Single Reactor System Research Articles

Wastewater Treatment System Optimization for Sustainable Operation of the SHARON–Anammox Process under Varying Carbon/Nitrogen Loadings

Partial nitritation (PN) coupled with the anaerobic ammonium oxidation (Anammox) process has improved ammonium removal in wastewater treatment plants (WWTPs). The operation conditions of this process, i.e., the dissolved oxygen (DO) and the influent ammonium and nitrite concentrations, drive the process to an equilibrium to suppress nitrite-oxidizing bacteria and achieve a proper nitrite over ammonium (NO2/NH4) ratio. This study aimed to implement a set of control strategies in a WWTP model BSM2-SHAMX, combining PN in a single reactor system for high-activity ammonia removal over nitrite (SHARON) to an Anammox reactor, using proportional–integrative–derivative (PID) control and model predictive control (MPC) in a cascade. For correct coupling, the PN should maintain an output NO2/NH4 ratio between 1 and 1.3, suitable for the Anammox process. In the cascade controller feedback loop, the primary control loop controls the NO2/NH4 ratio through the DO concentration from the secondary control loop, which guarantees better effluent nitrogen removal. The performance of the plant was assessed by evaluating the control strategies with different influent carbon/nitrogen (C/N) loadings. The study results showed that the MPC controllers provided better results, with an improvement of 36% in the operational cost compared to the base case with a cost around 26,000 EUR/d, and better nitrogen removal surpassing 90% removal, 10% more than the base case.

Biogas conversion to liquid fuels via chemical looping single reactor system with CO2 utilization

The chemical looping single reactor (CLSR) system utilizing calcium ferrite as oxygen carriers represents an innovative approach to biogas reforming, which has the potential to enhance the efficiency and sustainability of biogas production. In this process, an oxy-combustion burner supplies the necessary endothermic heat while CO2 is simultaneously utilized, resulting in an autothermal process that generates high-purity syngas. Nearly 20% higher CO2 utilization can be achieved compared to the tri-reforming, owing to the higher driving force for CO2 oxidation in the counter-current moving bed and steam knock-out before inletting the flue gas into the reactor bottom. Additionally, the CLSR system is robust to variations in biogas to oxygen carrier ratios and CO2 concentration of the inlet feedstock, maintaining the outlet syngas purity within 1% variation. The effects of temperature, pressure, heat integration, and additional H2O/CO2 flow rate on the system performance are discussed, and the optimized scenarios are used for liquid fuel generation. The proposed process achieves about 13% reduction in syngas requirement compared to the conventional tri-reforming for the same amount of liquid fuel production. The feasibility of the CLSR system is further experimentally verified under various conditions. The results reveal the occurrence of CO2 counter-oxidation reactions on the surface of calcium ferrite oxygen carriers and demonstrate that higher temperatures are beneficial for the CH4 reforming reaction.

Acid–Base Pretreatment and Enzymatic Hydrolysis of Palm Oil Mill Effluent in a Single Reactor System for Production of Fermentable Sugars

Palm oil mill effluent (POME) is one of the main agro-industrial wastewaters in Malaysia. Highly polluting POME is a serious threat to the environment. In recent years, the methods used to treat POME are inefficient and complex in terms of cost or environmental preservation. The main object of this research is to propose a single reactor system (SRS) obtained from POME wastewater discharge as a promising low-cost treatment and high-energy method for harvesting the fermentable sugar by applying acid–base–enzyme pretreatment and hydrolysis of POME by locally produced cellulase enzymes to enhance biofuel production. Several experiments were conducted to produce fermentable sugars through the statistical methods, including the characterization of POME, acid-base pretreatment, and enzymatic hydrolysis process for reducing sugar production. The one-factor-at-a-time (OFAT) results showed that the highest reducing sugar yield, 23.5 mg/mL of POME, was achieved by enzymatic hydrolysis in an SRS without having a separation and purification. Based on OFAT performance, optimization of two factors such as substrate concentration (total suspended solids, TSS %w/v) and enzyme loading (μmol/min) was carried out by applying face-centered central composite design (FCCCD) under the response surface methodology (RSM) to develop a second-order regression model. The optimum reducing sugar production was 26.6 mg/mL (53.14%) with the conditions of 5% w/v, TSS, and 80 μmol/min/mL of the enzyme dose. In addition, the results of this research can be further considered in biofuel production using other wastewaters to enhance biofuel production as well as wastewater treating functions and minimize the negative environmental impacts.

