Impact of influent characteristics on a partial nitritation SBR treating high nitrogen loaded wastewater

Favipiravir biotransformation by a side-stream partial nitritation sludge: Transformation mechanisms, pathways and toxicity evaluation

Information on biotransformation of antivirals in the side-stream partial nitritation (PN) process was limited. In this study, a side-stream PN sludge was adopted to investigate favipiravir biotransformation under controlled ammonium and pH levels. Results showed that free nitrous acid (FNA) was an important factor that inhibited ammonia oxidation and the cometabolic biodegradation of favipiravir induced by ammonia oxidizing bacteria (AOB). The removal efficiency of favipiravir reached 12.6% and 35.0% within 6 days at the average FNA concentrations of 0.07 and 0.02 mg-N L-1, respectively. AOB-induced cometabolism was the sole contributing mechanism to favipiravir removal, excluding AOB-induced metabolism and heterotrophic bacteria-induced biodegradation. The growth of Escherichia coli was inhibited by favipiravir, while the AOB-induced cometabolism facilitated the alleviation of the antimicrobial activities with the formed transformation products. The biotransformation pathways were proposed based on the roughly identified structures of transformation products, which mainly involved hydroxylation, nitration, dehydrogenation and covalent bond breaking under enzymatic conditions. The findings would provide insights on enriching AOB abundance and enhancing AOB-induced cometabolism under FNA stress when targeting higher removal of antivirals during the side-stream wastewater treatment processes.

Analysis of the Electricity Consumption in Municipal Wastewater Treatment Plants in Northeast China in Terms of Wastewater Characteristics

A municipal wastewater treatment plant plays an important role in treating urban sewage and reducing the quantity of pollutants discharged into rivers. However, the energy consumption of the municipal wastewater treatment industry is large. High energy consumption indirectly produces ecological damage, accelerates the energy crisis, and increases carbon emissions. For energy conservation and emission reduction in wastewater treatment plants, it is first necessary to identify the main factors influencing energy consumption. Electricity consumption accounts for more than 80% of the energy consumption of wastewater treatment plants. Wastewater quantity and wastewater quality have become the key influencing factors of energy conservation and consumption reduction in wastewater treatment plants. In this study, a municipal wastewater treatment plant in Northeast China was selected as the research object, and the measured data, such as air temperature, wastewater quantity, wastewater quality, and electricity consumption of the plant from 2017 to 2020 were statistically analyzed to explore the influences of temperature and wastewater quantity and wastewater quality indicators of influent and effluent on energy consumption. Firstly, the range of influent quantity in the wastewater treatment plant was large. The influent quantity in summer was high because some rainwater entered the sewage treatment plant. In winter, average daily electricity consumption (ADEC) was higher than that in summer. The relationship between ADEC and the wastewater quantity showed a positive correlation, and ADEC slowly increased with the increase in wastewater quantity. Electricity consumption per unit of wastewater (UEC) was negatively correlated with the wastewater quantity, but the correction coefficient in winter was larger than that in summer. Secondly, the ranges of chemical oxygen demand (COD_Cr) and ammonia nitrogen in influent were large, and the ranges of COD_Cr and ammonia nitrogen in effluent were small. Influent COD_Cr concentration was negatively correlated with influent ammonia nitrogen concentration. ADEC increased slightly with the increase in influent COD_Cr concentration. In winter, the increasing trend of ADEC with the influent COD_Cr concentration was higher than that in the summer. The increasing trend of UEC with the increase in influent COD concentration in summer was more significant than that in winter. Thirdly, influent COD_Cr in 11.6% of the samples exceeded the corresponding designed value, and influent ammonia nitrogen concentration in 41.4% of the samples exceeded the corresponding designed value. Effluent COD_Cr in 10.6% of the samples exceeded the First Level Class B standard in "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB18918-2002)", and unqualified COD_Cr in 94% of the effluent samples was ascribed to the unqualified ammonia nitrogen concentration in the influent samples. The electricity consumption level under abnormal conditions was higher than that under normal conditions. Fourthly, ADEC was positively correlated with the average daily COD_Cr reduction. The correction coefficient of ADEC with average daily COD_Cr reduction was greater in winter than that in summer. Fifthly, the average electricity consumption per unit of wastewater was close to the national average energy consumption, displaying the characteristics of high energy consumption in winter and low energy consumption in summer. The correlation analysis results of unit electricity consumption and temperature showed that when it was below 0 °C, the lower the temperature, the higher the electricity consumption. In Northeast China, the influences of seasons and temperatures on the electricity consumption of sewage plants were obvious. Accordingly, it is necessary to implement the diversion of rainwater and sewage, reduce the discharge of unqualified wastewater from enterprises, and take thermal insulation measures in winter. In addition, activated sludge microorganisms suitable for a low temperature area and the optimal scheduling of sewage pipe networks can also improve the operation and management of sewage treatment plants.

