Simultaneous nitrification and denitrification process in a new Tubificidae-reactor for minimizing nutrient release during sludge reduction

Nutrient release is reported as one of the main disadvantage of sludge reduction induced by aquatic worm. In this study, a Static Sequencing Batch Worm Reactor (SSBWR) was proposed with novel structure of perforated panels, combined aeration system and cycle operation. Effective simultaneous nitrification and denitrification were obtained owing to the stratified sludge layer containing aerobic and anoxic microzone formed on each carrier during most of the operation time in the SSBWR, which created suitable conditions for remarkable sludge reduction and nutrient removal. The results showed that the total nitrogen (TN) concentration, NO₃^?–N + NO₂^?–N concentration and NH₄⁺–N release could be reduced by 67.5%, 98.5% and 63.0%, respectively. And the soluble chemical oxygen demand (sCOD) released by sludge predation was also proved to provide a carbon source for denitrification leading to carbon release control and substantial cost savings. A schematic diagram of the stratified sludge layer and the mass balance of the nitrification–denitrification cycle were given, providing further insight into the nutrient (sCOD and nitrogen compounds) transformation during the worm predation in the SSBWR. For the mixed sludge liquid of 3000 mg TSS/L, 30 mg/L sCOD and 40 mg/L NO₃^?–N, the NO₃^?–N and NO₂^?–N came close to zero, and the sludge concentration, NH₄⁺–N release and sCOD release was reduced by 33.6%, 63.0% and 72.5%, respectively, during 48 h’ predation.     

Simultaneous nitrification and denitrification in a CEM (cation exchange membrane)-bounded two chamber system

A novel process was developed to induce a simultaneous oxidation of ammonia and denitrification in a single system consisting of two chambers separated by a cation exchange membrane. One was an anoxic chamber and the other was an aerobic chamber. The maximum mass flux via the membrane was calculated as 0.83 mg NH₄⁺-N/m² s in a batch test when the initial concentration of NH₄⁺ was 700 mg N/L. And it was observed that NO₃⁻ and NO₂⁻ moved via the membrane in a reverse direction when NH₄⁺ was transported. When the system was operated in a continuous mode by feeding a wastewater containing glucose and NH₄⁺, it was observed that soluble chemical oxygen demand and NH₄⁺ were simultaneously removed showing 99% and 71  86% of efficiency, respectively. Denitrification occurred in the anoxic chamber and nitrification was carried out in the aerobic chamber.     

Nitrate reduction by denitrifying bacteria in single and two stage continuous flow reactors

Denitrification by a mixed bacterial population of medium containing 1000 mg NO₃⁻-N1⁻¹ and acetate as carbon source was studied in batch, a single stage continuous flow stirred reactor (CFSTR) and a two stage CFSTR at 30°C. The optimum pH for denitrification, nitratase, nitrite reductase activities and growth was found to be 7.5 in batch culture. A single stage CFSTR growth limited by nitrate had an optimum denitrification rate of 0.13 mg NO₃⁻-N mg⁻¹ cells h at a residence time of 8 h. The experimentally observed carbon to nitrate ratio (mg CH₃ COO⁻-C mg⁻¹ NO₃⁻-N)was 1.7 for the dilution rates of 0.02–0.18 h⁻¹. For the second stage CFSTR, bacteria growing at the maximum rate of 0.25 h⁻¹ and not limited by nitrate had a denitrification rate of 0.24 mg NO₃⁻-N mg⁻¹ h. Dissolved oxygen (up to 9.5 mg 1⁻¹) did not effect denitrification rates in the second stage CFSTR. As the second stage CFSTR runs progressed extensive wall growth occurred and concurrently the output gas contained increasing quantities of nitrous oxide. A development from this study would be a two stage CFSTR with wall growth in the second stage which would make an efficient nitrate removal process.     

