Integrated side-stream reactor for biological nutrient removal and minimization of sludge production.

Integrated processes to reduce in situ the sludge production in wastewater treatment plants are gaining attention in order to facilitate excess sludge management. In contrast to post-treatments, such as anaerobic digestion which is placed between the activated sludge system and dewatering processes, integrated technologies are placed in the sludge return line. This study evaluates the application of an anoxic side-stream reactor (SSR) which creates a physiological shock and uncouples the biomass metabolism and diverts the activity from assimilation for biosynthesis to non-growth activities. The effect of this system in biological nutrient removal for both nitrogen and phosphorus was evaluated for the anaerobic, anoxic and aerobic reactors. The RedOx potential within the SSR was maintained at -150 mV while the sludge loading rate was modified by increasing the percentage of recycled activated sludge feed to the SSR (0 and 40% at laboratory scale and 0, 10, 50 and 100% at pilot scale). The use of the SSR presented a slight reduction of phosphorus removal but maintained the effluent quality to the required discharge values. Nitrogen removal efficiency increased from 75 to 86% while reducing the sludge production rate by 18.3%.

Grey water treatment at a sports centre for reuse in irrigation: a case study.

Grey water has long been considered a promising option for dealing with water scarcity and reuse. However, factors such as lack of macronutrients and low carbon content make its treatment challenging. The aim of this paper was to investigate the applicability of sequencing batch reactor (SBR) technology to on-site grey water treatment at a sports centre for reuse in irrigation. The results demonstrated that the regenerated water complied with microbiological parameters concerning restriction of solids and organic matter removal. Denitrification was not fully accomplished, but ammonium was totally oxidised and low concentrations of nitrates were achieved. Effluent with good appearance and no odour was used in an experimental study to irrigate a grid system containing natural and artificial grass sections. The conclusion is that SBR technology offers a promising treatment for grey water.

Simultaneous domestic wastewater treatment and renewable energy production using microbial fuel cells (MFCs).

Microbial fuel cells (MFCS) can be used in wastewater treatment and to simultaneously produce electricity (renewable energy). MFC technology has already been applied successfully in lab-scale studies to treat domestic wastewater, focussing on organic matter removal and energy production. However, domestic wastewater also contains nitrogen that needs to be treated before being discharged. The goal of this paper is to assess simultaneous domestic wastewater treatment and energy production using an air-cathode MFC, paying special attention to nitrogen compound transformations. An air-cathode MFC was designed and run treating 1.39 L d(-1) of wastewater with an organic load rate of 7.2 kg COD m(-3) d(-1) (80% removal efficiency) and producing 1.42 W m(-3). In terms of nitrogen transformations, the study demonstrates that two different processes took place in the MFC: physical-chemical and biological. Nitrogen loss was observed increasing in line with the power produced. A low level of oxygen was present in the anodic compartment, and ammonium was oxidised to nitrite and nitrate.

Combining partial nitritation and heterotrophic denitritation for the treatment of landfill leachate previous to an anammox reactor.

Landfill leachate can present extremely elevated concentrations of ammonium (up to 6,000 mg N-NH(4) (+) L(-1)) and a low biodegradable organic matter fraction. As an alternative to conventional systems, this wastewater can be treated on a more sustainable way by a fully autotrophic partial nitritation-anammox system. The operation of the first step of this system, the partial nitritation, is critical since the elevated concentrations of ammonium and nitrite in the reactor can severely inhibit ammonium oxidizing bacteria (AOB) activity. In this way, the inclusion of anoxic phases during the feeding events to promote the denitrification via nitrite can be a good option for upgrading the process performance and increasing the stability of the system. This paper deals with the evaluation of an anoxic-aerobic step-feed strategy for the operation of a partial nitritation SBR. Results of this study have revealed a decrease on the total nitrogen inside the reactor of more than 200 mg N L(-1) without prejudice on the partial nitritation process. Furthermore, this study has also allowed detecting an AOB activity reduction at the end of aerobic phases due to bicarbonate limitation and/or free nitrous acid inhibition.

Systematic model development for partial nitrification of landfill leachate in a SBR.

This study deals with partial nitrification in a sequencing batch reactor (PN-SBR) treating raw urban landfill leachate. In order to enhance process insight (e.g. quantify interactions between aeration, CO(2) stripping, alkalinity, pH, nitrification kinetics), a mathematical model has been set up. Following a systematic procedure, the model was successfully constructed, calibrated and validated using data from short-term (one cycle) operation of the PN-SBR. The evaluation of the model revealed a good fit to the main physical-chemical measurements (ammonium, nitrite, nitrate and inorganic carbon), confirmed by statistical tests. Good model fits were also obtained for pH, despite a slight bias in pH prediction, probably caused by the high salinity of the leachate. Future work will be addressed to the model-based evaluation of the interaction of different factors (aeration, stripping, pH, inhibitions, among others) and their impact on the process performance.

