Nutrient Removal Mechanisms Research Articles

A fuzzy neural network-based soft sensor for modeling nutrient removal mechanism in a full-scale wastewater treatment system

The nonlinearity and complicated biological phenomena existing in wastewater treatment processes (WWTP) make the operation and modeling of WWTP quite difficult. In this study, a hybrid learning method combining genetic algorithm with adaptive neuro-fuzzy inference system (GA-ANFIS) was serviced to estimate effluent nutrient concentrations in a full-scale biological wastewater treatment plant. The GA-ANFIS possessing a more flexible hybrid learning ability was adopted to capture the nonlinear relationships between the influent and effluent concentrations of pollutants. Having the capabilities of global and parallel optimization, GA was used to optimize the structure parameters of the fuzzy membership functions of GA-ANFIS. The real data collected from Korean Daewoo nutrient removal wastewater treatment plant were used to demonstrate the prediction efficiency of the proposed soft sensor with the aid of three performance indices of root mean square error, mean absolute percentage error, and squared correlation coefficient. The results indicate that the hybrid GA-ANFIS soft sensors outperform ANFIS-based soft sensors in terms of effluent prediction accuracy.

Mechanism of efficient nutrient removal and microbial analysis of a combined anaerobic baffled reactor–membrane bioreactor process

A combined ABR–MBR process consisting of an anaerobic baffled reactor (ABR) combined with an aerobic membrane bioreactor (MBR) treating municipal wastewater was investigated at controlled pH range 6.5–8.5 and at constant temperature 25 ± 1 °C. Total nitrogen (TN), ammonia (NH4 +–N), total phosphorus (TP), and chemical oxygen demand (COD) removal performances were evaluated by analyzing the mechanism for efficient nutrient removal. The results showed that the average removal rates of COD, NH4 +–N, TN, and TP reached 93, 99, 79, and 92 %, respectively, corresponding with the COD, NH4 +–N, TN, and TP effluent of 24 (18–31), 0.4 (0–0.8), 10.6 (8.8–12.9), and 0.31 (0.1–0.5) mg/L under the operational condition of hydraulic retention time (HRT) 7.5 h, recycle ratio 200 %, and dissolved oxygen 3 mg/L. The MBR enhanced NH4 +–N, TN, and TP removal rates of 13, 10, and 18 %, respectively, and the membrane retention reduced TP 0.17 mg/L. The process was able to maintain a stable performance with high-quality effluent. Analysis of the results by fluorescence in situ hybridization showed that the abundance of ammonia-oxidizing bacteria, nitrite-oxidizing bacteria, and phosphorus accumulating organisms as percentages of all bacteria in each compartment was stable. The enriched microorganisms in the system appear to be the main drivers of the process efficient for nutrient removal.

Carbon and nutrient removal from centrates and domestic wastewater using algal–bacterial biofilm bioreactors

The mechanisms of carbon and nutrient removal in an open algal-bacterial biofilm reactor and an open bacterial biofilm reactor were comparatively evaluated during the treatment of centrates and domestic wastewater. Comparable carbon removals (>80%) were recorded in both bioreactors, despite the algal-bacterial biofilm supported twice higher nutrient removals than the bacterial biofilm. The main carbon and nitrogen removal mechanisms in the algal-bacterial photobioreactor were assimilation into algal biomass and stripping, while stripping accounted for most carbon and nitrogen removal in the bacterial biofilm. Phosphorus was removed by assimilation into algal-bacterial biomass while no effective phosphorous removal was observed in the bacterial biofilm. Carbon, nitrogen and phosphorus removals of 91 ± 3%, 70 ± 8% and 85 ± 9%, respectively, were recorded in the algal-bacterial bioreactor at 10d of hydraulic retention time when treating domestic wastewater. However, the high water footprint recorded (0.5-6.7 Lm(-2)d(-1)) could eventually compromise the environmental sustainability of this microalgae-based technology.

