Bernhard Wett - Academia.edu (original) (raw)

Papers by Bernhard Wett

Water Research, 2015

Six methodologically different approaches were evaluated and compared regarding their suitability... more Six methodologically different approaches were evaluated and compared regarding their suitability to quantify and characterise granular anammox biomass. The investigated techniques were gravimetric analysis (GA), activity measurements (AM), Coulter counter analysis (CC), quantitative PCR (qPCR), heme protein quantification (HQ) and the novel image analysis technique Particle Tracking (PT). The focus was set on the development of fast, economic and user-friendly approaches for potential implementation in regular wastewater treatment plant (WWTP) monitoring. To test the effectiveness of each technique, two sample matrices were chosen at the WWTP Strass (Austria): i) sludge liquor of the DEMON tank, treating ammonium-rich reject water of anaerobic digestion via the deammonification process and rich in anammox biomass (SL), and ii) the mainstream biological stage, that has been enriched with anammox biomass for more than two years (B). In both of these plants hydro-cyclones are installed for density-fractioning of the sludge into a low- and a high-density fraction, thus leading to a characteristic anammox distribution in the investigated sample set. All investigated methods could statistically discriminate the SL samples. Heme quantification and qPCR were also able to correctly classify the B-samples and both methods showed a Pearson's correlation coefficient of 0.81. An asset of the PT and CC method is the additional qualitative characterization of granule size distribution that can help to better understand and optimise general process operation (cyclone operation duration and construction characteristics). In combination these two methods were able to elucidate the relationship of gross granule volume and actual biomass, excluding the dead volume of inner cavities and exopolymers. We found a linear sphere-equivalent-radius correction factor (3.96 ± 0.15) for investigated anammox granules, that can be used for the fast and reliable PT technique to avoid biomass overestimation. We also recommend routine HQ and PT analysis as ideal monitoring strategy for anammox abundance in wastewater facilities with the HQ technique entailing the further advantage of being also suited for non-granular anammox biomass.

Water Research, 2015

Making good use of existing water infrastructure by adding organic wastes to anaerobic digesters ... more Making good use of existing water infrastructure by adding organic wastes to anaerobic digesters improves the energy balance of a wastewater treatment plant (WWTP) substantially. This paper explores co-digestion load limits targeting a good trade-off for boosting methane production, and limiting process-drawbacks on nitrogen-return loads, cake-production, solids-viscosity and polymer demand. Bio-methane potential tests using whey as a model co-substrate showed diversification and intensification of the anaerobic digestion process resulting in a synergistical enhancement in sewage sludge methanization. Full-scale case-studies demonstrate organic co-substrate addition of up to 94% of the organic sludge load resulted in tripling of the biogas production. At organic co-substrate addition of up to 25% no significant increase in cake production and only a minor increase in ammonia release of ca. 20% have been observed. Similar impacts were measured at a high-solids digester pilot with up-stream thermal hydrolyses where the organic loading rate was increased by 25% using co-substrate. Dynamic simulations were used to validate the synergistic impact of co-substrate addition on sludge methanization, and an increase in hydrolysis rate from 1.5 d À1 to 2.5 d À1 was identified for simulating measured gas production rate. This study demonstrates co-digestion for maximizing synergy as a step towards energy efficiency and ultimately towards carbon neutrality.

Water Science & Technology

A separate rejection water treatment appears as a high-tech unit process which might be recommend... more A separate rejection water treatment appears as a high-tech unit process which might be recommendable only for specific cases of an upgrading of an existing wastewater treatment plant. It is not the issue of this paper to consider a specific separate treatment process itself but to investigate the influence of such a process on the overall plant performance. A plant-wide model has been applied as an innovative tool to evaluate effects of the implemented sidestream strategy on the mainstream treatment. The model has been developed in the SIMBA environment and combines acknowledged mathematical descriptions of the activated sludge process (ASM1) and the anaerobic mesophilic digestion (Siegrist model). The model's calibration and validation was based on data from 5 years of operating experience of a full-scale rejection water treatment. The impact on the total N-elimination efficiency is demonstrated by detailed nitrogen mass flow schemes including the interactions between the wastewater and the sludge lane. Additionally limiting conditions due to dynamic N-return loads are displayed by the model's state variables.

Proceedings of the Water Environment Federation, 2006

Implementation of a novel sidestream treatment configuration will provide the Blue Plains AWTP si... more Implementation of a novel sidestream treatment configuration will provide the Blue Plains AWTP sidestream treatment process the flexibility to operate in four different process modes including the MAUREEN, SHARON, STRASS and DEMON configurations. Each process confers specific benefits to the AWTP that will need to achieve stringent nutrient limits to support ongoing efforts within the Chesapeake Bay area. In order to maximize the operating cost savings, while also assuring that treatment goals are achieved, the MAUREEN process configuration can be deployed in two seasonal modes, providing differing levels of preferential nitritation and bioaugmentation. To maximize operating cost savings, when performance is not limited by temperature, configurations such as SHARON, STRASS or DEMON would be utilized.