Nitrite accumulation, denitrification kinetic and microbial evolution in the partial denitrification process: The combined effects of carbon source and nitrate concentration

The combined effects of carbon source (HAc, HPr, Glu, Glu + HAc) and nitrate concentration (40, 80 mg/L labeling as R₄₀, R₈₀) on partial denitrification (PD) were discussed at C/N ratio of 2.5 (COD = 100, 200 mg/L). The optimal NO₂^--N and NTR reached to 67.03 mg/L, 99.14% in HAc-R₈₀ system, and denitrification kinetics revealed the same conclusion, corresponding to higher COD utilization rate (CUR: 58.46 mgCOD/(gVSS·h)), nitrate reduction rate (N_aRR: 29.94 mgN/(gVSS·h)) and nitrite accumulation rate (N_iAR: 29.68 mgN/(gVSS·h)). The preference order was HAc > HPr > Glu + HAc > Glu in both R₄₀ and R₈₀ systems due to different metabolic pathways, however, the NO₂^--N accumulation and kinetic parameters of R₈₀ group were dramatically higher than those in R₄₀ for the same carbon source. The R₈₀ group facilitated more concentrated biodiversity (607-808 OTUs) with Terrimonas and norank_f_Saprospiraceae responsible for high NO₂^--N accumulation in HAc and HPr served systems, while norank_f_norank_o_Saccharimonadales and OLB13 dominated the Glu containing systems.

Free Nitrous Acid Inhibits Atenolol Removal during the Sidestream Partial Nitritation Process through Regulating Microbial-Induced Metabolic Types

Limited studies have attempted to evaluate pharmaceutical removal during the sidestream partial nitritation (PN) process. In this work, atenolol biodegradation by PN cultures was investigated by maintaining ammonium and pH at different levels. For the first time, free nitrous acid (FNA), other than ammonium, pH, and free ammonia, was demonstrated to inhibit atenolol removal, with biodegradation efficiencies of ∼98, ∼67, and ∼28% within 6 days at average FNA levels of 0, 0.03, and 0.19 mg-N L^-1, respectively. Ammonia-oxidizing bacteria (AOB)-induced metabolism was predominant despite varying FNA concentrations. In the absence of ammonium/FNA, atenolol was mostly biodegraded via AOB-induced metabolism (65%) and heterotroph-induced metabolism (33%). AOB-induced metabolism was largely inhibited (down to 29%) at 0.03 mg-N L^-1 FNA, while ∼27 and ∼11% were degraded via heterotroph-induced metabolism and AOB-induced cometabolism, respectively. Higher FNA (0.19 mg-N L^-1) substantially reduced atenolol biodegradation via heterotroph-induced metabolism (4%), AOB-induced metabolism (16%), and AOB-induced cometabolism (8%). Newly identified products and pathways were related to metabolic types and FNA levels: (i) deamination and decarbonylation (AOB-induced cometabolism, 0.03 mg-N L^-1 FNA); (ii) deamination from atenolol acid (heterotrophic biodegradation); and (iii) nitro-substitution (reaction with nitrite). This suggests limiting FNA to realize simultaneous nitrogen and pharmaceutical removal during the sidestream process.

Biofilm carriers for anaerobic ammonium oxidation: Mechanisms, applications, and roles in mainstream systems

The anaerobic ammonium oxidation (ANAMMOX) process was proposed as the most promising nitrogen removal process. Biofilm carriers were demonstrated to effectively enhance the anaerobic ammonium oxidating bacteria (AnAOB) retention. This paper reviews the effect of carrier properties on the AnAOB biofilm development according to the biofilm development process and the application state-of-art of three major kinds of conventional carriers, organic-based, inorganic-based carriers, and gel carriers, from the view of system performance and functional microorganisms. The carrier modification methods and purpose are thoroughly summarized and classified into three categories corresponding to various carrier defects. Four important aspects of the desirable carrier for the mainstream ANAMMOX process were proposed, including providing spatial configuration, enhancing the biomass retention, reinforcing the activity, and improving the growth environment, which needs to combine the advantages of organic and inorganic materials. Eventually, the future application directions of novel carriers for the ANAMMOX-based process were also highlighted.