Nitrification in porous media during rapid,unsaturated water flow

A substantial nitrification in rapid infiltration (RI) systems for wastewater treatment is a prerequisite for obtaining good N removal by denitrification. The purpose of this study is to investigate nitrification in porous media at conditions corresponding to RI treatment systems. Nitrification in six 50-cm porous media columns (98% weathered granite or sand and 2% field soil) during unsaturated leaching at constant flow rates of synthetic wastewater was investigated. Concentrations of NH₄-N between 20 and 60 mg l⁻¹ were applied and vertical concentration profiles of NO₃-N, NO₂-N and NH₄-N were measured for 54 d at 30°C (three columns) and for 140 d at 10°C (three columns). A time lag in nitrification of 20 d was found at 10°C. Complete nitrification was obtained after 3–5 at 30°C and after approximately 50 d at 10°C. Assuming first-order nitrification at steady-state, the corresponding first order reaction rate coefficients (k₁) for NO₃ production in the columns were estimated to be between 0.4 and 1 h⁻¹ at 10°C and between 6 and 9 h⁻¹ at 30°C. Steady-state NO₃ profiles were obtained between 1.5 and up to 9 weeks after the experiments were started. At the actual soil-air contents (0.10 cm³ air phase cm⁻³ soil), oxygen limitations were not observed during the experiments. Nitrogen loadings (water flow times N concentration) above 100 mg N 1⁻¹ cm h⁻¹ (1 g N m⁻² h⁻¹) caused NH₄ accumulation in the columns at 10°C and should probably be avoided during operation of RI system.     

Influence of sand layer depth and percolate impounding regime on nitrogen transformation in vertical-flow constructed wetlands treating faecal sludge

Four laboratory-scale units of vertical-flow constructed wetlands (VFCW) were fed once a week with faecal sludge (FS) at a constant solids loading rate (SLR) of 250 kg TS/(m².year) (equivalent to 260-300 g N/(m².week)) for a period of 12 weeks to study: i) the nitrification and denitrification potential of the sand layer of VFCWs and ii) the effect of percolate impounding regime (permanent or batch-impounding) on nitrogen transformation. The TN content of raw FS was characterised by 65% org-N, 34% NH₄-N and 1% NO_x-N. After FS application and a six-day impounding period, 8-13% TN were recovered in the percolate exhibiting the following composition: 70-80% NH₄-N, 25-30% org-N and <1% NO_x-N. A large fraction of the influent organic N (55%) was filtered in the bed and 24-29% of initial NH₄-N were lost due to nitrification and volatilisation. In permanent impounding systems, 8-11% TN were recovered in the percolate versus 13% in batch-operated beds. N loss was increased with sand layer depth (20-40 cm) under permanent impounding regimes.     

Simultaneous nitrification and denitrification in bench-scale sequencing batch reactors

Two bench-scale sequencing batch reactors were fed with domestic wastewater and operated in an anaerobic-aerobic sequence for 139 d. Denitrification during the aerated react period was observed and the factors influencing the extent of simultaneous nitrification and denitrification were examined. It was found that the influence of DO on the nitrification rate during the aerated react period could be described by a Monod kinetic with a high oxygen half-saturation coefficient for autotrophic nitrifiers (K_O.A) of 4.5 mg/l. The dependency of the denitrification rate on DO could be described by a mathematical switching function with a higher switching function constant than expected, meaning that the extent of aerobic denitrification was higher than usual. It was also observed that aerobic denitrification decreased with time over the aerated react period. For most of the time of reactor operation nitrite was the main NO_x species in the effluent, instead of the commonly expected nitrate. This led to the conclusion that the activity of Nitrobacter species was probably inhibited in the SBRs studied. It also demonstrated the importance of measuring nitrite in the effluent to ensure that the reactor performance and the extent of aerobic denitrification was not over-estimated.     

Denitrification kinetics of high nitrate concentration water: pH effect on inhibition and nitrite accumulation

The effect of pH variation, within the range 6.5, 7.0, 7.5, 8.5 and 9, on activated sludge denitrification of a synthetic wastewater containing 2700 mg/l NO₃-N was examined using bench-scale Sequencing Batch Reactors. Two major effects were observed. One, at pH values of 6.5 and 7.0, denitrification of a synthetic wastewater containing high nitrate levels was significantly inhibited. Two, denitrification was achieved at higher pH values of 7.5, 8.5 and 9.0, but the accumulation of nitrite increased significantly as mixed liquor pH increased with peak values of 250, 500 and 900 mg/l NO₂-N, respectively. As the pH rose, the specific rate of nitrate reduction increased. At the same time the specific rate of nitrite reduction increased in the absence of nitrate. In the presence of nitrate the specific rate of nitrite reduction remained constant, and the degree to which nitrite reduction increased in the absence of nitrate was a function of increasing pH. While increasing pH from 7.5 to 9.0 affected nitrite intermediate accumulation, the overall time for complete denitrification (reduction of both NO⁻₃ and NO⁻₂) was similar for the pH values of 7.5, 8.5 and 9.     