Biotechnology and bioengineering, Jan 2, 2015

As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary... more As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary nitrogen polishing steps are gaining popularity. For partial nitritation or nitritation-denitritation systems, anaerobic ammonia oxidation (anammox) polishing may be feasible to remove residual ammonia and nitrite from the effluent. Nitrogen polishing of mainstream nitritation-denitritation system effluent via anammox was studied at 25 °C in a fully anoxic moving bed bioreactor (MBBR) (V = 0.45 m(3) ) over 385 days. Unlike other anammox based processes, a very fast startup of anammox MBBR was demonstrated, despite nitrite limited feeding conditions (influent nitrite= 0.7 ± 0.59 mgN/L, ammonia= 6.13 ± 2.86 mgN/L, nitrate= 3.41 ± 1.92 mgN/L). The nitrogen removal performance was very stable within a wide range of nitrogen inputs. Anammox bacteria (AMX) activity up to 1 gN/m(2) /d was observed which is comparable to other biofilm based systems. It is generally believed that nitrate product...

Water research, Jan 21, 2015

The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redire... more The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redirection of organics from wastewater to energy generating processes in an efficient manner. A HRAS pilot plant was operated under controlled conditions resulting in concentrating the influent particulate, colloidal, and soluble COD to a waste solids stream with minimal energy input by maximizing sludge production, bacterial storage, and bioflocculation. The impact of important process parameters such as solids retention time (SRT), hydraulic residence time (HRT) and dissolved oxygen (DO) levels on the performance of a HRAS system was demonstrated in a pilot study. The results showed that maximum removal efficiencies of soluble COD were reached at a DO > 0.3 mg O2/L, SRT > 0.5 days and HRT > 15 min which indicates that minimizing the oxidation of the soluble COD in the high-rate activated sludge process is difficult. The study of DO, SRT and HRT exhibited high degree of impact on th...

Water Practice & Technology

In wastewater treatment modelling, energy information is not always immediately available. More d... more In wastewater treatment modelling, energy information is not always immediately available. More detailed energy information on a unit process level can be used to calibrate energy balance models serving for quantification of larger energy savings. Modelling energy footprint has lower uncertainty than other greenhouse gas equivalent footprint models, and is the prime candidate for minimizing costs and environmental impact. Due to their magnitude, and their larger number of equipment units, large wastewater treatment plants are associated with the largest margin for improvement.

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process th... more This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT = 30 min, solids retention time = 0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 °C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate + nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate + nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted...

Both cost issues on a microeconomic level and concerns about greenhouse gas emissions on a global... more Both cost issues on a microeconomic level and concerns about greenhouse gas emissions on a global level have become major driving forces towards a more efficient usage of energy in wastewater treatment WWT. This presentation describes Central European initiatives for operational optimisations, which came up with average energy saving potentials of about 30-50 % for existing utilities. A close-up on performance data of the WWTP Strass (Austria) is given – a case study that demonstrates large-scale feasibility of energy self-sufficiency. An annual net surplus in electric energy of 8 % of the total demand of the plant is fed to the public grid. Following key factors for energy-efficiency have been identified: Two-stage biological WWT optimises the transfer of less stabilised organics from the liquid train to the digesters. On-line control of intermittent aeration for enhanced nitrogen removal reduces demand for air supply. Latest generation of coupled-heat-power plants generates an ave...

Biotechnology and bioengineering, Jan 8, 2015

This work describes the development of an intermittently aerated pilot-scale process (V = 0.45 m3... more This work describes the development of an intermittently aerated pilot-scale process (V = 0.45 m3) operated for optimized efficient nitrogen removal in terms of volume, supplemental carbon and alkalinity requirements. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia concentration set-points. The unique feature of the ammonia-based aeration control was that a fixed dissolved oxygen (DO) set-point was used and the length of the aerobic and anoxic time (anoxic time = 25% of total cycle time) were changed based on the effluent ammonia concentration. Unlike continuously aerated ammonia-based aeration control strategies, this approach offered control over the aerobic solids retention time (SRT) to deal with fluctuating ammonia loading without solely relying on changes to the total SRT. This approach allowed the system to be operated at a total SRT with a small safety factor. The benefits of operating at an aggressive SRT were reduced hydraulic re...

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

This study describes the development of a modified activated sludge model No.1 framework to descr... more This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to pa...

