Novel partial nitritation treatment for anaerobic digestion liquor of swine wastewater using swim-bed technology

A swim-bed reactor using the biofringe acryl-fiber biomass carrier was used for partial nitritation treatment for anaerobic digestion liquor of swine wastewater. The sludge in the reactor demonstrated excellent settling properties, and the sludge volumetric index (SVI) was always about 50 ml g(-1). The mixed liquor suspended solids (MLSS) concentration was maintained above 10,000 mg l(-1) with a maximum of 16,800 mg l(-1). Satisfactory and stable partial nitritation was obtained at a nitrogen loading rate (NLR) of 1.9 kg-N m(-3) d(-1) without any operational control. Only a little nitrate was produced almost during the whole operational period and the nitrite to total oxidized nitrogen ratio (NO(2)-N/(NO(2)-N+NO(3)-N)) was always above 95%. In addition, the influence of temperature on partial nitritation efficiencies was also investigated and non-controlled efficiencies were maintained stably between 15 degrees C and 30 degrees C at an NLR of 1.9 kg-N m(-3) d(-1), but suddenly deteriorated when the temperature fell below 15 degrees C. Nitrite oxidizing bacteria were inhibited by free ammonia and free nitric acid, which prevented the conversion of nitrite to nitrate and the inhibition due to free nitric acid weaken with a decrease in temperature. It was apparent that these phenomena were crucial to the control of partial nitritation treatment.     

Nitrogen removal characteristics and biofilm analysis of a membrane-aerated biofilm reactor applicable to high-strength nitrogenous wastewater treatment

A membrane-aerated biofilm reactor (MABR) capable of simultaneous nitrification and denitrification in a single reactor vessel was developed to investigate the characteristics of nitrogen removal from high-strength nitrogenous wastewater, and biofilm analysis using microelectrodes and the fluorescence in situ hybridization (FISH) technique was performed. Mean removal percentages of total organic carbon (TOC) and nitrogen were 96% and 83% at removal rates of 5.76 g-C m(-2) d(-1) and 4.48 g-N m(-2) d(-1), respectively. For stable removal efficiency, constant washing of the biofilm was needed. Dissolved oxygen microelectrode measurement revealed that the biofilm thickness was about 1600 microm, and that oxygen penetrated about 300 to 700 microm, from the outer surface of the membrane. Furthermore, FISH analysis revealed that ammonia-oxidizing bacteria (AOB) were located near the outer surface of the membrane, whereas other bacteria were located from the inner to the outer part of the biofilm. Combining these results demonstrated that simultaneous nitrification and denitrification occurred in the biofilm of the MABR system. In addition, stoichiometric analysis revealed that after 130 d(-1), the free ammonia (FA) concentration ranged within the concentration causing inhibition of the growth of nitrite oxidizing bacteria (NOB) and that AOB consumed 86% of the oxygen supplied through the intra-membrane. These results indicate that nitrogen removal not via nitrate but via nitrite was mainly achieved in the MABR system.     

Multi-scale individual-based model of microbial and bioconversion dynamics in aerobic granular sludge

Aerobic granular sludge is a novel compact biological wastewater treatment technology for integrated removal of COD (chemical oxygen demand), nitrogen, and phosphate charges. We present here a multiscale model of aerobic granular sludge sequencing batch reactors (GSBR) describing the complex dynamics of populations and nutrient removal. The macro scale describes bulk concentrations and effluent composition in six solutes (oxygen, acetate, ammonium, nitrite, nitrate, and phosphate). A finer scale, the scale of one granule (1.1 mm of diameter), describes the two-dimensional spatial arrangement of four bacterial groups--heterotrophs, ammonium oxidizers, nitrite oxidizers, and phosphate accumulating organisms (PAO)--using individual based modeling (IbM) with species-specific kinetic models. The model for PAO includes three internal storage compounds: polyhydroxyalkanoates (PHA), poly phosphate, and glycogen. Simulations of long-term reactor operation show how the microbial population and activity depends on the operating conditions. Short-term dynamics of solute bulk concentrations are also generated with results comparable to experimental data from lab scale reactors. Our results suggest that N-removal in GSBR occurs mostly via alternating nitrification/denitrification rather than simultaneous nitrification/denitrification, supporting an alternative strategy to improve N-removal in this promising wastewater treatment process.     