Biofiltering of aquaculture effluents by halophytic plants: Basic principles, current uses and future perspectives

Halophytes comprise a promising group of plants for different applications due to their special physiological characteristics and biochemical composition. Their ability to grow in salt-affected habitats makes them useful for recycling the nutrient-containing effluents from saline aquacultures. The potential of different halophytes for nutrient uptake and remediation has been investigated in several laboratory and field studies and the application of natural and constructed wetlands. Various factors influence the filtration capacity of a halophyte biofilter for aquaculture effluents, such as salinity, flooding, nutrient level, root characteristics and technical applications. Those effects studied so far are characterized and those in need of further study are outlined. Technical aspects in artificial wetlands such as water flow direction, water level, hydraulic retention time and hydraulic loading rate, influence the transformation of the nutrients within the wetland and their uptake by the plants. Open as well as re-circulating systems are considered. Because soil processes are lacking, the application of hydroponic culture shifts the importance of nutrient removal toward plant uptake. This is important when besides the pure nutrient removal the recycling of the nutrients become a focus in terms of sustainability. The economic feasibility, including different utilization possibilities, of selected halophytes with filtering capacities is delineated. The economic attractiveness of a halophytic biofilter can also be upgraded by the use of salt-tolerant species with a commercial value. Modularized versions of waste water treatments by plants in temperate and tropic regions could help to reduce the nutrient load in the bodies of water and to recycle the nutrients. More effort is needed to determine the specific nutrient removal mechanisms within different types of wetlands planted with halophytes and to point out appropriate halophyte species and wetland conditions for different applications.

Modeling of land use and reservoir effects on nonpoint source pollution in a highly agricultural basin

Nonpoint source (NPS) pollution is tightly linked to land use activities that determine the sources and magnitudes of pollutant loadings to stream water. The pollutant loads may also be alleviated within reservoirs because of the physical interception resulting from changed hydrological regimes and other biochemical processes. It is important but challenging to assess the NPS pollution processes with human effects due to the measurement limitations. The objective of this study is to evaluate the effects of human activities such as land uses and reservoir operation on the hydrological and NPS pollution processes in a highly agricultural area-the Iowa River Basin-using the Soil and Water Assessment Tool (SWAT). The evaluation of model performance at multiple sites reveals that SWAT can consistently simulate the daily streamflow, and monthly/annual sediment and nutrient loads (nitrate nitrogen and mineral phosphorus) in the basin. We also used the calibrated model to estimate the trap efficiencies of sediment (∼78%) and nutrients (∼30%) in the Coralville Reservoir within the basin. These non-negligible effects emphasize the significance of incorporating the sediment and nutrient removal mechanisms into watershed system studies. The spatial quantification of the critical NPS pollution loads can help identify hot-spot areas that are likely locations for the best management practices.

Nutrients removal mechanisms in high rate algal pond treating rural domestic sewage in East China

This study focused on the evaluation of performance and mechanisms of a high-rate algal pond system (HRAP System) in nitrogen and phosphorus removal for rural domestic sewage treatment. A pilot scale HRAP System was located at Yangzhu Village, Jiangsu Province, east China, with treatment processes including a septic tank, two stages of HRAPs and an aquatic pond. Results showed that the HRAP System had a good performance in nutrient removal, especially in NH+4-N removal. Total removal efficiencies of COD, TN, NH+4-N and TP were 80, 51.8, 90.2 and 52.1%, respectively. About 61.6% of NH+4-N in the 1st-stage HRAP and 70.9% in the 2nd-stage HRAP were transformed into NO−3-N and NO2−-N through nitrification, and the nitrogen losses via ammonia volatilization was only 2.7% (for 1st-stage HRAP) and 8.8% (for 2nd-stage HRAP). The other 35.7% and 20.3% of NH+4-N removal were achieved by algae assimilation respectively. About 98.0% (for 1st-stage HRAP) and 84.8% (for 2nd-stage HRAP) removal of TN were attributed to algae sedimentation, while those through ammonia volatilization were only 2.0% (for 1st-stage HRAP) and 15.4% (for 2nd-stage HRAP), respectively. Therefore, the main mechanisms of NH+4-N removal in HRAP were nitrification and algae assimilation, and TN was mainly removed by algae sedimentation. About 50.7% (for 1st-stage HRAP) and 53.1% (for 2nd-stage HRAP) of phosphorus in the deposit were organic phosphates respectively, only 20.7% and 27.7% were calcium-bound and magnesium-bound phosphates. The removal mechanism of TP in HRAP could be mainly attributed to algae assimilation in forms of organic phosphate, and chemical precipitation in forms of calcium-bound and magnesium-bound.