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

The main challenge in implementing shortcut nitrogen removal processes for mainstream wastewater ... more The main challenge in implementing shortcut nitrogen removal processes for mainstream wastewater treatment is the out-selection of nitrite oxidizing bacteria (NOB) to limit nitrate production. A model-based approach was utilized to simulate the impact of individual features of process control strategies to achieve NO(-)2-N shunt via NOB out-selection. Simulations were conducted using a two-step nitrogen removal model from the literature. Nitrogen shortcut removal processes from two case studies were modeled to illustrate the contribution of NOB out-selection mechanisms. The paper highlights a comparison between two control schemes; one was based on online measured ammonia and the other was based on a target ratio of 1 for ammonia vs. NOx (nitrate + nitrite) (AVN). Results indicated that the AVN controller possesses unique features to nitrify only that amount of nitrogen that can be denitrified, which promotes better management of incoming organics and bicarbonate for a more efficien...

Water science and technology : a journal of the International Association on Water Pollution Research, 2014

Current anaerobic digestion models cannot properly simulate processes that are operated under hig... more Current anaerobic digestion models cannot properly simulate processes that are operated under high solids concentrations or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these systems without artificially recalibrating the model parameters. Specifically, we implemented the alternate acetate oxidizing mechanism that is more tolerant to ammonia than the standard aceticlastic pathway. Inhibition values were estimated and an empirical function has been used to apply ammonia inhibition. The model also relates metabolic activity to un-ionised species such as undissociated acetic acid as substrate (although not obligatory for all organisms) and unionised ammonia as inhibitor. The model relies on an equilibrium chemistry module (e.g. including the phosphate buffer), resulting in more accurate pH predictions, which is crucial for proper modeling of CO2 and NH3 stripping. Calibration results from thre...

Water science and technology : a journal of the International Association on Water Pollution Research, 2008

This paper presents benefits and potential drawbacks of thermal pre-hydrolysis of sewage sludge f... more This paper presents benefits and potential drawbacks of thermal pre-hydrolysis of sewage sludge from an operator's prospective. The innovative continuous Thermo-Pressure-Hydrolysis Process (TDH) has been tested in full-scale at Zirl wastewater treatment plant (WWTP), Austria, and its influence on sludge digestion and dewatering has been evaluated. A mathematical plant-wide model with application of the IWA Activated Sludge Model No.1 (ASM1) and the Anaerobic Digestion Model No.1 (ADM1) has been used for a systematic comparison of both scenarios--operational plant performance with and without thermal pre-hydrolysis. The impacts of TDH pre-hydrolysis on biogas potential, dewatering performance and return load in terms of ammonia and inert organic compounds (Si) have been simulated by the calibrated model and are displayed by Sankey mass flow figures. Implementation of full scale TDH process provided higher anaerobic degradation efficiency with subsequent increased biogas productio...

Water science and technology : a journal of the International Association on Water Pollution Research, 2007

Different digestion technologies for various substrates are addressed by the generic process desc... more Different digestion technologies for various substrates are addressed by the generic process description of Anaerobic Digestion Model No. 1. In the case of manure or agricultural wastes a priori knowledge about the substrate in terms of ADM1 compounds is lacking and influent characterisation becomes a major issue. The actual project has been initiated for promotion of biogas technology in agriculture and for expansion of profitability also to rather small capacity systems. In order to avoid costly individual planning and installation of each facility a standardised design approach needs to be elaborated. This intention pleads for bio kinetic modelling as a systematic tool for process design and optimisation. Cofermentation under field conditions was observed, quality data and flow data were recorded and mass flow balances were calculated. In the laboratory different substrates have been digested separately in parallel under specified conditions. A configuration of four ADM1 model re...

Water Research, 2015

Six methodologically different approaches were evaluated and compared regarding their suitability... more Six methodologically different approaches were evaluated and compared regarding their suitability to quantify and characterise granular anammox biomass. The investigated techniques were gravimetric analysis (GA), activity measurements (AM), Coulter counter analysis (CC), quantitative PCR (qPCR), heme protein quantification (HQ) and the novel image analysis technique Particle Tracking (PT). The focus was set on the development of fast, economic and user-friendly approaches for potential implementation in regular wastewater treatment plant (WWTP) monitoring. To test the effectiveness of each technique, two sample matrices were chosen at the WWTP Strass (Austria): i) sludge liquor of the DEMON tank, treating ammonium-rich reject water of anaerobic digestion via the deammonification process and rich in anammox biomass (SL), and ii) the mainstream biological stage, that has been enriched with anammox biomass for more than two years (B). In both of these plants hydro-cyclones are installed for density-fractioning of the sludge into a low- and a high-density fraction, thus leading to a characteristic anammox distribution in the investigated sample set. All investigated methods could statistically discriminate the SL samples. Heme quantification and qPCR were also able to correctly classify the B-samples and both methods showed a Pearson's correlation coefficient of 0.81. An asset of the PT and CC method is the additional qualitative characterization of granule size distribution that can help to better understand and optimise general process operation (cyclone operation duration and construction characteristics). In combination these two methods were able to elucidate the relationship of gross granule volume and actual biomass, excluding the dead volume of inner cavities and exopolymers. We found a linear sphere-equivalent-radius correction factor (3.96 ± 0.15) for investigated anammox granules, that can be used for the fast and reliable PT technique to avoid biomass overestimation. We also recommend routine HQ and PT analysis as ideal monitoring strategy for anammox abundance in wastewater facilities with the HQ technique entailing the further advantage of being also suited for non-granular anammox biomass.

