Henrik Aspegren

Storage and degradation of poly-β-hydroxybutyrate in activated sludge under aerobic conditions

This research analyses the accumulation and degradation of poly-beta-hydroxybutyrate (PHB) in experiments with pulse addition of acetate to samples of activated sludge from pilot-plant and full-scale wastewater treatment plants. The experiments are divided into two periods: a feast period defined as the time when acetate is consumed and a famine period when the added acetate has been exhausted. In the feast period the significant process occurring is the production of PHB from acetate. The produced PHB is utilised in the famine period for production of glycogen and biomass. According to modelling results approximately 90% of the total potential growth occurs in the famine period utilising the stored PHB. The degradation rate for PHB in the famine period is found to be dependent on the level of PHB obtained at the end of the feast period. It was found that multiple order kinetics gives a good description of the rate of PHB degradation. The examined sludge of low SRT origin is found to degrade PHB faster than long SRT sludge at high fractions of PHB. The observed yield of glycogen on PHB in the famine period is in the range of 0.22-0.33 g COD/g COD depending on the SRT. The storage pool of glycogen in the examined sludge is more slowly degraded than PHB (COD/COD/h).

Calcium phosphate precipitation in biological phosphorus removal systems

Abstract Since the early days of the use of the excess biological phosphorus removal (EBPR) process, it has been discussed whether and to what extent, chemical precipitation contributes to the phosphorus removal that is seen in the process. In this study, calcium phosphate precipitation in EBPR systems was investigated. Four laboratory-scale fill and draw activated sludge systems operating in parallel, fed with natural Ca-rich wastewater, with additions of acetate and phosphate were studied. Two of the systems were operated as EBPR systems and the remaining two as aerobic systems. The results showed that calcium phosphate precipitation occurred in all the systems at sufficiently high concentrations of calcium and phosphate. Based on differences in the effluent water, the Ca/P molar ratio of the precipitate was found to be around 1–1.3. Redissolution occurred when the concentrations of calcium and phosphate had fallen below the saturation curve for Ca3(PO4)2 at neutral pH, and below the saturation curve for CaHPO4 at pH ≈ 8.5. The results also showed that the concentration of phosphate in the effluent from the EBPR system could be substantially lower than from the aerobic system, for the same effluent concentration of calcium. This indicates that there is an important time factor involved, which implies that simple equilibrium equations cannot be used alone to judge whether or to what extent, precipitation will take place. The results suggest that at neutral pH the phosphate concentration must be at least 50 mg P l−1 at a calcium concentration of 100 mg Ca l−1, and in soft water much higher, before precipitation starts. This, together with the fact that redissolution starts at phosphate concentrations far above 1 mg P l−1 indicates that in most cases calcium phosphate precipitation in EBPR processes with municipal wastewater does not constitute a significant phosphorus removal mechanism.

Long-term population dynamics and in situ physiology in activated sludge systems with enhanced biological phosphorus removal operated with and without nitrogen removal

Quantitative fluorescence in situ hybridization (FISH) and the combination of FISH with microautoradiography (MAR) were used in order to study the long-term population dynamics (2.5 years) and the in situ physiology in two parallel activated sludge pilot systems with enhanced biological phosphorus removal (EBPR). The two systems received the same influent wastewater, but were differently operated (with and without nitrogen removal, respectively). Both systems showed a significant P removal that increased when different substrates (phosphorus (P), acetate and glucose, respectively) were added to the influent wastewater. Rhodocyclus-related bacteria were present in both systems in significant numbers (ranging from 4 to 28%) throughout the whole period. This supports the hypothesis that these bacteria occur in significant numbers in different types of well-operating EBPR activated sludge processes. However, we observed a lower correlation (< 0.5) for the amount of Rhodocyclus-related bacteria to the P content in activated sludge than previous studies (> 0.9). The Actinobacteria were the only additional group of bacteria which showed a similar degree of correlation to the P content in activated sludge as the Rhodocyclus-related bacteria--but only for the system without nitrogen removal. Significant amounts (< or = 12%) of glycogen-accumulating bacteria (GAOs) were detected in the system with nitrogen removal (but not in the other system), but had no, in contrast to previous observations, apparent negative effect on the overall EBPR performance. FISH-MAR indicated that a significant part of the Betaproteobacteria (part of them identified as Rhodocyclus-related bacteria) as well as the Actinobacteria were able to take up 33Pi, [3H]-acetate and [3H]-glucose under anaerobic-aerobic conditions. The contribution of anoxic 33Pi uptake under alternating anaerobic-anoxic conditions was significantly lower. Interestingly, not all Rhodocyclus-related bacteria showed uptake of these three radioactive substrates. This may be due to differences in metabolic state, physiological potential or genotype, not detectable by the present probe set for Rhodocyclus-related bacteria. Comparison of the 33Pi, [3H]-acetate and [3H]-glucose uptake by activated sludge after different fixation and incubation procedures showed that a part of the observed 33Pi uptake may have been caused by a combination of a biological and chemical or biologically induced chemical P adsorption.

