminate the environmental impact of reject water accumulation. This work indicates that BMED can not only achieve desalination of reject water, but also generate products that alleviate the operational pressure of factories. [ABSTRACT FROM AUTHOR]

The treatment of reject water containing concentrated ammonia and non-biodegradable organics is a challenging task in wastewater treatment plants. To address this problem, we propose a novel process consisting of a selective ammonium-exchange resin and an ammonia electrooxidation reaction (AmER-AOR). Because an alkaline condition is essential for direct ammonia oxidation, the use of a bipolar membrane (BPM) was helpful. Nonetheless, an initial pH of 13 and KOH addition were required to maintain a high alkalinity for the complete elimination of ammonia. The linear sweep voltammogram elucidated the high pH requirement and ammonia oxidation promotion. When the current density varied from 30 to 80 mA cm−2, 60 mA cm−2 showed the highest current efficiency (30.39%) and the lowest specific energy demand (95.3 kWh/kg-N), indicating the most energy-effective condition. Increasing the initial concentration of ammonia from 0.1 M to 0.5 M improved the current efficiency (51.57%), demonstrating an additional energy-effective strategy for the AmER-AOR. The energy efficiency of pure H2 production in the cathodic chamber was 30%. To estimate the viability for practical applications, reject water collected from a local wastewater treatment plant was applied in the AmER-AOR. Notably, no significant difference in the ammonia removal rate was observed with synthetic wastewater. To the best of our knowledge, this is the first study that employs a BPM as a separator and OH− supplier for direct ammonia oxidation. Our findings reveal that the AmER-AOR with a BPM has promising practical applicability in the treatment of reject water and energy production. [ABSTRACT FROM AUTHOR]

Efficient dewatering of sludge is necessary for its cost-effective transportation and final disposal. However, the common method of using polyferric sulfate (PFS) and polyacrylamide (PAM) requires a large amount of dosage and produces high iron ion content in the filtrate. This study examined a solution of applying polyamine (PA) coupled with inorganic coagulant PFS. The results demonstrated that using PFS + PA together could achieve the same or similar filtering rates as using PFS + PAM. The capillary suction time (CST) of PFS + PA (89.0 s) was equivalent to that of PFS (75.1 s) and better than that of PA (117.1 s) and raw sludge (RS, 403.8 s). Compared with PFS + PAM, the combination of PFS and PA efficiently removed Fe ions and chemical oxygen demand (COD) in sludge water content, with Fe ions in the sludge filtrate reduced by 97.8% and COD reduced by 78.9%, respectively. By analyzing the basic physicochemical properties of the sludge system, including the synergistic effect of coagulation and flocculation, sludge hydrolysis and flocculation, it indicated that PA + PFS could reduce bound water. These results demonstrated that combining PFS and PA to improve sludge dewatering performance is more beneficial than utilizing a coagulant or flocculant alone, even PFS + PAM. HIGHLIGHTS Pretreatment of sludge with minimal chemicals.; Reduction of metal content in the treated sludge filtrate.;

The current study evaluated the use of pumice, a volcanic mineral and common sand, in treating reverse osmosis membrane reject water (ROR) using a novel combined adsorption distillation (CAD) method. The CAD method is developed to separate the dissolved solids through adsorption distillation, i.e., leaving the vaporized distillate as freshwater and concentrated brine. The adsorption potential of pumice and sand was investigated at different adsorbent doses, i.e., 2, 5, and 10 g, and consecutive CAD adsorbent backwashing cycles. The improved results were achieved at a 10 g pumice dose. However, its adsorption efficiency declined in longer CAD cycles, i.e., due to the separated deposition of solids. After backwashing, the adsorbed and accumulated salts were slightly removed, and pumice adsorption capacity was maintained for up to 20 cycles of CAD. The properties of the pumice, i.e., before and after five CAD cycles and after backwashing, were characterized with scanning electron microscopic (SEM), elemental disruptive spectroscopy (EDS), and X-ray diffraction (XRD), which revealed that the porous structure of the pumice was completely accumulated with deposits of ionic salts, which were slightly washed away after backwashing, but accumulation remained continued in post-CAD cycles. The explored method revealed a high potential of pumice in water filtration. [ABSTRACT FROM AUTHOR]

The aim of the presented research was the assessment of phosphorus speciation impact on the precipitation of phosphorus in reject water using Ca(OH)2. To achieve this, phosphorus speciation (organic and inorganic phosphorus in suspension and in dissolved form) in reject water that is produced during sludge dewatering, after methane digestion in wastewater treatment plants (WWTPs), was determined. This study covered the materials from four WWTPs with different compositions of feedstock for anaerobic digestion (AnD). In one, the AnD process of primary and secondary sludge was carried out without co-substrate, while in three others, co-substrate (waste from the agri-food industry and external waste-activated sludge and fats from industrial plants) was examined. The investigation was conducted in batch reactors using doses of Ca(OH)2 ranging from 2500 to 5500 mg Ca/dm3. The percentage of phosphorus forms determined in the raw reject water was similar, with the dominant form being soluble reactive phosphorus (SPR) (percentage from 87 to 96%). The small differences observed were dependent on the composition of the AnD feedstock. The results showed that, in all analysed wastewater, very high (exceeding 99.9%) phosphate phosphorus removal efficiencies were obtained using Ca(OH)2 for short reaction times (t = 1 h). The efficiency of phosphate removal depended on pH but not on the forms of phosphorus in the analysed reject water. [ABSTRACT FROM AUTHOR]

Membrane contactors have proved to be effective for recovering ammonia from wastewater by absorbing it into a trapping solution. This study compares the performance of sulfuric acid and citric acid as trapping solutions in a pilot-scale plant for recovering ammonia from sludge digestion liquors using membrane contactors in a liquid-liquid configuration operating at pH 10 and a temperature of 37 °C and using ultrafiltration (UF) technology as pretreatment. The performance of the process using sulfuric acid at a lower pH (9.5) and temperature (30 °C) was also studied, as well as the advantage of including a CO 2 -stripping module in the process. The ammonia elimination efficiency was 88% and 86% when using sulfuric acid and citric acid, respectively. The nitrogen concentration of the produced ammonium sulfate and ammonium citrate reached 23.2 and 14.7 g NH 3 -N·L -1 , respectively. The ammonia elimination efficiency when using sulfuric acid decreased to 49% when decreasing the pH to 9.5 and to 85% when decreasing the temperature to 31 °C. UF technology was able to reduce the concentration of suspended solids by 90% and the chemical oxygen demand by 37%. However, the UF membranes for the pretreatment and the membrane contactors for ammonia recovery had to be constantly cleaned with acid due to scaling, which significantly increased maintenance efforts. The CO 2 -stripping module reduced the consumption of the caustic soda solution by 23% for increasing the pH level of the treated water. Finally, the specific energy consumption of the plant was 8 kWh·m -3 .