Biomass and Bioenergy, 2015

ABSTRACT Four start-up strategies were assayed in 75 dm3 continuous stirred-tank reactors to sele... more ABSTRACT Four start-up strategies were assayed in 75 dm3 continuous stirred-tank reactors to select the optimal conditions for the start-up of the demonstration BIO4GAS® plant. Two reactors were completely filled with manure and their temperature increased from 20 to 37 °C at either a slow or fast rate. The other two reactors were started at 37 °C with a seed sludge from a stably operating plant and their load (cattle manure) increased at a low or high rate. Reactor performance was monitored for 35 days. The composition and abundance of the methanogenic communities was determined using a phylogenetic microarray and quantitative PCR. All reactors performed successfully in terms of biogas production and experienced a steady start-up, with pH values above 7.3 and VFA/alkalinity ratios below 0.3, denoting stability. Similar methanogenic loads (averaging 5 × 107 g-1 of 16S rRNA gene copies) were detected in the cattle manure and seed sludge, however the methanogenic diversity was higher in the manure with dominance of Methanosarcina and subdominance of Methanocorpusculum and Methanobrevibacter. Starting-up the reactors with an initial full load of manure and progressively increasing the temperature entailed less changes in the sludge chemical environment and in the dynamics of the dominant methanogens. Using a rate of temperature increase of 0.61 K d−1 proved better than1.21 K d−1 with a methane yield of 103.8 dm3 kg−1 VS and a COD mass removal efficiency of 28.3%. The diverse methanogenic community in the manure easily adapted to reactor upsets due to forced overload conditions.

Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion... more Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion at very large utilities and can substantially reduce required digester volumes in space constrained large cities while also allowing for development of regionalized sludge receiving centers. In 2014, DC Water will begin operating a new solids processing train at the Blue Plains Advanced Wastewater Treatment Plant consisting of the CAMBI thermal hydrolysis process for solids pretreatment prior to mesophilic anaerobic digestion. A complete evaluation picture needs to take all impacts on downstream processes into account. The digestion performance at various solids loadings (collection of full-scale data); dewatering performance (full-scale belt-filter-press tests); sludge liquor treatment (DEMON-pilot); pathogen removal, odour issues and land application are discussed in the paper.

Österreichische Wasser- und Abfallwirtschaft, 2012

ABSTRACT Deammonification, the anaerobic oxidation of ammonium by use of anammox bacteria, has pr... more ABSTRACT Deammonification, the anaerobic oxidation of ammonium by use of anammox bacteria, has proved to be an efficient method of treating severely polluted process water from sludge treatment. Particular merits of this method in terms of the overall energy balance of the plant are the low power requirements and the fact that no organic carbon is needed. By shortening the conventional nitrogen conversion via nitrite, the deammonification method produces an increased amount of intermediate products, among which nitrous oxide has some climatic implications. A number of tests have, therefore, been conducted on the nitrous oxide emissions involved in this method. The tests were carried out at a DEMON plant for the treatment of digester supernatant at the sewage treatment plant of Strass in the Ziller valley in Tyrol, in operation since 2004 and run by Abwasserverband Achental-Inntal-Zillertal (AIZ). The results have shown that the proportion of nitrous oxide accounts for about 0.9 % to 1.3 % of the overall amount of treated nitrogen from the process water. These results are in the lower range as compared with other deammonification systems. Since the mechanism of nitrous oxide emission is not yet fully understood, a number of measurements have been performed under different operating conditions. While changes in the leading parameters pH and oxygen do not show any direct influence, increased nitrous oxide emissions have been seen to occur under conditions of nitrite accumulation. By preventing nitrite accumulation, the pH control of the singlestage DEMON process reduces the nitrous oxide emissions. An appropriate feed reservoir to harmonise process water intake prevents variations in operating conditions, which otherwise would cause increased nitrous oxide emissions.