Microwave catalytic conversion of acetylene for co-production of hydrogen and carbon nanotubes

Natural gas conversion to hydrogen and solid carbon can drastically reduce the carbon footprint. Microwave plasma pyrolysis is an emerging process for chemical industries to directly convert methane (CH4), the major component of natural gas, to hydrogen and carbon, which offers benefits such as fast process dynamics, flexibility, and high product yield. However, the formation of unwanted by-products, like acetylene (C2H2), will require extra cost for gas separation. Plasma pyrolysis of CH4 produces large amount of acetylene at downstream, which is currently used mainly for welding. To avoid gas separation and upgrade acetylene from the downstream of methane plasma reactor, a novel approach toward its transformation to carbon nanotubes (CNT) and pure hydrogen (H2) over Ni-based bimetallic catalyst driven by microwave irradiation has been reported in this work. The dominant gas product was hydrogen. Low concentrations of methane, ethane, and ethylene were observed in the product stream. Catalytic acetylene decomposition was carried out at 400 °C over Al2O3 supported Ni catalyst. The results showed that, at 400 °C, acetylene was dehydrogenated to CNT and hydrogen was the dominant gas in product stream over 10Ni-1Pd-Al2O3 catalyst. Characterizations of spent catalysts was conducted using Raman spectroscopy and transmission electron microscopy (TEM) to investigate the properties of carbon deposited over the catalyst during the catalytic acetylene decomposition. The results highlight that methane can be efficiently converted to hydrogen and CNT through 2-step process, microwave plasma and microwave catalytic conversion of intermediate acetylene, operated in a single reactor system driven by microwave.

Hydrogen Storage in Complex Metal Hydrides NaBH4: Hydrolysis Reaction and Experimental Strategies

Worldwide, hydrogen is gaining ground since it is a promising alternative energy source to conventional fuels, which include fossil fuel. Thus, numerous techniques to generate hydrogen have been suggested. This literature review describes the challenges and obstacles identified through a series of the publications that target the hydrolysis of sodium borohydride. This review present several catalysts and reactor systems for the generation of hydrogen gas using the hydrolysis of sodium borohydride, selecting articles in the literature that show a promising future for this technology, although some challenges lie ahead. Sodium borohydride has been widely considered as a low-cost hydrogen storage material with high gravimetric hydrogen capacity of about 10 wt.%. However, its thermodynamic stability seriously hinders the application of sodium borohydride to obtain hydrogen. The performances of the reviewed systems of sodium borohydride hydrolysis include analysis from both the thermodynamic and kinetic points of view. The feasibility of an efficient hydrogen generation system, where a mixture of sodium borohydride and catalysts is hydrolyzed, is considered. This review aims to provide a useful resource to aid researchers starting work on the generation of hydrogen gas using the hydrolysis of sodium borohydride, so they can select the catalysts and reactor systems that best suit them. Thus far, no single catalyst and reactor system can simultaneously meet all of the required standards for efficient practical applications.

Integration of complete elemental mass-balanced stoichiometry and aqueous-phase chemistry for bioprocess modelling of liquid and solid waste treatment systems − Part 3: Measuring the organics composition

Bioprocesses transform the components of the material entering single or multiple reactor systems from one kind to another without a change in total material exiting the system(s) in the solid, aqueous or gas phases. Provided that the correct measurements are made that can quantify the material content of the bioprocess products (outputs), the material content of the bioprocess reactants (inputs) can be determined from the bioprocess products via stoichiometry. Based on this principle of mass conservation, the augmented biomethane (AugBMP) and biosulphide (AugBSP) potential test procedures are proposed, which change the BMP from a stand-alone test to a bio-reactor on which a range of additional tests are made to determine the composition of biodegradable organics. The AugBSP, which is based on biological sulphate reduction, can replace the inaccurate gas measurements in the BMP with the more accurate aqueous sulphate and sulphide measurements. The suitability of these two procedures is evaluated from a theoretical and modelling perspective. The analytical tests required to determine the composition of influent organics, expressed as CxHyOzNaPbSc, are identified. Examples of the calculation procedure from the test results are given. It is concluded that the augmented BMP (AugBMP) and BSP (AugBSP) test procedures, supplemented by anaerobic digestion dynamic modelling, are as accurate as the analytical measurements for determining the composition of biodegradable organics, and also allow the hydrolysis rate of the biodegradable organics and the unbiodegradable fraction of the organics to be determined. Knowing these characteristics of organics fed to anaerobic digesters is important to predict the anaerobic digester performance and stability.