Comparisons of nitrite accumulation, microbial behavior and nitrification kinetic in continuous stirred tank (ST) and plug flow (PF) moving bed biofilm reactors

Two types of continuous stirred tank moving bed biofilm reactors (ST-MBBR) and plug flow MBBR (PF-MBBR) were compared for nitrification. PF-MBBR showed strong shock resistance to temperature, and ammonium oxidation ratio (AOR) was 9.63% higher than that in the ST-MBBR, although the average biomass and biofilm thickness of ST-MBBR were 7.32-18.59%, 9.44-14.06% higher than those in the PF-MBBR. Meanwhile, a lower nitrite accumulation ratio (NAR) was observed (54.88%) in the PF-MBBR than the ST-MBBR (78.92%) due to different operation modes, and the divergence was demonstrated by the microbial quantitative analysis. Nitrification kinetics revealed that the temperature coefficient (θ) in the ST-MBBR (1.068) was much higher than that in the PF-MBBR (1.006-1.015), proving the contrasting nitrification performances caused by temperature shock. According to the Monod equation, the half-saturation coefficient (K_N) in the ST-MBBR was 0.19 mg/L while it varied around 0.12-0.24 mg/L in the PF-MBBR, revealing various NH₄⁺ affinity owing to different biofilm thickness and microbial composition. Finally, MBBR optimization related to operation mode, temperature, and free ammonium (FA) inhibition for nitrite accumulation was discussed.

Deep-level nutrient removal and denitrifying phosphorus removal (DPR) potential assessment in a continuous two-sludge system treating low-strength wastewater: The transition from nitration to nitritation

In a continuous two-sludge denitrifying phosphorus removal (DPR) process of anaerobic anoxic oxic - moving bed biofilm reactor (AAO - MBBR), nitritation was practicable through the combined regulation of high temperature (T: 30-32 °C), short hydraulic retention time (HRT: 8 h) and low dissolved oxygen (DO: 1.0-1.5 mg/L). The system lasted for 90 days with stable nitrite accumulation ratio (NAR > 60%), and the total inorganic nitrogen (TIN) removal was 7% higher than complete nitrification. Ammonia oxidizing bacteria ((AOB) 6.18-9.41%) responsible for nitritation showed a clear relationship with NAR, but Nitrospira (2.11% → 2.35%) gradually outcompeted Nitrobacter (1.19% → 0.31%) under higher temperature. During the transition from nitration to nitritation, the DPR potential (characterized by ΔPO₄^3-/ΔNO_x^-) increased by 11.90% while the energy requirement of poly-β-hydroxyalkanoates (PHA) and glycogen (Gly) decreased by 12.58% and 14.50%, respectively, contributing to higher TIN (84.83%) and TP (97.45%) removals. DPR batch tests using different electron acceptors (NO₃^- .vs. NO₃^- + NO₂^-) revealed that removing 1 mg PO₄^3- only consumed 7.12 ± 0.25 mg PHA via NO₃^- + NO₂^- (.vs. 8.50 ± 0.12 mg PHA via NO₃^-) and 16% carbon source was saved although the DPR capability was suppressed as NO₂^- concentration exceeded 15 mg/L. Based on the achievement of nitritation, the feasibility of integrated DPR - Anammox in the AAO - MBBR system for deep-level nutrient removal was discussed.

Nitrification performance of high rate nitrifying trickling filters at low ammonia concentrations: does the aspect ratio matter?

Nitrifying trickling filters (NTFs) are often introduced to pre-treat waters before chlorination process, to reduce the ammonia-driven chlorine consumption in wastewater treatment. As a passive aerated system, the only power needed is to transport the water to the top of the filter for distribution. Thus, understanding the role of filter aspect ratio on ammonia oxidation might save energy cost. In the present study, a pilot-scale comparison NTF system was conducted on two filters with different aspect ratios (height/diameter) and the same specific surface area. The nitrification efficiencies of these two filters under relatively low influent ammonia-nitrogen concentrations (1.0-4.0 mg NH₄-N L^-1) were investigated. Results obtained from the present study indicated that the constructional aspect ratio of NTF showed no significant effect on nitrification performance of NTFs. Additionally, the operational parameters showed similar effects on nitrification in NTFs with different aspect ratios. Our findings could provide important information for the construction design of future NTFs.