Water Research, 2015

Six methodologically different approaches were evaluated and compared regarding their suitability... more Six methodologically different approaches were evaluated and compared regarding their suitability to quantify and characterise granular anammox biomass. The investigated techniques were gravimetric analysis (GA), activity measurements (AM), Coulter counter analysis (CC), quantitative PCR (qPCR), heme protein quantification (HQ) and the novel image analysis technique Particle Tracking (PT). The focus was set on the development of fast, economic and user-friendly approaches for potential implementation in regular wastewater treatment plant (WWTP) monitoring. To test the effectiveness of each technique, two sample matrices were chosen at the WWTP Strass (Austria): i) sludge liquor of the DEMON tank, treating ammonium-rich reject water of anaerobic digestion via the deammonification process and rich in anammox biomass (SL), and ii) the mainstream biological stage, that has been enriched with anammox biomass for more than two years (B). In both of these plants hydro-cyclones are installed for density-fractioning of the sludge into a low- and a high-density fraction, thus leading to a characteristic anammox distribution in the investigated sample set. All investigated methods could statistically discriminate the SL samples. Heme quantification and qPCR were also able to correctly classify the B-samples and both methods showed a Pearson's correlation coefficient of 0.81. An asset of the PT and CC method is the additional qualitative characterization of granule size distribution that can help to better understand and optimise general process operation (cyclone operation duration and construction characteristics). In combination these two methods were able to elucidate the relationship of gross granule volume and actual biomass, excluding the dead volume of inner cavities and exopolymers. We found a linear sphere-equivalent-radius correction factor (3.96 ± 0.15) for investigated anammox granules, that can be used for the fast and reliable PT technique to avoid biomass overestimation. We also recommend routine HQ and PT analysis as ideal monitoring strategy for anammox abundance in wastewater facilities with the HQ technique entailing the further advantage of being also suited for non-granular anammox biomass.

Water Research, 2015

Making good use of existing water infrastructure by adding organic wastes to anaerobic digesters ... more Making good use of existing water infrastructure by adding organic wastes to anaerobic digesters improves the energy balance of a wastewater treatment plant (WWTP) substantially. This paper explores co-digestion load limits targeting a good trade-off for boosting methane production, and limiting process-drawbacks on nitrogen-return loads, cake-production, solids-viscosity and polymer demand. Bio-methane potential tests using whey as a model co-substrate showed diversification and intensification of the anaerobic digestion process resulting in a synergistical enhancement in sewage sludge methanization. Full-scale case-studies demonstrate organic co-substrate addition of up to 94% of the organic sludge load resulted in tripling of the biogas production. At organic co-substrate addition of up to 25% no significant increase in cake production and only a minor increase in ammonia release of ca. 20% have been observed. Similar impacts were measured at a high-solids digester pilot with up-stream thermal hydrolyses where the organic loading rate was increased by 25% using co-substrate. Dynamic simulations were used to validate the synergistic impact of co-substrate addition on sludge methanization, and an increase in hydrolysis rate from 1.5 d À1 to 2.5 d À1 was identified for simulating measured gas production rate. This study demonstrates co-digestion for maximizing synergy as a step towards energy efficiency and ultimately towards carbon neutrality.

Water Science & Technology

A separate rejection water treatment appears as a high-tech unit process which might be recommend... more A separate rejection water treatment appears as a high-tech unit process which might be recommendable only for specific cases of an upgrading of an existing wastewater treatment plant. It is not the issue of this paper to consider a specific separate treatment process itself but to investigate the influence of such a process on the overall plant performance. A plant-wide model has been applied as an innovative tool to evaluate effects of the implemented sidestream strategy on the mainstream treatment. The model has been developed in the SIMBA environment and combines acknowledged mathematical descriptions of the activated sludge process (ASM1) and the anaerobic mesophilic digestion (Siegrist model). The model's calibration and validation was based on data from 5 years of operating experience of a full-scale rejection water treatment. The impact on the total N-elimination efficiency is demonstrated by detailed nitrogen mass flow schemes including the interactions between the wastewater and the sludge lane. Additionally limiting conditions due to dynamic N-return loads are displayed by the model's state variables.

Proceedings of the Water Environment Federation, 2006

Implementation of a novel sidestream treatment configuration will provide the Blue Plains AWTP si... more Implementation of a novel sidestream treatment configuration will provide the Blue Plains AWTP sidestream treatment process the flexibility to operate in four different process modes including the MAUREEN, SHARON, STRASS and DEMON configurations. Each process confers specific benefits to the AWTP that will need to achieve stringent nutrient limits to support ongoing efforts within the Chesapeake Bay area. In order to maximize the operating cost savings, while also assuring that treatment goals are achieved, the MAUREEN process configuration can be deployed in two seasonal modes, providing differing levels of preferential nitritation and bioaugmentation. To maximize operating cost savings, when performance is not limited by temperature, configurations such as SHARON, STRASS or DEMON would be utilized.