Enrichment of phosphate-accumulating organisms (PAOs) in a microfluidic model biofilm system by mimicking a typical aerobic granular sludge feast/famine regime

Wastewater treatment using aerobic granular sludge has gained increasing interest due to its advantages compared to conventional activated sludge. The technology allows simultaneous removal of organic carbon, nitrogen, and phosphorus in a single reactor system and is independent of space-intensive settling tanks. However, due to the microscale, an analysis of processes and microbial population along the radius of granules is challenging. Here, we introduce a model system for aerobic granular sludge on a small scale by using a machine-assisted microfluidic cultivation platform. With an implemented logic module that controls solenoid valves, we realized alternating oxic hunger and anoxic feeding phases for the biofilms growing within. Sampling during ongoing anoxic cultivation directly from the cultivation channel was achieved with a robotic sampling device. Analysis of the biofilms was conducted using optical coherence tomography, fluorescence in situ hybridization, and amplicon sequencing. Using this setup, it was possible to significantly enrich the percentage of polyphosphate-accumulating organisms (PAO) belonging to the family Rhodocyclaceae in the community compared to the starting inoculum. With the aid of this miniature model system, it is now possible to investigate the influence of a multitude of process parameters in a highly parallel way to understand and efficiently optimize aerobic granular sludge-based wastewater treatment systems.Key points• Development of a microfluidic model to study EBPR.• Feast-famine regime enriches polyphosphate-accumulating organisms (PAOs).• Microfluidics replace sequencing batch reactors for aerobic granular sludge research.

Effect of pH shock on single-stage biohythane production using gel-entrapped anaerobic microorganisms

A novel single-reactor system having entrapped anaerobic microorganisms has been developed to co-produce H2 and CH4. pH is one of the key operating and environmental parameters affecting the performance of a bio-system. This work aimed to investigate the pH shock effects on the novel biohythane system. The experiments were suddenly changing the original cultivation pH value of 6 into 4, 5, 7 or 8 for 4 h. The results indicate that a short pH shock could be used to regulate H2/CH4 composition without notably affecting biogas yield and chemical oxygen demand (COD) removal. Peak biohythane production was obtained after the pH shock to 8, having H2/CH4 yields of 11.5 ± 1.6/44.8 ± 3.1 mL/g COD. During pseudo steady-state conditions of effective cultivation periods, the values of H2 content in biohythane and COD removal efficiency were in ranges of 20–39% and 71–79%, respectively. The significances and applications of the experimental results have been discussed. The novelty of this work is elucidating a less-discussed field-operation problem of pH perturbances for a newly-developed biohythane system.

Short-Cut Nitrification of Iraqi Municipal Wastewater for Nitrogen Removal in a Single Reactor

Nitrogen components removal in wastewater treatment is an updated process that needs a continuous contribution of research. Traditionally, ammonium is removed by two biological ways, denitrification and nitrification. Here, it became necessary to suggest sustainable alternatives to control wastewater treatment strategies. In this work, a single reactor of high ammonium removal over nitrite process was operated, in which ammonium-oxidizing bacteria was used to convert ammonium to nitrite without sludge retention. The system was operated at aerobic conditions and a moderate temperature, at which the higher percentage of the desired ammonium oxidizer bacteria (AOB) over the undesired nitrite oxidizers bacteria (NOB) was achieved. The reactor was tested in a pilot plant scale to treat municipal wastewater with an average influent ammonium concentration value of 147.6 mg/l, flow rate 4.5 l/hr, hydraulic retention time (HRT) 24 hr, temperature 30-35 ºC, dissolved oxygen (DO) concentration 3.7 mg/l, and pH range 6.0–9.0. Removal efficiencies of 65 and 90 % were achieved for ammonium and nitrite, respectively. The Single reactor system is particularly suitable for the treatment of wastewater that contains high ammonium, giving 25% savings of the required oxygen to achieve complete nitrification.