Predictions of the Influent and Operational Conditions for Partial Nitritation with a Model Incorporating pH Dynamics

Ammonium partial oxidation to nitrite (i.e., partial nitritation) is required in a two-stage autotrophic nitrogen removal system, to provide effluent suitable for the anammox reaction. This study aims to establish influent (ammonium and bicarbonate concentrations) and operational (dissolved oxygen (DO) concentration and solids retention time (SRT)) conditions that favor partial nitritation. This is achieved through extending the nitritation and nitratation models to predict pH variation as well as the effects of pH, free ammonia (NH₃), and free nitrous acid (HNO₂) on the two reactions. Experiments were performed on a lab-scale sequencing batch reactor (SBR) operated for over 500 days to provide dynamic data for the calibration of model parameters, particularly those related to the NH₃ and HNO₂ inhibition on nitrite-oxidizing bacteria (NOB). The influent ammonium (19-84 mM) and bicarbonate (23-72 mM) were varied, which led to dynamic ammonium, nitrite, and nitrate data suitable for model calibration and validation. The model was able to well-describe pH dynamics as well as the inhibitory effects of NH₃ and HNO₂ on NOB. Model-based scenario analysis was then undertaken to establish the joint regions of influent ammonium and bicarbonate concentrations and the operational DO, temperature, and SRT conditions that favor partial nitritation. The results provide support to the design and optimization of partial nitritation reactors.

Rapid start-up of a nitritation granular reactor using activated sludge as inoculum at the influent organics/ammonium mass ratio of 2/1

Partial oxidation of ammonium to nitrite is a pre- and crucial step to achieve shortcut biological nitrogen removal from ammonium-rich wastewater. In the present study, a nitritation granular reactor using activated sludge as inoculum was started up in a sequencing batch reactor (SBR) at a fixed influent C/N ratio of 2:1. Variations in the reactor performance, functional bacteria activities, sludge morphology and bacterial community structure were investigated. Results showed the formation of compact granules was achieved in 55 days, and a stable nitrite accumulation rate of 0.68 kg N·m^-3·d^-1 was maintained in the following period. With a rapid growth of granular size, the total nitrogen removal by simultaneous nitritation/denitritation was progressively increased to 50%. In sludge granulation, the significant enrichment of r-strategist ammonium oxidizing bacteria (Nitrosomonas) was identified. Additionally, both high free ammonia concentration and extra nitrite competition by heterotrophic denitrifiers were critical to suppress nitrite oxidizing bacteria effectively.

Stoichiometric variation and loading capacity of a high-loading anammox attached film expanded bed (AAEEB) reactor

The nitrogen loading rate (NLR) of an anammox attached film expanded bed (AAFEB) reactor was increased from 5.0 to 60.0 gN/L/d. During the stable operational period, the TN removal efficiency maintained at 87.3 ± 2.5%, and a maximum nitrogen removal rate (NRR) of 44.9 ± 0.3 gN/L/d was achieved. Overload resulted in the sharp deterioration of reactor performance, the ratio of (Food/Microorganism)/SAA should be maintained at lower than 66 ± 7% to ensure the stable operation of the AAFEB reactor. New stoichiometric equations for the anammox process under the low NLR condition (5.0 gN/L/d) and the high NLR condition (50.0 gN/L/d) were proposed. The quantitative SAA-cytochrome heme C relationship was established for the first time that providing a simple way for monitoring the reactor performance. Substrate tolerance ability was significantly increased that proving the stability of the AAFEB reactor was continuously enhanced during the stable operational periods.

Combined heterogeneous Electro-Fenton and biological process for the treatment of stabilized landfill leachate

Treatment of stabilized landfill leachate is a great challenge due to its poor biodegradability. Present study made an attempt to treat this wastewater by combining electro-Fenton (E-Fenton) and biological process. E-Fenton treatment was applied prior to biological process to enhance the biodegradability of leachate, which will be beneficial for the subsequent biological process. This study also investigates the efficiency of iron molybdophosphate (FeMoPO) nanoparticles as a heterogeneous catalyst in E-Fenton process. The effects of initial pH, catalyst dosage, applied voltage and electrode spacing on Chemical Oxygen Demand (COD) removal efficiency were analyzed to determine the optimum conditions. Heterogeneous E-Fenton process gave 82% COD removal at pH 2, catalyst dosage of 50 mg/L, voltage 5 V, electrode spacing 3 cm and electrode area 25 cm². Combined E-Fenton and biological treatment resulted an overall COD removal of 97%, bringing down the final COD to 192 mg/L.