In a 3-year research project, a new approach to forecast biological N2O formation and emission at high-strength reject water treatment has been developed (ASM3/1_N2OISAH). It was calibrated by extensive batch-tests and finally evaluated by long-term measurement campaigns realized at three wastewater treatment plants (WWTPs) with different process configurations for nitrogen removal of reject water. To enable a model application with common full-scale data, the nitritation-connected supplementary processes that are responsible for N2O formation are not depicted in the model. Instead, within the new model approach the N2O formation is linked to the NH4-N oxidation rate by defining specific formation factors [N2O-Nform/NH4-Nox], depending on the concentrations of NO2 and O2 as well as the NH4 load. A comparison between the measured and the modeled N2O concentrations in the liquid and gas phase at the full-scale treatment plants prove the ability of the proposed modelling approach to represent the observed trends of N2O formation, emission and reduction using the standard parameter set of kinetics and formation factors. Thus, enabling a reliable estimation of the N2O emissions for different operational conditions. The measurements indicate that a formation of N2O by AOB cannot completely be avoided. However, a considerable reduction of the formed N2O was observed in an anoxic environment. Applying the model, operational settings and mitigation strategies can now be identified without extensive measurement campaigns. For further enhancement of the model, first results for kinetics of N2O reduction kinetics by denitrification processes were determined in laboratory-scale batch tests. HIGHLIGHTS A practical oriented model for the estimation of N2O emission has been developed relying on N2O formation factors.; The model is successfully validated based on several data sets from full scale WWTP with different process configurations.; Operational mitigation strategies were evaluated applying the new model.; The measurement results show a significant N2O reduction potential of the denitrification process.;

Microplastics (MPs) from households, stormwater, and various industries are transported to wastewater treatment plants (WWTPs), where a high proportion of them are captured before discharging their residuals to watersheds. Although recent studies have indicated that the removed MPs are mainly retained in wastewater sludge, sludge treatment processes have gained less attention in MP research than water streams at primary, secondary, and tertiary treatments. In this study, we sampled 12 different process steps in a tertiary-level municipal WWTP in central Finland. Our results showed that, compared to the plant influent load, three times more MPs circulated via reject water from the sludge centrifugation back to the beginning of the treatment process. Fibrous MPs were especially abundant in the dewatered sludge, whereas fragment-like MPs were observed in an aqueous stream. We concluded that, compared to the tertiary effluent, sludge treatment is the major exit route for MPs into the environment, but sludge treatment is also a return loop to the beginning of the process. Our sampling campaign also demonstrated that WWTPs with varying hydraulic conditions (such as the one studied here) benefit from disc filter-based tertiary treatments in MP removal. Highlights Dewatering by centrifugation was a step that removed a high number of MPs from the sludge.; Sludge retained especially the fibrous microplactics.; Reject water transported microplastics inside a wastewater treatment plant.; Disc filter-based tertiary treatment ensured removal of 99% of microplastics in wastewater.;

This paper reports long-term performance of a two-stage AMX® system with a capacity of 70 m3/d treating actual reject water. An air-lift granulation reactor performed partial nitritation (PN–AGR) at an average nitrogen loading rate (NLR) of 3.1 kgN/m3-d, producing an average effluent NO2-–N/NH4+–N ratio of 1.04. The average nitrogen removal rate of the system was 3.91 kgN/m3-d following an anaerobic ammonium oxidation (Anammox) stage moving bed biofilm reactor (A–MBBR). Although the total nitrogen concentrations in the reject water fluctuated seasonally, overall nitrogen removal efficiency (NRE) of the two-stage AMX® system was very stable at over 87%. The two-stage AMX® system, consisting of a PN–AGR followed by an A–MBBR, operated at a stable NLR of 1.86 kgN/m3-d (1.64 kgN/m3-d including the intermediate tank), which is 1.8 times higher (1.6 times including the intermediate tank) than other commercialized single-stage partial nitritation/Anammox (PN/A) processes (which operate at a NLR of about 1 kgN/m3-d). The PN–AGR was affected by high influent total suspended solids (TSS) loads, but was able to recover within a short period of 4 days, which confirmed that the two-stage PN/A process is resilient to TSS load fluctuations.

Anaerobic digestion of thermally hydrolyzed sludge was an important method for sludge treatment. But a large amount of rejected water (TRW) containing high ammonia was produced, which was difficult to treat. In this study, two-stage reactors were used for TRW treatment using partial nitrification-anammox technology. The results demonstrated that nitritation initiated rapidly. The NH4+–N conversion load reached 1300 mg N/(L·day) and could be further improved. The consumption of NH4+–N and the formation of NO2−–N were linear with time. So, the right ratio of NH4+–N/NO2−–N can achieve by controlling time for anammox. Dissolved oxygen and sludge concentration had important effects on nitritation. Increasing dissolved oxygen or sludge concentration can shorten the reaction time. Nitrosomonas were the dominant ammonia-oxidizing bacteria, and nitrite-oxidizing bacteria were not detected. Aerobic treatment achieved more than 50% chemical oxygen demand removal in TRW, and this water was used in an anammox reactor. Accumulated flocculent sludge could inhibit anammox activity but could be removed by increasing the flow velocity. The anammox reactor load was above 600 mg N/(L·day); even under high conductivity (18.2 ms/cm) condition, the load reached 320 mg N/(L·day), and the total nitrogen removal rate was greater than 85% under stable condition. After approximately 190 days of operation, the abundance of anammox bacteria decreased from 29% to less than 10%, but the reactor operated stably. The results demonstrated two-stage reactors were suitable for ammonia removal in TRW using partial nitrification-anammox technology. [ABSTRACT FROM AUTHOR]