Stable and high-rate nitrogen removal from reject water by partial nitrification and subsequent anammox

A combined process of partial nitrification (PN) and anaerobic ammonium oxidation (anammox) was carried out to treat reject water with a high concentration of ammonium and a low level of hardly biodegraded organic carbon. Stable treatment performance was obtained under high nitrogen loading rates of 5.7 kg-N/m³/day and 10.5 kg-N/m³/day for the PN and anammox reactors for more than 2 months, respectively. Successful nitrite accumulation was observed in the PN reactor, with an effluent NH₄-N/NO₂-N ratio of 1: 1.1 and marginal nitrate production, which is suitable for the subsequent anammox process. The strict control of DO concentration was adopted as the main manipulating strategy for the stable running of the PN reactor. And results indicated that the value of FA and FNA within a favorable range was essential for the successful operation of PN reactor. The anammox process was carried out in an up-flow fixed-bed reactor. The influent NH₄-N/NO₂-N ratio played a vital role in obtaining efficient nitrogen removal. The anammox reactor was successfully operated with a nitrogen removal rate of 9.1 kg-N/m³/day for 2 months, indicating high operational stability. Inorganic carbon was shown to have a positive impact on the high nitrogen removal rate during the combined process. In addition, the characteristics of the sludge in both reactors were investigated. The Stover–Kincannon model was used for kinetics studies. K_B and U_max were determined as 30.1 g/L/day and 13.9 g/L/day, respectively, for the PN reactor and 42.1 g/L/day and 31.2 g/L/day, respectively, for the anammox reactor.     

不同类型污泥接种源培养的好氧颗粒污泥脱氮性能比较

分别以活性污泥和厌氧颗粒污泥培养的好氧颗粒污泥为对象，对成熟污泥颗粒的脱氮性能进行了比较研究。结果表明，颗粒污泥驯化成熟之后，对氨氮的去除效果维持在95％左右，与其污泥接种源没有明显的相关关系；对一个降解周期内氮的形态分析表明，在颗粒污泥存在的反应器内发生了同步硝化反硝化。     

Segregation of biomass in cyclic anaerobic/aerobic granular sludge allows the enrichment of anaerobic ammonium oxidizing bacteria at low temperatures

A cyclic anaerobic/aerobic bubble column reactor was run for 420 days to study the competition for nitrite between nitrite oxidizing bacteria (NOB) and anaerobic ammonium oxidizing bacteria (Anammox) at low temperatures. An anaerobic feeding period with nitrite and ammonium in the influent followed by an aerated period was applied resulting in a biomass specific conversion rate of 0.18 ± 0.02 [gN(2) - N · gVSS(-1)· day(-1)] when the dissolved oxygen concentration was maintained at 1.0 mgO(2) · L(-1). An increase in white granules was observed in the reactor which were mainly located at the top of the settled sludge bed, whereas red granules were located at the bottom. FISH, activity tests, and qPCR techniques revealed that red biomass was dominated by Anammox bacteria and white granules by NOB. Granules from the top of the sludge bed were smaller and therefore had a higher aerobic volume fraction, a lower density, and consequently a slower settling rate. Sludge was manually removed from the top of the settled sludge bed to selectively remove NOB which resulted in an increased overall biomass specific N-conversion rate of 0.32 ± 0.02 [gN(2) - N · gVSS(-1) · day(-1)]. Biomass segregation in granular sludge reactors gives an extra opportunity to select for specific microbial groups by applying a different SRT for different microbial groups.     

