V. Parravicini

Effect of sewage sludge treatment and additional aerobic post-stabilization revealed by infrared spectroscopy and multivariate data analysis.

Sewage sludge samples representing different stages during waste water and sewage sludge treatment were collected at four Austrian municipal waste water treatment plants. Changes of sludge composition are reflected by a specific infrared spectroscopic pattern. Anaerobically digested sludge was subjected to aeration in lab-scale reactors in order to find out if post-aeration after anaerobic digestion provides enhanced organic matter degradation and stabilization. Spectral data were evaluated by means of multivariate statistics. Similar spectral characteristics of sludge degradation stages were visualized by principal component analysis. The effect of additional aerobic treatment of anaerobically stabilized sludge was revealed by discriminant analysis that distinguishes additionally aerated sludge from all the other degradation stages of sludge because of changes in the spectral pattern by increasing stabilization. Based on partial least squares regression (PLSR) a correlation coefficient of R(2)=0.91 was found between spectral characteristics and the chemical oxygen demand (COD).

Conserving Biodiversity in a Human-Dominated World: Degradation of Marine Sessile Communities within a Protected Area with Conflicting Human Uses

Conservation research aims at understanding whether present protection schemes are adequate for the maintenance of ecosystems structure and function across time. We evaluated long-term variation in rocky reef communities by comparing sites surveyed in 1993 and again in 2008. This research took place in Tigullio Gulf, an emblematic case study where various conservation measures, including a marine protected area, have been implemented to manage multiple human uses. Contrary to our prediction that protection should have favored ecosystem stability, we found that communities subjected to conservation measures (especially within the marine protected area) exhibited the greatest variation toward architectural complexity loss. Between 1993 and 2008, chronic anthropogenic pressures (especially organic load) that had already altered unprotected sites in 1993 expanded their influence into protected areas. This expansion of human pressure likely explains our observed changes in the benthic communities. Our results suggest that adaptive ecosystem-based management (EBM), that is management taking into account human interactions, informed by continuous monitoring, is needed in order to attempt reversing the current trend towards less architecturally complex communities. Protected areas are not sufficient to stop ecosystem alteration by pressures coming from outside. Monitoring, and consequent management actions, should therefore extend to cover the relevant scales of those pressures.

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.

A method to measure three-dimensional substratum rugosity for ecological studies: an example from the date-mussel fishery desertification in the north-western Mediterranean

The impact of date-mussel fishery on substratum rugosity was evaluated at Capo Noli and Isola di Bergeggi (Savona, north-western Italian coast) in the summer of 2004. A new measure of substratum rugosity was used as a surface-dependent index of complexity. The results were compared between impact and control sites using two-way analysis of variance and suggested that the mussel fishery reduces substratum complexity.

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.

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.