Biological Nutrient Removal Systems Research Articles

Optimization of A2O BNR processes using ASM and EAWAG Bio-P models: model formulation

This study is an extended and comprehensive analysis to accomplish optimal sizing for a biological nutrient removal (BNR) system with an A2O BNR activated sludge process using activated sludge models (ASM) kinetic models. A highly nonlinear activated sludge model combined with the EAWAG Bio-P module is formulated and optimized using a generalized reduced gradient solver. Primary and final clarifications are included with the A2O biotreatment scheme along with oxygen-supplying units. This paper includes a detailed description of model formulation, problem definition and discussion of optimal design in terms of capital (CAPEX) and operating (OPEX) cost estimates. The optimization problem is formulated and solved using typical cost factors and operating/design constraints applied to a typical illustrative system treating medium-strength wastewater. Results indicated that maintenance and sludge disposal expenditures represent more than 50% of the total annual cost and 80% of the annual running operating cost. Another major finding was that a primary clarifier is found to be cost ineffective in the A2O BNR process. Sensitivity of the optimal solutions and model performance to varying inflow conditions and to other effluent limits and model parameters will be discussed in another paper.

The effect of anoxia and anaerobia on ciliate community in biological nutrient removal systems using laboratory-scale sequencing batch reactors (SBRs)

Little is known about the effect of anaerobic and anoxic stages on the protozoan community in the activated sludge process and how this subsequently affects performance. Using a laboratory-scale BNR system the effect of different periods of anoxia on both the protozoan community and performance efficiency have been examined. Four SBRs were operated at two cycles per day using a range of combined anoxic/anaerobic periods (0, 60, 120 and 200 min). Effluent quality (TOC, BOD, TP, TN, NH 4–N, NO 3–N and NO 2–N), sludge settleability and ciliate community (species diversity and abundance) were analysed over a periods of up to 24 days of operation. The species richness and total abundance of ciliates were found to decrease with longer anoxic/anaerobic periods. Both, positive and negative significant correlations between the abundance of certain species and the period of anoxia was observed (e.g. Opercularia microdiscum, Epicarchesium granulatum), although other species (i.e. Acineria uncinata, Epistylis sp.) were unaffected by exposure to anoxia. In the laboratory-scale units, the 60 min anoxic/anaerobic period resulted in good process performance (TOC and BOD removal of 97–98% respectively), nitrification (80–90%), denitrification (52%) but poor levels of biological P-removal (12%); with the protozoan community moderately affected but still diverse with high abundances. Increasing the length of anoxia to up to 200 min did not enhance denitrification although P-removal rates increased to between 22 and 33%; however, ciliate species richness and total abundance both decreased and sludge settleability became poorer. The study shows that activated sludge ciliate protozoa display a range of tolerances to anoxia that result in altered ciliate communities depending on the length of combined anoxic/anaerobic periods within the treatment process. It is recommended that anoxic/anaerobic periods should be optimised to sustain the protozoan community while achieving maximum performance and nutrient removal.

Pilot-Scale Waste Activated Sludge Alkaline Fermentation, Fermentation Liquid Separation, and Application of Fermentation Liquid To Improve Biological Nutrient Removal

The use of sludge fermentative short-chain fatty acids (SCFA) as an additional carbon source of biological nutrient removal (BNR) has drawn much attention recently as it can reuse sludge organics, reduce waste activated sludge production, and improve BNR performance. Our previous laboratory study had shown that the SCFA production was significantly enhanced by controlling sludge fermentation at pH 10 with NaOH. This paper focused on a pilot-scale study of alkaline fermentation of waste activated sludge, separation of the fermentation liquid from the alkaline fermentation system, and application of the fermentation liquid to improve municipal biological nitrogen and phosphorus removal. NaOH and Ca(OH)(2) were used respectively to adjust the alkaline fermentation pH, and their effects on sludge fermentation and fermentation liquid separation were compared. The results showed that the use of Ca(OH)(2) had almost the same effect on SCFA production improvement and sludge volatile suspended solids reduction as that of NaOH, but it exhibited better sludge dewatering, lower chemical costs, and higher fermentation liquid recovery efficiency. When the fermentation liquids, adjusted with Ca(OH)(2) and NaOH respectively, were added continuously to an anaerobic-anoxic-aerobic municipal wastewater BNR system, both the nitrogen and phosphorus removals, compared with the control, were improved to the same levels. This was attributed to the increase of not only influent COD but also denitrifying phosphorus removal capability. It seems that the use of Ca(OH)(2) to control sludge fermentation at pH 10 for efficiently producing a carbon source for BNR is feasible.