Limnological characteristics of a subtropical constructed wetland in south Florida (USA)

The Everglades Nutrient Removal Project (ENRP) was a 1544 ha constructed wetland built by the South Florida Water Management District as part of Everglades restoration efforts. The limnology of this wetland is characterized over its 60-month operational history. The ENRP received agricultural runoff containing high levels of C, N, P and other dissolved constituents; had moderately high alkalinity with a circumneutral pH; and had low to moderate DO. The ENRP provided substantial treatment (concentration reduction from inflow to outflow) for Al, Fe, NH 4, NO x , SRP, TP, TSS and turbidity (high-treatment variables), while Secchi depth increased markedly. These changes were judged biologically significant. Dissolved oxygen, and water temperature had well defined annual cycles, while some level of seasonality was noted for Al, alkalinity, Ca, conductivity, DOC, Fe, hardness, K, Mg, Mn, Na, NH 4, pH, Secchi depth, SiO 2, TOC, TN, turbidity, and TSS. The ENRP was P limited based on TN:TP molar ratios. Dissolved ions were dominated by Ca, Cl, Na, and HCO 3; the stoichiometric balance of both major and minor ions was similar throughout the wetland. The downstream settling of TSS was associated with increased light penetration, but did not appear important in sediment accretion. The adsorption of P to Ca, and perhaps Al and Fe, precipitates is thought to have been an important nutrient removal mechanism. Although there was little net reduction in DOC, we speculate that some incoming material was degraded and replaced by new DOC produced within the wetland.

Effect of Aeration on Nutrient Removal Performance of Oxidation Ditch Systems

This paper evaluates the mechanism of nutrient removal in an oxidation ditch system using basic process stoichiometry and model simulation. Aeration intensity and the resulting dissolved oxygen concentration are identified as the main parameters defining the denitrification potential, and affecting the extent of nitrification/ denitrification processes, mainly because no clear anoxic/aerobic zones can be established in the system. For wastewater characteristics and a wastewater scheme tested with model simulation using ASM2d, process efficiency is highly influenced by the dissolved oxygen concentration in a narrow range of 0.4–0.8 mg/L. Enhanced biological phosphorus removal is also affected through the level of nitrate recycle into the anaerobic reactor. Diurnal variations in the influent at a constant aeration regime result in insufficient aeration during peak loads followed by overaerated periods, and in this way, cause temporal instability in nutrient removal performance. With the aid of dynamic simulations, the dissolved oxygen set-point control provides better effluent quality and process stability in terms of nutrient removal.

A Study on Organics and Nutrients Removal Mechanisms in Livestock Wastewater Treatment Using EGSB

An advanced way of treating livestock wastewater made use of both Autothermal Thermophilic Aerobic Digestion (ATAD), as a pre-step, and Expanded Granular Sludge Blanket (EGSB), as the post-step. As a result, the chemical oxygen demand (COD) concentration flowing out of the post step, including the EGSB, was 89mg/ℓ, while the suspended solid (SS) concentration was 28mg/ℓ, and the total nitrogen (TN) and total phosphorus (TP) concentrations were 62mg/ℓ and 5.7mg/ℓ, respectively. To maintain a high temperature in the ATAD reactor without external heating, the characteristics of influent were found to be very critical. The temperature of the ATAD reactor was significantly elevated only when the influent TSS was more 50,000mg/ℓ. The EGSB reactor was fed with increasingly higher livestock wastewater loading rates up to 6kg chemical oxygen demand (COD)/ m3/day and an average of 84.7% of the COD and 85.4% of the SS were removed in EGSB. Biogas was generated on the 47th day of operation in the EGSB after startup and its production increased at a rapid rate. The methane percentage within the biogas was initially low but it also increased rapidly, up to 73%. When the HRTs were 0.5-3 days, the COD removal efficiency was over 80%, but did show a increase as the HRT increased to 3 days.