Development of Aerobic Granular Sludge for Chemical Industries Wastewater Treatment

Background: The world’s chemical industries are confronted with formidable environmental regulatory challenges in treating their wastewaters. Aerobic granulation is increasingly drawing interest of researchers engaging work in the area of biological wastewater treatment. Objectives: The objective is to develop a new cost-effective technique for treatment of chemical industry effluents. The possibility and effectiveness of this new enhanced biological treatment system were determined through mean diameter, relative hydrophobicity, sphericity, and sludge volume index (SVI5) of aerobic microbial aggregates. Scanning electron microscopy (SEM) analysis was also used to characterize the granules. Methods: The granules were cultivated in a single sequencing batch reactor (SBR) system fed with synthetic ethylene glycol (MEG) wastewater. The characteristics of the aerobic granular sludge were monitored during the study period. Results: Aerobic granules with dense and strong microbial structure as well as excellent settling ability were cultivated. Developed granules had an average size of 8.21 ± 2 mm. The process of granulation resulted in an increased biomass concentration from about 2500 to 4750 mg/L. The microbial granular sludge was able to remove 97% of the influent COD at organic loading rate (OLR) of 2.0 kg COD/m3.day, at the end of the study. Conclusions: The findings of the present study revealed that aerobic granular sludge could be successfully developed in a SBR and is capable in treating the simulated chemical industries wastewater.

Combined SHARON and ANAMMOX processes for ammoniacal nitrogen stabilisation in landfill bioreactors

Stabilisation of ammoniacal nitrogen from solid waste and leachate significantly improved by combining novel processes like SHARON (single reactor system for high activity ammonia removal over nitrite) and ANAMMOX (anaerobic ammonium oxidation) with advantages of lower carbon requirements, aeration and N2O emissions. This paper deals with establishing combined SHARON-ANAMMOX processes in situ pilot-scale landfill bioreactors (LFBR). Molecular analysis in LFBR with changes in nitrogen, hydrazine, hydroxylamine confirmed aerobic and anaerobic ammonium oxidising bacteria (AOB & ANAMMOX) as key players in SHARON-ANAMMOX processes. In situ SHARON-ANAMMOX process was established in LFBR with total nitrogen and ammoniacal nitrogen removal efficiency of 84% and 71%, respectively at NLR of 1.2 kgN/m3/d in 147 d, compared to ammoniacal nitrogen removal of 49% at NLR of 1.0 kgNH4-N/m3/d in 336 d feasible in Control LFBR. Nitrogen massbalance demonstrated in situ SHARON-ANAMMOX advantageous than control LFBR with higher nitrogen transformation to N2 (50.8%) and lower residual nitrogen in solid waste (7.7%).

In situ nitrogen management in landfill bioreactors using combined sharon and anammox processes

Landfill bioreactors (LFBR) are gaining significant attention as sustainable alternative for conventional landfilling. Nitrogen management is an important issue in landfill bioreactors. The present study is to establish the combined SHARON (single reactor system for high activity ammonia removal over nitrite) and ANAMMOX (anaerobic ammonium oxidation) processes in landfill bioreactors for in situ nitrogen management. Laboratory scale landfill bioreactors (43 L volume capacity) as SHARON-ANAMMOX LFBR were loaded with mined municipal solid waste operated for 147 days at a nitrogen loading rate of 1.2 kg N/m3/d. The results showed a nitrogen removal efficiency of 84% with maximum partialnitritation efficiency of 56% and specific ANAMMOX activity of 0.7 mg Amm-N/mg MLVSS/d was achieved in the LFBR. Nitrogen transformations, biomass development and, hydrazine and hydroxylamine formation authenticated the aerobic ammonium oxidising bacteria (AOB) and anaerobic ammonium oxidising bacteria (AnAOB/ANAMMOX) activities responsible for combined SHARON-ANAMMOX processes in LFBR. 99% of the biogas in LFBR as N2 the end product confirmed the combined SHARON-ANAMMOX processes. The study successfully demonstrated the combined SHARON-ANAMMOX processes for in situ nitrogen management in landfill bioreactors with shorter start-up time and stable operation.