Ammonium removal in landfill leachate using SBR technology: dispersed versus attached biomass

Large concentrations and oscillations of ammonium nitrogen (NH₄⁺-N) in municipal landfill leachate pose considerable constraints to its further treatment in central wastewater treatment plants. The aim of this study was to evaluate and optimize two technologies for the pre-treatment of 600 L/day of landfill leachate: in particular, to optimize their operational conditions for NH₄⁺-N removal up to a level appropriate for discharge to sewers, i.e. <200 mg/L. Both technologies were based on a sequencing batch reactor (SBR), with two different biomass processes: (A) SBR with dispersed/flocculated biomass and (B) SBR with biomass attached to carriers. The results revealed that both technologies successfully reduced the NH₄⁺-N from 666 mg/L (on average) at the inflow to below 10 mg/L at the outflow with alkalinity adjustment in a 12-hour cycle. Both technologies achieved 96% removal efficiencies for NH₄⁺-N. However, SBR with dispersed biomass showed higher flexibility under varying conditions due to the shorter adaptation time of the biomass.

Combination of Fenton processes and biotreatment for wastewater treatment and soil remediation

There is a continuously increasing worldwide concern for the development of wastewater and contaminated soil treatment technologies. Fenton processes and biological treatments have long been used as common technologies for treating wastewater and polluted soil but they still need to be modified because of some defects (high costs of Fenton process and long remediation time of biotreatments). This work first briefly introduced the Fenton technology and biotreatment, and then discussed the main considerations in the construction of a combined system. This review shows a critical overview of recent researches combining Fenton processes (as pre-treatment or post-treatment) with bioremediation for treatment of wastewater or polluted soil. We concluded that the combined treatment can be regarded as a novel and competitive technology. Furthermore, the outlook for potential applications of this combination in different polluted soil and wastewater, as well as the mechanism of combination was also discussed.

Cultivation and characteristics of partial nitrification granular sludge in a sequencing batch reactor inoculated with heterotrophic granules

The aim of this study was to develop a simple operation strategy for the cultivation of partial nitrification granules (PNGs) treating an autotrophic medium. For this strategy, aerobic granular sludge adapted to high concentration organics removal was seeded in a sequencing batch reactor (SBR) with a height/diameter ratio of 3.8, and the ratio of organics to the ammonia nitrogen-loading rate (C/N ratio) in the influent was employed as the main control parameter to start up the partial nitrification process. After 86 days of operation, the nitrite accumulation rate reached 1.44 kg/(m³ day) in the SBR, and the removal efficiency of ammonia nitrogen (NH₄⁺-N) was over 95 %. The PNGs showed a dense and compact structure, with an excellent settling ability, a typical extracellular polymeric substance (EPS) composition, and a high ammonia oxidation activity. The high-throughput pyrosequencing results indicated that the microbial community structure in the granules was significantly influenced by the C/N ratio, and ammonia-oxidizing bacteria (AOB), including the r-strategist Nitrosomonas and k-strategist Nitrosospira genre, which accounted for approximately 40 % of the total biomass at the end of operation. The effective suppression of nitrite-oxidizing bacteria (NOB) growth was attributed to oxygen competition on the granular surface among functional bacteria, as well as the high free ammonia or free nitrous acid concentrations during the aeration period.

Semi-nitritation process producing optimum influent for anammox process in treatment of domestic wastewater

The process of anaerobic ammonium oxidation (Anammox) requires a proper ratio of NH4(+)-N and NO2(-)-N in the influent, which is difficult to control upon treating domestic wastewater. In this study, a control strategy of semi-nitritation (SN) process based on monitoring the pH profile and NH4(+)-N concentration in a sequencing batch reactor (SBR) was developed. The aeration time of each cycle in SN-SBR was calculated using the established equation tSN=tCOD+0.56αnS0/(S0-Sn). To verify the suitability of the control strategy, SN-SBR was operated continuously for 20 cycles, fed with real domestic wastewater with a fluctuating COD of 200-400 mg L(-1) and NH4(+)-N of 65-80 mg L(-1). The nitrogen removal performance of SN-anammox system using the developed control strategy was also monitored. Results showed that SN-SBR was able to generate a suitable ratio of NH4(+)-N to NO2(-)-N for the following anammox process, the TN removal rate of the SN-anammox system achieved 91.7 ± 0.4% and the average ammonium, nitrite and nitrate concentration of effluent was only 0.50 ± 0.24, 0.13 ± 0.09 and 4.9 ± 0.22 mg L(-1), respectively. This study has potential application in the treatment of domestic wastewater using combined SN-anammox process.