Removal of nitrogen and phosphorus from industrial wastewaters by phytoremediation using water hyacinth (Eichhornia crassipes (Mart.) Solms)

This paper elucidates the phytoremediation potential of water hyacinth (Eichhornia crassipes [Mart.] Solms) for TN and TP rich industrial wastewaters determined for 15 weeks under different set-ups of 2-fold (56 TN mg/l and 15.4 TP mg/l), 1-fold, 1/2-fold, 1/4-fold and 1/8-fold and a control with no nutrients in duplicate. A mass balance was conducted to evaluate the phytoremediation efficiencies and to identify the key mechanisms of nutrient removal from the wastewaters. Our results manifested that water hyacinth is a promising candidate for a batch removal of TN and TP from wastewaters. 100% removal of both TN and TP was observed at the end of the 9th week in all the set-ups mainly due to assimilation and the period between 6-9weeks became the optimum period after which complete harvesting is recommended. Plants having an age of 6 weeks are ideal to commence the free-floating wetland and 21 days hydraulic retention time (HRT) is recommended for optimum removal of TN and TP. Assimilation and denitrification were the key mechanisms of TN removal while assimilation and sorption became the prominent mechanisms in the removal of TP from wastewaters.

The capacity of duckweed to treat wastewater: ecological considerations for a sound design.

Duckweed species are promising macrophytes for use in sustainable wastewater treatment due to their rapid growth, ease of harvest, and feed potential as a protein source. This paper reviews growth rates of different duckweed species on wastewater and ammonia toxicity to duckweed and summarizes insights into the mechanism of organic matter and nutrient removal. Results were gained from laboratory experiments in small, shallow, duckweed-covered semicontinuous batch systems. Growth rates on different types of wastewater vary considerably among different species. Ammonia is toxic for duckweed in both the ionized and un-ionized forms. Duckweed, however, can be used to treat wastewater containing very high total ammonia concentrations as long as certain pH levels are not exceeded. The degradation of organic material is enhanced by duckweed through both additional oxygen supply and additional surface for bacterial growth. The duckweed mat with attached bacteria and algae is, independent of the loading rates, responsible for three-quarters of the total nitrogen (N) and phosphorus (P) loss in very shallow systems. Based on our results we suggest that full-scale pilot plants with duckweed should be shallower than the range encountered in the literature. A harvesting schedule that allows doubling times of 2 to 3.5 d, maintenance of a full coverage, and plug flow conditions are recommended.

Evaluation of Nitrogen Removal Potential in a Reed Filter Bed System by the 15N Tracer Method

The mechanisms of nutrient removal in a sand-filled reed filter bed (RFB) system involve filtration, sedimentation, plant uptake and microbial degradation in the soil-water interface and plant rhizosphere where the nitrification-denitrification process occurs. Information concerning these mechanisms, however, is limited, especially regarding the denitrification rate in a RFB system. With this in mind, the denitrification rates were directly measured using the 15N tracer method. In addition, the seasonal changes of the denitrification rates were investigated. Using a bench-scale RFB system and sand filter system without reeds, denitrification rates ranging from 0.0 to 5.5 (average 2.27) and 0.0 to 3.4 (average 1.48) g-N m2 d, respectively, were obtained. These values indicate that about 60 and 80% of inflow nitrogen loading was removed by denitrification. It was also found that 25% of inflow nitrogen loading in the RFB system was removed by plant uptake. The higher denitrification rate in the RFB system suggested that the microbial activity in the reed rhizosphere is of key importance for the nitrogen removal efficiency during the stationary phase of the reed's growth curve. As for their associated seasonal changes, the denitrification rates were proportional to air temperature, so that the denitrification rates were lowest during the winter. Although the denitrification rate in the RFB system was only 0.23 to 0.68 g-N/m2 d at 6.2 to 11.2 °C in December 1998, the increase of air temperature to 26.2 °C using a temperature-controlled room remarkably enhanced the denitrification rate to 2.95 g-N/m2 d. This result confirmed the possibility that the RFB system could maintain denitrification activity by controlling air temperature.