Life cycle assessment of a household solid waste source separation programme: a Swedish case study

The environmental impact of an extended property close source-separation system for solid household waste (i.e. a systems for collection of recyclables from domestic properties) is investigated in a residential area in southern Sweden. Since 2001, households have been able to source-separate waste into six fractions of dry recyclables and food waste sorting. The current system was evaluated using the EASEWASTE life cycle assessment tool. Current status is compared with an ideal scenario in which households display perfect source-separation behaviour and a scenario without any material recycling. Results show that current recycling provides substantial environmental benefits compared to a non-recycling alternative. The environmental benefit varies greatly between recyclable fractions, and the recyclables currently most frequently source-separated by households are often not the most beneficial from an environmental perspective. With optimal source-separation of all recyclables, the current net contribution to global warming could be changed to a net-avoidance while current avoidance of nutrient enrichment, acidification and photochemical ozone formation could be doubled. Sensitivity analyses show that thetype of energy substituted by incineration of non-recycled waste, as well as energy used in recycling processes and in the production of materials substituted by waste recycling, is of high relevance for the attained results.

Property-close source separation of hazardous waste and waste electrical and electronic equipment - A Swedish case study.

Through an agreement with EEE producers, Swedish municipalities are responsible for collection of hazardous waste and waste electrical and electronic equipment (WEEE). In most Swedish municipalities, collection of these waste fractions is concentrated to waste recycling centres where households can source-separate and deposit hazardous waste and WEEE free of charge. However, the centres are often located on the outskirts of city centres and cars are needed in order to use the facilities in most cases. A full-scale experiment was performed in a residential area in southern Sweden to evaluate effects of a system for property-close source separation of hazardous waste and WEEE. After the system was introduced, results show a clear reduction in the amount of hazardous waste and WEEE disposed of incorrectly amongst residual waste or dry recyclables. The systems resulted in a source separation ratio of 70 wt% for hazardous waste and 76 wt% in the case of WEEE. Results show that households in the study area were willing to increase source separation of hazardous waste and WEEE when accessibility was improved and that this and similar collection systems can play an important role in building up increasingly sustainable solid waste management systems.

Interactions between wastewater quality and phosphorus release in the anaerobic reactor of the EBPR process

Abstract Studies on enhanced biological phosphorus removal (EBPR) operation in activated sludge processes have been conducted on a pilot plant at the Sjolunda wastewater treatment plant in Malmo, Sweden, since 1986. The plant receives wastewater from a combined sewer system. The aim of this study was to investigate interactions between variations in the wastewater quality and the effect on the EBPR operation. The paper focuses on the overall role of the concentration of volatile fatty acids (VFA) in the influent wastewater on the EBPR process. Firstly, the relation between VFA, COD and phosphorus in the influent wastewater at the plant is examined. Secondly, the effect of pH on phosphate release under anaerobic conditions is investigated. Finally, the observed relation between phosphate release in the anaerobic zone in relation to the concentration of VFA in the influent wastewater is discussed. The pilot plant consists of two parallel, activated sludge systems with EBPR, one system with a solids retention time (SRT) of 4 days, operated without nitrification-denitrification and one system with a SRT of 21 days, operated with nitrification-denitrification. Results derived from daily, composite samples taken over 3 yr have formed the basis of a general description of the water quality and the performance of the process. In addition, intensive field studies and laboratory studies have been used as ways of investigating certain phenomena in more detail. The results of the pilot plant study showed that the concentration of total phosphorus on average was low in the effluent, below 0.5 mg P/l. Increased phosphorus concentrations were, however, observed on a number of occasions. High concentrations of phosphorus in the effluent were observed every year in July, which is the holiday period at industrial plants in Sweden. Other instances of increased phosphorus concentrations in the secondary effluent were recorded after prolonged periods of rain. Increasing flow rates due to rain lead to a dilution and a change in the composition of the COD in the influent wastewater. A laboratory study showed that the ratio of phosphorus release/HAc uptake depends on pH in the range of 6–8. At neutral pH a ratio of 0.35-0.4 mg P/mg COD was found. The results of an intensive field study on the pilot plant suggested a relationship of 0.5 mg P/mg COD. Hydrolysis and/or fermentation processes have to be taken into account when describing phosphorus release in the anaerobic reactor. However, it was clearly demonstrated that it is primarily the VFA in the influent wastewater that affect the release of phosphorus in the systems studied.

