Organic nitrogen transformations in a 4-stage Bardenpho nitrogen removal plant and bioavailability/biodegradability of effluent DON

Nitrogen species, specifically, the fate and occurrence of organic nitrogen (ON) within a 4-stage Bardenpho process bioreactor producing low total nitrogen (TN) effluents were investigated in this study. The results showed release of ON in primary anoxic zone and no ON release in the first aerobic zone of the process. The research included investigation of biodegradability/bioavailability of wastewater-derived effluent dissolved ON (DON). The final-effluent DON utilization was evaluated by two different bioassay protocols in the presence and absence of nitrate. About 28–57% of the effluent DON was bioavailable/biodegradable. Bioavailable (to algae and bacteria) DON (ABDON) and biodegradable (to bacteria) DON (BDON) results did not show significant differences in terms of quantity, but DON utilization rates by ABDON (0.13 day⁻¹) protocol were higher than that of the BDON (0.04 day⁻¹) protocol in the nitrate-removal samples. As a result, ABDON requires a shorter time to exert the bioavailable fraction due to symbiotic relationship between algae and bacteria. In the nitrate-containing samples, it appears that nitrate competes with labile DON as a nitrogen source to microorganisms in both ABDON and BDON protocols. The first order decay rate of DON in the presence of nitrate was 0.11 day⁻¹ and 0.02 day⁻¹ for ABDON and BDON, respectively.     

Measurements of dissolved organic nitrogen (DON) in water samples with nanofiltration pretreatment

Dissolved organic nitrogen (DON) measurements for water samples with a high dissolved inorganic nitrogen (DIN, including nitrite, nitrate and ammonia) to total dissolved nitrogen (TDN) ratio using traditional methods are inaccurate due to the cumulative analytical errors of independently measured nitrogen species (TDN and DIN). In this study, we present a nanofiltration (NF) pretreatment to increase the accuracy and precision of DON measurements by selectively concentrating DON while passing through DIN species in water samples to reduce the DIN/TDN ratio. Three commercial NF membranes (NF90, NF270 and HL) were tested. The rejection efficiency of finished water from the Yangshupu drinking water treatment plant (YDWTP) is 12%, 31%, 8% of nitrate, 26%, 28%, 23% of ammonia, 77%, 78%, 82% of DOC (dissolved organic carbon), and 83%, 87% 88% of UV₂₅₄ for HL, NF90 and NF270, respectively. NF270 showed the best performance due to its high DIN permeability and DON retention (∼80%). NF270 can lower the DIN/TDN ratio from around 1 to less than 0.6 mg N/mg N, and satisfactory DOC recoveries as well as DON measurements in synthetic water samples were obtained using optimized operating parameters. Compared to the available dialysis pretreatment method, the NF pretreatment method shows a similar improved performance for DON measurement for aqueous samples and can save at least 20 h of operating time and a large volume of deionized water, which is beneficial for laboratories involved in DON analysis. DON concentration in the effluent of different treatment processes at the YDWTP and the SDWTP (Shijiuyang DWTP) in China were investigated with and without NF pretreatment; the results showed that DON with NF pretreatment and DOC both gradually decreased after each water treatment process at both treatment plants. The advanced water treatment line, including biological pretreatment, clarification, sand filtration, ozone-BAC processes at the SDWTP showed greater efficiency of DON removal from 0.37 to 0.11 mg N L⁻¹ than that at the YDWTP, including pre-ozonation, clarification and sand filtration processes from 0.18 to 0.11 mg N L⁻¹.     

Occurrence and treatment of wastewater-derived organic nitrogen

Dissolved organic nitrogen (DON) derived from wastewater effluent can participate in reactions that lead to formation of nitrogenous chlorination by-products, membrane fouling, eutrophication, and nitrification issues, so management of DON is important for both wastewater reuse applications and nutrient-sensitive watersheds that receive discharges from treated wastewater. This study documents DON occurrence in full-scale water/wastewater (W/WW) treatment plant effluents and assesses the removal of wastewater-derived DON by several processes (biodegradation, coagulation, softening, and powdered activated carbon [PAC] adsorption) used for advanced treatment in wastewater reuse applications. After varying levels of wastewater treatment, the dominant aqueous nitrogenous species shifts from ammonia to nitrate after aerobic processes and nitrate to DON in tertiary treatment effluents. The fraction of DON in total dissolved nitrogen (TDN) accounts for at most 52% in tertiary treated effluents (median = 13%) and 54% in surface waters impacted by upstream wastewater discharges (median = 31%). The 5-day biodegradability/bioavailability of DON (39%) was higher, on average, than that of dissolved organic carbon (DOC, 26%); however, upon chlorination, the DON removal (3%) decreased significantly. Alum coagulation (with ≥8 mg/L alum per mg/L DOC) and lime softening (with pH 11.3-11.5) removed <25% of DON and DOC without selectivity. PAC adsorption preferentially removed more DOC than DON by 10% on average. The results provided herein hence shed light on approaches for reducing organic nitrogen content in treated wastewater.     

Removal of ammonia from contaminated air in a biotrickling filter - denitrifying bioreactor combination system

The removal of gaseous ammonia in a system consisting of a biotrickling filter, a denitrification reactor and a polishing bioreactor for the trickling liquid was investigated. The system allowed sustained treatment of ammonia while preventing biological inhibition by accumulating nitrate and nitrite and avoiding generation of contaminated water. All bioreactors were packed with cattle bone composite ceramics, a porous support with a large interfacial area. Excellent removal of ammonia gas was obtained. The critical loading ranged from 60 to 120 gm(-3)h(-1) depending on the conditions, and loadings below 56 gm(-3)h(-1) resulted in essentially complete removal of ammonia. In addition, concentrations of ammonia, nitrite, nitrate and COD in the recycle liquid of the inlet and outlet of each reactor were measured to determine the fate of nitrogen in the reactor, close nitrogen balances and calculate nitrogen to COD ratios. Ammonia absorption and nitrification occurred in the biotrickling filter; nitrate and nitrite were biologically removed in the denitrification reactor and excess dissolved COD and ammonia were treated in the polishing bioreactor. Overall, ammonia gas was very successfully removed in the bioreactor system and steady state operation with respect to nitrogen species was achieved.     

Total nitrogen removal in a hybrid, membrane-aerated activated sludge process

The hybrid (suspended and attached growth) membrane biofilm process (HMBP) is a novel method to achieve total nitrogen removal from wastewater. Air-filled hollow-fiber membranes are incorporated into an activated sludge tank, and a nitrifying biofilm develops on the membranes, producing nitrite and nitrate. By suppressing bulk aeration, the bulk liquid becomes anoxic, and the nitrate/nitrite can be reduced with influent BOD. The key feature that distinguishes the HMBP from other membrane-aerated processes is that it is hybrid; heterotrophic bacteria are kept mainly in suspension by maintaining low bulk liquid BOD concentrations. We investigated the HMBP's performance under a variety of BOD and ammonium loadings, and determined the dominant mechanisms of nitrogen removal. Suspended solids increased with the BOD loadings, maintaining low bulk liquid BOD concentrations. As a result, nitrification rates were insensitive to the BOD loadings, remaining at 1gNm(-2)day(-1) for BOD loadings ranging from 4 to 17gBODm(-2)day(-1). Nitrification rates decreased during short-term spikes in bulk liquid BOD concentrations. Shortcut nitrogen removal was confirmed using microsensor measurements, showing that nitrite was the dominant form of oxidized nitrogen produced by the biofilm. Fluorescence in situ hybridization (FISH) showed that ammonia oxidizing bacteria (AOB) were dominant throughout the biofilm, while nitrite oxidizing bacteria (NOB) were only present in the deeper regions of the biofilm, where the oxygen concentration was above 2mg/L. Denitrification occurred mainly in the suspended phase, instead of in the biofilm, decreasing the potential for biofouling. When influent BOD concentrations were sufficiently high, full denitrification occurred, with total nitrogen (TN) removal approaching 100%. These results suggest that the process is well-suited for achieving concurrent BOD and TN removal in activated sludge.     

城镇污水处理厂尾水中氮磷形态及光谱特征分析

为了进一步探究污水厂尾水排放对受纳水体的潜在影响,选取巢湖流域采用3种典型处理工艺(氧化沟、SBR、A²/O工艺)的7座污水厂为研究对象,分析了尾水中氮、磷的形态及水体中溶解性有机质(DOM)的光谱特征。结果表明,不同工艺对TN、TP、COD等指标均具有很好的去除效果且无明显差异。尾水中颗粒态总氮(PN)占比在13.4%以下,主要以溶解态总氮(DTN)形式存在,其中溶解态无机氮(DIN)占比高于溶解态有机氮(DON)。尾水中颗粒态总磷(PP)占比在10.1%~66.7%,磷主要以溶解态总磷(DTP)形式存在,其中溶解态无机磷(DIP)占比在60%以上。DOM的三维荧光光谱显示,不同工艺尾水中的DOM均具有4类荧光特征峰,其中腐殖酸类物质C峰与紫外区类富里酸物质A峰较为明显。根据DOM的荧光特性参数(HIX值<4、FI值>1.9、BIX值>1.0),各污水厂出水中的DOM主要为自生来源。由此表明,污水处理厂削减了大量的入河碳、氮、磷等负荷,其尾水可用于城市河道生态补水水源,实现城市污水资源再生利用。     