The effect of urban landfill leachate characteristics on the coexistence of anammox bacteria and heterotrophic denitrifiers.

Heterotrophic denitrification coexists with the anammox process contributing to N removal owing to the biodegradable organic matter supply from urban landfill leachate and the decay of microorganisms. Both biomasses consumed nitrite increasing the nitrite requirements of the system. The aim of this paper is the study of the causes which induce the system to decrease nitrogen removal efficiency. In this study, urban landfill leachate has been treated in an anammox Sequencing Batch Reactor (SBR) for 360 days. The anammox reactor treated on average 0.24 kgN m(-3) d(-1) obtaining nitrogen removal efficiencies up to 89%. The results demonstrated that i) a suitable influent nitrite to ammonium molar ratio is a crucial factor to avoid troubles in the anammox reactor performance; ii) an excess of nitrite implied nitrite accumulation in the reactor; iii) a lower nitrite supply than the necessary for the system could force a loss of specific anammox activity due to nitrite competition with denitrifiers. These results pointed out the importance of the previous partial-nitritation process control in order to obtain a correct influent nitrite to ammonium molar ratio for the anammox reactor. In addition, sudden variation of the leachate characteristics must be avoided.

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.

Data evaluation of full-scale wastewater treatment plants by mass balance.

Measured data of wastewater treatment plants (WWTPs) often contains errors. These errors can prohibit the use of WWTP data for process evaluation, process design, benchmarking or modelling purposes. In this paper a practical stepwise methodology is presented to check WWTP data using mass balances. The presented results show that poor WWTP data quality leads to large errors when calculating key operational conditions such as the solids retention time (SRT), oxygen consumption (OC) and the different internal conversions rates. By improving WWTP data quality using mass balance calculations useful new information becomes available for process evaluation, WWTPs design and benchmarking.

Selection between alcohols and volatile fatty acids as external carbon sources for EBPR.

The purpose of this paper is to provide a basis for selecting alcohols (i.e. ethanol and methanol) or short-chain volatile fatty acids (VFAs) (i.e. acetate and propionate) as the external carbon sources for enhanced biological phosphorus removal (EBPR) from wastewaters in adapted or unadapted activated sludge. When ethanol is used in an unacclimated process, a period of adaptation is required by polyphosphate-accumulating organisms (PAOs). From 0 to 140 days of ethanol acclimatizing, the P release and uptake rates increased to 6.2 and 7.0 mgP-PO(3)4(-)g(-1)VSSh(-1), respectively. PAOs in ethanol-enriched sludge produced poly-beta-hydroxyvalerate (PHV) (81.9%) as the main polyhydroxyalkanoate (PHA) and reached an effluent phosphate concentration close to zero (0.10 mgP-PO(3)4(-)L(-1)). On the other hand, methanol was not used by PAOs in 30-day ethanol-acclimated sludge in short-term tests. If EBPR needs to be incidentally supported by substrate addition, VFAs are preferred; for long-term addition also ethanol can be considered.

Heterotrophic denitrification on granular anammox SBR treating urban landfill leachate.

The anammox process was applied to treat urban landfill leachate coming from a previous partial nitritation process. In presence of organic matter, the anammox process could coexist with heterotrophic denitrification. The goal of this study was to asses the stability of the anammox process with simultaneous heterotrophic denitrification treating urban landfill leachate. The results achieved demonstrated that the anammox process was not inactivated by heterotrophic denitrification. Moreover, part of the nitrate produced by anammox bacteria and part of the influent nitrite were removed by heterotrophic denitrifiers with associated biodegradable organic matter consumption. In this sense, the contribution on nitrogen removal of each process was calculated using a nitrogen mass balance methodology. An 85.1+/-5.6% of the nitrogen consumption was achieved via anammox process while the average heterotrophic denitrifiers contribution was 14.9+/-5.6%. Heterotrophic denitrification was limited by the available easily biodegradable organic matter.

Partial ammonium oxidation to nitrite of high ammonium content urban landfill leachates.

In an effort to treat N-rich streams in a more sustainable way, recent years have seen the development of new technologies, most of which are based on autotrophic denitrification via nitrite (anammox). In order to attain a suitable influent for that process, the wastewater must be treated by partially oxidising the ammonium to nitrite. In that aspect, this article presents the start-up and operation of a Partial Nitritation Sequencing Batch Reactor (PN-SBR) treating urban landfill leachates. Stable partial nitritation has been reached treating high ammonium loads (1-1.5 kg Nm(-3)d(-1)), demonstrating the feasibility of this technology as a previous step of anammox process. This study has also given away the importance of pH influence over ammonium oxidising bacteria (AOB) activity, thus it has been possible to determine the values of the half inhibition constants for free ammonia (k(I,FA)=605.48+/-87.18 mg N-NH L(-1)) and free nitrous acid (k(I,FNA)=0.49+/-0.09 mg N-HNO2 L(-1)), as well as the half-saturation constant for bicarbonate (k(HCO3-) = 0.01 +/- 0.16 mg CL(-1)).

Biological nutrient removal by applying SBR technology in small wastewater treatment plants: carbon source and C/N/P ratio effects.

SBR technology is considered an alternative to conventional processes such as Phoredox, Five-stage Bardenpho, among the others for treating nutrients in wastewaters. It is especially applicable to small communities of a just few people to a population equivalent (p.e) up to 4000. In this paper, biological nutrient removal using SBR technology in a single reactor is presented. Biological nutrient removal requires a sequence of anaerobic-anoxic-aerobic phases with multiple feeding events over one cycle. This filling strategy was adapted to enhance denitrification and phosphate release, using the easily biodegradable organic matter from the wastewater. In spite of using this feeding strategy, the organic matter concentration can be insufficient. The results show that biological nutrient removal was successfully achieved by using only one reactor, working with a low organic matter concentration in the influent (C/N/P ratio of 100:12:1.8). Nevertheless, when the C/P ratio was lower than 36 g COD x g(-1) P-P04, an accumulation of phosphate was observed. After that, the system responded quickly and returned to ideal conditions (C/P ratio of 67 g COD x g(-1) P-PO4), taking only 15 days to achieve the complete nutrient removal. Furthermore, the operational conditions and the synthetic wastewater used conferred a selective advantage to polyphosphate accumulating organisms (PAOs) over glycogen accumulating non-poly-P organisms (GAOs) as shown by the FISH analysis performed.

A model for the simulation of the SHARON process: pH as a key factor.

The SHARON process allows partial nitrification of wastewaters with high ammonium content and, when coupled with the Anammox process, represents a more sustainable alternative for N-removal than a conventional nitrification-denitrification. In this work, a mathematical model describing a continuously aerated SHARON reactor is presented. Special attention was given to the pH, because it affects substrates availability and inhibition phenomena, implementing an algorithm for its calculation. Since ammonium-oxidizing and nitrite-oxidizing organisms are inhibited by their own substrates, ammonia and nitrous acid respectively, Haldane kinetics was used in both nitrification steps. A preliminary evaluation of the model using historical experimental data generated in a lab-scale SHARON reactor, fed with synthetic substrate, is also presented, corroborating that the quality of the obtained effluent is highly dependent on pH.

Model-based evaluation of an on-line control strategy for SBRs based on OUR and ORP measurements.

Application of control strategies for existing wastewater treatment technologies becomes necessary to meet ever-stricter effluent legislations and reduce the associated treatment costs. In the case of SBR technology, controlling the phase scheduling is one of the key aspects of SBR operation. In this study a calibrated mechanistic model based on the ASM1 was used to evaluate an on-line control strategy for the SBR phase-scheduling and compare it with the SBR's performance using no control strategy. To evaluate the performance, reference indices relating to the effluent quality, the required energy for aeration and the treated wastewater volume were used. The results showed that it is possible to maintain optimal SBR performance in the studied system at minimal costs by on-line control of the length of the aerobic and anoxic phases.

An on-line optimisation of a SBR cycle for carbon and nitrogen removal based on on-line pH and Our: the role of dissolved oxygen control.

A pilot plant sequencing batch reactor (SBR) was applied in a wastewater treatment plant treating urban wastewater focused on carbon and nitrogen removal. From an initial predefined step-feed cycle definition, the evolution of the on-line monitored pH and calculated oxygen uptake rate (OUR) were analysed in terms of knowledge extraction. First, the aerobic phases of the SBR cycle were operated using an On/Off dissolved oxygen (DO) control strategy that concluded with a sinusoidal pH profile that made detecting the "ammonia valley" difficult. After changing to fuzzy logic control of the dissolved oxygen and by adding an air flow meter to the pilot plant, the pH evolution and on-line calculated OUR showed a clearer trend during the aerobic phases. Finally, a proposed algorithm for adjusting the aerobic phases of the SBR for carbon and ammonia removal is presented and discussed.

Energy saving in a wastewater treatment process: an application of fuzzy logic control.

Many uncertain factors affect the operation of Wastewater Treatment Plants. Due to the complexity of biological wastewater treatment processes, classical methods show significant difficulties when trying to control them automatically. Consequently soft computing techniques and, specifically, fuzzy logic appears to be a good candidate for controlling these ill-defined, time-varying and non-linear systems. This paper describes the development and implementation of a Fuzzy Logic Controller to regulate the aeration in the Taradell Wastewater Treatment Plant. The main goal of this control process is to save energy without decreasing the quality of the effluent discharged. The fuzzy controller integrates the information coming from two different signals: the Dissolved Oxygen and Oxidation-Reduction Potential values. The simulation results proved that fuzzy logic is a good tool for controlling the aeration of the wastewater treatment plant. The results obtained show that energy savings of more than 10% can be achieved using aeration fuzzy control and at the same time still keeping the good removal levels.

Microbial electrosynthesis of butyrate from carbon dioxide.

This work proves for the first time the bioelectrochemical production of butyrate from CO2 as a sole carbon source. The highest concentration of butyrate achieved was 20.2 mMC, with a maximum butyrate production rate of 1.82 mMC d(-1). The electrochemical characterisation demonstrated that the CO2 reduction to butyrate was hydrogen driven. Production of ethanol and butanol was also observed opening up the potential for biofuel production.

Enhancing biological nitrogen removal in a small wastewater treatment plant by regulating the air supply.

Most of the small wastewater treatment plants in Catalonia were not designed to remove nutrients. However, the large safety margins built into their original engineering design has meant that, in many cases, it has been possible to remove part of the nitrogen without being controlled. This paper focuses on the practical experience carried out in one of these facilities, the Bisbal wastewater treatment plant, aimed at enhancing the biological nitrogen removal using simple, low-cost, easy-to-operate measurement and control. The control strategy, which is based on air supply regulation, was previously designed using simulation studies. A dissolved oxygen monitoring system was installed into the facility, while nitrogen concentrations were analysed every day. Optimal dissolved oxygen profiles in the oxidation ditch were identified, while the air supply strategy was modified according to the variations in the influent.

Wastewater nitrogen removal in Sbrs, applying a step-feed strategy: from lab-scale to pilot-plant operation.

One of the problems of nitrogen removal from wastewater when applying sequencing batch reactor (SBR) technology, is the specific use of organic matter for denitrification purposes. Since easily biodegradable organic matter is rapidly consumed under aerobic or anoxic conditions (i.e. aerobic oxidation or anoxic denitrification, respectively), it is an important factor to consider when scaling up SBRs from the laboratory to real plant operation. In this paper, we present the results obtained in relation to scaling up reactors from lab-scale to pilot-plant scale, treating real wastewater from two different locations: the laboratory and in situ, respectively. In order to make using easily biodegradable organic matter more efficient, the filling phases of SBR cycles were adjusted according to a step-feed strategy composed of 6 anoxic-aerobic events. Feeding only occurred during anoxic phases. The results obtained demonstrated that the methodology may be useful in treating real wastewater with high carbon and nitrogen variations, as it always kept effluent levels lower than the official standards require (effluent total COD lower than 125 mg COD/L and effluent Total Nitrogen lower than 15 mg N/L).

A hybrid supervisory system to support WWTP operation: implementation and validation.

Integrated operation of Wastewater Treatment Plants is still far from being solved. A reasonable proposal should link advanced and robust control algorithms to some knowledge-based techniques, allocating the detailed engineering to numerical computations, while delegating the logical analysis and reasoning to supervisory intelligent systems. This paper describes the development and implementation of a knowledge-based Hybrid Supervisory System to support the operation of a real Wastewater Treatment Plant. The system integrates different reasoning modules, overcoming the limitations in the use of each single technique, while providing an agent based architecture with additional modularity and independence. It is structured into three separated levels: data gathering, diagnosis, and decision support. The different tasks of the system are performed in a seven-step cycle: data gathering and update, diagnosis, supervision, prediction, communication, actuation, and evaluation phase. In spite of certain reservations of the scientific community about the use of these techniques, the system is successfully performing real-time support to the operation of the Granollers facility since September 1999. Results of the first four-month validation period are shown and discussed. An example of the system behavior is also shown in the paper. The conclusions indicate the key steps which are necessary to transfer the system to another facility.