Biotechnology and bioengineering, Jan 2, 2015

As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary... more As nitrogen discharge limits are becoming more stringent, short-cut nitrogen systems and tertiary nitrogen polishing steps are gaining popularity. For partial nitritation or nitritation-denitritation systems, anaerobic ammonia oxidation (anammox) polishing may be feasible to remove residual ammonia and nitrite from the effluent. Nitrogen polishing of mainstream nitritation-denitritation system effluent via anammox was studied at 25 °C in a fully anoxic moving bed bioreactor (MBBR) (V = 0.45 m(3) ) over 385 days. Unlike other anammox based processes, a very fast startup of anammox MBBR was demonstrated, despite nitrite limited feeding conditions (influent nitrite= 0.7 ± 0.59 mgN/L, ammonia= 6.13 ± 2.86 mgN/L, nitrate= 3.41 ± 1.92 mgN/L). The nitrogen removal performance was very stable within a wide range of nitrogen inputs. Anammox bacteria (AMX) activity up to 1 gN/m(2) /d was observed which is comparable to other biofilm based systems. It is generally believed that nitrate product...

Water research, Jan 21, 2015

The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redire... more The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redirection of organics from wastewater to energy generating processes in an efficient manner. A HRAS pilot plant was operated under controlled conditions resulting in concentrating the influent particulate, colloidal, and soluble COD to a waste solids stream with minimal energy input by maximizing sludge production, bacterial storage, and bioflocculation. The impact of important process parameters such as solids retention time (SRT), hydraulic residence time (HRT) and dissolved oxygen (DO) levels on the performance of a HRAS system was demonstrated in a pilot study. The results showed that maximum removal efficiencies of soluble COD were reached at a DO > 0.3 mg O2/L, SRT > 0.5 days and HRT > 15 min which indicates that minimizing the oxidation of the soluble COD in the high-rate activated sludge process is difficult. The study of DO, SRT and HRT exhibited high degree of impact on th...

Water Practice & Technology

In wastewater treatment modelling, energy information is not always immediately available. More d... more In wastewater treatment modelling, energy information is not always immediately available. More detailed energy information on a unit process level can be used to calibrate energy balance models serving for quantification of larger energy savings. Modelling energy footprint has lower uncertainty than other greenhouse gas equivalent footprint models, and is the prime candidate for minimizing costs and environmental impact. Due to their magnitude, and their larger number of equipment units, large wastewater treatment plants are associated with the largest margin for improvement.

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process th... more This paper deals with an almost 1-year long pilot study of a nitritation-denitritation process that was followed by anammox polishing. The pilot plant treated real municipal wastewater at ambient temperatures. The effluent of high-rate activated sludge process (hydraulic retention time, HRT = 30 min, solids retention time = 0.25 d) was fed to the pilot plant described in this paper, where a constant temperature of 23 °C was maintained. The nitritation-denitritation process was operated to promote nitrite oxidizing bacteria out-selection in an intermittently aerated reactor. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia and nitrate + nitrite concentrations. The unique feature of this aeration control was that fixed dissolved oxygen set-point was used and the length of aerobic and anoxic durations were changed based on the effluent ammonia and nitrate + nitrite concentrations. The anaerobic ammonia oxidation (anammox) bacteria were adapted...

Both cost issues on a microeconomic level and concerns about greenhouse gas emissions on a global... more Both cost issues on a microeconomic level and concerns about greenhouse gas emissions on a global level have become major driving forces towards a more efficient usage of energy in wastewater treatment WWT. This presentation describes Central European initiatives for operational optimisations, which came up with average energy saving potentials of about 30-50 % for existing utilities. A close-up on performance data of the WWTP Strass (Austria) is given – a case study that demonstrates large-scale feasibility of energy self-sufficiency. An annual net surplus in electric energy of 8 % of the total demand of the plant is fed to the public grid. Following key factors for energy-efficiency have been identified: Two-stage biological WWT optimises the transfer of less stabilised organics from the liquid train to the digesters. On-line control of intermittent aeration for enhanced nitrogen removal reduces demand for air supply. Latest generation of coupled-heat-power plants generates an ave...

Biotechnology and bioengineering, Jan 8, 2015

This work describes the development of an intermittently aerated pilot-scale process (V = 0.45 m3... more This work describes the development of an intermittently aerated pilot-scale process (V = 0.45 m3) operated for optimized efficient nitrogen removal in terms of volume, supplemental carbon and alkalinity requirements. The intermittent aeration pattern was controlled using a strategy based on effluent ammonia concentration set-points. The unique feature of the ammonia-based aeration control was that a fixed dissolved oxygen (DO) set-point was used and the length of the aerobic and anoxic time (anoxic time = 25% of total cycle time) were changed based on the effluent ammonia concentration. Unlike continuously aerated ammonia-based aeration control strategies, this approach offered control over the aerobic solids retention time (SRT) to deal with fluctuating ammonia loading without solely relying on changes to the total SRT. This approach allowed the system to be operated at a total SRT with a small safety factor. The benefits of operating at an aggressive SRT were reduced hydraulic re...