Optimization of a single-stage, partial nitritation/anammox (PN/A) process for a reject water treatment in a continuous-flow, moving bed biofilm reactor (MBBR) was presented. Response surface method (RSM) was combined with simulation experiments conducted with the validated mathematical model of PN/A in MBBR. The total inorganic nitrogen (TIN) removal efficiency was the response parameter. Eight independent variables were taken into consideration: reject water flow rate (Q), inflow concentrations of the total ammonium nitrogen (TAN), chemical oxygen demand (COD), alkalinity (ALK), pH, temperature (T), dissolved oxygen concentration in the bulk liquid (DO) and aeration time within 60 min intermittent aeration cycle (AERON). Eleven interactions between independent variables were found as significant (p < 0.05). The interaction of AERON*DO had the highest impact on the PN/A process. Optimal values of the controlled variables were found for two cases of MBBR operation. Verification of the optimization was done by the simulation and comparison with the data from the empirical experiments. Under the conditions of the fixed hydraulic retention time of about 38 h, volumetric nitrogen loading rate of 0.48 kgN/m3d, T of 22.5°C, TAN of 750 gN/m3 and optimized values of DO = 3.0 gO2/m3, AERON = 0.54 h, pH = 7.5, ALK = 80 molHCO3/m3, COD = 775 gO2/m3, the predicted TINrem was 78% which is consistent with PN/A performance observed in the technical-scale MBBR systems. [ABSTRACT FROM AUTHOR]

In the paper, the results of studies on changes in the concentration of selected polycyclic aromatic hydrocarbons (PAHs) in the reject water coming from aerobic stabilization of sewage sludge process were given. The sewage sludge samples originating from a treatment of municipal wastewater treatment plant and an industrial coking wastewater treatment plant were investigated. A technological study was conducted using a municipal sewage sludge (control sample) and a mixture of municipal and industrial sewage sludge simultaneously. Aerobic stabilization of sewage sludge process was carried out for 21 days. The concentration of PAHs was determined at the beginning of the experiment (day 0) and in seven-day intervals: after 7, 14 and 21 days. The initial concentration of PAHs in the reject water coming from the municipal sewage sludge was over 44 g/dm3. Industrial sewage sludge was heavily loaded with polycyclic aromatic hydrocarbons. In a reject water of the mixture of municipal and industrial sludge, the initial content of PAHs reached over 5200 g/dm3. During aerobic stabilization of sewage sludge, a decrease in PAHs concentration in reject water was observed. After 21 days of the experiment, the decrease of the sum of analyzed PAHs was in the range of 62-98%. [ABSTRACT FROM AUTHOR]

Most studies on the impact of reject waters recycled from sludge processing in the multi-phase activated sludge process focus on anaerobic sludge treatment in large wastewater treatment plants, leaving apart the processes of aerobic sludge stabilization often used in smaller facilities in rural and suburban areas. The article presents the results of tests carried out in three small and medium-sized wastewater treatment plants with biological removal of biogenic compounds that use aerobic stabilization to process sludge. The research concerned the quantity and quality of reject waters generated in the process of aerobic stabilization and dewatering of sewage sludge and their impact on the multi-phase activated sludge process. The results showed that the average volume of generated reject waters ranged from 3.2 to 5% of the incoming wastewater volume. The average share of organic compounds and total nitrogen loads contained in reject waters did not usually exceed 5–10% of the loads in raw wastewater but reached almost 50% in the case of total phosphorus. Studies indicated that the composition of the supernatant from aerobic stabilization is strongly dependent on the course of the process. The best quality was obtained for cyclic operation of the aerobic stabilization tank with 16 h of aeration and 8 h of settling. The results also showed the negative impact of sudden discharges of reject waters from sludge processing to a multi-phase biological reactor, which can be reduced by using an appropriate equalization tank and pretreatment of the side stream to reduce the recirculation of phosphorus. [ABSTRACT FROM AUTHOR]

The potential of activated sludge from a membrane bioreactor (MBR) to remove nitrogen from anaerobic digester supernatant was tested at various volumetric exchange rates (n) (0.1, 0.2 and 0.3 d-1) and dissolved oxygen concentrations (DO) (0.5, 2.5 and 3.0 mg/L). The high abundance of ammonium-oxidizing bacteria (7.2%) in the sludge caused the ammonium removal efficiency to exceed 97%, independently of DO and n. However, DO and n affected the process rate; thus, the time necessary for ammonium removal ranged from 4 to 8 h. At DOs of 2.5 and 3.0 mg/L, nitrogen removal reached 79.8%-89.0% although external carbon was not added. The nitrogen removal efficiency was highest (91.5%) at an n of 0.3 d-1 and a DO of 0.5 mg/L. Thus, this variant, which had the highest availability of substrate and the lowest availability of oxygen, stimulated the cooperation of aerobic nitrifiers, denitrifiers and anammox microorganisms, which were present in the biomass. The high rate of endogenous oxygen uptake indicated the degradation of intracellularly stored organics, which may have supported denitrification. These results indicate that the biological treatment of nitrogen-rich supernatant by highly concentrated MBR sludge in a side-stream is an advantageous alternative to treatment in the main-stream of wastewater treatment plants. [ABSTRACT FROM AUTHOR]