Experimental Investigation and Reaction Kinetics Modeling of Biomass Formation, Substrate Consumption and Product Formation During Startup of Fixed-Bed Cultures with Immobilized Lactococcus lactis ssp. lactis

Lactic acid bacteria (LAB) like Lactococcus lactis ssp. lactis are used in food industry as well as for production of bacteriocins and optically pure lactic acid. Fixed-bed processes are highly productive but mathematical description is often complex. The aim of this work was to establish a mathematica model for process design. Biomass formation, lactose consumption and lactate production during start-up of fixed-bed cultures with immobilized L. lactis was investigated experimentally and described by a reaction kinetics model. Appropriate modeling and simulation of fixed-bed processes require biomass data. Therefore, a low-volume multiple fixed-bed reactor system (Multiferm) was used to investigate biomass formation of a L. lactis strain during the start-up phase of fixed-bed cultivation. The generation of data in parallel experiments was fast and easily compared to larger single reactor systems. Biomass data obtained from both fractions, retained and free suspended biomass, was used for modeling and simulation, together with data for lactose and lactate. The underlying Luedeking-Piret-like model structure was developed based on the results from suspension cultivations with the same strain. The fixed-bed system was described as perfusion culture with cell retention. For this, merely four additional parameters had to be defined to extend the suspension model to fixed-bed cultures. Experimental trends and steady states of both biomass fractions besides substrate and product could be described very well. Thus, this model could be used for process layout during process development.

Developments in fluidized bed conversion of solid fuels

A summary is given on the development of fluidized bed conversion (combustion and gasification) of solid fuels. First, gasification is mentioned, following the line of development from the Winkler gasifier to recent designs. The combustors were initially bubbling beds, which were found unsuitable for combustion of coal because of various drawbacks, but they proved more useful for biomass where these drawbacks were absent. Instead, circulating fluidized bed boilers became the most important coal converters, whose design now is quite mature, and presently the increments in size and efficiency are the most important development tasks. The new modifications of these conversion devices are related to CO2 capture. Proposed methods with this purpose, involving fluidized bed, are single-reactor systems like oxy-fuel combustion, and dual-reactor systems, including also indirect biomass gasifiers.

Polyethylene with Reverse Co‐monomer Incorporation: From an Industrial Serendipitous Discovery to Fundamental Understanding

A triethylaluminium(TEAl)-modified Phillips ethylene polymerisation Cr/Ti/SiO2 catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell of the catalyst particle. DRIFTS, EPR, UV-Vis-NIR DRS, STXM, SEM-EDX and GPC-IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear-chain polyethylene in the Ti-abundant catalyst particle shell and high molecular weight short-chain branched polyethylene in the Ti-scarce catalyst particle core. Co-monomers for the short-chain branched polymer were generated in situ within the TEAl-impregnated confined space of the Ti-scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high-performance polyethylene from a single reactor system using this modified Phillips catalyst.

Moisture barrier properties of thin organic-inorganic multilayers prepared by plasma-enhanced ALD and CVD in one reactor.

A widely used application of the atomic layer deposition (ALD) and chemical vapour deposition (CVD) methods is the preparation of permeation barrier layers against water vapour. Especially in the field of organic electronics, these films are highly demanded as such devices are very sensitive to moisture and oxygen. In this work, multilayers of aluminium oxide (AlO x ) and plasma polymer (PP) were coated on polyethylene naphthalate substrates by plasma-enhanced ALD and plasma-enhanced CVD at 80℃ in the same reactor, respectively. As precursor, trimethylaluminium was used together with oxygen radicals in order to prepare AlO x , and benzene served as precursor to deposit the PP. This hybrid structure allows the decoupling of defects between the single AlO x layers and extends the permeation path for water molecules towards the entire barrier film. Furthermore, the combination of two plasma techniques in a single reactor system enables short process times without vacuum breaks. Single aluminium oxide films by plasma-enhanced ALD were compared to thermally grown layers and showed a significantly better barrier performance. The water vapour transmission rate (WVTR) was determined by means of electrical calcium tests. For a multilayer with 3.5 dyads of 25-nm AlO x and 125-nm PP, a WVTR of 1.2 × 10 −3 gm−2d−1 at 60℃ and 90% relative humidity could be observed.

