Nitrogen Removal Capability Research Articles

Nitrogen removal from wastewater treatment lagoons

In an attempt to gain a better understanding of ammonia and nitrogen removal processes in multi-pond wastewater treatment lagoons, an analysis was carried out of data obtained during regular monitoring of Lagoon 115E at the Western Treatment Plant in Melbourne. To do this, a contour plot approach was developed that enables the data to be displayed as a function of pond number and date. Superimposition of contour plots for different parameters enabled the dependence of ammonia and nitrogen removal rates on various lagoon characteristics to be readily assessed. The importance of nitrification as an ammonia removal mechanism was confirmed. Temperature, dissolved oxygen concentration and algal concentration all had a significant influence on whether or not sizeable nitrifier populations developed and persisted in lagoon waters. The analysis made it evident that a better understanding of microbial, chemical and physical processes in lagoons is needed before their nitrogen removal capabilities can be predicted with confidence.

Nutrient removal and starch production through cultivation of Wolffia arrhiza

Wolffia arrhiza, a small weed found mostly in tropical and subtropical water environments, exhibits a high growth rate and consequently absorbs large amounts of nitrogen and phosphorus. Its vegetative frond contains 40% protein on a dry weight basis and its turion, which is the dormant form, has a similar starch content. The applicability of this weed to nutrient removal from secondary-treated waste water combined with starch resource production was evaluated. The nitrogen and phosphorus removal capabilities of the vegetative frond and the optimal conditions for inducing of the formation of turions from harvested biomass of vegetative fronds for the production of starch were investigated using artificial nutrient solutions. The vegetative frond showed high contents of nitrogen (6–7% of the total dry weight) and phosphorus (1–2% of the total dry weight). The nutrient removal rates of the vegetative frond were estimated to be 126 mg-N/m 2/d and 38 mg-P/m 2/d under a continuous flow condition. For turion formation from the vegetative fronds, a low nutrient concentration and a high plant density were most effective. Under the optimum conditions, the starch production rate was estimated to be 6 g-starch/m 2 (nutrient removal tank)/d.

Ａｌｃａｌｉｇｅｎｅｓ ｆａｅｃａｌｉｓを導入した好気活性汚泥法におけるＮ２Ｏ放出および窒素除去特性

Immobilized Alcaligenes faecalis, a typical heterotrophic nitrifier, was added into activated sludge to make A. faecalis predominant genus in the activated sludge. Responses of the systems to variation of DO, pH and quantities of inoculated A. faecalis were tested and behaviors of the systems were evaluated. Experimental results showed that: the systems containing A. faecalis generally produced N2O 5 times less than those containing only activated sludge. In addition, the systems containing A. faecalis had a higher total nitrogen removal capability, average total nitrogen removal efficiencies of them were 10% higher than those of the activated sludge systems. Little influences appeared to TOC removal after the addition of immobilized A. faecalis. Among the experimental conditions, low DO concentration, high amount of A. faecalis and neutral pH led to low N2O emission and high total nitrogen removal. Therefore, increasing quantity of A. faecalis in activated sludge should be encouraged for controlling N2O emission and removing nitrogen in wastewater treatment. N2O producing ways were put forth to explain the influences of DO on N2O emission, and relative quantities of autotrophic nitrifying denitrifying organisms and heterotrophic nitrifiers were suggested to have significance in affecting behaviors of activated sludge toward N2O emission. On the other hand, serious accumulation of NO2-N and NO3-N resulted in high N2O emission, to reduce NO2-N and NO3-N quickly and thoroughly was thus suggested for both reducing N2O emission and improving nitrogen removal.

Ａｌｃａｌｉｇｅｎｅｓ ｆａｅｃａｌｉｓを導入した活性汚泥法の通性嫌気条件におけるＮ２Ｏ放出および排水処理特性

Alcaligenes faecalis, a typical heterotrophic nitrifying and denitrifying bacterium, was added into activated sludge and was made to be a dominant species in the activated sludge ecosystem under anoxic conditions. Influent COD to total nitrogen ratios (C:N) and quantities of the inoculated A. faecalis were changed to test the responses of the systems. The systems' behaviors of N2O emission and wastewater treatment were evaluated. On the other hand, a batch experiment was also conducted in which Helium (He) was used to bubble an activated sludge system. Characteristics of N2O emission from the system were tested. Experimental results showed that N2O production of the systems containing A. faecalis was generally about 50% less than those of the control reactors containing only activated sludge. In addition, the former systems had a higher total nitrogen removal capability, and their average total nitrogen removal efficiencies were about 7-56% higher than those of the control activated sludge systems. Moreover, TOC removal efficiencies of the systems containing A. faecalis were a little higher than those of the control systems. On the other hand, more alien A. faecalis addition and higher influent C:N ratio led to lower N2O emission and better effluent water qualities. Therefore, increasing A. faecalis' population in activated sludge should be encouraged for controlling N2O emission and upgrading wastewater treatment capability under anoxic conditions. Batch experiments showed that bubbling led to higher N2O production. A critical He flowrate existed corresponding to the highest N2O production yield.