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

This study describes the development of a modified activated sludge model No.1 framework to descr... more This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to pa...

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

The main challenge in implementing shortcut nitrogen removal processes for mainstream wastewater ... more The main challenge in implementing shortcut nitrogen removal processes for mainstream wastewater treatment is the out-selection of nitrite oxidizing bacteria (NOB) to limit nitrate production. A model-based approach was utilized to simulate the impact of individual features of process control strategies to achieve NO(-)2-N shunt via NOB out-selection. Simulations were conducted using a two-step nitrogen removal model from the literature. Nitrogen shortcut removal processes from two case studies were modeled to illustrate the contribution of NOB out-selection mechanisms. The paper highlights a comparison between two control schemes; one was based on online measured ammonia and the other was based on a target ratio of 1 for ammonia vs. NOx (nitrate + nitrite) (AVN). Results indicated that the AVN controller possesses unique features to nitrify only that amount of nitrogen that can be denitrified, which promotes better management of incoming organics and bicarbonate for a more efficien...

Water science and technology : a journal of the International Association on Water Pollution Research, 2014

Current anaerobic digestion models cannot properly simulate processes that are operated under hig... more Current anaerobic digestion models cannot properly simulate processes that are operated under high solids concentrations or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these systems without artificially recalibrating the model parameters. Specifically, we implemented the alternate acetate oxidizing mechanism that is more tolerant to ammonia than the standard aceticlastic pathway. Inhibition values were estimated and an empirical function has been used to apply ammonia inhibition. The model also relates metabolic activity to un-ionised species such as undissociated acetic acid as substrate (although not obligatory for all organisms) and unionised ammonia as inhibitor. The model relies on an equilibrium chemistry module (e.g. including the phosphate buffer), resulting in more accurate pH predictions, which is crucial for proper modeling of CO2 and NH3 stripping. Calibration results from thre...

Water science and technology : a journal of the International Association on Water Pollution Research, 2008

This paper presents benefits and potential drawbacks of thermal pre-hydrolysis of sewage sludge f... more This paper presents benefits and potential drawbacks of thermal pre-hydrolysis of sewage sludge from an operator's prospective. The innovative continuous Thermo-Pressure-Hydrolysis Process (TDH) has been tested in full-scale at Zirl wastewater treatment plant (WWTP), Austria, and its influence on sludge digestion and dewatering has been evaluated. A mathematical plant-wide model with application of the IWA Activated Sludge Model No.1 (ASM1) and the Anaerobic Digestion Model No.1 (ADM1) has been used for a systematic comparison of both scenarios--operational plant performance with and without thermal pre-hydrolysis. The impacts of TDH pre-hydrolysis on biogas potential, dewatering performance and return load in terms of ammonia and inert organic compounds (Si) have been simulated by the calibrated model and are displayed by Sankey mass flow figures. Implementation of full scale TDH process provided higher anaerobic degradation efficiency with subsequent increased biogas productio...

Water science and technology : a journal of the International Association on Water Pollution Research, 2007

Different digestion technologies for various substrates are addressed by the generic process desc... more Different digestion technologies for various substrates are addressed by the generic process description of Anaerobic Digestion Model No. 1. In the case of manure or agricultural wastes a priori knowledge about the substrate in terms of ADM1 compounds is lacking and influent characterisation becomes a major issue. The actual project has been initiated for promotion of biogas technology in agriculture and for expansion of profitability also to rather small capacity systems. In order to avoid costly individual planning and installation of each facility a standardised design approach needs to be elaborated. This intention pleads for bio kinetic modelling as a systematic tool for process design and optimisation. Cofermentation under field conditions was observed, quality data and flow data were recorded and mass flow balances were calculated. In the laboratory different substrates have been digested separately in parallel under specified conditions. A configuration of four ADM1 model re...

Water Research, 2015

Six methodologically different approaches were evaluated and compared regarding their suitability... more Six methodologically different approaches were evaluated and compared regarding their suitability to quantify and characterise granular anammox biomass. The investigated techniques were gravimetric analysis (GA), activity measurements (AM), Coulter counter analysis (CC), quantitative PCR (qPCR), heme protein quantification (HQ) and the novel image analysis technique Particle Tracking (PT). The focus was set on the development of fast, economic and user-friendly approaches for potential implementation in regular wastewater treatment plant (WWTP) monitoring. To test the effectiveness of each technique, two sample matrices were chosen at the WWTP Strass (Austria): i) sludge liquor of the DEMON tank, treating ammonium-rich reject water of anaerobic digestion via the deammonification process and rich in anammox biomass (SL), and ii) the mainstream biological stage, that has been enriched with anammox biomass for more than two years (B). In both of these plants hydro-cyclones are installed for density-fractioning of the sludge into a low- and a high-density fraction, thus leading to a characteristic anammox distribution in the investigated sample set. All investigated methods could statistically discriminate the SL samples. Heme quantification and qPCR were also able to correctly classify the B-samples and both methods showed a Pearson's correlation coefficient of 0.81. An asset of the PT and CC method is the additional qualitative characterization of granule size distribution that can help to better understand and optimise general process operation (cyclone operation duration and construction characteristics). In combination these two methods were able to elucidate the relationship of gross granule volume and actual biomass, excluding the dead volume of inner cavities and exopolymers. We found a linear sphere-equivalent-radius correction factor (3.96 ± 0.15) for investigated anammox granules, that can be used for the fast and reliable PT technique to avoid biomass overestimation. We also recommend routine HQ and PT analysis as ideal monitoring strategy for anammox abundance in wastewater facilities with the HQ technique entailing the further advantage of being also suited for non-granular anammox biomass.

