Biological Nutrient Removal Systems Research Articles

Changes in anoxic denitrification rate resulting from prefermentation of a septic, phosphorus-limited wastewater.

A preliminary bench-scale study of parallel University of Cape Town (UCT) biological nutrient removal systems showed improvement in anoxic denitrification rates resulting from prefermentation of a septic (i.e., high volatile fatty acid [VFA] content), phosphorus-limited (i.e., total chemical oxygen demand/total phosphorus [TP] ratio < 40:1) wastewater. Net phosphorus removals due to enhanced biological phosphorus removal (EBPR) were only improved marginally by prefermentation in spite of significant increases in anaerobic phosphorus release, polyhydroxyalkanoate formation, and higher anoxic and aerobic uptakes. This probably was due to the high VFA/TP ratio in the raw influent relative to the VFA requirements for EBPR because enough VFAs were already present for phosphorus removal prior to prefermentation. An additional assessment of prefermentation using parallel UCT systems with step feed of 50% of the influent to the anoxic zone was completed. This second phase quantified the effect of prefermentation in a step-feed scenario, which prioritized prefermentation use to enhance denitrification rather than EBPR. While specific denitrification rates in the anoxic zone were significantly improved by prefermentation, high denitrification in the clarifiers and aerobic zones (simultaneous denitrification) made definitive conclusions concerning the potential improvements in total system nitrogen removal questionable. The prefermented system always showed superior values of the zone settling velocity and sludge volume index and the improvement became increasingly statistically significant when the prefermenter was performing well.

The Effects of Diquat Dibromide on Biological Wastewater Treatment Plants

The objective of the study was to investigate the fate and effects of diquat dibromide which is the active ingredient in formulations used to control the growth of roots into sewers when applied as Razorooter and mixed with raw sewage, settled sewage, and activated sludge, and when introduced into activated sludge wastewater treatment systems. Both fully aerobic and biological nutrient removal (BNR) activated sludge systems were used for experimental purpose, and both continuous flow and batch reactors were used. The sorption of diquat by both raw sewage particles and activated sludge suspended solids was determined. Diquat dibromide concentrations ranged from 0.93 to 12.6 mg/L in the influent flow. Both the fully aerobic and two full biological nutrient removal systems were fed municipal sewage spiked with diquat dibromide, and operated at a mixed liquor temperature of 10°C and an MCRT of 10 days. One of the BNR systems was a control system. The results showed that only about 20% of the diquat in raw sewage flow was removed by adsorptions to the sewage solids, but 80% or more of the diquat was removed in activated sludge systems. When the influent diquat dibromide concentration was approximately 1 mg/L, over 99% of the diquat dibromide was removed by the activated sludge process. Some of the removal was believed to be by biodegradation. The diquat dibromide used in this study had no observable detrimental effects on any of the biological processes of the continuous flow fully aerobic and BNR activated systems.

Effects of oxygen on anoxic biodegradation of benzoate during continuous culture.

In this study, various amounts of oxygen were added to denitrifying chemostats receiving benzoate to mimic the input of oxygen to anoxic zones of biological nutrient removal systems. The effect of oxygen on the biodegradative capability of the mixed-microbial culture for benzoate was investigated. The anoxic benzoate biodegradative capability of the culture was not significantly changed as the mass flowrate of oxygen was increased to 40% of the input benzoate chemical oxygen demand (COD) mass flowrate, but was decreased approximately 70% when the mass flowrate of oxygen was increased to 70% of the input benzoate COD mass flowrate. The decrease in the anoxic benzoate biodegradative capability was due primarily to the loss of the denitrifying enzymes (measured by the anoxic pyruvate-degrading ability) and not to the loss of the key anoxic catabolic enzyme (benzoyl-coenzyme A reductase). The proportional increase in the concentration of nitrate as the residual terminal electron acceptor and the lack of synthesis of aerobic ring-cleavage enzymes as the oxygen input to the chemostat was increased suggest that the mixed microbial culture preferred oxygen to nitrate as the terminal electron acceptor, but degraded benzoate using the anoxic metabolic pathway. The concentration of the mixed microbial culture increased as the oxygen input to the chemostat was increased, suggesting that the oxygen was used by cytochrome cbb3 rather than quinol oxidase because the energetic yield of cytochrome cbb3 is higher than that of quinol oxidase or the nitrogen oxide reductases.