好氧反硝化在短程硝化反硝化工艺中的作用研究

采用SBR反应器处理垃圾渗滤液，研究了短程硝化反硝化过程中好氧反硝化的作用。结果表明，SBR反应器的亚硝化效果良好，氨氮几乎完全被氧化为NO2^- -N；该系统的活性污泥中同时存在能还原NO3^- -N和NO2^- -N的好氧反硝化菌，还原NO3^- -N的好氧反硝化菌和氨氧化菌的数量及其总活性高于NO2^- -N氧化菌，这是SBR反应器能够长期维持亚硝化状态的重要原因；有机物浓度越高则好氧反硝化速率越快，此时氨氮均被氧化为NO2^- -N，当有机物浓度达到某临界值时，好氧反硝化速率几乎保持不变；溶解氧浓度越低则好氧反硝化速率越快，释放出的OH^-会导致pH值升高。好氧反硝化对于维持和促进SBR反应器的短程硝化反硝化具有重要的作用。     

Free nitrous acid inhibition on the aerobic metabolism of poly-phosphate accumulating organisms

In full-scale wastewater treatment systems, phosphorus removal typically occurs together with nitrogen removal. Nitrite, an intermediate of both the nitrification and denitrification processes, can accumulate in the reactor. The inhibitory effect of nitrite/free nitrous acid (FNA) on the aerobic metabolism of poly-phosphate accumulating organisms (PAOs) is investigated. A culture highly enriched (90 ± 5%) in Candidatus “Accummulibacter phosphatis”, a well-known PAO, was used to perform a series of batch experiments at various nitrite and pH levels. FNA was found to inhibit all key aerobic metabolic processes performed by PAOs, namely PHA oxidation, phosphate uptake, glycogen replenishment and growth. The inhibitory effect on the anabolic processes (growth, phosphate uptake and glycogen production) was much stronger than that on the catabolic processes (PHA oxidation). 50% inhibition on all anabolic processes occurred at FNA concentrations of approximately 0.5 × 10^?3 mg HNO₂–N/L (equivalent to 2.0 mg NO₂^?–N/L at pH 7.0), while full inhibition occurred at FNA concentrations of approximately 6.0 × 10^?3 mg HNO₂–N. These concentrations could be found in full-scale wastewater treatment systems that achieve nitrogen removal via the nitrite pathway. In comparison, PHA oxidation remained at 40–50% of the highest rate at FNA concentrations in the range 2.0 × 10^?3–10.0 × 10^?3 mg HNO₂–N/L. Interestingly, PAOs were able to reduce nitrite under aerobic conditions (DO ≈ 3 mg/L), with the rate increasing substantially with the FNA concentration. The inhibition on phosphate uptake was found to be reversible.     

The question of nitrification in the Passaic River, New Jersey: Analysis of historical data and experimental investigation

Historical NH₄⁺ and NO₃⁻ data from six stations on the Passaic River, New Jersey, were analyzed. The data for five of the stations span 1963 to 1976, and for the sixth station 1947 to 1976. Some of the conclusions reached are as follows:

1. (1) The concentration of NH₄⁺ fluctuated widely, but the trend was towards an increase with time.

2. (2) The concentration of NH₄⁺ was elevated during a period of extreme drought (1963 to 1966).

3. (3) The concentration of NO₃⁻ tended to increase smoothly with time.

4. (4) The concentration of NH₄⁺ increases longitudinally (with downstream travel).

5. (5) The loads (concentration × stream-flow) of both nitrogen species tended to increase with time.

6. (6) Substantial NO₃⁻ enters the stream from non-point sources.

7. (7) The potential for instream nitrification is not fully realized, as represented by elevated levels of NH₄⁺.