High rate nitrogen removal in an alum sludge-based intermittent aeration constructed wetland

A new development on treatment wetland technology for the purpose of achieving high rate nitrogen removal from high strength wastewater has been made in this study. The laboratory scale alum sludge-based intermittent aeration constructed wetland (AlS-IACW) was integrated with predenitrification, intermittent aeration, and step-feeding strategies. Results obtained from 280 days of operation have demonstrated extraordinary nitrogen removal performance with mean total nitrogen (TN) removal efficiency of 90% under high N loading rate (NLR) of 46.7 g N m(-2) d(-1). This performance was a substantial improvement compared to the reported TN removal performance in literature. Most significantly, partial nitrification and simultaneous nitrification denitrification (SND) via nitrite was found to be the main nitrogen conversion pathways in the AlS-IACW system under high dissolved oxygen concentrations (3-6 mg L(-1)) without specific control. SND under high dissolved oxygen (DO) brings high nitrogen conversion rates. Partial nitrification and SND via nitrite can significantly reduce the demand for organic carbon compared with full nitrification and denitrification via nitrate (up to 40%). Overall, these mechanisms allow the system to maintaining efficient and high rate TN removal even under carbon limiting conditions.     

分子氨和亚硝态氮对鳜鱼成鱼的急性毒性试验

活体运输过程中,水体中往往积累了较高浓度的分子氨和亚硝态氮。为了探讨分子氨和亚硝态氮在鳜鱼成鱼运输水体中的安全浓度,在水温为18～20℃,盐度为3‰～4‰,pH7.31～7.57,溶解氧(DO)8.2～8.5mg/L 的条件下,采用常规的生物毒性试验方法,研究分子氨和亚硝态氮对鳜鱼成鱼(adult Siniperca chuatsi)毒性的影响。结果表明,分子氨对鳜鱼成鱼24、48、96h 的半数致死浓度(LC50)分别为0.389、0.295、0.193 mg/L 和安全浓度为0.0193mg/L;亚硝态氮对鳜鱼成鱼24、48、96h 的半数致死浓度分别为196.32、91.69、75.4 mg/L,安全浓度7.54mg/L。因此,水体中分子氨对鳜鱼成鱼的毒性作用非常明显,易造成鱼体的死亡,而鳜鱼成鱼对亚硝态氮的耐受性稍强。建议保活运输过程中要加强水体的监测,有效地控制水体中氨氮与亚硝态氮的浓度,以提高成活率。     

Combined nitritation-anammox: advances in understanding process stability

Efficient nitrogen removal from wastewater containing high concentrations of ammonium but little organic substrate has recently been demonstrated by several full-scale applications of the combined nitritation-anammox process. While the process efficiency is in most cases very good, process instabilities have been observed to result in temporary process failures. In the current study, conditions resulting in instability and strategies to regain efficient operation were evaluated. First, data from full-scale operation is presented, showing a sudden partial loss of activity followed by recovery within less than 1 month. Results from laboratory-scale experiments indicate that these dynamics observed in full scale can be caused by partial inhibition of the ammonia oxidizing bacteria (AOB), while anammox inhibition is a secondary effect due to temporarily reduced O(2) depletion. Complete anammox inhibition is observed at 0.2 mg O(2) · L(-1), resulting in NO(2)(-) accumulation. However, this inhibition of anammox is reversible within minutes after O(2) depletion. Thus, variable AOB activity was identified as the key to reactor stability. With appropriate interpretation of the online NH(4)(+) signal, accumulation of NO(2)(-) can be detected indirectly and used to signal an imbalance of O(2) supply and AOB activity (no suitable online NO(2)(-) electrode is currently available). Second, increased abundance of nitrite-oxidizing bacteria (NOB; competing with anammox for NO(2)(-)) is known as another cause of instability. Based on a comparison of parallel full-scale reactors, it is suggested that an infrequent and short-term increased O(2) supply (e.g., for maintenance of aerators) that exceeds prompt depletion of oxygen by AOB may have caused increased NOB abundance. The volumetric air supply as a proxy for O(2) supply thus needs to be linked to AOB activity. Further, NOB can be washed out of the system during regular operation if the system is operated at a sludge age in the range of 45 days and by controlling the air supply according to the NO(3)(-) concentration in the treated effluent. Early detection of growing NOB abundance while the population is still low can help guide process operation and it is suggested that molecular methods of quantifying NOB abundance should be tested.     