Quantitative estimation of the role of denitrifying phosphate accumulating organisms in nutrient removal

It has been reported that a proportion of polyphosphate-accumulating organisms (PAOs) can denitrify or utilize nitrate as an electron acceptor. The usage of denitrifying-PAO (DN-PAO) can relieve the competition for COD between denitrification and phosphorus removal because they can treat nitrate and phosphate by using the same carbon source. To effectively use DN-PAO for biological nutrient removal (BNR), a new system was proposed in which an anaerobic phase is placed at the influent end, followed by he anoxic and external nitrification phase. In this study, the lab-scale proposed system (A2N system) was operated with a municipal wastewater 1) to confirm stable settlement of DN-PAO in the proposed system, 2) to quantitatively estimate the fraction of different groups of organisms like denitrifiers without polyphosphate accumulating capability, aerobic-PAO and DN-PAO and 3) to estimate the advantages of DN-PAO's presence in the system. Moreover, batch experiments in which anoxic and aerobic phosphate uptake rates (PUR) were measured were also carried out. The activity of DN-PAO was observed throughout the experimental period by the batch experiment. From the results of the calculation of COD utilized by each group of organisms, it was concluded that the proposed system could accumulate much more PAO (as DN-PAO) than conventional BNR systems. Moreover, they were responsible for both EBPR and denitrification.

Simultaneous biological nutrient removal: evaluation of autotrophic denitrification, heterotrophic nitrification, and biological phosphorus removal in full-scale systems.

Simultaneous biological nutrient removal (SBNR) is the biological removal of nitrogen and phosphorus in excess of that required for biomass synthesis in a biological wastewater treatment system without defined anaerobic or anoxic zones. Evidence is growing that significant SBNR can occur in many systems, including the aerobic zone of systems already configured for biological nutrient removal. Although SBNR systems offer several potential advantages, they cannot be fully realized until the mechanisms responsible for SBNR are better understood. Consequently, a research program was initiated with the basic hypothesis that three mechanisms might be responsible for SBNR: the reactor macroenvironment, the floc microenvironment, and novel microorganisms. Previously, the nutrient removal capabilities of seven full-scale, staged, closed-loop bioreactors known as Orbal oxidation ditches were evaluated. Chemical analysis and microbiological observations suggested that SBNR occurred in these systems. Three of these plants were further examined in this research to evaluate the importance of novel microorganisms, especially for nitrogen removal. A screening tool was developed to determine the relative significance of the activities of microorganisms capable of autotrophic denitrification and heterotrophic nitrification-aerobic denitrification in biological nutrient removal systems. The results indicated that novel microorganisms were not substantial contributors to SBNR in the plants studied. Phosphorus metabolism (anaerobic release, aerobic uptake) was also tested in one of the plants. Activity within the mixed liquor that was consistent with current theories for phosphorus-accumulating organisms (PAOs) was observed. Along with other observations, this suggests the presence of PAOs in the facilities studied.

The nomographic design approach to recycled water treatment by the nitritation process

The side-stream generated recycled water in the wastewater treatment plants is characterized as high in both nitrogen concentration and fluctuation of load. Thus, the design approach for recycle water management became an important part of the biological nutrient removal system design. The application of nitrogen removal from recycled water using the nitritation process has recently been increased due to economical reasons associated with an effective carbon allocation as well as the minimization of aeration cost. The concept of nitritation reactor design related to an inhibition of nitrite oxidizer has not been fully practiced in reality because of the limited field experiences. In this paper, a new approach has been proposed to determine reactor size and oxygen requirement in nitritation process design. The SRT-based design approach has been examined based on a series of laboratory experiments.