Uneven Distribution of Microcolony Forming Bacteria in Secondary Clarifiers of Biological Nutrient Removal Systems

Uneven Distribution of Microcolony Forming Bacteria in Secondary Clarifiers of Biological Nutrient Removal Systems

Using Sludge Fermentation Liquid To Improve Wastewater Short-Cut Nitrification-Denitrification and Denitrifying Phosphorus Removal via Nitrite

Wastewater biological nutrient removal (BNR) by short-cut nitrification-denitrification (SCND) and denitrifying phosphorus removal via nitrite (DPRN) has several advantages, such as organic carbon source saving. In this paper, a new method, i.e., by using waste activated sludge alkaline fermentation liquid as BNR carbon source, for simultaneously improving SCND and DPRN was reported. First, the performance of SCND and DPRN with sludge fermentation liquid as carbon source was compared with acetic acid, which was commonly used in literatures. Sludge fermentation liquid showed much higher nitrite accumulation during aerobic nitrification than acetic acid (81.8% versus 40.9%), and the former had significant anoxic denitrification and phosphorus uptake. The soluble phosphorus and total nitrogen removal efficiencies with sludge fermentation liquid were much higher than with acetic acid (97.6% against 73.4% and 98.7% versus 79.2%). Then the mechanisms for sludge fermentation liquid showed higher SCND and DPRN than acetic acid were investigated from the aspects of wastewater composition, microorganisms assayed by 16S rRNA gene clone library, and fluorescence in situ hybridization. More NO(2)(-)-N accumulated by the use of sludge fermentation liquid was attributed to be more humic acids in the influent, which inhibited nitrite oxidizing bacteria (NOB) more serious than ammonia oxidizing bacteria (AOB), and more AOB but less NOB were observed in the BNR system. The reasons for sludge fermentation liquid BNR system exhibiting greater short-cut denitrifying phosphorus removal were that there were less glycogen accumulating organisms and more phosphorus accumulating organisms and anoxic denitrifying phosphorus removal bacteria with higher nitrite reductase activity.

Pushing the hydraulic retention time envelope in Modified Ludzack Ettinger systems

This study demonstrated the feasibility of operating a biological nutrient-removal employing Modified Ludzack Ettinger (MLE), at a reduced hydraulic retention time (HRT) of 5.5 h. The MLE process not only achieved full nitrification and 75–80% total nitrogen removal, at temperatures as low as 12 °C but also reduced the net observed biomass yield by 28% relative to the full-scale plant to 0.31 g VSS g −1 COD r. Biomass settleability drastically improved relative to the conventional activated sludge (CAS) full-scale plant as reflected by sludge volume index (SVI) of 97 mL g −1 versus 202 mL g −1. Respirometric studies indicated that the heterotrophic biokinetic coefficients for the conventional activated sludge and the MLE systems were very similar and consistent with literature values for primary effluent. However, biomass-specific nitrification rates in the MLE system of 0.14 g NH 4-N g −1 VSS d −1 at 20 °C were 55% higher than in the CAS, with both systems having comparable nitrification temperature correction coefficients of 1.084 for (CAS) and 1.092 in (MLE). This study confirmed through both pilot testing and modeling that biological nutrient removal (BNR) systems treating low strength municipal wastewater can be designed for overall HRT as low as 5 h in cold climates. Furthermore, the process achieved significant biomass yield reduction due to anoxic consumption of organic matter.

Experimental evaluation of decrease in the activities of polyphosphate/glycogen‐accumulating organisms due to cell death and activity decay in activated sludge

Decrease in bacterial activity (biomass decay) in activated sludge can result from cell death (reduction in the amount of active bacteria) and activity decay (reduction in the specific activity of active bacteria). The goal of this study was to experimentally differentiate between cell death and activity decay as the cause of decrease in bacterial activity. By means of measuring maximal anaerobic phosphate release rates, verifying membrane integrity by live/dead staining and verifying presence of 16S rRNA with fluorescence in situ hybridization (FISH), the decay rates and death rates of polyphosphate-accumulating organisms (PAOs) in a biological nutrient removal (BNR) system and a laboratory phosphate removing sequencing batch reactor (SBR) system were determined, respectively, under famine conditions. In addition, the decay rate and death rate of glycogen-accumulating organisms (GAOs) in a SBR system with an enrichment culture of GAOs were also measured under famine conditions. Hereto the maximal anaerobic volatile fatty acid uptake rates, live/dead staining, and FISH were used. The experiments revealed that in the BNR and enriched PAO-SBR systems, activity decay contributed 58% and 80% to the decreased activities of PAOs, and that cell death was responsible for 42% and 20% of decreases in their respective activities. In the enriched GAOs system, activity decay constituted a proportion of 74% of the decreased activity of GAOs, and cell death only accounted for 26% of the decrease of their activity.

Effect of cycle changes on simultaneous biological nutrient removal in a sequencing batch reactor (SBR)

The destabilization of a microbial population is sometimes hard to solve when different biological reactions are coupled in the same reactor as in sequencing batch reactors (SBRs). This paper will try to guide through practical experiences the recovery of simultaneous nitrogen and phosphorus removal in an SBR after increasing the demand of wastewater treatment by taking advantage of its flexibility. The results demonstrate that the length of phases and the optimization of influent distribution are key factors in stabilizing the system for long‐term periods with high nutrient removal (88%, 93% and 99% of carbon, nitrogen and phosphorus, respectively). In order to recover a biological nutrient removal (BNR) system, different interactions such as simultaneous nitrification and denitrification and also phosphorus removal must be taken into account. As a general conclusion, it can be stated there is no such thing as a perfect SBR operation, and that much will depend on the state of the BNR system. Hence, the SBR operating strategy must be based on a dynamic cycle definition in line with process efficiency.

Biological nitrogen and phosphorus removal by filamentous bacteria in pure culture

The availability of excess nutrients (phosphorus (P) and nitrogen (N)) in wastewater systems causes many water quality problems. These problems include eutrophication whereby algae grow excessively and lead to depletion of oxygen, death of the aquatic life and bad odours. Biological phosphorus removal has gained attention because the condition of wastewater is manipulated in order to facilitate nutrient removal by the microbial communities in the wastewater. It has been reported that filamentous bacteria are capable of removing P at a similar or higher rate to that of heterotrophic bacteria. It has also been reported that conditions that facilitate biological nitrogen removal promote bulking in a biological nutrient removal system. The aim of the project was therefore to evaluate the role of filamentous bacteria in biological nutrient removal (BNR) processes. For denitrification this was achieved by performing the nitrate reduction preliminary screening test followed by batch tests. Neisser staining was used to locate polyphosphate granules in cells. All Neisser positive isolates were evaluated for P accumulation employing batch tests. The findings of this study demonstrated that 29% of the isolates were true denitrifiers, 3% were sequential denitrifiers, 11% were nitrate respirers, 13% were non-denitrifiers and 45% were nitrate respirers at high concentrations (1 g/. and 0.5 g/.) and true denitrifiers at low concentrations (0.2 g/.). The results of the nitrate reduction batch test demonstrated that up to 18.46 mg/. nitrate was reduced to nitrogen gas. 53% of the isolates reduced nitrite, 33% resulted in nitrite accumulation and 9% did not react to nitrite. Of the 38 isolates 16% were positive for the Neisser stain, 34% were positive for the glycogen stain and 79% were positive for the PHB stain. Batch test results showed phosphate accumulation of up to 17.12 mgP/.. It was demonstrated by this study therefore, that filamentous bacteria have the potential to biologically remove nutrients. These research findings will serve as a basis for further investigations.

Effects of integrated fixed film activated sludge media on activated sludge settling in biological nutrient removal systems

Integrated fixed film activated sludge (IFAS) is an increasingly popular modification of conventional activated sludge, consisting of the addition of solid media to bioreactors to create hybrid attached/suspended growth systems. While the benefits of this technology for improvement of nitrification and other functions are well-demonstrated, little is known about its effects on biomass settleability. These effects were evaluated in parallel, independent wastewater treatment trains, with and without IFAS media, both at the pilot (at two solids residence times) and full scales. While all samples demonstrated good settleability, the Control (non-IFAS) systems consistently demonstrated small but significant ( p < 0.05) improvements in settleability relative to the IFAS trains. Differences in biomass densities were identified as likely contributing factors, with Control suspended phase density > IFAS suspended phase density > IFAS attached phase (biofilm) density. Polyphosphate content (as non-soluble phosphorus) was well-correlated with density. This suggested that the attached phases had relatively low densities because of their lack of anaerobic/aerobic cycling and consequent low content of polyphosphate-accumulating organisms, and that differences in enhanced biological phosphorus removal performance between the IFAS and non-IFAS systems were likely related to the observed differences in density and settleability for the suspended phases. Decreases in solids retention times from 8 to 4 days resulted in improved settleability and increased density in all suspended phases, which was related to increased phosphorus content in the biomass, while no significant changes in density and phosphorus content were observed in attached phases.

Membrane fouling propensity of denitrifying organisms

The impact of denitrification on membrane fouling propensity was investigated using three different sludges, i.e. conventional activated sludge (CAS), ordinary heterotrophic organisms (OHO) and denitrifying phosphorous accumulating organisms (DPAO) taken from a lab-scale biological nutrient removal (BNR) system. Fouling propensity was evaluated with the modified filtration index (MFI), soluble microbial products (SMP), bound extracellular polymeric substances (bEPS), and relative hydrophobicity (RH). The tests indicated that DPAO denitrification decreased cake layer resistance, as indicated by 45% reduction in MFI as compared to an increase of 123 and 52% for CAS and OHO denitrification. Pore blocking fouling was greater in CAS and OHO than DPAO. However, SMP increased after CAS and OHO denitrification but decreased in DPAO while bEPS increased in all cases. DPAO denitrification also increased RH of bEPS but decreased carbohydrate/protein ratio, possibly due to carbohydrate utilization in EPS by OHO under substrate limiting conditions for denitrification, substantiating the reduction in cake layer resistance in DPAO denitrification. CAS fouling during denitrification was more severe than BNR sludges as reflected by higher MFI, SMP and bEPS production.

Effects of the sludge reduction system in MBR on the membrane permeability

For the sludge volume reduction, gravity thickening and mechanical thickening processes have been mainly applied. However, these processes usually cause several problems such as large footprint, low thickening efficiency, etc. To solve these problems, a sludge reduction system using submerged membrane in a reactor with excess sludge from a biological nutrient removal (BNR) system was investigated. Both lab and pilot scale experiments for sludge reduction were carried out. The hydraulic retention time (HRT) was in a range of 4.5–6.7 days during the experimental period. A flat-sheet membrane with a mean pore size of 0.08 µm was used and operated at a flux range of 7–20 L/m 2·h. During the experimental period, concentrations of BOD and SS were maintained less than 8 mg/L, 3 mg/L, respectively, which indicated the high quality of treated wastewater. While extracellular polymeric substances (EPS) were lowest at a coagulant concentration of 15 ppm, soluble microbial product (SMP) concentrations did not have any correlation with coagulant concentrations. The critical flux was observed in a range of 18–24 L/m 2·h. These results suggested that the sludge reduction system using membrane bioreactor (MBR) could be applied as one of suitable processes to overcome problems of conventional processes such as gravity and mechanical thickening.

Carbon‐nitrogen‐phosphorus removal and biofilm growth characteristics in an integrated wastewater treatment system involving a rotating biological contactor

AbstractA new rotating biological contactor‐packed media technology (RBC‐PMT) is locally innovated using light polyethylene Amazon screen material as disc media. A single‐stage co‐current fed of this type, which is connected with a series of equalization tanks as an integrated wastewater treatment system (IWWTS), showed good carbon‐nitrogen‐phosphorus (C‐N‐P) removal and unveiled biofilm growth characteristics noteworthy for treating pollutants in wastewater.The equalization tanks approached facultative anaerobic conditions while the RBC‐PMT exhibited a completely aerated system, both with a slightly alkaline pH, whose temperatures are ranging from 21 to 24 °C, and both performed as biological nutrient removal systems. The combined nutrient removal efficiency at high organic loading rate (HOLR) and low organic loading rate (LOLR) showed fair chemical oxygen demand (COD) removal at 65.68 and 67.89%, respectively. Nitrate‐nitrogen removal demonstrated good removal at 79.17% at HOLR and 83.43% at LOLR. There was excellent phosphate‐phosphorus removal determined at 91.64 and 94.35% at high and low OLRs, respectively. This indicates that increasing the organic loading rate decreases the C‐N‐P removal in the IWWTS.Biofilm growth was characterized by the selection and survival of microorganisms present under aerobic environmental conditions in the RBC‐PMT system and their respective metabolism in removing C‐N‐P substrates. Yeasts, coliform bacteria particularly E. coli, Cyanobacteria, and benthic diatoms were dominant microorganisms found upon oil‐immersion microscopy. Protozoans and algae including Chlorococcum, Chlorella, Diatoma, Tribonema, Oscillatoria, Euglena, and other motile rotifiers were also dominantly found in the biofilm samples. Biofilm growth is observed and its average thickness was measured to be 7.71 µm at HOLR and 2.81 µm at LOLR. Thicker biofilm at HOLR has caused the reduced rate of diffusion of the microorganisms and their metabolic products as manifested by the low C‐N‐P removal during HOLR. Copyright © 2009 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Effects of Heavy Metals on the Specific Ammonia and Nitrate Uptake Rates in Activated Sludge

Abstract Toxicity of heavy metals on activated sludge has already been considered as an important factor in the biological nutrient removal (BNR) system. This study identified the inhibition of nit...

The invisible BNR plant provides high quality effluent and recreational area for densely populated urban area

In a densely populated area, a large wastewater treatment plant (WWTP) has been constructed in the underground. The plant is practically “invisible” to visitors and neighbours, and the ground level is used as a park and sport facilities in order to avoid the “not in my backyard” phenomenon. The WWTP has a 5-stage biological nutrient removal system utilizing the denitrifying PAO (dPAO) with a step feed in order to treat the weak sewage with higher nutrient removal requirement. Although the underground installation could be expected to increase plant operating temperature, the temperature increase was only 1°C. The polished final effluent from a sand filter produced average TN and TP concentrations of 5.11 mg/L and 0.91 mg/L, respectively with SS concentrations of 0.61 mg/L, indicating that the dPAO system combined with sand filter effectively produced a high quality effluent.

Comparative studies on membrane fouling between two membrane-based biological nutrient removal systems

Two lab scale membrane-based biological nutrient removal systems were operated using municipal wastewater at a hydraulic retention time of 6 h and a solids retention time of 10 days. Membrane fouling parameters i.e. fouling rate, extracellular polymeric substance (EPS), soluble microbial product (SMP), particle size and sludge volume index (SVI) were monitored. It appeared that both systems showed similar membrane fouling trends with close fouling rate of 4.4 × 10 −2 LMH/kPa h. Fouling rate was more influenced by SMP than bound EPS. The higher protein/carbohydrate ratio in SMP was related with higher fouling rate. SVI and floc size were closely linked to each other and SVI was affected more by the bound protein/total protein ratio than the amount of bound protein. A statistical analysis confirmed that SMP impacts membrane fouling more significantly than floc size, the bound protein/total protein ratio and bound EPS. Biofilm layer deposited on the membrane played a beneficial role in denitrification, removing as much as 1.5 mg N/L, and was primarily impacted by dissolved oxygen (DO) and transmembrane pressure (TMP) rather than chemical oxygen demand rejection and attached biomass. The amount of nitrate reduction increased at lower DO condition (less than 2 mg/L) and the denitrification increased membrane fouling.

The beneficial role of intermediate clarification in a novel MBR based process for biological nitrogen and phosphorus removal

AbstractBACKGROUND: A novel membrane bioreactor (MBR) is described, employing an intermediate clarifier. Unlike the established function of a final clarifier in a conventional biological nutrient removal system, the role of an intermediate clarifier has rarely been studied. Thus, this work focused on explaining the fate of nutrients in the intermediate clarifier, as influenced by the hydraulic retention time (HRT) of the preceding anaerobic bioreactor.RESULTS: The system was tested with two different anaerobic/anoxic/aerobic biomass fractions of 0.25/0.25/0.5 (run 1) and 0.15/0.35/0.45 (run 2) using synthetic wastewater. The major findings of the study were that phosphorus (P) removal was affected by the role of the intermediate clarifier. In run 1, P was removed at a rate 0.16 g d−1 in the intermediate clarifier while in run 2, additional P was released at 0.49 g d−1. The nitrogen (N) removal efficiencies were 74 and 75% for runs 1 and 2 respectively, while P removal was 91 and 96%. P uptake by denitrifying phosphate accumulating organisms (DPAOs) accounted for 41–52% of the total uptake in the MBR.CONCLUSIONS: This study found that the intermediate clarifier assisted chemical oxygen demand (COD), N, and P removal. With respect to the fate of P, the intermediate clarifier functioned as an extended anaerobic zone when the HRT of the preceding anaerobic zone was insufficient for P release, and as a pre‐anoxic zone when the anaerobic HRT was adequate for P release. Copyright © 2008 Society of Chemical Industry

Effect of biologically mediated pH change on phosphorus removal in BNR system for piggery waste treatment

Since applicable amount of animal waste to farm land has been greatly reduced because of the nutrient overload, nitrogen and phosphorus removal from animal waste has received a great attention. This study was conducted to evaluate how phosphorus was removed during biological nutrient removal (BNR) from piggery waste using laboratory and full scale units operated at 25 to 40°C. The phosphorus removal was performed by chemical precipitation with struvite and hydroxyapatite (HAP), cellular formation, it is basically related with pH and organic and nitrogen loads resulting in influent COD/N ratios. The removal efficiencies increased from 50 to 90% as COD/N ratios increased to 6 to 7, but carbon was not limited beyond this ratio for denitrification resulting in a stable pH. Overall, about 70% of the phosphorus removal was due to the precipitates of struvite and/or HAP, and the remaining removal was due to the cellular P formation. Any significant temperature effect on phosphorus removal was not observed within the operating temperature. In order to maximize phosphorus removal in BNR system, additional anoxic stage must be furnished prior to discharge its final effluent after oxic stage.

Reduction of Nitrous Oxide Formation from a Biological Nutrient Removal System in Wastewater Treatment – Factors of Aeration, External Carbon and pH

Reduction of Nitrous Oxide Formation from a Biological Nutrient Removal System in Wastewater Treatment – Factors of Aeration, External Carbon and pH

Design implications on denitrifying PAO in BNR plant

Denitrifying phosphorus accumulating organism (dPAO) has received a great attention because it could utilize the internally stored cellular carbon both for P uptake and denitrification at the anoxic stage resulting in increased phosphorus and nitrogen removal in BNR (biological nutrient removal) system. However, its unique characteristics have not been well described with the real plants so far. The study results indicated that the overall P removal efficiencies could be improved as much as 25%, but it depends greatly on temperature. The estimated fraction of dPAO in PAO was decreased as the temperature decreased. The greatest drawback of dPAO is the lower P uptake rate at lower temperatures. The maximum advantage of using dPAO can be expected at a system operated at a higher temperature above 15°C.