Efficiency of Sidestream Nitritation for Modern Two-Stage Activated Sludge Plants.

The operational costs of wastewater treatment plants (WWTPs) are mainly driven by electric power consumption, making the energy-efficient operation an all-time present target for engineers and operators. A well known approach to reduce the demand for purchased electricity is the operation of an anaerobic sludge stabilisation process. Although anaerobic digesters make it possible to recover large quantities of energy-rich methane gas, additional strategies are required to handle the increased internal return flow of nitrogen, which arises with the sludge dewatering effluent (SDE).

Influence of road salt thawing peaks on the inflow composition and activated sludge properties in municipal wastewater treatment.

Operational data over 2 years from three large Austrian wastewater treatment plants (WWTPs) with design capacities of 4 million, 950,000 and 110,000 population equivalent (PE) were examined. Salt peaks, due to thawing road salt were detected and quantified by electrical conductivity, temperature and chloride measurement in the inflow of the WWTPs. Daily NaCl inflow loads up to 1,147 t/d and PE-specific loads of 0.

A method to estimate the direct nitrous oxide emissions of municipal wastewater treatment plants based on the degree of nitrogen removal.

The greenhouse gas nitrous oxide (NO) is produced in activated sludge tanks as a byproduct of nitrification and heterotrophic denitrification. Insufficient knowledge on how microbiological NO generation and degradation pathways impact NO emissions in activated sludge tanks still hampers the development of effective mitigation strategies. Our research contributes to overcome this gap by quantifying NO emissions through extensive measurement campaigns at ten full-scale wastewater treatment plants and correlating them to relevant operating parameters by multivariate regression analysis.

Quantifying methane emissions from anaerobic digesters.

In this research, sources of methane emissions of an anaerobic digester (AD) system at a municipal wastewater treatment plant (WWTP) with 260,000 population equivalent (PE) capacity were detected by a non-dispersive infrared (NDIR) camera. The located emissions were evaluated qualitatively and were documented with photographs and video films. Subsequently, the emission sources were quantified individually using different methods like the Flux-Chamber method and sampling from the digester's circulation pipe.

Nitrous oxide emissions from aerobic granular sludge.

The emissions of climate-relevant nitrous oxides from wastewater treatment with aerobic granular sludge (AGS) are of special interest due to considerable structural as well as microbiological differences compared with flocculent sludge. Due to the compact and large structures, AGS is characterised by the formation of zones with different dissolved oxygen (DO) and substrate gradients, which allows simultaneous nitrification and denitrification (SND). NO emissions from AGS were investigated using laboratory-scale SBR fed with municipal wastewater.

Comparison of aerobic granulation in SBR and continuous-flow plants.

Up to now, aerobic granulation of activated sludge is only realised in SBRs, where the discontinuous feed and sedimentation allow the formation of dense granules with excellent settling properties. However, aerobic granulation in continuous-flow plants (CFP) is gaining more and more interest in order to exploit the advantages of these excellent sludge properties to construct compact and efficient WWTP. Within the scope of this project, a SBR and CFP were operated in parallel to investigate the aerobic granulation of activated sludge and to compare the biomass in terms of their structure and settling behavior.

Rheology and friction loss of raw and digested sewage sludge with high TSS concentrations: a case study.

High total suspended solids (TSS) digestion of municipal sewage sludge reduces the required space and volume for digestion plants. However, an important consequence of high TSS is the major influence on sludge rheology. The present case study investigates the rheology of sludge from a 130 m high solids digestion pilot plant at Vienna's main wastewater treatment plant (4 M PE).

Energy consumption of agitators in activated sludge tanks - actual state and optimization potential.

Depending on design capacity, agitators consume about 5 to 20% of the total energy consumption of a wastewater treatment plant. Based on inhabitant-specific energy consumption (kWh PE a; PE is population equivalent, assuming 120 g chemical oxygen demand per PE per day), power density (W m) and volume-specific energy consumption (Wh m d) as evaluation indicators, this paper provides a sound contribution to understanding energy consumption and energy optimization potentials of agitators. Basically, there are two ways to optimize agitator operation: the reduction of the power density and the reduction of the daily operating time.

The influence of temperature and SRT on high-solid digestion of municipal sewage sludge.

The influence of temperature and solids retention time (SRT) on high-solid digestion of municipal sewage sludge was investigated in laboratory-scale reactors. Digestion with high-solid concentration reduces the required digestion volume and is advantageous for urban areas. The experimental conditions comprised total suspended solids (TSS) in digested sludge between 4.

Energy requirements for waste water treatment.

The actual mathematical models describing global climate closely link the detected increase in global temperature to anthropogenic activity. The only energy source we can rely on in a long perspective is solar irradiation which is in the order of 10,000 kW/inhabitant. The actual primary power consumption (mainly based on fossil resources) in the developed countries is in the range of 5 to 10 kW/inhabitant.

Utilization of activated sludge plants for enhanced treatment of combined sewage.

A process is introduced which utilizes secondary clarifiers for the treatment of combined sewage. Under storm water conditions, surplus sewage bypasses the aeration tanks after primary treatment and is directly introduced into the secondary clarifiers. The hydraulic capacity of existing activated sludge plants can be increased without additional tank volume.

Biogas from sugar beet press pulp as substitute of fossil fuel in sugar beet factories.

Sugar beet press pulp (SBP) accumulates as a by-product in sugar factories and it is generally silaged or dried to be used as animal food. Rising energy prices and the opening of the European Union sugar market has put pressure on the manufacturers to find alternatives for energy supply. The aim of this project was to develop a technology in the treatment of SBP that would lead to savings in energy consumption and would provide a more competitive sugar production from sugar beets.