A potential new role for fungi in a wastewater MBR biological nitrogen reduction system

The fastidious nature of nitrifying bacteria has caused many operational problems for wastewater treatment plants employing some form of biological nutrient removal. Research in the field has focused solely on meeting the requirements of this group of bacteria. Recently fungi have been recognized to perform denitrification at greater rates than bacteria. Combining fungi nitrification ability and resistance to inhibitory chemicals, there is the potential for development of a new fungi based biological nitrogen removal system. From the data reviewed, the system would have several significant advantages over conventional biological nutrient removal systems. This paper reviews the ability of fungi to carry out biological nitrogen removal and the potential performance of a fungi based system. Key words: fungi, biological nutrient removal, nitrification, denitrification, membrane bioreactor.

Filamentous Chloroflexi (green non-sulfur bacteria) are abundant in wastewater treatment processes with biological nutrient removal.

Most filamentous bacteria in biological nutrient removal (BNR) processes have not been identified beyond their morphotype and simple staining reactions. Furthermore, the majority of sludge filaments observed under the microscope do not hybridize to commonly used phylogenetic probes for well characterized bacterial phyla such as the Proteobacteria, Actinobacteria, Firmicutes and BACTEROIDETES: Specific 16S rRNA-targeted oligonucleotide probes were designed for the phylum Chloroflexi (green non-sulfur bacteria) and optimized for use in fluorescence in situ hybridization. Chloroflexi have been implicated in BNR systems by phylogenetic identification of filamentous bacteria isolated by micromanipulation from sludge and culture-independent molecular phylogenetic surveys. The predominant morphotype responding to the probes was filamentous and these filaments were generally abundant in 10 Australian full-scale and two laboratory-scale BNR samples examined. Filamentous bacteria responding to a subdivision 1 Chloroflexi probe were rare in the samples, whereas subdivision 3 Chloroflexi filaments were very common in some sludges. This is in direct contrast to results obtained from molecular phylogenetic surveys of BNR systems where most sludge 16S rDNA clones belong to subdivision 1 and only a few to subdivision 3. It is suggested that filamentous bacteria belonging to the Chloroflexi phylum account for a large fraction of phylogenetically uncharacterized filaments in BNR systems and are likely to be abundant in such systems on a global scale.

Microbial evaluation of activated sludge and filamentous population at eight Czech nutrient removal activated sludge plants during year 2000

The long-term project on the survey of filamentous microorganisms, which started in 1996, was finished in 2000 by the survey of eight Czech activated sludge plants with biological nutrient removal (BNR) systems. At all plants with enhanced biological nutrient removal, specific microbial population (mostly from the point of view of filaments occurrence), operational problems (presence of biological foaming, bulking) and plant operation were observed periodically and longer than 1 year. In our paper the relationship between the composition of activated sludge (especially filaments) consortia and modification of the process with nutrient removal is discussed. At the surveyed plants Type 0092 and Microthrix parvicella were identified as dominant Eikelboom filamentous types.

The Effects of Prefermentation Upon Biological Nutrient Removal Systems with Septic, COD Limited Influent Wastewater

The Effects of Prefermentation Upon Biological Nutrient Removal Systems with Septic, COD Limited Influent Wastewater

Modification and expansion of a pure oxygen WWTP for biological nutrient removal (BNR)

A pure oxygen activated sludge system was converted to a VIP configuration BNR (biological nutrient removal) system wherein three of the five pure oxygen sections were retained, and performance was compared to that of a side-by-side air aeration MUCT (modified UCT) system. Because the pure oxygen BNR system could not obtain good nitrification, its treatment capacity had to be downgraded from 113,550 m3/d to a flow of only 60,000 m3/d. At the lesser flow, it was determined that adequate nitrification and improved denitrification could be accomplished in the pure oxygen system by continuously seeding it with 100% of the WAS from the MUCT system. Fortunately, while the capacity of the pure oxygen system had to be downgraded, it was determined that the capacity of the MUCT system was substantially greater than its design flow, and the combined system is capable of treating the entire design flow. However, this requires increasing the operating sludge age of the MUCT system. The pure oxygen BNR system performed better phosphorus removal than the MUCT system, both before and after seeding with the MUCT WAS. Apparently this was because the MUCT system was operated at a substantially higher sludge age than the pure oxygen system. However, both systems have consistently discharged effluent phosphorus concentrations of less than 2.0 mg/L TP, which is the Chesapeake Bay standard. Even with improved nitrification and denitrification in the pure oxygen BNR system, neither it nor the MUCT system have proven to be capable of meeting the Virginia Chesapeake Bay goal of 10 mg/L total nitrogen in the effluent.