Biological nutrient removal from wastewater to reach acceptable levels is needed to protect water resources and avoid eutrophication. The start-up of an anaerobic ammonium oxidation (anammox) process from scratch was investigated in a 20 L sequence batch reactor (SBR) inoculated with a mixture of aerobic and anaerobic sludge at 30 ± 0.5 °C with a hydraulic retention time (HRT) of 2–3 days. The use of NH4Cl, NaNO2, and reject water as nitrogen sources created different salinity periods, in which the anammox process performance was assessed: low (<0.2 g of Cl−/L), high (18.2 g of Cl−/L), or optimum salinity (0.5–2 g of Cl−/L). Reject water feeding gave the optimum salinity, with an average nitrogen removal efficiency of 80%, and a TNRR of 0.08 kg N/m3/d being achieved after 193 days. The main aim was to show the effect of a hydrazine addition on the specific anammox activity (SAA) and denitrification activity in the start-up process to boost the autotrophic nitrogen removal from scratch. The effect of the anammox intermediate hydrazine addition was tested to assess its concentration effect (range of 2–12.5 mg of N2H4/L) on diminishing denitrifier activity and accelerating anammox activity at the same time. Heterotrophic denitrifiers' activity was diminished by all hydrazine additions compared to the control; 5 mg of N2H4/L added enhanced SAA compared to the control, achieving an SAA of 0.72 (±0.01) mg N/g MLSS/h, while the test with 7.5 mg of N2H4/L reached the highest overall SAA of 0.98 (±0.09) mg N g/MLSS/h. The addition of trace amounts of hydrazine for 6 h was also able to enhance SAA after inhibition by organic carbon source sodium acetate addition at a high C/N ratio of 10/1. The start-up of anammox bacteria from the aerobic–anaerobic suspended biomass was successful, with hydrazine significantly accelerating anammox activity and decreasing denitrifier activity, making the method applicable for side-stream as well as mainstream treatment. [ABSTRACT FROM AUTHOR]

In the present study, the influence of bioaugmentation strategy on the co-treatment of 13% v/v reject water and municipal wastewater at a decreasing temperature was evaluated. The experiment was performed in two identical laboratory sequencing batch reactors with the active volume of 8 L. Each one was operated using a 12-hour cycle at sludge retention time of 3 d. The SBR A was bioaugmented with a mixture of wild-living bacteria and Archaea in a dose 0.25 ml. In turn, the comparative reactor (SBR B) was non-bioaugmented, the Archaea product was replaced with an equal volume of dechlorinated tap water. The experiment was divided into 3 phases, each with a different temperature range (20, 15 and 10°C). The temperature reduction did not adversely affect the process performance in the bioaugmented and non-bioaugmented system. Significant removal efficiencies were achieved in both SBRs. The major differences were observed for the COD content in the bioaugmented SBR at a temperature of 10°C. In this case, statistically lower concentrations in the effluent were observed in the bioaugmented system than in the non-bioaugmented one. Additionally, at a temperature of 10°C, an improved process performance was observed in the Archaea presence, but the differences were of no statistical significance. [ABSTRACT FROM AUTHOR]

Sludge quality in terms of dewaterability, reject water characteristics as well as foaming phenomena is a concern either economically or environmentally. In this work the difference in sludge quality between mesophilic and thermophilic anaerobic digested waste activated sludge is compared using completely stirred tank reactors. For mesophilic sludge, the mean capillary suction time (CST) in seconds, extent of dewaterability (% water removed), ammonia nitrogen (Nammon in mg/l) and the soluble COD (CODsol in mg/l) are 852 ± 180, 62.9 ± 1.7, 1484 ± 153.5, and 2315.7 ± 407.6 respectively. Meanwhile the foaming potential (FP) and foam stability (IS) are 4.4 ± 1.7 and 0.7 ± 0.1. Whereas, the mean CST, extent of dewaterability, Nammon and CODsol are 1109 ± 211, 65 ± 1.8, 1581 ± 120.5, and 4740.6 ± 1122.8 for the thermophilic sludge respectively. With a maximum organic loading rate achieved at 2.82 g-VS/l/d, the CST, Nammon and CODsol concentration as well as the FP are significantly better as sludge quality for the mesophilic sludge. [ABSTRACT FROM AUTHOR]

Nutrients, heavy metals, micropollutants, and organic contaminants are all present in the minimal liquid discharge (MLD) discharge water as the MLD is designed to recover 95 % of the water from the wastewater, and the remaining 5 % is disposed of through conventional or advanced disposal strategies. The rejected brine cannot be utilized or discarded without eliminating the impurities. Microalgae cultivation in brine medium has been extensively researched for potential in the utilization of nutrients in the medium for its growth, and the harvested biomass can be beneficial and can become one of the efficient brine management strategies. The microalgae technique is considered sustainable and ecologically friendly compared to other brine management strategies because it generates zero secondary pollutants and provides income through biomass valorization. This review investigates the characteristics of brine from various MLD sectors; Tolerance of microalgae species in brine medium; Microalgae bioremediation and the mechanism adapted for the removal of nutrients, pollutants and other contaminants from the brine; Case studies that implemented microalgae-based brine management; and sloping microalgae solar evaporation pond system. Most significantly, the waste can be recovered as value-added bioproducts for the various sectors fulfilling the Sustainable Development Goals through microalgae brine management. [Display omitted] • Tolerance of microalgae species in the brine medium with tested conditions • Mechanism adapted by microalgae in the removal of pollutants from brine medium. • Solar microalgae evaporation pond system for the brine management strategy [ABSTRACT FROM AUTHOR]

Reject water separated from digested sludge may be a potential source of nutrients due to its high content. However, most often, reject water after sludge dewatering is directed to sewage lines at wastewater treatment plants, negatively affecting their operation, especially in the biological part. The activities related to sludge conditioning before dewatering have a direct impact on the quality of the reject water. The reject water of raw digested sludge is characterized by very high concentrations of ammonium nitrogen, at 1718 mgN-NH4+/dm3; phosphates, at 122.4 mgPO43−/dm3; and chemical oxygen demand (COD), at 2240 mgO2/dm3. The objective of the research was to determine the impact of selected sludge conditioning methods on the quality of reject water obtained after sludge dewatering. The following parameters were analyzed in the reject water: the chemical oxygen demand (COD), phosphates, ammonium nitrogen, and total suspended solids (TSS). It has been observed that the sludge sonification process increases the content of impurities (COD, phosphates) in reject water with an increase in the amplitude of the ultrasonic field. On the other hand, the chemical reagents cause a decrease in the concentration of the pollutants with an increase of the chemical dose. It has been found that the inorganic coagulant PIX 113 gives much better results regarding the reduction of contamination than the polyelectrolyte Zetag 8180.