Biomass and Bioenergy, 2015

ABSTRACT Four start-up strategies were assayed in 75 dm3 continuous stirred-tank reactors to sele... more ABSTRACT Four start-up strategies were assayed in 75 dm3 continuous stirred-tank reactors to select the optimal conditions for the start-up of the demonstration BIO4GAS® plant. Two reactors were completely filled with manure and their temperature increased from 20 to 37 °C at either a slow or fast rate. The other two reactors were started at 37 °C with a seed sludge from a stably operating plant and their load (cattle manure) increased at a low or high rate. Reactor performance was monitored for 35 days. The composition and abundance of the methanogenic communities was determined using a phylogenetic microarray and quantitative PCR. All reactors performed successfully in terms of biogas production and experienced a steady start-up, with pH values above 7.3 and VFA/alkalinity ratios below 0.3, denoting stability. Similar methanogenic loads (averaging 5 × 107 g-1 of 16S rRNA gene copies) were detected in the cattle manure and seed sludge, however the methanogenic diversity was higher in the manure with dominance of Methanosarcina and subdominance of Methanocorpusculum and Methanobrevibacter. Starting-up the reactors with an initial full load of manure and progressively increasing the temperature entailed less changes in the sludge chemical environment and in the dynamics of the dominant methanogens. Using a rate of temperature increase of 0.61 K d−1 proved better than1.21 K d−1 with a methane yield of 103.8 dm3 kg−1 VS and a COD mass removal efficiency of 28.3%. The diverse methanogenic community in the manure easily adapted to reactor upsets due to forced overload conditions.

Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion... more Thermal-hydrolyses (TH) has become an increasingly popular pre-treatment step to sludge digestion at very large utilities and can substantially reduce required digester volumes in space constrained large cities while also allowing for development of regionalized sludge receiving centers. In 2014, DC Water will begin operating a new solids processing train at the Blue Plains Advanced Wastewater Treatment Plant consisting of the CAMBI thermal hydrolysis process for solids pretreatment prior to mesophilic anaerobic digestion. A complete evaluation picture needs to take all impacts on downstream processes into account. The digestion performance at various solids loadings (collection of full-scale data); dewatering performance (full-scale belt-filter-press tests); sludge liquor treatment (DEMON-pilot); pathogen removal, odour issues and land application are discussed in the paper.

Österreichische Wasser- und Abfallwirtschaft, 2012

ABSTRACT Deammonification, the anaerobic oxidation of ammonium by use of anammox bacteria, has pr... more ABSTRACT Deammonification, the anaerobic oxidation of ammonium by use of anammox bacteria, has proved to be an efficient method of treating severely polluted process water from sludge treatment. Particular merits of this method in terms of the overall energy balance of the plant are the low power requirements and the fact that no organic carbon is needed. By shortening the conventional nitrogen conversion via nitrite, the deammonification method produces an increased amount of intermediate products, among which nitrous oxide has some climatic implications. A number of tests have, therefore, been conducted on the nitrous oxide emissions involved in this method. The tests were carried out at a DEMON plant for the treatment of digester supernatant at the sewage treatment plant of Strass in the Ziller valley in Tyrol, in operation since 2004 and run by Abwasserverband Achental-Inntal-Zillertal (AIZ). The results have shown that the proportion of nitrous oxide accounts for about 0.9 % to 1.3 % of the overall amount of treated nitrogen from the process water. These results are in the lower range as compared with other deammonification systems. Since the mechanism of nitrous oxide emission is not yet fully understood, a number of measurements have been performed under different operating conditions. While changes in the leading parameters pH and oxygen do not show any direct influence, increased nitrous oxide emissions have been seen to occur under conditions of nitrite accumulation. By preventing nitrite accumulation, the pH control of the singlestage DEMON process reduces the nitrous oxide emissions. An appropriate feed reservoir to harmonise process water intake prevents variations in operating conditions, which otherwise would cause increased nitrous oxide emissions.