Nitrifying Biomass Research Articles

Kinetic parameters for 17α-ethinylestradiol removal by nitrifying activated sludge developed in a membrane bioreactor

The synthetic hormone 17α-ethinylestradiol (EE2) is primarily removed in wastewater treatment plants (WWTPs) by sorption, and nitrifying biomass has been shown to be responsible for EE2 biodegradation. Membrane bioreactor (MBR) technology was chosen to develop a community of autotrophic, nitrifying micro-organisms and determine kinetic parameters for EE2 biodegradation. Biological inhibition by azide was applied to differentiate sorption from biodegradation. Activated sludge (AS) was acclimated in the MBR to a substrate specific to autotrophic biomass and resulted in an increase in nitrifying activity. Acclimated AS was used to successfully biodegrade EE2 (11% increase in EE2 removal), and the overall removal of EE2 was determined to be 99% (sorption + biodegradation). AS used directly from a WWTP without acclimation removed EE2 only through sorption (88% removal of EE2). Therefore, higher nitrifying activity developed by acclimating AS allowed almost complete removal of EE2.

Removal of Pharmaceutical and Personal Care Products (PPCPs) under nitrifying and denitrifying conditions

The contribution of volatilization, sorption and transformation to the removal of 16 Pharmaceutical and Personal Care Products (PPCPs) in two lab-scale conventional activated sludge reactors, working under nitrifying (aerobic) and denitrifying (anoxic) conditions for more than 1.5 years, have been assessed. Pseudo-first order biological degradation rate constants ( k biol) were calculated for the selected compounds in both reactors. Faster degradation kinetics were measured in the nitrifying reactor compared to the denitrifying system for the majority of PPCPs. Compounds could be classified according to their k biol into very highly ( k biol > 5 L g SS −1 d −1), highly (1 < k biol < 5 L g SS −1 d −1), moderately (0.5 < k biol < 1 L g SS −1 d −1) and hardly ( k biol < 0.5 L g SS −1 d −1) biodegradable. Results indicated that fluoxetine (FLX), natural estrogens (E1 + E2) and musk fragrances (HHCB, AHTN and ADBI) were transformed to a large extent under aerobic (>75%) and anoxic (>65%) conditions, whereas naproxen (NPX), ethinylestradiol (EE2), roxithromycin (ROX) and erythromycin (ERY) were only significantly transformed in the aerobic reactor (>80%). The anti-depressant citalopram (CTL) was moderately biotransformed under both, aerobic and anoxic conditions (>60% and >40%, respectively). Some compounds, as carbamazepine (CBZ), diazepam (DZP), sulfamethoxazole (SMX) and trimethoprim (TMP), manifested high resistance to biological transformation. Solids Retention Time (SRT aerobic >50 d and <50 d; SRT anoxic >20 d and <20 d) had a slightly positive effect on the removal of FLX, NPX, CTL, EE2 and natural estrogens (increase in removal efficiencies <10%). Removal of diclofenac (DCF) in the aerobic reactor was positively affected by the development of nitrifying biomass and increased from 0% up to 74%. Similarly, efficient anoxic transformation of ibuprofen (75%) was observed after an adaptation period of 340 d. Temperature (16–26 °C) only had a slight effect on the removal of CTL which increased in 4%.

Cometabolic degradation and inhibition kinetics of 1,2‐dichloroethane (1,2‐DCA) in suspended‐growth nitrifying systems

Cometabolic degradation of 1,2‐dichloroethane (1,2‐DCA) and its inhibitory impact on nitrification were investigated by the use of a mixed suspended‐growth culture enriched for nitrifiers. 1,2‐DCA was found to be cometabolically degradable by the nitrifier culture. This degradation rate was found to be dependent on the initial 1,2‐DCA level. The first‐order 1,2‐DCA degradation rate constants ranged between 0.42 and 0.87 L (g VSS)−1 h−1. Increase in NH4‐N utilization favoured cometabolic degradation of 1,2‐DCA. The amount of 1,2‐DCA degraded per unit mass of NH4‐N strongly correlated with initial NH4‐N and 1,2‐DCA concentrations, ranging between 50 mg L−1 and 200 mg L−1 and 1600 µg L− and 100,000 µg L−1, respectively. The presence of 1,2‐DCA caused inhibition of oxygen uptake and NH4‐N utilization. In spite of the adverse effect of 1,2‐DCA on the nitrifying biomass, the system had a high capacity for cometabolic removal of this compound even at inhibitory concentrations. 1,2‐DCA had mainly mixed inhibitor characteristics, but at low concentrations (<25,000 µg/L) it acted rather as a competitive inhibitor. The inhibition constants belonging to 1,2‐DCA, K ic (the dissociation constant of the enzyme–inhibitory compound complex) and K iu (the dissociation constant of the enzyme–substrate–inhibitory compound complex) were determined to be 6000–8000 µg L−1 and 188,000–200,000 µg L−1, respectively.

Quantitative and qualitative effects of bioaugmentation on ammonia oxidisers at a two-step WWTP

Large waste water treatment plants (WWTP) often operate nitrification in two different process environments: the cold-dilute sewage is treated in the mainstream nitrification/denitrification system, while the high strength ammonia liquors from sludge dewatering are treated in a separate high temperature reactor (SBR). This study investigates transfer from nitrifier biomass into a two-stage WWTP, commonly referred to as bioaugmentation. Besides the quantitation of ammonia oxidising bacteria (AOB), community differences were analysed with two techniques, denaturing gradient gel electrophoresis and real-time PCR melt curve analysis. It was shown that, without bioaugmentation, two distinct AOB communities establish in the mainstream and in the SBR, respectively. A gradual shift of the two AOB communities with increasing pump rates between the systems could be demonstrated. These molecular findings support process engineering experience, that cycling of waste activated sludge improves the ability of AOB to adapt to different process environments.

Biodegradation of the endogenous residue of activated sludge

This study evaluated the potential biodegradability of the endogenous residue in activated sludge subjected to batch digestion under either non-aerated or alternating aerated and non-aerated conditions. Mixed liquor for the tests was generated in a 200 L pilot-scale aerobic membrane bioreactor (MBR) operated at a 5.2 days SRT. The MBR system was fed a soluble and completely biodegradable synthetic influent composed of sodium acetate as the sole carbon source. This influent, which contained no influent unbiodegradable organic or inorganic materials, allowed to generate sludge composed of essentially two fractions: a heterotrophic biomass X H and an endogenous residue X E, the nitrifying biomass being negligible (less than 2%). The endogenous decay rate and the active biomass fraction of the MBR sludge were determined in 21-day aerobic digestion batch tests by monitoring the VSS and OUR responses. Fractions of X H and X E: 68% and 32% were obtained, respectively, at a 5.2 days SRT. To assess the biodegradability of X E, two batch digestion units operated at 35 °C were run for 90 days using thickened sludge from the MBR system. In the first unit, anaerobic conditions were maintained while in the second unit, alternating aerated and non-aerated conditions were applied. Data for both units showed apparent partial biodegradation of the endogenous residue. Modeling the batch tests indicated endogenous residue decay rates of 0.005 d −1 and 0.012 d −1 for the anaerobic unit and the alternating aerated and non-aerated conditions, respectively.

Comparison of five organic wastes regarding their behaviour during composting: Part 2, nitrogen dynamic

This paper aimed to compare household waste, separated pig solids, food waste, pig slaughterhouse sludge and green algae regarding processes ruling nitrogen dynamic during composting. For each waste, three composting simulations were performed in parallel in three similar reactors (300 L), each one under a constant aeration rate. The aeration flows applied were comprised between 100 and 1100 L/h. The initial waste and the compost were characterized through the measurements of their contents in dry matter, total carbon, Kjeldahl and total ammoniacal nitrogen, nitrite and nitrate. Kjeldahl and total ammoniacal nitrogen and nitrite and nitrate were measured in leachates and in condensates too. Ammonia and nitrous oxide emissions were monitored in continue. The cumulated emissions in ammonia and in nitrous oxide were given for each waste and at each aeration rate. The paper focused on process of ammonification and on transformations and transfer of total ammoniacal nitrogen. The parameters of nitrous oxide emissions were not investigated. The removal rate of total Kjeldahl nitrogen was shown being closely tied to the ammonification rate. Ammonification was modelled thanks to the calculation of the ratio of biodegradable carbon to organic nitrogen content of the biodegradable fraction. The wastes were shown to differ significantly regarding their ammonification ability. Nitrogen balances were calculated by subtracting nitrogen losses from nitrogen removed from material. Defaults in nitrogen balances were assumed to correspond to conversion of nitrate even nitrite into molecular nitrogen and then to the previous conversion by nitrification of total ammoniacal nitrogen. The pool of total ammoniacal nitrogen, i.e. total ammoniacal nitrogen initially contained in waste plus total ammoniacal nitrogen released by ammonification, was calculated for each experiment. Then, this pool was used as the referring amount in the calculation of the rates of accumulation, stripping and nitrification of total ammoniacal nitrogen. Separated pig solids were characterised by a high ability to accumulate total ammoniacal nitrogen. Whatever the waste, the striping rate depended mostly on the aeration rate and on the pool concentration in biofilm. The nitrification rate was observed as all the higher as the concentration in total ammoniacal nitrogen in the initial waste was low. Thus, household waste and green algae exhibited the highest nitrification rates. This result could mean that in case of low concentrations in total ammoniacal nitrogen, a nitrifying biomass was already developed and that this biomass consumed it. In contrast, in case of high concentrations, this could traduce some difficulties for nitrifying microorganisms to develop.

Population dynamics of nitrite oxidizers in nitrifying granules

The competition between Nitrospira and Nitrobacter species was analyzed in this work under conditions of excess of nitrite. A population of nitrite oxidizing bacteria (NOB) was developed from nitrifying biomass grown as granules with a mean diameter of 0.8 mm, whose feed was switched from ammonium to nitrite. The initial population distribution of the granules was: 60% Nitrosomonas and 30% Nitrospira and it evolved to 45% Nitrobacter and 40% Nitrospira measured 177 days after the change in the feeding. The disappearance of Nitrosomonas allowed the development of an important population of Nitrobacter demonstrating that these organisms, characterized by being r strategists NOB, are poor competitors when oxygen is the limiting substrate. Interestingly, the physical structure of the granules was not altered by the change of its microbial composition during the 220 days of operation.

Surplus activated sludge dewatering in pilot-scale sludge drying reed beds

A pilot-scale experiment on dewatering of surplus activated sludge (SAS) is presented, where two pilot-scale vertical flow, sludge drying reed beds (SDRBs), planted with Phragmites australis are used. The bottom of the beds is filled with cobbles, connected to the atmosphere through perforated PVC ventilation tubes, in order to achieve oxygen diffusion through the overlying porous medium that is colonized by roots and an abundant nitrifying biomass. Two layers of gravel, of decreasing size from bottom to top, make the drainage layer where the reeds are planted. The two beds were fed according to the following cycle: one week feeding with SAS at rates one 30 kg/m 2/year and the other 75 kg/m 2/year, and resting for three weeks. The results show that planted SDRBs can effectively dewater SAS from domestic sewage, the produced residual sludge presents a high dry weight content, the degree of volume reduction depends upon the initial SAS concentration and can be of the order of 90%, and decomposition of organic matter and high levels of mineralization can be achieved. Furthermore, the percolating water is not septic. The fertilizer value of the treated SAS, which contains no added chemicals, is comparable to that of SAS treated by other methods.

Modelling respirometric tests for the assessment of kinetic and stoichiometric parameters on MBBR biofilm for municipal wastewater treatment

Moving Bed Biofilm Reactor (MBBR) technology is a suitable option for up-grading and retro-fitting wastewater treatment plants. Although being introduced in late 80s, design and operational guidelines of MBBR are mainly based on empirical approaches. This work was aimed to assess the biokinetics on both detached and undisturbed biofilm samples from a large pilot-scale MBBR treating pre-settled municipal wastewater. Experimental OUR profiles of heterotrophic biomass in detached and undisturbed biofilm have been obtained with respirometric tests and then modelled with an extended version of ASM3 which assumes biomass growth to take place on both readily biodegradable substrate and storage products. Results indicated the storage mechanism to be prevalent for heterotrophic biomass growth, with a 80% fraction of soluble substrate converted into storage products. The active heterotrophic biomass in the film was estimated in detached biofilm samples; on average, it corresponded to a 39% fraction of particulate COD. Tests on undisturbed biofilm were carried out to quantify autotrophic ammonia and nitrite removal, showing an effective specialisation of the nitrifying biomass. The parameters obtained could support a more rational design approach for the moving-bed biofilm process.

Nitrifying biocathode enables effective electricity generation and sustainable wastewater treatment with microbial fuel cell

Simultaneous organics removal and nitrification using a novel nitrifying biocathode microbial fuel cell (MFC) reactor were investigated in this study. Remarkably, the introduction of nitrifying biomass into the cathode chamber caused higher voltage outputs than that of MFC operated with the abiotic cathode. Results showed the maximum power density increased 18% when cathode was run under the biotic condition and fed by nitrifying medium with alkalinity/NH4+-N ratio of 8 (26 against 22 mW/m2). The voltage output was not differentiated when NH4+-N concentration was increased from 50 to 100 mg/L under such alkalinity/NH4+-N ratio. However, interestingly, the cell voltage rose significantly when the alkalinity/NH4+-N ratio was decreased to 6. Consequently, the maximum power density increased 68% in compared with the abiotic cathode MFC (37 against 22 mW/m2). Polarization curves demonstrated that both activation and concentration losses were lowered during the period of nitrifying biocathode operation. Ammonium was totally nitrified and mostly converted to nitrate in all cases of the biotic cathode conditions. High COD removal efficiency (98%) was achieved. In light of the results presented here, the application of nitrifying biocathode is not only able to integrate the nitrogen and carbon removal but also to enhance the power generation in MFC system. Our system can be suggested to open up a new feasible way for upgrading and retrofitting the existing wastewater treatment plant by the use of MFC-based technologies.

Expert control for a stable operation of a partial nitrification system to treat highly concentrated ammonium wastewater

This work presents the application of expert control strategies for a successful and stable operation of partial nitrification. A high-strength ammonium wastewater was treated in a continuous pilot plant with a configuration of three reactors in series plus a settler. The system was operated at mild temperature (around 25 degrees C) and at high sludge retention time to obtain a significant nitrifying biomass concentration. The implemented control system with expert supervisory rules provided a stable and robust operation of the partial nitrification system even when the pilot plant was subjected to several disturbances as change in influent concentration, failure of aeration in one reactor and operation with variable biomass concentration. The control system was based on local feedback control loops for dissolved oxygen and pH with proper setpoints for nitrite oxidizing bacteria (NOB) inhibition and an inflow control loop based on Oxygen Uptake Rate (OUR) measurements, which allowed working at the current maximum ammonium oxidation capacity. Two additional expert rules were implemented for automatically determine the required OUR setpoint in accordance with the biomass activity and to produce a fast load decrease when a system overload was detected.

Total and stable washout of nitrite oxidizing bacteria from a nitrifying continuous activated sludge system using automatic control based on Oxygen Uptake Rate measurements

Partial nitrification (ammonium oxidation to nitrite) has gained a lot of interest among researchers in the last years because of its advantages with respect to complete nitrification (ammonium oxidation to nitrate): decrease of oxygen requirements for nitrification, reduction of COD demand and CO 2 emissions during denitrification and higher denitrification rate and lower biomass production during anoxic growth. In this study, an extremely high-strength ammonium wastewater (3000–4000 mg N L −1) was treated in a continuous pilot plant with a configuration of three reactors in series plus a settler. The system was operated under the maximum possible volumetric nitrogen loading rate, at mild temperature (around 25 °C), with high sludge retention time (around 30 d) and significant nitrifying biomass concentration (average of 1800 ± 600 mg VSS L −1). The implemented control loops transformed the system, which was operating with complete nitrification, into a continuous partial nitrification system. Nitrite oxidizing bacteria (NOB) washout was accomplished with local control loops for pH and dissolved oxygen (DO) with proper setpoints for NOB inhibition (pH = 8.3 and DO = 1.2–1.9 mg O 2 L −1) and with an inflow control loop based on Oxygen Uptake Rate (OUR) measurements, which allowed working at the maximum ammonium oxidation capacity of the pilot plant in each moment. This operational strategy maximized the difference between ammonia oxidizing bacteria (AOB) and NOB growth rates, which is the key point to achieve a fast and stable NOB washout. The results showed a stable operation of the partial nitrification system during more than 100 days and NOB washout was corroborated with fluorescence in-situ hybridization (FISH) analysis.

Characteristics of nitrifying granules developed in an air pulsing SBR

Nitrifying bacteria are characterized by low biomass yields and slow activity rates, the enhancement of nitrifying biomass retention by promoting the formation of granules would allow improving nitrification process. The use of a pulsing sequencing batch reactor (SBR) was tested to produce nitrifying granules minimizing the air consumption. After 400 days of operation, 1.07 g VSS/L of granular biomass with a mean diameter of 0.9 mm was accumulated in the system. The maximal nitrate production rate reached a value of 0.3 kg N/(m 3 d). Sporadic nitrite accumulations were registered and attributed to oxygen diffusion limitations which were solved improving the granule-liquid mass transfer with a liquid recirculation system. FISH technique was used in order to identify the main populations in the nitrifying granules; Nitrosomonas spp. and Nitrospira spp. were identified as the main ammonia and nitrite oxidizing population, respectively. With the introduction of liquid recirculation in the reactor the ammonia oxidation efficiencies improved and the proportion of Nitrospira spp. increased from 1% to 15%.

Use of a mathematical optimisation procedure for model calibration and enhancement of nitrogen removal in high-load systems

A mathematical optimisation method utilising the BLIND algorithm was used for model calibration and subsequent simulations on an ASM No.1. based platform. The calibration of model parameters was fulfilled with the use of operational data of a large wastewater treatment plant (of 80000 m3·d-1 capacity) owing a high-load activated sludge stage (sludge age of 1.8-2.5 d) with a subsequent nutrient removal biofiltration system. The calibrated model was applied for the optimisation of the multi-point addition of nitrifying biomass (i.e. step-seeding) and air supply in the high load system that has a bioreactor with plug flow characteristics. Results of model simulation showed, that with addition of nitrifyers in three points may enhance nitrification by about 9% comparing to the single point addition at the head of the reactor. Nitrogen removal can be further increased by about 8% with optimising air supply along the reactor length. Results showed, that the step-seeding concept may convey a potential in nitrogen removal enhancement in combined systems with separate nitrification/denitrification units, since optimised addition of the biomass can be easily performed.

In situ characterization of nitrifying biofilm: Minimizing biomass loss and preserving perspective

Methods for characterizing nitrifying bacteria within biofilms are of key importance to understand and optimize the nitrification kinetics of attached growth treatment facilities. In this work, we propose an analytical protocol based upon environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy (CSLM) in combination with fluorescent in situ hybridization (FISH) to characterize the structure of nitrifying biofilm as it remains attached to the original reactor substratum. This protocol minimizes the loss of mass and distortion of in situ perspective commonly associated with traditionally applied microscopic techniques and thereby enables a more accurate estimation of the nitrifying biomass within biofilm attached to the substratum. The use of ESEM eliminates the destructive preparatory procedures associated with traditional scanning electron microscopy and thus the loss of mass and shrinking of the samples. ESEM is used in this study to evaluate the percent coverage of the substratum with biofilm and the biofilm thickness. CLSM–FISH is used to determine cell counts in the biofilm and to characterize the undisturbed substratum/biofilm interface. By hybridizing and analyzing the nitrifying biofilm using CLSM as it remains attached to the substratum, the loss of material and distortion of in situ perspective associated with the biofilm detachment process is minimized. Moreover, by conducting the CLSM analysis directly on the nitrifying biofilm as it remains attached to the substratum it is shown that cell counts at the substratum/biofilm interface differ significantly from that located above the interface.

Start-up of a pilot-scale membrane bioreactor to treat municipal wastewater

The start-up of a pilot-scale membrane bioreactor equipped with submerged ultrafiltration membranes to treat municipal wastewater has been studied. Attention has been paid to determine membrane separation effects on biomass development in a reactor operated without inoculation. Moreover, the activated sludge model no. 1 has been applied to model biological removal processes. Filtration alone (without biodegradation) removed more than 70% of the influent total COD due to the high particulate COD fraction typically present in municipal wastewaters. Filtration action, retaining bacteria, allowed a rapid increase of the heterotrophic activity permitting to reach efficiencies in COD removal greater than 90% in one to two days. On the other hand, nitrogen removal process needs a few days (five to twenty depending on operational conditions) to develop and stabilise in the reactors because of the required development of the nitrifying biomass. Biomass development was confirmed using respirometric techniques. The activated sludge model no. 1 with minor modification was capable of simulating reasonably well the biological processes development in the MBR.

Effects of some herbicides on the microbiological characteristics of soil nitrogen cycle under maize plantation

Nitrogen is a key element for the living organisms and influence not only for the quantity but for the quality of the yield, considerable. Availability of nitrogen from the soil is influenced by several microbiological processes of the Nitrogen-cycle. Among the intensive agricultural production the herbicide application cannot be omitted more information needs therefore about the inhibitor effect of herbicides on the different microorganisms.An experiment was set up on calcareous chernozem soil under maize culture. Effect of four different herbicides (Acenit, Frontier, Merlin, and Wing) was investigated. The effect of herbicides was measured to four microbiological parameters of the Nitrogencycle (abundance of nitrifying bacteria, nitrate solubilisation, biomass nitrogen and urease enzyme activity). There were singledouble- and five times of recommended doses of herbicides applied for two onsecutive vegetation periods.From the results of the different doses of herbicides, the following can be stated:– The Acenit has a stimulating effect on nitrifying bacteria in general. The Frontier and Merlin also influenced the quantity of nitrifyers, however in certain cases decreased in another cases increased the number of bacteria.– The double doses and five times doses of herbicides was found to be increasing the nitrate content of soil, -especially in 2006.– The quantity of microbial biomass nitrogen increased in the 60% of treatments and decreased in the 40% of the treatments.– Except of the result of Wing in 2006 and Merlin in 2005, the effect of simple dose herbicides was the smallest on the urease enzyme activity. According to the results the effect of Merlin was positive; the effect of Wing was negative on the soil enzyme’s activity.Regarding the application of four different herbicides in three different doses on the microbiological parameters of soil (at two consecutive years-) in 39% of the treatments has resulted a significant inhibitory effect, 28% of the treatments, however have significant stimulating effect on the parameters measured. More than 50% of the inhibitory effect was measured in case of the Wing, at more than 50% of the Frontier the microbiological parameters have not changed.

The effect of hydroxylamine on the activity and aggregate structure of autotrophic nitrifying bioreactor cultures

Addition of hydroxylamine (NH2OH) to autotrophic biomass in nitrifying bioreactors affected the activity, physical structure, and microbial ecology of nitrifying aggregates. When NH2OH is added to nitrifying cultures in 6-h batch experiments, the initial NH3-N uptake rates were physiologically accelerated by a factor of 1.4-13. NH2OH addition caused a 20-40% decrease in the median aggregate size, broadened the shape of the aggregate size distribution by up to 230%, and caused some of the microcolonies to appear slightly more dispersed. Longer term NH2OH addition in fed batch bioreactors decreased the median aggregate size, broadened the aggregate size distribution, and decreased NH3-N removal from >90% to values ranging between 75% and 17%. This altered performance is explained by quantitative fluorescence in situ hybridization (FISH) results that show inhibition of nitrifying populations, and by qPCR results showing that the copy numbers of amoA and nxrA genes gradually decreased by up to an order-of-magnitude. Longer term NH2OH addition damaged the active biomass. This research clarifies the effect of NH2OH on nitrification and demonstrates the need to incorporate NH2OH-related dynamics of the nitrifying biomass into mathematical models, accounting for both ecophysiological and structural responses.

The role of tannins in conventional and membrane treatment of tannery wastewater

The role that tannins play in tannery wastewater treatment has been evaluated employing a pilot Membrane Bioreactor (MBR) plant and a full scale Conventional Activated Sludge Process (CASP) plant conducted in parallel. The proposed methodology has established the preliminary use of respirometry to examine the biodegradability of a selection of commercial products (synthetic and natural tannins); the subsequent analysis, by means of spectrophotometric reading and RP-IPC (Reverse-Phase Ion-Pair) liquid chromatography, estimates the concentrations of natural tannins and naphthalenesulfonic tanning agents in the influent and effluent samples. The results show that a consistent percentage of the Total Organic Carbon (TOC) in the effluent of the biological phase of the plants is attributable to the presence of natural and synthetic (Sulfonated Naphthalene-Formaldehyde Condensates, SNFC) tannins (17% and 14% respectively). The titrimetric tests that were aimed at evaluating the levels of inhibition on the nitrifying biomass samples did not allow a direct inhibiting effect to be associated with the concentration levels of the tannin in the effluent. Nonetheless, the reduced specific growth rates of ammonium and nitrite oxidising bacteria imply that a strong environmental pressure is present, if not necessarily due to the concentration of tannins, due to the wastewater as a whole. The differences that have emerged by comparing the two technologies (CASP and MBR), in regards to the role that tannins play in terms of biodegradability, did not appear to be significant.

Automatic set-point titration for monitoring nitrification in SBRs

Nitrification is usually the bottleneck of biological nitrogen removal processes. In SBRs systems, it is not often enough to monitor dissolved oxygen, pH and ORP to spot problems which may occur in nitrification processes. Therefore, automated supervision systems should be designed to include the possibility of monitoring the activity of nitrifying populations. Though the applicability of set-point titration for monitoring biological processes has been widely demonstrated in the literature, the possibility of an automated procedure is still at its early stage of industrial development. In this work, the use of an at-line automated titrator named TITAAN (TITrimetric Automated ANalyser) is presented. The completely automated sensor enables us to track nitrification rate trend with time in an SBR, detecting the causes leading to slower specific nitrification rates. It was also possible to perform early detection of toxic compounds in the influent by assessing their effect on the nitrifying biomass. Nitrifications rates were determined with average errors+/-10% (on 26 tests), never exceeding 20% as compared with UV-spectrophotometric determinations.