Ammonia and phenol removal in an internal-circulate sequencing batch airlift reactor

An internal-circulate sequencing batch airlift reactor (IC-SBAR) has been developed to evaluate the efficiency of phenol and ammonia removal in treating synthetic wastewater. This study examined the effect of operation cycle on this system. Results showed that above 97.0% removal efficiencies of ammonia and phenol were achieved, which indicated that ammonia and phenol removals were not related to operation cycle. The average removal efficiency of 91.7% for chemical oxygen demand (COD) was achieved when the static/aerobic/settling time was 240 min/440 min/40 min. It was found that COD removal efficiency increased due to the time of operation cycle being prolonged. The average removal efficiencies of total inorganic nitrogen (TIN) were 65.8, 69.3 and 68.9% when average TIN concentrations were 78.0, 97.6 and 88.4 mg/L, respectively, in the influent. A cycle study showed that most phenol was degraded by aerobic microbes. Increasing the static time from 120 to 240 min resulted in the accumulation of NO2(-)-N, which indicated that the structures of the nitrifying bacterial community were changed.

GeoChip-based analysis of microbial community of a combined nitritation-anammox reactor treating anaerobic digestion supernatant

A combined nitritation-anammox reactor was established to treat anaerobic digestion supernatant. The reactor achieved a nitrogen loading rate of 0.5 kg N/(m(3)·d) and total nitrogen removal efficiency of 85% after 140 days' operation. To examine the microbial community responsible for the process, GeoChip 4.0, a high-throughput, microarray-based metagenomic tool, was adopted to measure microbial functional potential under different percentages of digestion supernatant. Intriguingly, our results showed that microbial community composition in a stably functioning bioreactor were significantly different under varying environmental conditions. Functional gene diversities decreased with increasing percentages of digestion supernatant. Genes involved in organic remediation and metal resistance were highly abundant, revealing new metabolic potentials in addition to nitrogen and carbon removal. Compared to the significant decrease of genes involved in denitrification and nitrification caused by inhibition of the digestion supernatant, relative abundances of genes for anammox remained relatively stable. This could be partially attributed to the protection of biofilm, which was vital for the stable performance of nitrogen removal. In addition, nitrogen compounds, C/N ratio and the operation parameters (pH and temperature) were the key variables shaping the microbial community, contributing to a total of 76.64% of the variance of the reactor.

Integration of denitrifying phosphorus removal via nitrite pathway, simultaneous nitritation-denitritation and anammox treating carbon-limited municipal sewage

High nutrients removal above 90% from carbon-limited municipal sewage was obtained without adding external carbon source. Achieving nitritation was a prerequisite to improve nutrients removal. Denitrifying phosphorus (P) removal using nitrite as electron acceptor was the key pathway in anoxic zone, where nitrogen removal reached above 60% and average denitrifying P removal was 88%. Simultaneous nitritation/denitritation and anaerobic ammonia oxidation (anammox) possibly contributed to nitrogen removal of 26-36% in aerobic zone. Quantitative PCR assays presented that the abundance of anammox bacteria under nitritation was more than that under complete nitrification. The largest amount of anammox bacteria was 1.32×10(6)copies/gVSS, about 5.6 times increase over a period of 255days. Nitrite concentration of 17mg/L in aerobic zone inhibited anammox bacteria. Quantitative results suggested possible occurrence of anammox. Based on performance of nitritation, combining heterotrophic denitrification with autotrophic nitrogen removal is an effective strategy to improve nutrients removal from carbon-limited wastewater.