Nutrient removal potential of emergent ( Scirpus articulatus ) and floating ( Lemna major ) macrophytes

Nutrient removal capacity of Lemna major (floating macrophyte) was compared with Scirpus articulatus (emergent macrophyte) in hypertrophic mesocosms held in situ . While Lemna removed orthophosphate mainly from waterphase, Scirpus on the other hand, took up their phosphorus exclusively from the sediment. Plant recovery of both nitrogen and phosphorus was high in emergent macrophyte than in floating macrophyte. Introduction of macrophyte resulted in decline of denitrifying bacteria, but increase in heterotrophic bacterial populations. Counts of heterotrophic bacterial population were significantly higher in case of Lemna than in Scirpus . Decline of phytoplankton number was more pronounced in case of Lemna due to its shading effect compared to Scirpus . It'is concluded that reclamation ability of floating Lemna was short lived because of nutrient removal mainly from water phase whereas, the nutrient removal mechanism in emergent Scirpus was primarily through the root system from the sediment. Differential rates of nutrient storage was responsible for short term nutrient uptake by Lemna , whereas, it was reverse in case of Scirpus .

｀１５´Ｎトレーサー法を用いたヨシフィルターの窒素除去性能に関する研究

The mechanisms of nutrient removal in sand-filled reed filter bed system (RFB system) are explained by filtration, sedimentation, plant uptake and microbial degradation occurring in soil-water interface and in the plant rhizosphere, which includes nitrification-denitrification process. There is, however, little information on it, especially information on denitrificaton rate in RFB system has not been obtained. The objective of this study is to measure denitrification rates using 15N tracer method and investigate seasonal changes of them throughout a year. The results of bench-scale RFB system using 15N tracer method showed that the denitrification rates of the RFB and the sand tank without reeds ranged from 0.0∼5.5 (average 2.28) and 0.0∼3.4 (average 1.48) g-N · m-2 · d-1, respectively. These values mean that about 60% in the RFB and about 80% in the sand tank for inflow nitrogen loading were removed by denitrification. A part of remaining nitrogen loss in nitrogen balance of the RFB tank might be caused by plant uptake. High denitrification rate in the RFB suggested that microbial activity in the reed rhizosphere played an important role in nitrogen removal efficiency during the stationary phase of reed's growth curve.

Nutrient removal mechanisms in constructed wetlands and sustainable water management

Constructed wetland systems are used to treat domestic and industrial wastewater and agricultural runoff. In this field study the influence of hydraulic loading, retention time, water column depth and phosphorus (P) concentrations of influent wastewater on P and nitrogen (N) removal was examined in experimental constructed wetland systems. Five constructed wetlands with a surface area of 150 m2, were developed in the field. Results showed that P concentrations of water from outlets of all five systems decreased (from as low as 11% decrease for the system which received wastewater with average P concentration of 8.2 mg P L−1 to as high as 48.9% decrease for the system which received wastewater with average P concentration of 3.58 mg P L−1) compared to the influent water. The N concentrations in the outlet water were also decreased in all five systems (from as low as 26.3% decrease to as high as 77.5% decrease) compared to the influent water. The total P and N in the wetland sediment increased in the first year in all five systems but were unchanged at the end of the second year. The study showed that low hydraulic loading and greater retention times positively enhanced removal of P and N from wastewater in constructed wetland systems.

Nutrient removal mechanisms in constructed wetlands and sustainable water management

Constructed wetland systems are used to treat domestic and industrial wastewater and agricultural runoff. In this field study the influence of hydraulic loading, retention time, water column depth and phosphorus (P) concentrations of influent wastewater on P and nitrogen (N) removal was examined in experimental constructed wetland systems. Five constructed wetlands with a surface area of 150 m2, were developed in the field. Results showed that P concentrations of water from outlets of all five systems decreased (from as low as 11% decrease for the system which received wastewater with average P concentration of 8.2 mg P L−1 to as high as 48.9% decrease for the system which received wastewater with average P concentration of 3.58 mg P L−1) compared to the influent water. The N concentrations in the outlet water were also decreased in all five systems (from as low as 26.3% decrease to as high as 77.5% decrease) compared to the influent water. The total P and N in the wetland sediment increased in the first year in all five systems but were unchanged at the end of the second year. The study showed that low hydraulic loading and greater retention times positively enhanced removal of P and N from wastewater in constructed wetland systems.