Pre-denitrification and pre- and post-denitrification treatment of high-ammonia landfill leachate

This bench-scale study investigated the nitrogen-removal capabilities of two different biological process configurations treating methanogenic-state landfill leachate containing up to 1200 mg N/L of ammonia. The first configuration was a pre-denitrification system known as the modified Ludzack-Ettinger (MLE) process. Large clarifier sludge recycle flows, set to yield clarifier recycle ratios of 7:1 and 8:1, were evaluated as a means to reduce effluent NOx concentrations. A pre- and post-denitrification system, known as the four-stage Bardenpho process, was the second configuration evaluated. The MLE systems (20 day aerobic solids retention time (SRT)) were capable of producing effluent containing about 50 mg N/L of ammonia and 200-235 mg N/L of total inorganic nitrogen (ammonia + NOx) when treating leachate containing approximately 1200 mg N/L of ammonia. In contrast, effluent from the four-stage Bardenpho system contained less than 1 mg N/L of ammonia and 15 mg N/L of NOx, when treating 1100 mg N/L ammonia leachate. An aerobic number 1 SRT of 20 days (total aerobic SRT approximately equal to 40 days) was used with aerobic number 1 and clarifier sludge recycle ratios of 4:1 and 3:1, respectively. The ammonia-removal potential of both systems was clearly demonstrated but each system also showed certain disadvantages, characteristic of each process.Key words: ammonia-N, anoxic denitrification, leachate treatment, nitrification, pre-denitrification.

Biological treatment of a high ammonia leachate: influence of external carbon during initial startup

This research program investigated the total nitrogen removal capabilities of two pre-denitrification systems treating methanogenic municipal landfill leachate. During the startup phase, which is the focus of this paper, the ammonia concentration of the leachate was artificially and incrementally increased from about 200 mg N/L (“base”) to 1200 mg N/L (“target”) to simulate higher strength wastes. The initial attempt to reach the target ammonia concentration resulted in the accumulation of ammonia in both systems, with eventual nitrification failure. The second attempt was successful, with the only difference in procedures being the rate at which an external carbon source (methanol) was added to support anoxic denitrification. Preliminary data obtained from both systems, during the startup phase, indicated that the addition of external carbon to the anoxic reactor could significantly affect system performance during initial startup and operation. Firstly, the simultaneous increase in carbon loading with ammonia loading, to enable high rates of anoxic denitrification, was found to result in greater heterotrophic assimilation of ammonia in the anoxic reactor (i.e. 30% vs 10%) compared to the case when carbon loadings were not increased to match NOx production. The higher rate of anoxic ammonia assimilation, during the second attempt, was sufficient to supplement nitrification ammonia removal and prevent the accumulation of ammonia within the systems. Secondly, during the first attempt, it was found that increasing anoxic carbon loadings, after ammonia had accumulated in the systems, with the intent of increasing denitrification and assimilating excess ammonia, ultimately resulted in complete failure of nitrification. The increased denitrification returned additional alkalinity to the systems and resulted in reactor pH levels increasing by about 1 pH unit. The increase in pH raised the “free” ammonia fraction, of “total” ammonia, by almost an order of magnitude. It is believed that increases in aerobic “free” ammonia levels, resulting from the existing “total” ammonia levels and the increased pH, caused the nitrification failure.

The bioaugmentation of sequencing batch reactor sludges for biological phosphorus removal

The development of enhanced biological phosphorus removal (EBPR) through the bioaugmentation of a conventional activated sludge was studied. The objectives of the study were to evaluate the phosphorus removal capability of a sequencing batch reactor (SBR) when started with conventional activated sludge and augmented with a pure culture of Acinetobacter lwoffii. The effect of the addition of the pure culture on the reactor start up time, the settling properties of the sludge and on COD and nitrogen removal was also investigated. The effect of the removal of up to 70% of the bioaugmented biomass and its substitution with unconditioned sludge from a conventional sewage treatment plant was determined. This study has demonstrated that bioaugmentation can convert a conventional sewage works activated sludge to an EBPR sludge in 14 days. The sludge produced shows resilience to influent phosphate fluctuations, low D.O. and biomass replacement. The COD and nitrogen removal capabilities of the sludge and its settling properties are not affected by the addition of the pure culture.

The bioaugmentation of sequencing batch reactor sludges for biological phosphorus removal

The development of enhanced biological phosphorus removal (EBPR) through the bioaugmentation of a conventional activated sludge was studied. The objectives of the study were to evaluate the phosphorus removal capability of a sequencing batch reactor (SBR) when started with conventional activated sludge and augmented with a pure culture of Acinetobacter lwofii. The effect of the addition of the pure culture on the reactor start up time, the settling properties of the sludge and on COD and nitrogen removal was also investigated. The effect of the removal of up to 70% of the bioaugmented biomass and its substitution with unconditioned sludge from a conventional sewage treatment plant was determined. This study has demonstrated that bioaugmentation can convert a conventional sewage works activated sludge to an EBPR sludge in 14 days. The sludge produced shows resilience to influent phosphate fluctuations, low D.O. and biomass replacement. The COD and nitrogen removal capabilities of the sludge and its settling properties are not affected by the addition of the pure culture.

Enhancement of nitrogen removal in subsurface flow constructed wetlands employing a 2-stage configuration, an unsaturated zone, and recirculation

Constructed wetland technology is currently evolving into an acceptable, economically competitive alternative for many wastewater treatment applications. Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been as successful at nitrification. This is primarily due to oxygen limitations. Nitrification does occur in conventional wetland treatment systems, but typically requires long hydraulic retention times. This paper describes a study that first evaluated the capability of subsurface flow constructed wetlands to treat a high strength seafood processor wastewater and then evaluated passive aeration configurations and effluent recirculation with respect to nitrogen treatment efficiency. The first stage of a 2-stage wetland treatment system exhibited a relatively short hydraulic retention time and was designed for BOD removal only. The second stage wetland employed an unsaturated inlet zone and effluent recirculation to enhance nitrification. Results indicate that organic loading, and thus BOD removal, in the first stage wetland is key to optimal nitrification. Passive aeration through an unsaturated inlet zone and recirculation achieved up to 65-70 per cent ammonia nitrogen removal at hydraulic retention times of about 3.5 days. Inlet zone configuration and effluent recirculation is shown to enhance the nitrogen removal capability of constructed wetland treatment systems.

Enhancement of nitrogen removal in subsurface flow constructed wetlands employing a 2-stage configuration, an unsaturated zone, and recirculation

Constructed wetland technology is currently evolving into an acceptable, economically competitive alternative for many wastewater treatment applications. Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been as successful at nitrification. This is primarily due to oxygen limitations. Nitrification does occur in conventional wetland treatment systems, but typically requires long hydraulic retention times. This paper describes a study that first evaluated the capability of subsurface flow constructed wetlands to treat a high strength seafood processor wastewater and then evaluated passive aeration configurations and effluent recirculation with respect to nitrogen treatment efficiency. The first stage of a 2-stage wetland treatment system exhibited a relatively short hydraulic retention time and was designed for BOD removal only. The second stage wetland employed an unsaturated inlet zone and effluent recirculation to enhance nitrification. Results indicate that organic loading, and thus BOD removal, in the first stage wetland is key to optimal nitrification. Passive aeration through an unsaturated inlet zone and recirculation achieved up to 65–70 per cent ammonia nitrogen removal at hydraulic retention times of about 3.5 days. Inlet zone configuration and effluent recirculation is shown to enhance the nitrogen removal capability of constructed wetland treatment systems.

Nitrogen removal in a semi-continuous process

Laboratory tests using synthetic feed were conducted to evaluate the nitrogen removal capabilities of the continuously fed intermittently decanted (CFID) process. Experimental results were in general agreement with theoretically predicted values. Ammonia removal is governed by the extent of nitrification during aeration, and the level of leakage during settling and decantation. The former is controlled by the aerobic SRT, with the critical value being approx. 5 days at 13–18°C and <2.5 days at 25–26°C. Ammonia leakage is controlled by hydraulic parameters. For a given nominal hydraulic residence time, short cycle, short settling and short decantation times are conducive to low leakage. Total removal of nitrogen can be obtained if a well nitrifying system is allowed to denitrify. Denitrification is affected primarily by the anoxic fraction of the cycle. The specific denitrification rate ranged from 0.014 to 0.037 g N g SS −1 day −1, which is comparable to reported values for internal or endogenous denitrification in conventional systems.