Using sludge fermentation liquid to improve wastewater short-cut nitrification-denitrification and denitrifying phosphorus removal via nitrite

Wastewater biological nutrient removal (BNR) by short-cut nitrification-denitrification (SCND) and denitrifying phosphorus removal via nitrite (DPRN) has several advantages, such as organic carbon source saving. In this paper, a new method, i.e., by using waste activated sludge alkaline fermentation liquid as BNR carbon source, for simultaneously improving SCND and DPRN was reported. First, the performance of SCND and DPRN with sludge fermentation liquid as carbon source was compared with acetic acid, which was commonly used in literatures. Sludge fermentation liquid showed much higher nitrite accumulation during aerobic nitrification than acetic acid (81.8% versus 40.9%), and the former had significant anoxic denitrification and phosphorus uptake. The soluble phosphorus and total nitrogen removal efficiencies with sludge fermentation liquid were much higher than with acetic acid (97.6% against 73.4% and 98.7% versus 79.2%). Then the mechanisms for sludge fermentation liquid showed higher SCND and DPRN than acetic acid were investigated from the aspects of wastewater composition, microorganisms assayed by 16S rRNA gene clone library, and fluorescence in situ hybridization. More NO(2)(-)-N accumulated by the use of sludge fermentation liquid was attributed to be more humic acids in the influent, which inhibited nitrite oxidizing bacteria (NOB) more serious than ammonia oxidizing bacteria (AOB), and more AOB but less NOB were observed in the BNR system. The reasons for sludge fermentation liquid BNR system exhibiting greater short-cut denitrifying phosphorus removal were that there were less glycogen accumulating organisms and more phosphorus accumulating organisms and anoxic denitrifying phosphorus removal bacteria with higher nitrite reductase activity.     

A^2/O+MBBR集成工艺处理印染废水

简要介绍印染废水的水质特点及改良传统活性污泥法(A2/O)+移动床生物膜反应(MBBR)工艺集成技术;重点介绍A2/O+MBBR工艺处理印染污水的运行效果。结果显示,在进水量20~60 L/h,溶解氧(DO)质量浓度1.5~4.5 mg/L,污泥回流比50%~90%,硝化液回流比250%~350%,好氧池污泥质量浓度(MLSS)2.0~3.5 g/L,好氧池悬浮填料装填比25%(体积比)的操作条件下连续稳定运行200天后,出水COD去除效果、氨氮去除效果、总磷去除效果、总氮去除效果远远优于《城镇污水处理厂污染物排放标准》的一级A标准。     

运用序列式生物膜反应器处理味精污水工艺研究

味精污水中含有较高的氨氮离子,序列式生物膜反应器(SBBR)能够有效实现味精污水的同步硝化与反硝化反应,减少设备占有面积和节约处理时间。经过实验得出,当溶氧(DO)为3~4mg/L能够有效地满足生物膜中好氧菌的生长需要,又不会破坏生物膜内的厌氧环境,当pH值为8.0时,温度为30℃时,对味精生产中产生的污水的化学需氧量(COD)去除率高达95.34%,氨氮的去除率达到95.78%,生物需氧量(BOD5)去除率94.1%。     

High rate partial nitrification treatment of reject wastewater

Partial nitrification (PN) treatments on reject wastewater were carried out. Dissolved oxygen concentration was limited by controlling air flowrate, which was the main operational strategy in this study. Stable PN performance was obtained during continuous operation for 80 days, with a maximum nitrogen loading rate (NLR) of 4.2 kg-N m⁻³ day⁻¹ and ammonium conversion rate of 2.1 kg-Nm⁻³ day⁻¹. The production of nitrite oxidizers was assumed to be responsible for the nitrogen loss in the reactor. The ratios of NO₂⁻–N/ (NO₂⁻–N + NO₃⁻–N) were always above 99.9%, and BOD removal efficiencies were also stable at around 70% even if a sharp increase in NLR was applied during the stable period. Additionally, bacterial consortia analysis showed ammonium-oxidizing bacteria were the dominant microorganisms, which provided evidence for the long-term stable performance of this PN reactor. During the experiment, sludge setting properties deteriorated due to the absence of a biomass carrier. The stable performance of partial nitrification from reject wastewater demonstrated the feasibility of the operation strategy in this study.     

Emission and control of nitrous oxide from a biological wastewater treatment system with intermittent aeration

Nitrous oxide (N2O) can be emitted as a by-product of the process of nitrogen removal from wastewater. Two methods of complete denitrification and media application were studied in lab-scale intermittent aeration reactors fed with domestic wastewater to refine methods of controlling the N2O emission rate. A study on cyclic patterns showed that the highest N2O emission rate was at the beginning of the aerobic phase rather than the anoxic phase. This was probably because the nitrifying bacteria had accumulated nitrite nitrogen (NO2-) under low DO conditions. Methanol as an external carbon source was added during the anoxic phase to reduce nitrate nitrogen (NO3-) when denitrification was completed. The N2O emission rates in both the aerobic and anoxic phases were significantly influenced by residual NO3-, increasing monotonically as the concentration of NO3- in the reactor increased. Over 95% of average N2O emissions in both the aerobic and anoxic phases were prevented when methanol was added. The biofilm reactor showed similar patterns to those of the non-biofilm reactor in track behavior, but the former was more effective in the reduction of N2O emissions.     

Partial nitrification treatment for high ammonium wastewater from magnesium ammonium phosphate process of methane fermentation digester liquor

This study investigated partial nitrification treatment of methane fermentation digester liquor effluent from magnesium ammonium phosphate precipitation process in a swim-bed reactor. The reactor was operated at a temperature of 35 °C and pH between 7.5 and 7.8. Partial nitrification was achieved at the onset of the experiments even though conventional activated sludge was used as seed sludge. The maximum nitrite production rate was 1.0 kg NO₂-N/m³/d at a nitrogen loading rate of 2.0 kg-N/m³/d. The average effluent NO₂-N/NH₄-N ratio and the effluent NO₃-N concentration were 1.04 ± 0.34 and 5.7 mg/l, respectively, during the stable experiment periods. After 150 days of operation, the sludge volume index value decreased to 15 ml/g and the mean particle size of suspended sludge increased by approximately 3 times from 80 to 260 μm. Comparison of mineral analysis between the seed sludge and the partial nitrification sludge demonstrated that the mineral content of the latter increased approximately three-fold in comparison to that of the former. High Ca concentration was considered to be closely related to dense floc formation and superior settleability of the sludge. Both DGGE and DNA clone analysis verified that there were significant microbiological differences between the samples taken at different time periods. Nitrosomonas was confirmed to be the predominant species after stable partial nitrification performance was obtained. The overall results of this study validated our previous results that swim-bed reactor technology could be successfully used as a pre-treatment technology for anammox treatment.     

Nitrogen removal from wastewater using simultaneous nitrate reduction and anaerobic ammonium oxidation in single reactor

The effects of C/N ratio and total organic carbon (TOC) loading on nitrogen removal through simultaneous nitrate reduction and anaerobic ammonium oxidation in a single reactor were examined. Granular sludge taken from a methane fermentation reactor was placed in an upflow reactor and supplied with synthetic wastewater containing nitrate at a C/N ratio of 1 to grow heterotrophic denitrifying bacteria. When nitrogen removal ratio reached 30%, anammox sludge attached to nonwoven-carrier was added into the same reactor and then ammonia was added to the synthetic wastewater. Nitrogen removal ratio was markedly increased to 80-94%. In this system, nitrogen removal ratio was affected by C/N ratio and TOC loading, not by the amount of granular sludge. A stable isotopic analysis using 15N-labeled nitrate showed that N2 gas was formed by anammox reaction.     

Partial nitritation treatment of underground brine waste with high ammonium and salt content

Underground brine waste containing high concentrations of ammonium and with a salinity of 3% is usually generated during the production of methane gas and iodine in the gas field of Chiba Prefecture, Japan. In this study, one swim-bed reactor, packed with a novel acrylic fiber biomass carrier (Biofringe), was applied to the partial nitritation treatment of this kind of underground brine waste. A stable nitrite production rate of 1.6 kg NO₂-N m^− 3 d^− 1 was obtained under a nitrogen loading rate of 3.0 kg-N m^− 3 d^− 1, at a pH of 7.5 and a temperature of 25 °C. Nitrate production was negligible and the effluent NO₂-N/NO_x-N ratio was above 98% due to the successful inhibition of nitrite-oxidizing bacterial activity. Free ammonia was considered to be the main factor for inhibiting the activity of nitrite-oxidizing bacteria. A microbial community shift was demonstrated by 16S rRNA analysis, and it was shown that the ammonium-oxidizing bacteria became the predominant species after successful nitrite accumulation was observed.     

Comparison of partial and full nitrification processes applied for treating high-strength nitrogen wastewaters: microbial ecology through nitrous oxide production

The goal of this study was to compare the microbial ecology, gene expression, biokinetics, and N2O emissions from a lab-scale bioreactor operated sequentially in full-nitrification and partial-nitrification modes. Based on sequencing of 16S rRNA and ammonia monooxygenase subunit A (amoA) genes, ammonia oxidizing bacteria (AOB) populations during full- and partial-nitrification modes were distinct from one another. The concentrations of AOB (XAOB) and their respiration rates during full- and partial-nitrification modes were statistically similar, whereas the concentrations of nitrite oxidizing bacteria (XNOB) and their respiration rates declined significantly after the switch from full- to partial-nitrification. The transition from full-nitrification to partial nitrification resulted in a protracted transient spike of nitrous oxide (N2O) and nitric oxide (NO) emissions, which later stabilized. The trends in N2O and NO emissions correlated well with trends in the expression of nirK and norB genes that code for the production of these gases in AOB. Both the transient and stabilized N2O and NO emissions during partial nitrification were statistically higher than those during steady-state full-nitrification. Based on these results, partial nitrification strategies for biological nitrogen removal, although attractive for their reduced operating costs and energy demand, may need to be optimized against the higher carbon foot-print attributed to their N2O emissions.     

Chemical nitrite oxidation in acid solutions as a consequence of microbial ammonium oxidation

In long-term experiments with membrane aerated biofilm reactors we observed complete nitrite oxidation in highly concentrated ammonium nitrite solutions with a contaminant pH decrease to values below 3. The maximum initial concentration for ammonium was 42 mM and for nitrite was 41 mM. We hypothesized that (1) acid-tolerant ammonium oxidizing bacteria were responsible for the pH decrease, and (2) chemical processes caused complete nitrite oxidation at low pH values. To test this hypothesis we set up a mechanistic computer model based on kinetic data from literature and we validated the model with additional experiments. The simulations fitted the measurements very well. Additionally, an experiment with the inhibitor allylthiourea showed that ammonium-oxidizing bacteria were active at pH values far below 5.5. Experiments in a sterile reactor confirmed the chemical nitrite oxidation to nitrate. Nitrogen balances revealed that 8 +/- 4% of the initial nitrogen (ammonium, nitrite, and nitrate) were lost during the cycles. On the basis of measurements and simulations we concluded that volatilization was responsible for the significant nitrogen loss. We estimated that about half of the lost nitrogen volatilized as nitrous acid HNO2. The rest mainly volatilized as dinitrogen N2 and nitrous oxide N2O.     

Patchy biofilm coverage can explain the potential advantage of BGAC reactors

An adsorbing biofilm carrier, like granular activated carbon (GAC), can be the source of an extra flux of pollutant to the biofilm in addition to the bulk liquid. This double flux can improve the performance of a biological GAC (BGAC) reactor as compared to a nonabsorbing carrier reactor but only under conditions of pollutant partial penetration in the biofilm. Pollutant partial penetration in a biofilm often occurs in treatment processes where very low effluent concentrations are required. However, under these conditions, adsorption in BGAC reactors is questionable and requires the existence of biofilm free areas on the GAC carrier. The purpose of this investigation is to prove that under normal BGAC fluidized bed reactor operational conditions patchy biofilm coverage with exposed areas of GAC develops. Adsorption and desorption through these exposed areas can explain the widely debated advantage of BGAC reactors regarding higher biofilm activity. The patchy-like nature of the biofilm coverage on the GAC particles was verified using experimental and modeling tools. Comparison between a nonadsorbing granular carbon carrier and a GAC carrier with an atrazine degrading biofilm (Pseudomonas ADP) under conditions of atrazine partial penetration in the biofilm showed higher biodegradation and lower effluent atrazine concentrations in the BGAC reactor.