Local strategies for efficient management of solid household waste – the full-scale Augustenborg experiment

A system with property-close source-separation of thirteen different solid household waste fractions in a residential area in southern Sweden, including the implementation of new systems for source-separation of food waste, waste electric and electronic equipment, hazardous waste and fat, oils and grease was monitored over a 2-year period. Continuous weighing of disposed waste and repeated waste composting analyses were used to investigate recycling behaviour of households in the area and to monitor the composition of disposed waste. Results show that 34% of the total amount of generated waste was currently diverted to material recycling. The removal of recyclables from residual waste could be significantly increased, as more than 80% of all waste in the area (bulky waste excluded) was either covered by the Producer Responsibility Ordinances on packaging and newspaper or constitutes food waste suitable for biogas production. Food waste still represented almost 30% of all residual waste in the study area and was thus the fraction with the greatest potential (on weight basis) for increased source-separation.

The Urban Water System - a Future Swedish Perspective

It is argued, that the use of water can no longer be regarded as an almost free commodity. The idea to assess and value the environmental impact of the water use represents a true change of paradigm. The key issue is that any future wastewater treatment system has to be evaluated according to a quantitative criterion. This has to consider: •hygienic aspects: we believe that nobody will accept a lower hygienic standard than today. •environmental impact: the wastewater impact on the environment has steadily increased the need for better treatment. We need to be prepared for changes in the society by having a readiness manifested as continuing dynamic research environment in this area. Too often the knowledge build-up has been re-active instead of pro-active. •economising resources: wastewater treatment looks and probably should look quite different in densely populated urban areas and in rural areas. Considering resource handling one has to consider already invested capital costs, land use, water re-use, organic and nutrient use and re-use, as well as overall use of energy. •user aspects: technical functionality, economy and liability in different aspects require profound consideration. A sustainable wastewater treatment has to adapt to a local environment and the total resource demand has to be calculated, including a direct environmental impact on receiving waters, air and soil as well as energy consumption and nutrient recycling. Thus, there is an apparent need for. •quantitative performance index: the quest for sustainable development has to be based on objective reasons as well as subjective ones. An integrated performance index is part of a necessary decision making model for the design and operation of wastewater treatment systems. In this index, it is evident that a trade-off should be made between the pursued quality of the process outputs (liquid, solids, gas) and the associated efforts (investments, operation) required to achieve this considering the inputs (wastewater). In order to make this trade-off, however, a common framework is needed to quantitatively compare the different objectives. A metric to judge the sustainability of different options will facilitate a fruitful dialogue between e.g. politicians, ecologists, engineers and economists. Only a truly interdisciplinary approach can help to solve the challenges ahead. (Less)

New Projects, Building on Previous Experience

In the years after the Bo01 project, new developments were made in the Western Harbor area in Malmo (Fig. 6.1). A large development site was also built in the Hyllie area, south of the city center (Fig. 6.2). Much of the experience gathered in relation to solid waste management from previous development areas came to be used in the development of these two sites.

From Idea to Reality: The City as a Test Bed

Little guidance is provided for local actors in their work toward achievement of national environmental objectives related to waste management and the overall goal stated in national waste plans. Thus, there is a need for proactive and innovative measures to be taken at municipal level. In Malmo, different geographical areas of the city have been used as a test bed for innovative waste management strategies. This has provided possibilities for parallel introduction of different technologies, full-scale management systems, and information strategies, and thus comparative evaluations of these.