Anoxic phases are the main N2O contributor in partial nitritation reactors treating high nitrogen loads with alternate aeration

Partial nitritation (PN) reactors treating complex industrial wastewater can be operated by alternating anoxic-aerobic phases to promote heterotrophic denitrification via NO2(-). However, denitrification under stringent conditions can lead to high N2O production. In this study, the suitability of including anoxic phases in a PN-SBR treating real industrial wastewater was assessed in terms of process performance and N2O production. The PN-SBR was operated successfully and, when the HCO3(-):NH4(+) molar ratio was adjusted, produced a suitable effluent for a subsequent anammox reactor. 10-20% of the total influent nitrogen was removed. N2O production accounted for 3.6% of the NLR and took place mainly during the anoxic phases (60%). Specific denitrification batch tests demonstrated that, despite the availability of biodegradable COD, NO2(-) denitrification advanced at a faster rate than N2O denitrification, causing high N2O accumulation. Thus, the inclusion of anoxic phases should be avoided in PN reactors treating industrial wastewaters with high nitrogen loads.

Population dynamics of nitrifying bacteria for nitritation achieved in Johannesburg (JHB) process treating municipal wastewater

Population dynamic of nitrifying bacteria was investigated for nitrogen removal from municipal wastewater. Nitritation was established with nitrite accumulation ratios above 85%. Quantitative PCR indicated that Nitrospira was dominant nitrite oxidizing bacteria (NOB) and Nitrobacter was few. During nitritation achieving, Nitrobacter was firstly eliminated, along with inhibition of Nitrospira bioactivities, then Nitrospira percentage declined and was finally washed out. Nitritation establishment depended on inhibiting and eliminating of NOB rather than ammonia oxidizing bacteria (AOB) enriching. This is the first study where population dynamics of Nitrobacter and Nitrospira were investigated to reveal mechanism of nitritation in a continuous-flow process. Phylogenetic analysis of AOB indicated that Nitrosomonas-like cluster and Nitrosomonas oligotropha were dominant AOB, accounting for 81.6% of amoA gene clone library. Community structure of AOB was similar to that of complete nitrification system with long hydraulic retention time, but different from that of nitritation reactor with low DO concentration.

Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system

The aim of this study was to determine the effectiveness of dairy wastewater treatment in the integrated technology based on the simultaneous use of the activated sludge method (AS) and a hydrophyte system (HS) (AS-HS), in this case, common reed (Phragmites australis) or common cattail (Typha latifolia). Experiments were conducted in an innovative reactor exploited in the fractional-technical scale at the loads of 0.05 mg BOD5/mg.d.m. d (biochemical oxygen demand) and 0.10 mg BOD5/mg.d.m d. The AS--HS enabled improving the removal effectiveness ofbiogenes characterized by concentrations of Ntot., N-NH4 and Ptot. In contrast, the integrated system had no significant reducing effect either on concentrations of organic compounds characterized by BOD5 and chemical oxygen demand parameters or on the structure of AS in the sequencing batch-type reactors.

Comparative performance of air-lift partial nitritation processes with attached growth and suspended growth without biomass retention

Partial nitritation is an essential first step in anaerobic ammonium oxidation. This study compared the performance of air-lift partial nitritation reactors with attached growth (AG) and suspended growth (SG) without biomass retention using ammonium-rich recirculated liquor produced from the dewatering of anaerobically digested sludge. The steady-state results showed that the AG can effectively retain ammonium-oxidizing bacteria (AOB) with high activity and allow minimizing biomass discharge (approximately 10 mg volatile suspended solids/L) in the effluent. The nitrogen loading (based on the total reactor volume) satisfying the effluent characteristics could be suggested to be 0.42 g N/L/d for the SG, and 0.76 g N/L/d for the AG, respectively. Compared with the SG, the AG achieved a higher ammonium loading rate (approximately 1.8 times), maximal ammonium oxidation activity (48 mg N/L-h based on liquid-phase volume) under a short hydraulic retention time (HRT) and a long solids retention time (SRT > 80 d). The overall performance confirmed that AG is a promising configuration for partial nitritation in terms of the process stability, maximization of the AOB activity and minimization of the effluent biomass under a short HRT and high nitrogen loading rate.

Start-up of the completely autotrophic nitrogen removal process using low activity anammox inoculum to treat low strength UASB effluent

The start-up of the completely autotrophic nitrogen removal process was examined in a sequencing batch reactor (SBR) using low activity anoxic ammonium oxidation (anammox) inoculum. The SBR received effluent from an upflow anaerobic sludge blanket (UASB) that treated low strength wastewater. The volumetric nitrogen loading rate (vNLR) was first 0.24 ± 0.11 kg Nm(-3)d(-1) and then reduced to 0.10 ± 0.02 kg Nm(-3)d(-1). The average specific anammox activity was 2.27 ± 1.31 mg N (gVSS h)(-1), at 30°C representing an increase of 161% compared to the inoculum. The decrease in vNLR did not significantly affect anammox activity, but resulted in a decrease of denitrifying heterotrophic activity to very low levels after the first 30 days owing to the decrease of organic loading rate (OLR). Fluorescence in situ hybridization (FISH) analysis confirmed the stable presence of anammox bacteria in biomass. Numerous filamentous microorganisms were present, several of which were in a state of endogenous respiration.