VALIDATING A VEGETATIVE FILTER STRIP PERFORMANCE MODEL

Vegetative filter strips (VFS) reduce losses of nutrients, solids, and other materials from land area treated with fertilizers and manures. A number of models are available that simulate nutrient and sediment transport in VFS. While VFS effectiveness is considered to depend on lengths of pollutant source area and VFS areas, few published studies have tried to validate these models using variable pollutant source area and VFS area. The objective of this study was to validate an event-based nutrient transport model (Chaubey et al., 1995) that simulates soluble nutrient transport in VFS. This model links three sub-models: modified Green-Ampt infiltration, non-linear kinematic wave overland flow routing, and a nutrient transport component. The nutrient transport component considers infiltration as the only mechanism of pollutant removal from runoff. Data from a field plot experiment were used to validate the model. The model was executed using an uncalibrated runoff component, a calibrated runoff component, and measured runoff. The concentrations of parameters entering the VFS from three different poultry litter application lengths (6.1, 12.2, and 18.3 m) were not significantly different. However, predicted concentrations at subsequent lengths were different for all the three poultrylitter application lengths. This finding was consistent with the observed data. Model execution with the uncalibrated runoff component, calibrated runoff component, and measured runoff underpredicted concentrations and mass transport at various locations along the length of the VFS. Underprediction of concentration was judged to be the reason for underprediction of mass transport. The agreement between the observed and predicted concentrations and mass transport, however, improved when runoff predictions from the calibrated runoff component and measured runoff were used. This suggests that accurate prediction of infiltration and runoff is critical for accurate prediction of concentration mass transport. Furthermore, since concentration was underpredicted even when measured runoff was used, this study suggests that the nutrient transport component might be improved, possibly by including nutrient removal mechanisms other than infiltration.

Carcoar Wetland – A Wetland System for River Nutrient Removal

During December, 1991 the NSW Department of Water Resources commenced construction of an artificial wetland at the upstream end of Carcoar Dam near Blayney in central western NSW. The principal function of the wetland is to reduce nutrient inputs, especially phosphorus, from the Belubula River into Carcoar storage and consequently lower the incidence of blue-green algal blooms which occur most summers. The wetland is a multi-faceted project involving substantial research and community involvement. Construction of the wetland weir and levees was completed during April, 1992. Stage one of the wetland planting program ran from October to December, 1992 with stage two scheduled for the same period in 1993. The wetland will not be operational until December, 1993. However, even at this early point in the project, significant experience has been gained in design, construction, planting and establishment of comprehensive community involvement programs for large constructed wetlands on the flood plain. This paper outlines the background to the wetland, the design of the wetland system and its construction primarily as a nutrient removal mechanism in the Belubula River. The paper also outlines the direction of research undertaken and the role and nature of community involvement in various aspects of the project.

A mass balance method for assessing the potential of artificial wetlands for wastewater treatment

Artificial wetlands have been shown to have potential for treating wastewaters. An experimental artificial wetland is described together with a mass balance method for quantifying system performance, major nutrient storage components and nutrient removal mechanisms. The experimental systems were capable of a high level of performance. Percentage load removals for chemical oxygen demand, total nitrogen and total phosphorus were 86, 95 and 99%, respectively. Plant biomass was found to be the major nutrient storage compartment with plant nutrient uptake being the major removal mechanism. It was found that overall system performance could be described by a simple first order, steady state model. System design and hydrology were considered important factors in determining treatment performance. Designs must maximize wastewater-rootzone contact. The experimental systems used an upflow hydraulic format to achieve this design objective.

A conceptual model of nutrient cycling in wetlands used for wastewater treatment: A literature analysis

A conceptual model of nutrient dynamics in wetlands used for wastewater treatment provided the basis for reviewing the literature on the subject. Papers were selected in order to describe the storages and transfers of the conceptual model. This approach serves to develop an understanding of wetland systems behavior and allows easy identification of gaps in the literature and of research needs. The consensus of the literature is that incorporation into peat is the major long-term mechanism for phosphorus removal, whereas denitrification is very significant for nitrogen removal. Long-term, mass balance studies are required in order to identify and quantify the nutrient removal mechanisms and assess the potential of different wetland types for treating wastewater. Areas particularly lacking mass balance studies include hydrology, decomposition processes, and physicochemical reactions between water and wetland soils.