Item (7) was puzzling because conditions in the Passaic, especially in the summer, appear to be favorable for nitrification. The point was clarified, in part through an experimental investigation.River water samples, with and without added NH₄Cl, were incubated, and the course of the first step of nitrification was followed through the appearance of NO₂⁻. (The second step of nitrification was inactive during the experimental period.) The added NH₄Cl enhanced nitrification in samples from the uppermost stations (native NH₄⁺-N approximately 0.1 mg l⁻¹, but had little or no effect in samples from the middle and lower reaches (native NH₄⁺-N > 0.5 mg l⁻¹). Consequently, it was inferred that over most of the river's mainstem the growth of NH₄⁺-oxidizing bacteria was not substrate limited. There was also no indication of other nutrient limitations or of the presence of any inhibitors. This led to a projection of a 60-fold increase in the population density of planktonic NH₄⁺-oxidizers over a certain stretch of the river. However, no increase in the most-probable-number (MPN) of NH₄⁺-oxidizing bacteria was observed, which is consistent with item (7). In fact, at the end of a quiescent segment of the river the MPN's were anomalously low. This is attributed to the removal of cells from the water column through settling. This reasoning is extended to suggest that, throughout the river, settling may be the mechanism preventing a response of planktonic nitrifiers to the enrichment with NH₄⁺ from pollution sources. In turn, this could prevent a full expression of the potential for nitrification.The analyses are discussed from a regulatory perspective. It is concluded that the nitrification component of the Passaic's self-purification capacity is overburdened, and first became so in 1953.     

High nitrate denitrification in continuous flow-stirred reactors

Continuous flow stirred reactors were used to evaluate the maximum denitrification specific removal rates for influent solutions made from NH₄NO₃, CaNO₃, KNO₃ and UO₂ fuel fabrication waste water. Nitrate substrate concentrations ranged from 0.01 to 20 kg NO₃/m³. Values for U_max (maximum specific substrate removal rate per unit mass of microorganisms per unit time, days⁻¹) were determined using graphical solutions to the Lineweaver-Burk equations. For NH₄NO₃ solutions at nitrate substrate concentrations <6 kg NO₃/m³ the value for U_max was found to be 1.73 days⁻¹. At nitrate substrate concentrations >6 kg NO₃/m³ a nonlinear relationship was observed in the Lineweaver-Burk plots indicating nitrate substrate inhibition. Specific removal rates at nitrate concentrations >6 kg NO₃/m³ averaged <1.0 days⁻¹. Ammonia toxicity may also have occurred as the pH of the mixed liquor was near 8. Methanol concentrations as high as 11.6 kg CH₃OH/m³ did not inhibit denitrification rates. The highest specific removal rates recorded (3.13 ± 0.56 days⁻¹) were with influents made from UO₂ fuel fabrication waste water.     

Erratum to “Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities”

The status of nitrate (NO₃⁻), nitrite (NO₂⁻) and ammonium (NH₄⁺) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate δ¹⁵N and δ¹⁸O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields).The exponential increase in NO₃⁻-δ¹⁵N along with the NO₃⁻ reduction and clear δ¹⁸O/δ¹⁵N slopes of NO₃⁻ (∼ 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO₃⁻ contamination via active denitrification and reduced nitrification.Our results showed that NO₃⁻ and NH₄⁺ contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Nitrogen transformations and retention in planted and artificially aerated constructed wetlands

Nitrogen (N) processing in constructed wetlands (CWs) is often variable, and the contribution to N loss and retention by various pathways (nitrification/denitrification, plant uptake and sediment storage) remains unclear. We studied the seasonal variation of the effects of artificial aeration and three different macrophyte species (Phragmites australis, Typha angustifolia and Phalaris arundinacea) on N processing (removal rates, transformations and export) using experimental CW mesocosms. Removal of total nitrogen (TN) was higher in summer and in planted and aerated units, with the highest mean removal in units planted with T. angustifolia. Export of ammonium (NH₄⁺), a proxy for nitrification limitation, was higher in winter, and in unplanted and non-aerated units. Planted and aerated units had the highest export of oxidized nitrogen (NO_y), a proxy for reduced denitrification. Redox potential, evapotranspiration (ETP) rates and hydraulic retention times (HRT) were all predictors of TN, NH₄⁺ and NO_y export, and significantly affected by plants. Denitrification was the main N sink in most treatments accounting for 47-62% of TN removal, while sediment storage was dominant in unplanted non-aerated units and units planted with P. arundinacea. Plant uptake accounted for less than 20% of the removal. Uncertainties about the long-term fate of the N stored in sediments suggest that the fraction attributed to denitrification losses could be underestimated in this study.     