应用工艺智能优化控制系统降低污水厂能耗

生物工艺智能优化系统（BIOS）是一个前馈优化系统，通过获得A／O工艺实时的在线数据（如氨氮、硝酸盐氮、进水流量、混合液悬浮物浓度），BIOS系统不断进行模拟计算，然后按照生物反应器进水的污染物负荷状况来提供最佳的DO设定值；同时为达到最佳的TN去除率，BIOS系统还对好氧区回流至缺氧区的内回流比（IRQ）进行了优化。BIOS系统在美国康涅狄格州En-field污水厂的实际应用情况表明，该系统能提高脱氮效率36％，同时降低曝气量19％。     

Effluent dissolved organic nitrogen and dissolved phosphorus removal by enhanced coagulation and microfiltration

Plants aiming to achieve very low effluent nutrient levels (<3 mg N/L for N, and <0.1 mg P/L for P) need to consider removal of effluent fractions hitherto not taken into account. Two of these fractions are dissolved organic nitrogen (DON) and dissolved non-reactive phosphorus (DNRP) (mainly composed of organic phosphorus). In this research, enhanced coagulation using alum (at doses commonly employed in tertiary phosphorus removal) followed by microfiltration (using 0.22 μm pore size filters) was investigated for simultaneous effluent DON and dissolved phosphorus (DP) fractions removal. At an approximate dose of 3.2 mg Al(III)/L, corresponding to 1.5 Al(III)/initial DON-N and 3.8 Al(III)/initial DP-P molar ratios, maximum simultaneous removal of DON and DP was achieved (69% for DON and 72% for DP). At this dose, residual DON and DP concentrations were found to be 0.3 mg N/L and 0.25 mg P/L, respectively. Analysis of the trends of removal revealed that the DNRP removal pattern was similar to that commonly reported for dissolved reactive phosphorus. Since this study involved intensive analytical work, a secondary objective was to develop a simple and accurate measurement protocol for determining dissolved N and P species at very low levels in wastewater effluents. The protocol developed in this study, involving simultaneous digestion for DON and DNRP species, was found to be very reliable and accurate based on the results.     

电解法深度处理生活垃圾焚烧厂渗滤液研究

采用三元电极对垃圾焚烧厂渗滤液的生化-混凝出水进行电解处理，研究了其处理效果及影响因素。结果表明，在电解反应过程中COD的降解符合三级反应动力学，其t时刻的出水浓度为：Ct=（2kt＋C0^-2）^-0.5；电流、pH值、电解时间、氯离子浓度、进水COD浓度对有机物去除率的影响较大，而极间距、温度和极水比则影响较小。此外，考察了该电极对氮化合物的去除效果。结果表明，在电解过程中亚硝态氮很快被氧化成硝态氮，之后氨氮转化为氮气，总氮基本以硝态氮的形式存在。     

生物催化滤池处理高氨氮水源水

针对生物滤池处理高氨氮水源水过程中硝酸盐、亚硝酸盐积累的问题,提出一种能够同时去除"三氮"污染物的强化过滤技术——生物催化滤池。该技术将传统生物过滤与催化还原反应相结合,在生物过滤去除氨氮的同时,钯/锡双金属催化滤料可将硝酸盐氮和亚硝酸盐氮还原为氮气。在滤池的滤速为10 m/h时,对氨氮和TOC的去除率分别为82. 12%和71. 94%,主要依靠生物滤层内微生物的降解作用来去除;对硝酸盐氮和亚硝酸盐氮的去除率分别为58. 22%和78. 65%,主要通过催化还原滤料的化学反应来去除;滤池出水浊度<3 NTU。生物催化滤池在生化反应和催化还原的共同作用下能够有效缓冲低温、高氨氮、高硝酸盐氮、高亚硝酸盐氮以及高TOC等特殊条件下短时间连续冲击,具有较强的抗冲击负荷能力,保证产水水质稳定。生物催化滤池可以作为微污染水源水的预处理工艺,保障后续工艺的稳定运行,具有良好的应用前景。     

生物沸石滤池去除微污染水源水中氨氮的挂膜启动

对沸石滤料生物滤池处理微污染水源水中低浓度氨氮的挂膜启动性能进行了研究。试验结果表明,挂膜过程可以根据氨氮、亚硝酸盐氮、硝酸盐氮浓度的变化分为三个阶段：初期沸石发挥本身对铵离子的吸附交换性能,氨氮去除率达88％以上;中期开始出现生物硝化作用,亚硝酸盐积累明显,硝酸盐出水浓度不稳定,氨氮去除率稳定,但下降至65％左右;后期硝化反应稳定进行,亚硝酸盐迅速转化为硝酸盐,氨氮去除率稳定在60％以上。生物沸石滤池挂膜同时应考察亚硝酸盐氮、硝酸盐氮浓度变化,在出水亚硝酸氮明显积累后又稳定降低,且硝酸盐氮稳定积累时方可认为挂膜成功。进出水pH值的变化可以指示硝化反应的进行程度和生物膜形成阶段。     

Reactivity and chemical characterization of effluent organic nitrogen from wastewater treatment plants determined by Fourier transform ion cyclotron resonance mass spectrometry

In advanced wastewater treatment plants that achieve high levels of nitrogen (N) removal, up to one-third of the N in effluent is organic, herein referred to as effluent organic N (EON). While we know that inorganic N is highly labile, it is unclear what fraction of EON is bioavailable. In this study, we demonstrate the utility of a method that can be used to examine the reactivity of EON in natural receiving waters to better understand both the ecosystem response and the potential bioavailability of EON. The technique is suitable for analyzing polar organic matter in natural waters; electrospray ionization coupled with Fourier transform mass spectrometry. Bioassays were performed on samples collected at the end of the biological process from two wastewater treatment plants achieving advanced N removal. The samples were concentrated, and then added to natural water samples collected from the oligohaline James River, a major tributary of the Chesapeake Bay. Our results demonstrate that while the lignin-like fraction of the effluent dissolved organic matter (some of which contains N) was conserved, a large portion of aliphatic and aromatic compounds containing N was removed (79-100%) during incubations, while other compounds were produced. Furthermore, the two effluents exhibited differences in the degree of degradation and type of degradation, which can be related both to the various processes employed in the two WWTPs and the dramatic differences in the type of influent they received. These findings suggest that EON is highly reactive in the natural environment and that simple assays examining net consumption or production of bulk dissolved organic N pools are inadequate for assessing the bioavailability of EON.     

Treatment of low strength domestic wastewater using the anaerobic filter

A laboratory scale anaerobic filter packed with synthetic high surface area trickling filter media was used to treat a low strength domestic wastewater averaging 288 mg 1⁻¹ COD. The filter was operated for 60 days after reaching steady-state at 20, 25, 35°C at a loading rate of 0.02 lb COD ft⁻³ day⁻¹ and 24 h hydraulic retention time. Filter effluent BOD₅ averaged 38 mg 1⁻¹ providing an average removal rate of 79%, and effluent COD averaged 78 mg 1⁻¹, corresponding to a 73% removal rate. Removal efficiencies showed very little sensitivity to daily fluctuations in influent wastewater quality. The filter performance at 25 and 35°C was not significantly different, but BOD and TSS removal efficiency declined a: 20°C. Gas production averaged 0.027 ft⁻³ of gas per ft³ of influent wastewater, or 1.875 ft³ of gas per pound of influent COD. Gas composition averaged 30% nitrogen, 65% methane, and 5% carbon dioxide. Ammonia nitrogen and sulfides both increased during treatment. It is concluded that the anaerobic filter is a promising candidate for treatment of low strength wastewaters and that post treatment for sulfides and ammonia may be necessary.     

Organic removal by denitritation and methanogenesis and nitrogen removal by nitritation from landfill leachate

A system consisting of a two-stage UASB and anoxic-oxic reactor was used to enhance COD and nitrogen removal from landfill leachate. To improve denitrification efficiency, the raw leachate with recycled final effluent was pumped into the first-stage UASB (UASB1) to carry out simultaneous denitrification and methanogenesis. The results over 180 d show that the maximum organic removal rate in UASB1 and UASB2 was 12.5 and 8.5 kgCODm(-3)d(-1) in the oxic zone of the A/O reactor, respectively. The COD and biochemical oxygen demand (BOD5) removal efficiency of the system was 80-92% and about 99%, respectively. Without controlling temperature (17-30 degrees C) and dissolved oxygen (0.5-4.0 mgL(-1)), the maximum NH4+-N removal rate was 0.68 kg NH4+-Nm(-3)d(-1), and about 99% of NH4+-N removal was obtained by nearly complete nitritation. The 81-93% total nitrogen removal was obtained by complete denitrification in the UASB1 and in the anoxic zone of the A/O reactor. Fluorescence in situ hybridization (FISH) analysis of the sludge samples from A/O reactor showed that ammonia oxidizing bacteria (AOB) consisted 4% of the eubacterium, while nitrite oxidizing bacteria (NOB) counted less than 0.2% of that. The study shows that the main factors achieving and maintaining nitritation are a proper range of free ammonia concentration obtained by dilution recycled final effluent that inhibits NOB but not AOB; effective control on aeration time by indication of "ammonia valley" on pH profile; and highly efficient denitrification and its reproducing alkalinity to result in pH above 8.5.     

Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10-30, 3-10, 1-3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.     

基于数学模拟的污水厂运行分析——建模与体检

在北美、欧洲、南非等国家和地区,污水处理工艺模拟已经广泛应用于污水处理的开发、设计、提标改造和优化运行管理等方面,成为污水处理行业的标准实践。在国内,污水处理工艺模拟应用起步较晚,正处于发展阶段。应用工艺模拟技术对污水处理厂进行管理,一方面可以大大提高运营管理水平;另一方面也可为实现智慧化水厂奠定基础。以东莞大岭山连马污水处理厂作为示范,建立并校正了该污水处理厂的工艺模型,应用模型对污水处理厂运行现状进行体检,寻找边界运行条件。结果表明,在设计流量条件下的运行过程中,当MLSS低于3 000 mg/L、进水TN高于20 mg/L时,出水氨氮有超标风险;当进水TN达到36 mg/L时,若要保证出水水质稳定达标,COD必须大于200 mg/L,当MLSS为6 000 mg/L时,最大处理水量为8.5×104m3/d。     

喷射环流反应器同步硝化反硝化机理的研究

喷射环流反应器在好氧条件下具有良好的脱氮性能,其对氨氮和总氮的去除率分别达到80%和70%以上,且两者的去除率成正比.试验测定了反应器出水中NOx^--N的含量,结果表明出水中的氮主要以氨氮和亚硝酸盐氮的形式存在,证明该反应器在硝化过程中实现了对亚硝酸盐的积累.反应器的脱氮效果随进水C/N值的增加而提高,证明了异养硝化细菌的存在.对废水处理过程中产生的废气进行气相色谱分析,结果表明废气中氮气的含量比空气的增加了0.24%,证明反应器中发生了反硝化反应.综合试验结果表明,喷射环流反应器中的脱氮机理为亚硝酸盐型同步硝化反硝化.     

Evaluation of the catalytic reduction of nitrate for the determination of dissolved organic nitrogen in natural waters

The catalytic reduction of nitrate ions into nitrogen gas was tested to partly remove dissolved inorganic nitrogen (DIN) before the determination of dissolved organic nitrogen (DON). Experiments were conducted on nitrate solutions enriched with natural organic matter (NOM) isolates previously extracted from surface waters. Three catalysts Pd-In/Al2O3, Pd-Sn/Al2O3 and Pd/SnO2 were tested. Their noble metal (palladium) and promoter metal (indium or tin) contents are 5 and 1.75 wt%, respectively. Preliminary experiments performed on a solution containing 17 amino acids showed that most compounds were removed by less than 15%, probably due to sorption onto the catalysts. Reduction of nitrate in absence of NOM was complete after 20 min of reaction time and the removal of DIN was about 80% (about 19% formation of ammonium). In the presence of NOM (DOC 20 mgC/L, DON 0.67 mg N/L), the kinetic of nitrate reduction was slower and the reduction in DIN content was limited to 15% i.e. selectivity toward ammonium reached 85%. Adsorption tests showed a similar removal of both DOC and DON of about 70% and 30% onto Pd-Sn/Al2O3 and Pd/SnO2 catalysts, respectively, which confirmed that NOM probably compete with nitrate for active catalytic sites. In conclusion, catalytic reduction of nitrate before DON determination cannot be used because of DON sorption and low DIN removal.