Membrane contactors are among the available technologies that allow a reduction in the amount of ammoniacal nitrogen released into the environment through a process called transmembrane chemical absorption (TMCA). This process can be operated with different substances acting as trapping solutions; however, strong inorganic acids have been studied the most. The purpose of this study was to demonstrate, at laboratory scale, the performance of citric acid as a capturing solution in TMCA processes for recovering ammonia as an organic fertilizer from anaerobic digestor reject water using membrane contactors in a liquid-liquid configuration and to compare it with the most studied solution, sulfuric acid. The experiments were carried out at 22 °C and 40 °C and with a feed water pH of 10 and 10.5. When the system was operated at pH 10, the rates of recovered ammonia from the feed solution obtained with citric acid were 10.7-16.5 percentage points (pp) lower compared to sulfuric acid, and at pH 10.5, the difference decreased to 5-10 pp. Under all tested conditions, the water vapor transport in the system was lower when using citric acid as the trapping solution, and at pH 10 and 40 °C, it was 5.7 times lower. When estimating the operational costs for scaling up the system, citric acid appears to be a better option than sulfuric acid as a trapping solution, but in both cases, the process was not profitable under the studied conditions.

The aim of the research was to determine the possibility of using and adapting regression models for a description of constructed wetland systems treating reject water from aerobic sewage sludge stabilization. The P-k-C* model was investigated along with related models. The research was carried out using reject water from aerobic sewage sludge stabilization in dairy wastewater treatment plant (WWTP) belonging to Mlekovita in Wysokie Mazowieckie. The main components of the research installation were two vertical flow constructed wetland beds with passive aeration operating at 0.1 m/d hydraulic load. The following parameters were used for modeling: BOD5, COD, N-NH4 + and temperature. Air temperature was also monitored. [ABSTRACT FROM AUTHOR]

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In the paper, the extension of mathematical model of partial nitritation-anammox process in a moving bed biofilm reactor (MBBR) is presented. The model was calibrated with a set of kinetic, stoichiometric and biofilm parameters, whose values were taken from the literature and batch tests. The model was validated with data obtained from: laboratory batch experiments, pilot-scale MBBR for a reject water deammonification operated at Himmerfjärden wastewater treatment and pilot-scale MBBR for mainstream wastewater deammonification at Hammarby Sjöstadsverk research facility, Sweden. Simulations were conducted in AQUASIM software. The proposed, extended model proved to be useful for simulating of partial nitritation/anammox process in biofilm reactor both for reject water and mainstream wastewater at variable substrate concentrations (influent total ammonium-nitrogen concentration of 530 ± 68; 45 ± 2.6 and 38 ± 3 gN/m3 - for reject water - and two cases of mainstream wastewater treatment, respectively), temperature (24 ± 2.8; 15 ± 1.1 and 18 ± 0.5°C), pH (7.8 ± 0.2; 7.3 ± 0.1 and 7.4 ± 0.1) and aeration patterns (continuous aeration and intermittent aeration with variable dissolved oxygen concentrations and length of aerated and anoxic phases). The model can be utilized for optimizing and testing different operational strategies of deammonification process in biofilm systems. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is a widely used technique to treat organic waste and produce biogas. This article presents a practical approach to increase biogas yield of an AD system using a microbial electrosynthesis system (MES). The biocathode in MES reduces carbon dioxide with the supplied electrons and protons (H+) to form methane. We demonstrate that the MES is able to produce biogas with over 90% methane when fed with reject water obtained from a local wastewater treatment plant. The optimised cathode potential was observed in the range of −0.70 V to −0.60 V and optimised feed pH was around 7.0. With autoclaved feed, these conditions allowed methane yields of about 9.05 mmol/L(reactor)-day. A control experiment was then carried out to make a comparison between open circuit and MES methanogenesis. The highest methane yield of about 22.1 mmol/L(reactor)-day was obtained during MES operation that performed 10–15% better than the open circuit mode of operation. We suggest and describe an integrated AD-MES system, by installing MES in the reject water loop, as a novel approach to improve the efficiency and productivity of existing waste/wastewater treatment plants. [ABSTRACT FROM AUTHOR]

BACKGROUND The objectives of this study were to provide a detailed qualitative and quantitative characterization of different reject water types and to evaluate the effect of temperature and type of external organic carbon source on short‐cut nitrification/denitrification process performance for the treatment of reject water with a high ammonia content. RESULTS: According to the results reject water originating from the sludge dewatering unit is characterized by a high ammonium‐nitrogen content which can be further increased upon pre‐treating the sludge in a thermal‐hydrolysis unit, a low carbon to nitrogen ratio, a low biodegradability and contributes approximately 75% of the total ammonium‐nitrogen load of the recycled flows. It is anticipated that the process can be sustained even at low temperatures (15°C). The temperature effect on both nitritation/denitritation rates is described by an Arrhenius equation with activation energies equal to 37.6 and 39.6 kJ mol−1 respectively. The addition of an organic carbon source rich in easily biodegradable compounds can provide for the achievement of high denitritation rates (in the order of 10 mgNO2‐N gVSS‐1 h−1). CONCLUSION: An interesting low cost option to reserve on‐site an easily biodegradable organic carbon source by integrating different processes in a wastewater treatment plant is primary sludge hydrolysis. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The CANON process is a promising method for nitrogen removal in wastewaters with low organic carbon content like reject water. This study investigated the effect of important factors for optimization of the CANON process through inhibition of nitrite-oxidizing bacteria (NOB). In the acclimation period, complete ammonium removal and 43.3% total N removal were obtained at hydraulic retention time of 12 h, temperature of 30°C ± 0.5°C and DO equal to 7-9 mg/L. The effects of air flow rate (AFR) (representative of DO), SRT and C/N were evaluated. Air flow rate was the most important factor for controlling the process, but the effect of SRT was negligible. When AFR was increased from 100 to 500 mL/min, both ammonium removal efficiency (33-43% to 81-83%) and nitrite accumulation (nitritation, 40 mgN/L to 100-120 mgN/L) were increased, but with increasing AFR to 1000 mL/min only ammonium removal efficiency was increased and because of better condition (high DO) for NOBs, nitritation was decreased. C/N had an effect like AFR of 1000 and only increased ammonium removal efficiency and total N removal. With increasing AFR and C/N, both OUR and AUR were increased, but SVI was decreased. [ABSTRACT FROM AUTHOR]