浮游微生物作用下河流水系氮的变化

以日本岐阜县境内的长良川及其支流为对象，研究了浮游微生物作用下河流水系在好氧、厌氧条件下的氮、磷变化特性。结果表明：①河流水系浮游微生物中含有丰富的硝化与反硝化菌，当NH4^＋-N含量较高时，好氧条件下NH4^＋-N到NO2^- -N的亚硝化反应、NO2^- -N到NO3^- -N的硝化反应和厌氧条件下NO3^- -N到NO2^- -N的还原反应明显存在。②受溶解氧（DO）和碳源有机物的影响，河流水系中浮游微生物的反硝化能力较差，导致水体中存在不同程度的NO3^- -N积累。另外由于底泥与河水的接触面小，故反硝化过程成为氮净化的限制因素。③对于DO充足的水体，NO3^- -N浓度较NO2^- -N、NH4^＋-N浓度高，因此NO^-3-N、NO2^- -N、NH4^＋-N的浓度顺序成为继DO后判断河流水质好坏的又一标准。④浮游微生物对磷基本没有去除作用。     

Effect of exogenous carbon sources on removal of inorganic nutrient by the nitrification-denitrification process

A bench scale study was undertaken to examine the effects of exogenous carbon substrates on the removal of inorganic nitrogen and phosphorus by a simple nitrification-denitrification process. Each plastic tank reactor was subjected to a 7-h aeration followed by a 5-h anoxic stage. Methanol, glucose and sodium acetate, at the concentrations equivalent to theoretical COD values of 100 and 200 mg O₂ l⁻¹ were used as external carbon sources and were added to the reactors prior to the anoxic stage. Effects of these additions on biological phosphate release were also investigated. The results showed that 94% of NH₄⁺-N was removed at the end of the aeration period. During the anoxic stage, reduction of nitrate to nitrogen gas was recorded and the denitrification process was significantly enhanced by the addition of organic carbon substrates. At the end of the anoxic stage, over 90% reduction was achieved in the tanks with exogenous carbon substrates while only 47% of NO₃⁻-N was removed in the control reactors. Among the three substrates, sodium acetate was the most efficient and effective source, followed by methanol and glucose. Addition of sodium acetate not only increased the amount of nitrate reduction but also enhanced the rate of N removal especially when a high dosage of sodium acetate was used. With respect to phosphorus removal, 88% ortho-P was removed after the aerobic stage. Throughout the anoxic stage, P concentration was maintained at about 2 mg l⁻¹ in both control and methanol treated reactors. However, significant increase in effluent P content was recorded in both sodium acetate and glucose treatments indicating that phosphorus was released from the bacterial cells during the anoxic stage. The amount of P-release in these two treatments was related to the concentrations of the carbon substrate used.     

Factors affecting nutrient loads in some Iowa streams

The export and concentration of inorganic nitrogen and total phosphorus from 34 watersheds in a northwestern Iowa lake district were measured during March 1971–August 1973. Annual nutrient losses were approximately 0.35 kg ha⁻¹ P. 6.7 kg ha⁻¹ NO₃-N, and 1.0 kg ha⁻¹ NH₃-N. A statistical analysis of the relationship between land-use and plant nutrients was used to determine differences among streams. Animal units in feedlots were significantly correlated with phosphorus and ammonia nitrogen (mg l⁻¹ and kg ha⁻¹ yr⁻¹). Nitrate nitrogen was negatively correlated with the percentage of watershed in marshland. Tile drainage and surface runoff from grasslands, feedlots, cornfields, and soybean fields were analyzed for nitrogen and phosphorus in spring 1974: mean values are given.     

Nitrate removal, communities of denitrifiers and adverse effects in different carbon substrates for use in denitrification beds