Nitritation and denitrifying phosphorus removal via nitrite pathway from domestic wastewater in a continuous MUCT process

Nitritation and denitrifying P removal under mode of nitritation and nitrification was investigated in continuous MUCT process treating domestic wastewater. Nitritation was established through short hydraulic retention time to 6 h and low dissolved oxygen concentration of 0.3-0.5 mg/L. Nitritation was stabilized for 95 days with average nitrite accumulation ratio over 90%. Ammonia and total nitrogen removal under nitritation reached 99% and 83%, respectively, much better than complete nitrification. Real-time quantitative PCR assays presented that cell numbers and percentages of ammonia oxidizing bacteria (AOB) population had a clear correlation with nitrite accumulation ratios. The highest percentage of AOB was 13% of total bacterial population. P removal was mainly completed by denitrifying P removal of about 90% occurring in anoxic zone. The P removal efficiency under nitritation was 30% higher than that under complete nitrification. Denitrifying P removal under nitritation was highly beneficial to the treatment of wastewater with limiting carbon source.

Effect of powdered activated carbon technology on short-cut nitrogen removal for coal gasification wastewater

A combined process consisting of a powdered activated carbon technology (PACT) and short-cut biological nitrogen removal reactor (SBNR) was developed to enhance the removal efficiency of the total nitrogen (TN) from the effluent of an upflow anaerobic sludge bed (UASB) reactor, which was used to treat coal gasification wastewater (CGW). The SBNR performance was improved with the increasing of COD and TP removal efficiency via PACT. The average removal efficiencies of COD and TP in PACT were respectively 85.80% and 90.30%. Meanwhile, the NH3-N to NO2-N conversion rate was achieved 86.89% in SBNR and the total nitrogen (TN) removal efficiency was 75.54%. In contrast, the AOB in SBNR was significantly inhibited without PACT or with poor performance of PACT in advance, which rendered the removal of TN. Furthermore, PAC was demonstrated to remove some refractory compounds, which therefore improved the biodegradability of the coal gasification wastewater.

Closed-loop control of ammonium concentration in nitritation: convenient for reactor operation but also for modeling

A mathematical biofilm model was developed to describe nitritation in aerobic granular reactor operating in continuous mode. The model includes the automatic closed-loop control of ammonium concentration in the effluent. This is integrated in a ratio control strategy to maintain the proportion between the dissolved oxygen (DO) and the total ammonia nitrogen (TAN) concentrations in the reactor effluent at a desired value. The model was validated with a large set of experimental results previously reported in the literature. The model was used to study the effect of DO and TAN setpoints on the achievement of full nitritation, as well as to establish the appropriate required range of the DO/TAN concentration ratio to be applied. Nitritation at 20 °C was tested experimentally and simulated with the model. Additionally, the importance of controlling the TAN concentration was highlighted with different scenarios, in which periodic disturbances were applied mimicking a poor control situation.

Nitrogen management in landfill leachate: application of SHARON, ANAMMOX and combined SHARON-ANAMMOX process

In today's context of waste management, landfilling of Municipal Solid Waste (MSW) is considered to be one of the standard practices worldwide. Leachate generated from municipal landfills has become a great threat to the surroundings as it contains high concentration of organics, ammonia and other toxic pollutants. Emphasis has to be placed on the removal of ammonia nitrogen in particular, derived from the nitrogen content of the MSW and it is a long term pollution problem in landfills which determines when the landfill can be considered stable. Several biological processes are available for the removal of ammonia but novel processes such as the Single Reactor System for High Activity Ammonia Removal over Nitrite (SHARON) and Anaerobic Ammonium Oxidation (ANAMMOX) process have great potential and several advantages over conventional processes. The combined SHARON-ANAMMOX process for municipal landfill leachate treatment is a new, innovative and significant approach that requires more research to identify and solve critical issues. This review addresses the operational parameters, microbiology, biochemistry and application of both the processes to remove ammonia from leachate.