The autothermal termophilic aerobic digestion (ATAD) technology is used in the municipal and industrial wastewater treatment plants (WWTPs) with personal equivalent up to 30.000. The process provides a high level of sewage sludge stabilization and its hygienization. The main operation problems are caused by the high concentration of nitrogen and phosphorus in the reject water from sewage sludge treatment and air purification (odor removal). Reject water usually is returned to the main sewage treatment, which has a negative impact, especially on the sewage treatment systems based on the sequence batch reactors (SBR). Applying high-performance and expensive separate reject water treatment methods such as SHARON, Anammox or CANON in small facilities is not justified economically. The article presents the research results concerning the effectiveness of applying subsurface vertical flow constructed wetlands (SS VF) for reject water treatment from the ATAD process. An innovative type of bed filling was used, which was produced from waste (ash from a heat and power plant). The efficiency of reject water treatment during the research period was on average at 45.6% for ammonia nitrogen, 32.3% for total phosphorus and 85.1% for BOD5. Applying SS VF beds for separate reject water treatment might ensure a stable and effective functioning of municipal WWTPs by decreasing the load of biological part of a WWTP. [ABSTRACT FROM AUTHOR]

Sidestream granular activated sludge grown on anaerobic digester dewatering centrate was bioaugmented and selectively retained to enable high nitrification performance of a 2.5-day aerobic SRT non-nitrifying flocculent activated sludge system at 12 °C. Sidestream-grown granules performed enhanced biological phosphorus removal (EBPR) and short-cut nitrogen removal via nitrite. After bioaugmentation, EBPR continued in the mainstream but ammonia oxidation was eventually to nitrate. Low effluent NH 3 -N concentrations from 0.6 to 1.7 mg/L were achieved with nitrification solely by granules, thus enabling denitrification and nitrogen removal. Molecular microbial analyses of flocs and granules also suggested that nitrifying organisms persisted on granules with minimal nitrifier loss to flocs. Mainstream granule mass at the end of bioaugmentation testing was 1.7 times the amount of sidestream granules added, indicating mainstream granular growth. Nitrite and nitrate availability during the unaerated feeding period encouraged significant growth of ordinary heterotrophs in mainstream granules, but nevertheless mainstream nitrification capacity was sustained. [ABSTRACT FROM AUTHOR]

Reverse osmosis (RO) is well known as an efficient tool to remove different kinds of pollutants and is successfully applied to treat municipal or industrial wastewater. Present wastewater discharge regulations require more and more efficient removal of ammonia and phosphates. To increase the efficiency of their removal, new technologies should be applied. The application of RO for biologically treated wastewater can be considered as an alternative to modernization of the biological treatment. Conventional biological wastewater treatment plants (WWTPs) apply aerobic or anaerobic sewage sludge digestion. It causes problems with reject water (RW) produced during sewage sludge dewatering. RW is usually returned to the beginning of the treatment process which results in a decrease of treatment efficiency. This occurs mainly due to a high load of ammonia nitrogen in RW, the concentration of ammonia nitrogen reaches 2,000 mg N–NH4 + /L. The paper presents a novel approach to removing ammonia from RW using RO membrane techniques. The developed technique provides efficient treatment of RW, RO concentrate utilization and production of quality water used for technological purposes in WWTPs. Removed ammonia and other pollutants are added to sludge and are withdrawn together with dewatered sludge. The presented data show that application of RO techniques provides more economically reasonable and reliable solution of wastewater treatment and reuse than conventional biological tools. A flow diagram of the process that describes principles of RW treatment by RO and ammonia balance is presented. The research indicated that the use of RO in full scale in municipal and industrial WWTPs which utilizes anaerobic or aerobic sewage sludge digestion would result in a significant decrease of contamination load in RW. [ABSTRACT FROM AUTHOR]

The fate of glyphosate and its metabolite AminoMethylPhosponic acid (AMPA) was followed at the catchment of the Sûre river, mainly characterized by small population density and small and medium-sized wastewater treatment plants (WWTPs). A high concentration of AMPA was found in water samples collected in inlet from different wastewater streams, the industry being the main contributor, while glyphosate resulted mainly in domestic origin. The two molecules were also monitored in the anaerobic digestion as in the supernatant produced after centrifugation (reject water). A total of 0.0713 and 2.24 g/d of glyphosate and AMPA respectively were regularly returned to the activated sludge tank (AST) indicating a 20% impact of the sludge management line on the global wastewater mass balance. Finally, the use of Constructed Wetlands (CWs) in Vertical Flow (VF) configuration was tested as a suitable technology to retain both glyphosate and AMPA (90 and up to 50% elimination respectively) and minimize their discharge into surface water. [Display omitted] • Non-agricultural application of glyphosate is relevant for urban emission. • The origin of AMPA is mostly related to industry rather than glyphosate. • Concentrations of AMPA and glyphosate are relevant in reject water. • Vertical Flow Constructed Wetland is 90% efficient towards glyphosate. • AMPA degradation in the soil is sensitive to the wetland loading regime. [ABSTRACT FROM AUTHOR]

Although the anammox process is extensively applied for the treatment of NH4-rich wastewater, new technical solutions overcoming the operational difficulties remain an important task. An innovative design of anammox-based set-up was employed to improve sludge settling under high ammonium load. The set-up included a completely mixed bioreactor with suspended and immobilised activated sludge. To prevent sludge flotation, recycled suspended sludge was additionally treated in an aerated tank at dissolved oxygen (DO) concentration of 1.5 ± 0.2 mg/l followed by processing in a flow-homogeniser. Introduction of these elements resulted in a 3.5-fold increase in total nitrogen removal efficiency (TNRE). The bioreactor achieved maximal TNRE of 86% corresponding to total nitrogen removal rate of 0.77 kg N/m3/d under defined optimal conditions: temperature of 35 ± 2°C, DO of 0.6 ± 0.2 mg/l, hydraulic retention time of 12 h, and dose of suspended sludge of 1.5 ± 0.1 g total suspended solids (TSS)/l. A weakly attached sludge was first described as a technologically important factor. Suspended, weakly and firmly attached sludge exhibited the highest heterotrophic, nitrifying, and anammox activities, respectively. New probes were constructed to detect anammox bacteria by fluorescence in situ hybridisation. Probe forCandidatus‘Jettenia’ could be recommended for widespread use. [ABSTRACT FROM PUBLISHER]