Denitrification beds are containers filled with wood by-products that serve as a carbon and energy source to denitrifiers, which reduce nitrate (NO₃⁻) from point source discharges into non-reactive dinitrogen (N₂) gas. This study investigates a range of alternative carbon sources and determines rates, mechanisms and factors controlling NO₃⁻ removal, denitrifying bacterial community, and the adverse effects of these substrates. Experimental barrels (0.2 m³) filled with either maize cobs, wheat straw, green waste, sawdust, pine woodchips or eucalyptus woodchips were incubated at 16.8 °C or 27.1 °C (outlet temperature), and received NO₃⁻ enriched water (14.38 mg N L⁻¹ and 17.15 mg N L⁻¹). After 2.5 years of incubation measurements were made of NO₃⁻-N removal rates, in vitro denitrification rates (DR), factors limiting denitrification (carbon and nitrate availability, dissolved oxygen, temperature, pH, and concentrations of NO₃⁻, nitrite and ammonia), copy number of nitrite reductase (nirS and nirK) and nitrous oxide reductase (nosZ) genes, and greenhouse gas production (dissolved nitrous oxide (N₂O) and methane), and carbon (TOC) loss. Microbial denitrification was the main mechanism for NO₃⁻-N removal. Nitrate-N removal rates ranged from 1.3 (pine woodchips) to 6.2 g N m⁻³ d⁻¹ (maize cobs), and were predominantly limited by C availability and temperature (Q₁₀ = 1.2) when NO₃⁻-N outlet concentrations remained above 1 mg L⁻¹. The NO₃⁻-N removal rate did not depend directly on substrate type, but on the quantity of microbially available carbon, which differed between carbon sources. The abundance of denitrifying genes (nirS, nirK and nosZ) was similar in replicate barrels under cold incubation, but varied substantially under warm incubation, and between substrates. Warm incubation enhanced growth of nirS containing bacteria and bacteria that lacked the nosZ gene, potentially explaining the greater N₂O emission in warmer environments. Maize cob substrate had the highest NO₃⁻-N removal rate, but adverse effects include TOC release, dissolved N₂O release and substantial carbon consumption by non-denitrifiers. Woodchips removed less than half of NO₃⁻ removed by maize cobs, but provided ideal conditions for denitrifying bacteria, and adverse effects were not observed. Therefore we recommend the combination of maize cobs and woodchips to enhance NO₃⁻ removal while minimizing adverse effects in denitrification beds.     

Denitrification with a bacterial disc unit

An enclosed rotating disc unit was operated anaerobically as a denitrifying system, with methanol as the hydrogen donor. As the bacterial population became established, denitrification rate increased by 1·5 mg NO₃⁻—N reduced m⁻² h⁻², to a maximum rate of 260 mg NO₃⁻—N reduced m⁻²h⁻¹. The C:N ratio necessary for complete denitrification was found to be 2·6:1. Optimum pH for denitrification lay in the range between pH 7·0 and 8·5. Q₁₀ values were 1·38 between 10 and 30°C, −2·66 above 30°C and 13·06 below 10°C.     

Nitrogen pollution and source identification in the Haicheng River basin in Northeast China

A survey was conducted in the Haicheng River near Liaodong Bay to analyze the characteristics and sources of the in-stream nitrogen pollution throughout the year 2010. The results indicated that the total nitrogen (TN) concentrations in the river water all exceeded the GB3838-2002 standard for Class V guideline of 2.0 mg/l at all sampling sites during the sampling seasons. Ammoniacal nitrogen (NH₃-N) dominated TN during the spring season, while nitrate nitrogen (NO₃-N) dominated during the summer and autumn seasons. Different forms of nitrogen had significant seasonal variations (p < 0.01 or p < 0.05). Only NH₃-N and NO₃-N displayed distinct spatial differences at p < 0.05 and p < 0.001, respectively. Most forms of nitrogen were interrelated with physicochemical parameters during different seasons, displaying nitrification and denitrification processes that occurred in the river rather than seasonal biological demand. Based on the nitrogen parameters, the 30 sampling sites were divided into three clusters, by which the pollution sources from chemical nitrogen fertilizers, animal wastes, domestic sewage, and industrial wastewater were identified. Generally, the Haicheng River basin provided about 700 tons of the annual TN flux, contributing to the eutrophication of the Liaodong Bay and Bohai Sea.     

Simultaneous carbon and nitrogen removal from high strength domestic wastewater in an aerobic RBC biofilm

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage field systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500-750 mg/l (113-169 as NO3(-)-N) are commonly found. A novel biofilm in a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH4(+)-N removal rates of 8.7-25.9 g COD/m2 d and 0.81-1.85 g N/m2 d for the corresponding loadings of 10.0-32.0 g COD/m2 d and 1.0-3.35 g N/m2 d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m2 d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m2 d at a high load of 3.35 g N/m2 d and 32 g COD/m2 d showing a possible inhibition of the process. A simultaneous 44-63% removal of nitrogen was also achieved without any significant NO2(-)-N or NO3(-)-N build-up. The second and third stages, almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH4(+)-N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification. The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy.