H. Kroiss

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. These goals were met by the anaerobic digestion of SBP for biogas production. Lab-scale experiments confirmed the suitability of SBP as substrate for anaerobic bacteria. Pilot-scale experiments focused on process optimization and procedures for a quick start up and operational control. Both single-stage and two-stage process configurations showed similar removal efficiency. A stable biogas production could be achieved in single-stage at a maximum volumetric loading rate of 10 kgCSB/(m(3) x d). Degradation efficiency was 75% for VS and 72% for COD. Average specific gas production reached 530 NL/kgCOD(SBP) or 610 NL/kgVS(SBP). (CH(4): 50 to 53%). The first large-scale biogas plant was put into operation during the sugar processing period 2007 at a Hungarian sugar factory. Digesting approximately 50% of the SBP (800 t/d, 22%TS), the biogas produced could substitute about 40% of the natural gas required for the thermal energy supply within the sugar processing.

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%. Investigations on site showed that during digested sludge post-aeration anoxic phases for denitrification are needed to provide stable process conditions. In this way the pH value can be kept in a more favourable range for micro-organisms and concrete structures. Additionally, inhibition of the biological process due to nitrite accumulation can be avoided. By optimising the aeration/pause ratio approximately 45% of total nitrogen in digested sludge can be removed. This significantly improves nitrogen removal efficiency at the wastewater treatment plant. NH(4)-removal occurs mainly through nitritation and denitritation with an efficiency of 98%. The costs/benefit analysis shows that post-aeration of digested sludge results in an increase of total annual costs for wastewater treatment of only 0.84%, corresponding to 0.19 Euro/pe/a. Result of molecular biological analyses (DGGE) indicate that all four ammonium-oxidizing bacteria species present in activated sludge can survive anaerobic digestion, but only two of them can adapt in the digested sludge post-aeration tanks. Additionally, in the post-aerated digested sludge a further ammonium-oxidizing bacteria species was identified.

Cost comparison of wastewater treatment in Danubian countries.

This paper investigates the costs of wastewater treatment (including sludge management) within the Danube catchment countries A, CZ, SK, HU, SL, RO, BG and UA. TK is considered as well. Additionally, the paper compares the total costs of wastewater management (including sewage) with the incomes in the different countries. The annual costs of wastewater treatment in Austria are about 30 euro/p.e. y for large plants with nitrogen and phosphorus removal. In low income countries of the Danube and Black Sea catchment areas they are at a maximum 30% lower than in Austria. However, the incomes in countries like Bulgaria, Romania or Ukraine are 85% to 90% lower. The total annual costs for wastewater management (sewer development plus treatment) amount at least to 90 euro/p.e. y. Considering the level of income in those countries, financing of wastewater management completely by charges of the population equivalents connected is not feasible. Therefore other approaches for financing wastewater treatment are required.

daNUbs: Lessons learned for nutrient management in the Danube Basin and its relation to Black Sea euthrophication

The results of the daNUbs-project deliver a basis for a proper management of nutrients in the Danube Basin. The understanding of the sources, pathways, and sinks of nutrients in the Basin and their effects on the Western ad North-Western Black Sea (WBS) ecosystem has been improved. Quantitative models on the emission of nutrients, their transport along the rivers, and their impact on the WBS have been further developed and combined. Phosphorus loads discharged by the Danube are 30–50% lower than in the 1980s (dissolved P even to a higher extent). Nitrogen emissions have decreased considerably as well. The lower nutrient discharges from the Danube have led to a significant improvement in the WBS ecosystem. Current low discharges of N and P to the WBS are the result of (1) improved nutrient removal from waste water in Germany, Austria, and Czech Republic, (2) reduced P-discharges from detergents and (3) the consequences of the economic crisis in central and eastern European countries following the political changes of 1989/1990. As the decrease is partly due to the economic breakdown in the formerly communist countries, economic development in these countries has to go along with proper nutrient management. Otherwise, the situation in the WBS ecosystem will deteriorate again.

Benchmarking of large municipal wastewater treatment plants treating over 100,000 PE in Austria.

During a six-year period the Austrian Benchmarking System was developed. The main objectives of this benchmarking system are the development of process indicators, identification of best performance and determination of cost reduction potentials. Since 2004 this system is operated via an internet platform and automated to a large extent. Every year twenty to thirty treatment plants use the web-based access to this benchmarking platform. The benchmarking procedure comprises data acquisition, data evaluation including reporting and organised exchange of experience for the treatment plant managers. The process benchmarking method links the real costs with four defined main processes and two support processes. For wastewater treatment plants with a design capacity >100,000 PE these processes are further split up into sub-processes. For each (sub-) process the operating costs are attributed to six cost elements. The specific total yearly costs and the yearly operating costs of all (sub-)processes are related to the measured mean yearly pollution load of the plant expressed in population equivalents (PE(110): 110 gCOD/d corresponding to 60 g BOD(5)/d)). The specific capital costs are related to the design capacity (PE). The paper shows the benchmarking results of 6 Austrian plants with a design capacity >100,000 PE representing approximately 30% of the Austrian municipal wastewater treatment plant capacity.

Evaluating the success of sewer reconstruction by using carbamazepine as anthropogenic marker in groundwater

The antiepileptic drug carbamazepine is a useful anthropogenic marker in groundwater to detect and quantify sewer exfiltration. In 2003 its application on a city wide scale enabled the identification of a trunk sewer in extremely bad structural status with an exfiltration (of wastewater into groundwater) rate in the adjacent area of around 5% compared to an average of approximately 1% in other parts of the city. After a reconstruction of the trunk sewer investigations were carried out again in 2008. Due to the reconstruction a decrease in exfiltration to roughly 3% could be achieved, which equals a reduction of exfiltration by about 45%. Thus carbamazepine emerged as suitable anthropogenic marker to assess sewer exfiltration and to evaluate the success of reconstruction measurements on a regional scale.

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. In this way the pH value can be kept in a more favourable range for micro-organisms and concrete structures. Additionally, under the process conditions applied nitrite accumulation would inhibit the stabilisation process if denitrification is not adequately applied. By optimising the aeration/pause ratio approximately 45% of total nitrogen in digested sludge can be removed. NH4-removal occurs through nitrification and denitrification with an efficiency of 98%. This significantly improves nitrogen removal efficiency at the wastewater treatment plant. The costs/benefit analysis shows that post-aeration of digested sludge results in an increase of total annual costs for wastewater treatment of only 0.84%, corresponding to 0.19 Euro/pe/a. Specific costs for nitrogen removal (0.32 Euro/kgN) are comparable with other biological processes for N-removal in reject water.

Phosphorus in Water Quality and Waste Management

Phosphorus (P) is a key element for all living systems. Phosphorus is a component of DNA and RNA and indispensable for the energetic metabolism (ADP/ATP) of living beings. Phosphorus cannot be substituted in these biological functions by any other element. The tremendous growth of global population is therefore linked to a proportional increase of phosphorus requirement for the production of food, which actually to a large extent is depending on the use of mineral phosphorus fertiliser. Many natural (aquatic) ecosystems are controlled by restricted availability of phosphorus which represents one important factor for high biodiversity. The anthropogenic increase of phosphorus flows therefore has the potential to cause severe negative effects on natural (aquatic) ecosystems (see section 2).1 Roughly 80 90% of the extracted phosphate rock is used for food production and nutrition. Given that P is a non-renewable resource and the global reserves are limited (contrary to nitrogen another essential nutrient) the aspects of scarcity and recycling/recovery have to be considered. Today’s global mine production and reserves of phosphate rock (average P2O5 content is 31 % (P 13.5 %), ranges from 26 34 % (P 11 15 %) (Kratz et al, 2007; Steen, 1998) are reported ca. 160 Mio t/a and 16 billion tons, respectively (USGS, 2010). This gives a static lifetime for the reserves of some 120 years, a number which has been similarly reported by several authors before (Rohling, 2007; Wagner, 2005; Rosmarin, 2004; Pradt, 2003; Steen, 1998; Herring et al., 1993), others come to lifetimes up to hundreds of years (EFMA, 2000). Phosphate ore is produced mostly from open pit mines, resulting in dust emissions and large quantities of tailings (mining wastes). Villabla and colleagues (2008) report material and energy consumption data for the production of 1 ton of P2O5 (Table 1). Another major waste is produced at a later stage when wet phosphoric acid (H3PO4) is produced from phosphate rock concentrate using sulphuric acid. This so-called phosphogypsum (ca. 5 tons per ton of wet H3PO4) is normally disposed of at sea or in large-scale settling ponds. It has very little use because it contains a considerable number of impurities such as Cadmium and radioactive elements (Villabla et al., 2008).

Anaerobe biologische Sulfatentfernung aus Industrieabwässern am Beispiel einer Viskosefabrik

KurzfassungIm Rahmen eines vierjährigen Forschungsprojektes wurde am Institut für Wassergüte, Ressourcenmanagement und Abfallwirtschaft, Fakultät für Bauingenieurwesen, Technische Universität Wien die grundsätzliche Brauchbarkeit des anaeroben Reinigungskonzeptes zur Behandlung ausgewählter Abwasserströme aus einer Zellstoff-Viskosefaserfabrik in Labor-bzw. Pilotversuchen überprüft. Ziel der Untersuchungen war die Ermittlung der möglichen Belastungskennwerte und der tolerierbaren H2S-Konzentrationen, um einen stabilen Prozess und eine optimierte Sulfatentfernung zu gewährleisten. Da im zu behandelnden Abwasser die CSB-Fracht für eine vollständige Sulfatentfernung limitiert war, wurde angestrebt, die sulfatreduzierenden Bakterien bei der Substratkonkurrenz mit den Methanbakterien durch die Steuerung der Prozessbedingungen zu unterstützen. Die Untersuchungsergebnisse lieferten die Auslegungsdaten für die großtechnische Anlage zur Sulfatreduktion.SummaryLong term lab-scale experiments were performed at the Institute for Water Quality, Resources and Waste Management, at the Faculty of Civil Engineering, Vienna University of Technology to investigate the feasibility of the anaerobic process to treat wastewater from a pulp and viscose fibre industry. In particular, 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. Since the wastewater did not contain enough COD for complete sulphate removal it was of main interest to determine favourable process conditions to steer the substrate competition in favour of sulphate reduction. Further experiments in bench-scale permitted to evaluate applicable COD-loading rates and gain fundamental information about process stability and optimization for large scale implementation.

New Regulations for the Treatment of Combined Sewage in Austria — Based on Minimum Requirements and Water Quality Criteria

The minimum requirements for receiving water protection from combined sewer overflows laid down in the draft of the new regulations for Austria result in a significant reduction of the discharges of raw wastewater, suspended solids and heavy metals from urban sewer systems. For this reason it is not advisable to design CSOs on the basis of water quality criteria alone. However the minimum requirements for CSO design have to be characterised by a reasonable cost-benefit ratio. It was recommended to initially set low requirements (e.g. minimum efficiencies requiring specific volumes of storage tanks not exceeding 10–15 m3/ha impervious area) for CSOs located in less sensitive (“normal”) waters, and to make provision for potential upgrading. Development of minimum requirements in form of percentage load reduction requirements (instead of construction guidelines) for the entire catchment (instead of single CSO structures) makes planning significantly more flexible.