Undiluted reject water from the dewatering of anaerobic sludge with an average total nitrogen content of 718 ± 117 mg L ( n = 63) was used to start-up autotrophic nitrogen removal in three different pilot-scale (3 m) deammonification configurations: (1) biofilm; (2) activated sludge sequence batch; and (3) two-staged (nitritation-anammox). Time- and concentration-based aeration control with alternating aerobic/anaerobic phases was applied for all reactor configurations. All reactors were initiated without anammox-specific inoculum, and biofilm was grown onto blank carriers. During the initial start-up period, biological nitrogen removal was found to be inhibited by an excessive free ammonia content (>10 mg-N L), resulting from the use of high-strength reject water as the process feed. After implementation of free ammonia control by pH adjustment to 6.5-7.5, propagation of the deammonification process was observed with increased nitrogen removal with slight accumulation of NO -N. The highest total nitrogen removal rates were achieved with the single-reactor biofilm- and sludge-based deammonification processes (1.04 and 0.30 kg-N m day, respectively). The critical factors for successful start-up and stable operation of deammonification reactors turned out to be control of pH below 7.5, dissolved oxygen at 0.3-0.8 mg-O L and influent solids values below 1000 nephelometric turbidity units. Microbial analysis demonstrated that highest anammox enrichment was achieved in the biofilm reactor (9.40 × 10 copies g total suspended solids). These data demonstrate the potential of an in-situ grown sludge- or biofilm-based concept for the development and propagation of deammonification process. [ABSTRACT FROM AUTHOR]

The long-term sustainability of an anaerobic ammonium oxidation (anammox) process in a moving bed biofilm reactor (MBBR) treating highly concentrated (mean of 740 mg NH -N L) wastewater was demonstrated by 1600 days of efficient operation. A high maximum total nitrogen removal rate (TNRR) of 1.5 g N m d was achieved at the low temperature of 20 °C. For nitrogen removal recovery in cases of nitrite inhibition, anammox intermediate nitric oxide (NO) was tested in batch experiments as an N-removal accelerating agent. The effect of the addition of various NO dosages (8-72 mg NO-N L) was studied under inhibitory nitrite concentrations (>100 mg NO -N L) for anammox bacteria. Optimal maintained NO concentration was 58 mg NO-N L and brought about the highest biofilm-specific anammox activity (SAA). Compared to a blank test, the minimum concentration of added NO of 40 mg NO-N L showed a statistically significant ( p < 0.05) accelerating effect on SAA. No inhibition of SAA by NO was observed, although at NO concentrations exceeding 72 mg NO-N L, the acceleratory effect upon SAA was decreased by 8%. Changes in the bacterial consortia involved in nitrogen conversion were determined concurrently for the different nitrogen removal rates and operational conditions. Quantities of Planctomycetales clone P4 strains, which are the closest (99% similarity) relative to Candidatus Brocadia fulgida, increased from 1 × 10 to 1 × 10 anammox gene copies per g total suspended solids during reactor operation days 568-1600, which was determined by quantitative polymerase chain reaction. During the operation of the MBBR, the abundance of ammonium-oxidizing bacteria (AOB) increased proportionally (up to 30%). The abundance of nitrite-oxidizing bacteria (NOB) did not increase (remaining below 10%) during days 232-860. AOB became predominant over NOBs owing to the inhibition of free ammonia spiking on NOBs. [ABSTRACT FROM AUTHOR]

Recently the treatment of reject waters generated during dewatering of digested sewage sludge has become a matter of a concern in wastewater treatment plants. The problem of reject waters is that the concentration of ammonia and orthophosphates is relatively high compared to influent composition. In traditional treatment approach, side-streams are recycled to the main wastewater stream, sometimes causing its temporary overcharging. This study comes up with a novel two-step method of treatment real reject water. To this end, a membrane contactor system with a vacuum sweep mode for its ammonia removal efficiency was examined. In the second step, a new biocomposite, eggshells modified with ferric and zirconium oxide, as an effective adsorbent of orthophosphates was investigated. It turned out that application of the membrane contactor system can lead to a 98.9 ± 0.1% reduction in ammonium concentrations in the feed and producing pure ammonium solution concentrated almost three times as much. The investigation was performed at a temperature of 60 °C and an initial pH of the feed of 12.0. Subsequently, orthophosphates were removed from the pre-treated reject waters. For the adsorbent dosage of 15 g·L −1 with a pH of 4.38, the orthophosphate removal efficiency was 92.4 ± 0.1%. During adsorption the adsorbent was chemically and mechanically stable. The proposed mechanism of orthophosphate bound by ferric and zirconium oxide modified eggshells is based on a strong interaction between positively charged adsorbent surface and the negative orthophosphate ions in the solution. The present study confirmed that the membrane contactor process can be applied for effective removal of ammonium from reject water during wastewater treatment, while adsorption on metal oxide modified eggshells may be an attractive alternative to conventional orthophosphate removal processes. The level of the pollutants remained in the effluent after the process in the system was low in comparison to the initial side-stream, thus the effluent can be recycled to the main wastewater stream without causing its temporary overcharging. [ABSTRACT FROM AUTHOR]