EXPLORING PORPHYRA SPECIES FOR USE AS NITROGEN SCRUBBERS IN INTEGRATED AQUACULTURE

Carmona, R.1, Kraemer G. P.2, Zertuche, J. A.3, Chanes, L.4, Chopin, T.5, Neefus C.4,6 &amp; Yarish, C.1 1Dept. of Ecol. and Evol. Biol., University of Connecticut, One University Place, Stamford, CT 06901, USA; 2Department of Environmental Sciences, State University of New York, Purchase, NY 10577 USA; 3IIO, Universidad Autonoma de Baja California. Ensenada,B.C., Mexico; 4DGETI‐CBTis41, Mexico; 5CCSA, Dept. of Biol., University of New Brunswick, Saint John, N.B., E2L 4L5, Canada; 6Department of Plant Biology, University of New Hampshire, Durham, NH 03824, USAFinfish mariculture along the Northeast US coast continues to develop into a strong industry. At a regional level, mariculture can be a significant contributor to nutrient loading in coastal waters. Since macroalgae are able to concentrate nutrients and grow at high rates, they can be an useful tool for alleviating this problem. In addition, seaweed mariculture is by itself a multi‐billion dollar industry, with the red alga Porphyra (nori) valued at over $US 1.8 billion. Local species and strains of Porphyra from the Northeast U.S.A. are being studied to determine their capacity as nutrient scrubbers under different nutrient and temperature conditions. P. purpurea was grown under two N sources (NO3‐ vs. NH4+). The fastest growth (up to 13% d‐1) and greatest N content (ca. 7% DW) were measured in plants grown at 300 µM NH4+. Short‐term NH4+ uptake by P. purpurea (strains from Maine and Long Island Sound) and by P. amplissima was not saturated at 150 µM, the highest concentration tested. The P. purpurea isolate from Maine took up NH4+ faster than did the Long Island Sound isolate. NH4+ uptake by P. amplissima was faster than uptake by either P. purpurea strain. The high growth rates obtained and the ability for N uptake and tissue accumulation make these species suitable for using as a biological nutrient removal system.

STEP FEEDING STRATEGY FOR ENHANCING NITROGEN AND PHOSPHORUS REMOVAL IN AOAO PROCESS

This study describes a biological process containing anaerobic/oxide/anoxic/oxide (AOAO) stages, which incorporates a stepwise feeding strategy to enhance nitrogen and phosphorus removal efficiencies. In the experimental reactors, synthetic wastewater was fed into the anaerobic stage and anoxic stage separately, while the substrates and nutrients were successfully consumed without recycling either nitrified effluent or external carbon sources. Experimental results demonstrated that the anoxic stage was provided an intrinsic sufficient carbon source and caused NOx (NO2-N + NO3-N) concentration to reduce from 11.85 mg/l to 5.65 mg/l. The total Kjeldahl nitrogen (TKN) removal rate was between 81.81% and 93.96%, while the PO4-P removal ratio was between 93% and 100%. The substrate fed into the anaerobic at flow rate Q1 and into the anoxic at flow rate Q2. In addition, three different ratios were performed with Q1/Q2 varied from 7/3, 8/2 to 9/1. The AOAO process clearly saves nearly one-third of the energy compared to the typical Biological nutrient removal (BNR) system A2O process.

Full-scale demonstration of biological nutrient removal in a single tank SBR process

Complete biological nutrient removal (BNR) in a single tank, sequencing batch reactor (SBR) process, is demonstrated here at full-scale on a typical domestic wastewater. The unique feature of the UniFed process is the introduction of the influent into the settled sludge blanket during the settling and decant periods of the SBR operation. This achieves suitable conditions for denitrification and anaerobic phosphate release which is critical to successful biological phosphorus removal. It also achieves a "selector" effect, which helps in generating a compact, well settling biomass in the reactor. The results of this demonstration show that it is possible to achieve well over 90% removal of COD, nitrogen and phosphorus in such a process. Effluent quality achieved over a six-month operating period directly after commissioning was: 29 mg/l COD, 0.5 mg/l NH4-N 1.5 mg/l NOx-N and 1.5 mg/l PO4-P (50%-iles of daily samples). During an 8-day, intensive sampling period, the effluent BOD5 was < 2 mg/l in all samples and the total phosphorus averaged 0.17 mg/l in the effluent. Detailed sampling and analysis during one cycle and at various depths clearly showed the deliberate stratification achieved in the tank during the settling and decant period, allowing biochemical reactions to occur during this normally "non-productive" period. The simplicity and flexibility of the UniFed system allows it to be used in numerous applications, particularly for industrial situations where a high degree of uncertainty of the wastewater composition during the design stage or where changing requirements based on changes on the production side are present. The single tank operation without any recycle also reduces the capital costs for a full BNR system compared to the comparatively complex continuous flow processes.

External nitrification in biological nutrient removal activated sludge systems

A biological nutrient removal (BNR) activated sludge (AS) scheme incorporating external nitrification in a fixed media system is evaluated. A laboratory scale investigation of the scheme indicates that it holds considerable potential for BNRAS system intensification through major reduction in sludge age and oxygen demand and significant improvement in sludge settleability. Because the BNRAS system is not required to nitrify, its anoxic mass fraction can be considerably enlarged at the expense of the aerobic mass fraction creating conditions that (i) allow it to achieve high N removals with domestic wastewaters with high TKN/COD ratios and (ii) promote anoxic P uptake polyphosphate accumulating organisms (PAO) to develop in the system. From this, and earlier investigations with conventional BNR systems, it appears that anoxic P uptake biological excess P removal (BEPR) is only about two thirds of aerobic P uptake BEPR. Inclusion of anoxic P uptake PAOs in, and exclusion of nitrifiers from, the BNRAS system are not essential for the scheme. However, conditions that promote aerobic P uptake to maximize BEPR, are also conducive to nitrifier growth, which, if supported in the BNRAS system, would require virtual complete nitrification in the fixed media system to avoid nitrate interference with BEPR. Before the scheme can be implemented at large scale, an engineering and economic evaluation is required to quantify its potential benefits and savings.

Laboratory Scale Experimentation for RBCOD Production from OFMSW for BNR Systems: Results and Kinetics

In this paper results of a laboratory-scale experimentation on anaerobic fermentation of the organic fraction of municipal solid wastes (OFMSW) are presented. The aim of the experimentation was the evaluation of the production of readily biodegradable COD to be used in biological nutrient removal (BNR) plants. A 3.5 l glass reactor was built and the process was run under mesophilic conditions (32°C) without pH control. A batch test and five runs at different hydraulic retention times were performed, at 1.5, 3, 4, 5, and 6 days, respectively. An intermittent step-feed strategy was adopted. The feeding material came from the selective collection of municipal solid wastes, and was shredded and diluted with tap water. The kinetics of the hydrolytic process has been characterised by two parameters. The kinetic model has been related to the hydraulic retention time and can be used for design purposes.

Improvment of nitrogen and phosphorus removal in the anaerobic-oxic-anoxic-OXIC (AOAO) process by stepwise feeding

This investigation incorporated a stepwise feeding strategy into the biological process containing anaerobic/oxide/anoxic/oxide (AOAO) stages to enhance nitrogen and phosphorus removal efficiencies. Synthetic wastewater was fed into the experimental reactors during the anaerobic and anoxic stages and the substrates/nutrients were successfully consumed without recycling either nitrified effluent or external carbon source. An intrinsic sufficient carbon source developed during the anoxic stage and caused the NOx (NO2-N+NO3-N) concentration to be reduced from 11.85mg/l to 5.65mg/l. The total Kjeldahl nitrogen (TKN) removal rate was between 81.81%∼93.96% and the PO4-P removal ratio ranged from 93%∼100%. The substrate fed into the anaerobic with a Q1 flow rate and a Q2 into the anoxic reactor. The three difference experiments contained within this study produced Q1/Q2 that varied from 7/3, 8/2, and 9/1. The AOAO process saved nearly one-third of the energy compared with typical biological nutrient removal (BNR) system A2O processes.

Effect of variations in flow rate and concentrations of influent on the nitrogen removal performance of the aerobic-anoxic-aerobic process

During a rain event municipal wastewater treatment plants experience a rapid change in the inflow conditions. The effect of the rapid change in a flow rate and/or concentrations on the nitrogen removal performance was studied by using results from the lab-scale experiment and simulation analysis. The mathematical model was developed for simulating the dynamic behavior of a biological nutrient removal system, and the validity of the model was confirmed with data from the experiment. Computed results and the experimental data showed that the net inflow of nitrogen compound through the reaction basin was controlled mainly by the flow rate and the reaction rate was subject to the loading rate in the transient state. The pulse-shaped perturbation with the low organic and nitrogen load resulted in the lesser performance of nitrogen removal than the perturbation with the increased load.

Characterization of Simultaneous Nutrient Removal in Staged, Closed‐Loop Bioreactors

This research was conducted in the context of an overall research project directed at better understanding and controlling simultaneous biological nutrient removal (SBNR) in full‐scale wastewater treatment plants. The basic hypothesis of the overall research is that three general mechanisms are responsible for SBNR and that all three can operate, to different degrees, within any biological nutrient removal (BNR) system. The three mechanisms are (1) biological reactor (bioreactor) mixing patterns that allow the anoxic and anaerobic zones necessary for BNR to develop, referred to as the bioreactor macroenvironment, (2) the development of anoxic and anaerobic zones within the floc, referred to as the floc microenvironment, and (3) the presence of novel microorganisms. System design and operating parameters will determine the relative importance of each mechanism. The objective of the overall research project is to identify the factors affecting the relative contributions of the three mechanisms to SBNR, thereby allowing SBNR to be implemented and controlled more effectively in full‐scale plants. In the research reported in this paper the operating characteristics of seven full‐scale wastewater treatment plants using the staged, closed‐loop bioreactor process known as Orbal were evaluated to determine the degree of SBNR occurring. Low effluent total nitrogen concentrations from a process without distinct anoxic zones indicate that simultaneous nitrification and denitrification occur reliably in these facilities. Nitrogen removal is encouraged at these facilities by use of solids retention times sufficiently long to allow nitrifiers to grow under the low dissolved oxygen concentrations in channel 1 of the process. Environmental conditions are relatively uniform throughout each channel, and distinct anoxic and aerobic zones do not seem to form. This suggests that the anoxic conditions necessary for denitrification may develop principally within the biological flocs. Biological nitrogen removal was characterized using the International Association on Water Quality Activated Sludge Model Number 1. Influent and effluent total phosphate and biochemical oxygen demand data and microbiological observations suggest that biological phosphorus removal occurs. Distinct anaerobic zones were not observed, but anaerobic conditions may develop within the lower portion of channel 1. These systems are good candidates for further study of SBNR.

Ecological Engineering of Bioreactors for Wastewater Treatment

Biological nutrient removal (BNR) systems remove carbon, nitrogen, and phosphorus from wastewaters through biodegradation of organic compounds, oxidation of ammonia-N to nitrate-N, reduction of nitrate-N to N2 gas, and sequestration of phosphorus as polyphosphate. The microbial community in such systems is complex because it must contain heterotrophic bacteria capable of aerobic respiration, anaerobic respiration, and fermentation; specialized heterotrophic bacteria that can store polyphosphate; and autotrophic nitrifying bacteria that can withstand long periods without oxygen. Although the basic design principles for BNR systems are reasonably well established, it is becoming apparent that a greater understanding of the microbial interactions involved is required to increase system reliability. For example, although the environment established for the selection of phosphorus accumulating organisms was thought to give them a strong competitive advantage over other heterotrophic bacteria, this has turned out not to be the case. Rather, glycogen accumulating organisms can compete quite effectively in the same environment. Furthermore, BNR systems have suffered from problems with sludge settleability, even though many of the system characteristics are considered to be conducive to the suppression of filamentous bacteria. Finally, the use of molecular techniques has revealed that the autotrophic nitrifying bacteria are different from those that had been considered to be present. This paper reviews the microbial ecology of BNR systems, establishes how molecular biology techniques are changing our understanding of that ecology, and suggests ways in which engineering control can be exerted over community structure, thereby increasing the reliability of BNR systems.