AEROBIC AND ANAEROBIC AMMONIUM OXIDISING BACTERIA ENRICHMENT FROM MINED MUNICIPAL SOLID WASTE IN SHARONANAMMOX PROCESS

Ammoniacal nitrogen removal by novel processes like Single reactor system for high activity ammonia removal over nitrite (SHARON) and Anaerobic ammonium oxidation (ANAMMOX) processes are currently considered as advantageous than conventional processes. It requires aerobic ammonium oxidising bacteria (AOB) and anaerobic ammonium oxidising bacteria (AnAOB) to conduct the SHARON and ANAMMOX processes. This paper presents the feasibility of enriching the AOB and AnAOB using mined municipal solid waste (MSW) in batch reactors for a period of 37 days. In AOB reactor with nitrogen loading of 0.5 kg N/d showed Partial Nitritation Efficiency of 82.6% with 3.8 × 108 MPN/100mL of AOB population obtained. AnAOB reactor enriched with anammox biomass efficiently removed 78% of ammonia with the specific anammox activity reached up to 0.10 mg NH4-N/mg MLVSS/d. The nitrogen transformations along with the formation of intermediates (hydrazine and hydroxylamine), biomass development, free ammonia and free nitrous acid concentrations in the batch reactors confirmed the enrichment AOB and AnAOB biomass activity using mined MSW. (Keywords: Mined municipal solid waste, ammoniacal nitrogen removal, aerobic ammonium oxidising bacteria and anammox)

Simplification of the Biomass to Ethanol Conversion Process by Using the Whole Medium of Filamentous Fungi Cultivated Under Solid-State Fermentation

A novel simplified configuration is proposed for the conversion of biomass to ethanol using whole medium enzymatic cocktails (WM) and enzymatic extracts (EE) from different filamentous fungi (Trichoderma reesei, Aspergillus niger, and Aspergillus oryzae) cultivated under solid-state fermentation (SSF) for the hydrolysis of steam-exploded sugarcane bagasse (SESB). The hydrolyzed material derived from the saccharification of SESB using the combinations A. niger WM + T. reesei EE, A. oryzae WM + A. niger EE, and A. niger EE + T. reesei WM resulted in the best biomass conversion yields (66, 65, and 64 % of the theoretical reducing sugar yields, respectively). The best ethanol production (84 % of the theoretical yield) was obtained using the material hydrolyzed by a combination of A. oryzae WM + A. niger EE. The enzymatic conversion of SESB using on-site produced enzymes from the whole SSF cultivation medium, followed by an ethanol production step, is a potential configuration for the biomass to ethanol conversion process. This novel simplified configuration would enable the use of a single reactor system, avoiding the need for additional separation steps.

Electrodischarge technology and equipment to produce new carbon nanomaterials

A continuous and nonwaste process is proposed that consists of a set of simultaneous operations concerning the electrodischarge treatment of carbon liquid in reactors through exposure to high temperatures and pressures generated by a plasma discharge channel, the selection and separation of the processed sub-stance in filtering or centrifugal separating devices, and the recirculation of the purified material in a closed hydraulic system. The product, depending on the method used for the selection and separation, is a thick pasty mass or a dry powder mixture containing various modifications of carbon: fullerenes, nanotubes, and nanodiamonds (up to 10% of the total weight). A prototype of the electric equipment has been built to provide processing performance of from 0.02 to 1.5 kg/hour. It has a maximum installed capacity of 5 kV A, and the specific energy consumption ranges from 0.1 to 10 MJ/kg. The surge-current generator with microprocessor control was designed for industrial applications. It allows achieving the maximum discharge pulse recurrence frequency of 200 Hz, which is limited by the time of the medium’s relaxation and the dielectric strength’s restoration in the discharge gap. This ensures the versatile regulation and a shift in the corresponding processing performance of the single-reactor systems in the range from 0.4 to 30 kg/hour. This technology is complemented with the developed method for the enrichment of the produced ultrafine powder. It consists of an original sequence of physical and chemical methods (magnetic separation, acid treatment, chromatographic purification, etc.) and can increase the targeted selectivity of the processed products.

Biological Nutrient Removal Model No. 2 (BNRM2): a general model for wastewater treatment plants

This paper presents the plant-wide model Biological Nutrient Removal Model No. 2 (BNRM2). Since nitrite was not considered in the BNRM1, and this previous model also failed to accurately simulate the anaerobic digestion because precipitation processes were not considered, an extension of BNRM1 has been developed. This extension comprises all the components and processes required to simulate nitrogen removal via nitrite and the formation of the solids most likely to precipitate in anaerobic digesters. The solids considered in BNRM2 are: struvite, amorphous calcium phosphate, hidroxyapatite, newberite, vivianite, strengite, variscite, and calcium carbonate. With regard to nitrogen removal via nitrite, apart from nitrite oxidizing bacteria two groups of ammonium oxidizing organisms (AOO) have been considered since different sets of kinetic parameters have been reported for the AOO present in activated sludge systems and SHARON (Single reactor system for High activity Ammonium Removal Over Nitrite) reactors. Due to the new processes considered, BNRM2 allows an accurate prediction of wastewater treatment plant performance in wider environmental and operating conditions.