Interest in organic waste(water) processing by anaerobic digestion to produce biogas as renewable energy source has increased significantly in recent years. The characteristics of the digested effluents vary depending on the feedstocks treated, and different handling alternatives are possible. This study reviews advances in science and technology in the specific field of nutrient (nitrogen and phosphorus) management from biogas digester effluents during the last two decades (from 1995 to 2014) using a bibliometric approach. Information concerning publications as representative of the outputs of scientific research, and concerning patents as representative of the outputs of technological development was retrieved from specialised databases and analysed systematically. The number of publications was twice the number of patents. Production followed a rising trend (in both cases, partial productivity in the last 5 years was >45%). The USA, China, and Japan were the three most prolific countries when considering the joint production of publications and patents. However, while the number of publications was higher than the number of patents for the USA, the opposite was true for China and Japan. The institutions which published more (and also the most cited items) were mainly European, whereas Asian countries were more active in filing for patents even though the patents from the USA were more frequently cited. Relative interest in particular nutrient management alternatives and their evolution were identified. Reducing the consumption of resources, implementing integral solutions, and circular economy approaches will be among key issues in future studies and development to promote sustainability. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is a widely used technique to treat organic waste and produce biogas. This article presents a practical approach to increase biogas yield of an AD system using a microbial electrosynthesis system (MES). The biocathode in MES reduces carbon dioxide with the supplied electrons and protons (H+) to form methane. We demonstrate that the MES is able to produce biogas with over 90% methane when fed with reject water obtained from a local wastewater treatment plant. The optimised cathode potential was observed in the range of −0.70 V to −0.60 V and optimised feed pH was around 7.0. With autoclaved feed, these conditions allowed methane yields of about 9.05 mmol/L(reactor)-day. A control experiment was then carried out to make a comparison between open circuit and MES methanogenesis. The highest methane yield of about 22.1 mmol/L(reactor)-day was obtained during MES operation that performed 10–15% better than the open circuit mode of operation. We suggest and describe an integrated AD-MES system, by installing MES in the reject water loop, as a novel approach to improve the efficiency and productivity of existing waste/wastewater treatment plants.

[Display omitted] • Domestic sewage & PNA-treated reject water are polished to 4.5 mg/L by anoxic PDA. • External COD supply is finally canceled profiting by enhanced sewage utilization. • Clustered anammox bacteria in compact granule strengthen performance and robustness. • Uronic acid and special protein in EPS promote granulation and pollutant adsorption. • Orderly activated Thauera , Brocadia , Competibacter in PDA cycle coordinate N removal. Partial denitrification/anammox (PD/A) has been recently applied to co-treat domestic wastewater and nitrate-containing anammox effluent. However, studies regarding its performance without external organic supplement, spatial characteristics within sludge aggregates, and chronological changes of active microorganisms along PD/A cycle have rarely been reported. Herein, one-stage PD/A unit extremely and simultaneously polished anammox-pretreated reject water (NH 4 +-N: 65.4 ± 5.7 mg/L, COD: 199.7 ± 23.2 mg/L) and domestic wastewater (NO 3 −-N: 81.6 ± 7.8 mg/L, TN: 85.8 ± 8.9 mg/L, COD: 338.2 ± 29.0 mg/L) to 4.5 ± 2.1 mg/L without external organic carbon supply. Protective "granules-in-granule" aggregates with densely clustered anammox bacteria embedded in homogeneous denitrifying Thauera prevailed in PD/A system, surviving disadvantages from complex wastewater. Uronic acids and β-sheet proteins in outer extracellular matrix facilitated granulation and pollutants adsorption, while tryptophan- and aromatic-like proteins with tighter secondary structure in inner extracellular matrix maintained granular robustness. Importantly, succession of active microorganisms along the PD/A cycle was revealed by transcript-level analysis for the first time. In PD-period, stimulated Thauera contributed to rapid nitrite accumulation. In subsequent anammox-period, Ca.Brocadia was activated to conduct advanced nitrogen removal, which accompanied the timely nitrate-to-nitrite reduction by Thauera and Ca.Competibacter. Elusimicrobia was active throughout the PD/A cycle, which is conducive to eliminate the dependence of PD process on external carbon source by decomposing complex organics in actual wastewater. Protective granular structure, orderly activation and harmonious cooperation of functional consortia facilitated practical nitrogen removal rate of 0.6 ± 0.1 kg-N/m3/d under anoxic condition, which sheds light on engineering application of anammox technology. [ABSTRACT FROM AUTHOR]

• The review provides concentration ranges for sidestream characteristics in WWRFs. • THP mainly affects COD and N content in anaerobic digestion sidestream. • The effect of THP on P is not significant due to precipitation inside AD. • A list of characteristics to measure before selecting sidestream processes is given. This review compiles information on sidestream characteristics that result from anaerobic digestion dewatering (conventional and preceded by a thermal hydrolysis process), biological and primary sludge thickening. The objective is to define a range of concentrations for the different characteristics found in literature and to confront them with the optimal operating conditions of sidestream processes for nutrient treatment or recovery. Each characteristic of sidestream (TSS, VSS, COD, N, P, Al3+, Ca2+, Cl−, Fe2+/3+, Mg2+, K+, Na+, SO 4 2−, heavy metals, micro-pollutants and pathogens) is discussed according to the water resource recovery facility configuration, wastewater characteristics and implications for the recovery of nitrogen and phosphorus based on current published knowledge on the processes implemented at full-scale. The thorough analysis of sidestream characteristics shows that anaerobic digestion sidestreams have the highest ammonium content compared to biological and primary sludge sidestreams. Phosphate content in anaerobic digestion sidestreams depends on the type of applied phosphorus treatment but is also highly dependent on precipitation reactions within the digester. Thermal Hydrolysis Process (THP) mainly impacts COD, N and alkalinity content in anaerobic digestion sidestreams. Surprisingly, the concentration of phosphate is not higher compared to conventional anaerobic digestion, thus offering more attractive recovery possibilities upstream of the digester rather than in sidestreams. All sidestream processes investigated in the present study (struvite, partial nitrification/anammox, ammonia stripping, membranes, bioelectrochemical system, electrodialysis, ion exchange system and algae production) suffer from residual TSS in sidestreams. Above a certain threshold, residual COD and ions can also deteriorate the performance of the process or the purity of the final nutrient-based product. This article also provides a list of characteristics to measure to help in the choice of a specific process. [Display omitted] [ABSTRACT FROM AUTHOR]