Modelling of enhanced CSO treatment in secondary clarifiers with a modified Activated Sludge Model no. 3.

An alternative approach for combined water treatment as opposed to its CSO discharge into receiving water is its bypass to the inlet of secondary clarifiers (SC). To analyse the processes and to evaluate the performance of this approach, experiments and numerical modelling were carried out. In batch and pilot scale experiments major effects were identified and quantified.

Post-aeration of anaerobically digested sewage sludge for advanced COD and nitrogen removal: results and cost-benefit analysis at large-scale.

At a large Austrian municipal wastewater treatment plant enhanced stabilisation of anaerobically digested sewage sludge was required in order to get a permit for landfill disposal of the dewatered stabilized sludge. By implementing a post-aeration treatment after anaerobic digestion the organic content of the anaerobically well digested sludge can be decreased by 16%. Investigations at this plant showed that during digested sludge post-aeration anoxic phases are needed to provide stable process conditions.

Aeration of anaerobically digested sewage sludge for COD and nitrogen removal: optimization at large-scale.

The paper will report about the experiences at an Austrian large wastewater treatment plant of 720,000 population equivalents, where anaerobically digested sewage sludge is further stabilised under aerobic conditions. Enhanced stabilisation of the anaerobically digested sludge was required at the plant in order to get a permit for landfill disposal of the dewatered stabilized sludge. By implementing a post-aeration treatment (SRT approximately 6d; 36 degrees C) after anaerobic digestion the organic content of the anaerobically well digested sludge can be decreased by 16%.

Application of anaerobic biological treatment for sulphate removal in viscose industry wastewater.

Long term lab-scale and bench-scale experiments were performed to investigate the feasibility of the anaerobic process to treat wastewater from a pulp and viscose fibre industry. Anaerobic wastewater treatment enables an advantageous combination of COD, sulphate and zinc removal from viscose wastewater. The aim of the investigations was to evaluate the influence of the free sulphide concentration on COD and sulphate removal efficiency and on the substrate competition between sulphate reducing and methanogenic bacteria.

The main wastewater treatment plant of Vienna: an example of cost effective wastewater treatment for large cities.

Two-stage activated sludge plants succeed in stable treatment efficiency concerning carbon removal and nitrification with far less reactor tank volume than conventional single stage systems. In case of large treatment plants this fact is of great economic relevance. Because of the very small specific volume of these two-stage treatment plants in comparison with low loaded single-stage plants, internal cycles have to be applied to ensure sufficient nitrogen removal.

Evaluating the stabilisation degree of digested sewage sludge: investigations at four municipal wastewater treatment plants.

Further reduction of volatile suspended solids (VSS) during a post-stabilisation step was applied to evaluate the stabilisation degree of digested sewage sludge. For this purpose digested sludge was collected at four municipal wastewater treatment plants (WWTPs) and further stabilised in lab-scale chemostat reactors either under anaerobic or aerobic conditions. Experimental results showed that even in adequately digested sludge a consistent amount of VSS was degraded during aerobic post-stabilisation.

Nutrient removal process development and full scale implementation at the 4 million p.e. main treatment plant of Vienna, Austria.

The Main Treatment Plant of Vienna is in extension for 4 million p.e. and very stringent nutrient removal requirements.

Optimum aerobic volume control based on continuous in-line oxygen uptake monitoring.

Dynamic adaptation of the aerated volume to changing load conditions is essential to maximise the nitrogen removal performance and to minimise energy consumption. A control strategy is presented which provides optimum aerobic volume control (OAV-control concept) based on continuous in-line oxygen uptake monitoring. For ammonium concentrations below 1 mg/l the oxygen uptake rate shows a strong and almost linear dependency on the ammonium concentration.

The effect of low sludge age on wastewater fractionation (S(S), S(I)).

In lab-scale experiments at the 2-stage activated sludge pilot plant of Vienna's central WWTP it is shown that the wastewater soluble COD concentration, which is inert to a sludge with SRT < 1 d (SI(A)) is about double compared to the S(I) concentration in sludge with SRT > 10 d (SI(B)). Unexpectedly the ratio of SI(A)/SI(B) is independent of the sludge age between SRTs of 0.4 and 1.

Two stage activated sludge plants--influence of different operational modes on sludge bulking and nitrification.

Conventional two stage activated sludge plants often lack sufficient nutrient removal performance due to substrate limitation for denitrification in the second stage. For the extension of the Vienna Main WWTP a two stage concept has been developed and tested by means of a pilot plant (scale 1:10.000).

Comparison of different operational modes of a two-stage activated sludge pilot plant for the extension of the Vienna STP.

A pilot plant has been operated over a period of two years in order to investigate the performance and the operating characteristics of the plant concept developed for the extension of the main Vienna STP and to develop a simulation model which will be applied for operation support of the full stage plant. The pilot plant is a two stage activated sludge plant, each stage comprising of four aeration tanks and a clarifier tank. The pilot plant layout allows three different operational modes, each of which has been operated for several periods.

A new approach towards modelling of the carbon degradation cycle at two-stage activated sludge plants.

A pilot plant has been operated in order to investigate the performance and operating characteristics of the plant concept developed for the extension of the main Vienna STP. Due to the different operational modes included in the plant concept, modelling of the carbon degradation becomes of crucial importance. A new activated sludge model is introduced which combines parts of the carbon degradation model concepts as they have been released in the ASM1-model and the ASM3-model, respectively.