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| 2. |
- Olsson, Jesper, 1975-, et al.
(författare)
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Anaerobic co-digestion of sludge and microalgae grown inmunicipal wastewater : A feasibility study
- 2018
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 77:3, s. 682-694
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Tidskriftsartikel (refereegranskat)abstract
- In this study a natural mix of microalgae grown in wastewater of municipal character was co-digested with sewage sludge in mesophilic conditions, in both batch and semi-continuous modes. The semicontinuous experiment was divided into two periods with OLR 1 (Organic Loading Rate) of 2.4 kg VS m3 d-1 and HRT1 (Hydraulic Retention Time) of 15 days, and OLR2 of 3.5 kg VS m3 d-1 and HRT2 of 10 days respectively. Results showed stable conditions during both periods. The methane yield was reduced when adding microalgae (from 200 ± 25 NmL CH4 g VSin-1 , to 168±22 NmL CH4 g VSin-1). VS reduction was also decreased by 51%. This low digestability was confirmed in the anaerobic batch test. However, adding microalgae improved the dewaterability of the digested sludge. The high heavy metals content in the microalgae resulted in a high heavy metals content in the digestate, making it more difficult to reuse the digestate as fertilizer on arable land. The heavy metals are thought to originate from the flue gas used as a CO2 source during the microalgae cultivation. Therefore the implementation of CO2 mitigation via algal cultivation requires careful consideration regarding thesource of the CO2-rich gas.
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| 3. |
- Olsson, Jesper, 1975-, et al.
(författare)
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Co-digestion of cultivated microalgae and sewage sludge from municipal waste water treatment
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- One way to meet the increased demand for biogas in the society is to use microalgae as substrate. These algae would be cultivated in a treatment step of photobioreactors for reject water from sludge dewatering facilities. In the present study, a co-digestion experiment was established where sludge from a municipal wastewater treatment plant was fermented with harvested microalgae cultivated in lake water from lake Mälaren. The experiment was carried out as a BMP-test (Biochemical Methane Potential) under mesophilic condition (37°C) with fermentation bottles, where 0, 12, 25 and 37%, of the sludge was replaced with harvested microalgae. The results showed that the biogas production was improved with 12% for the bottles with 12% microalgae compared with the bottles with only sludge as a substrate. In the bottles with 25% and 37% microalgaes the gas production was slightly reduced compared with the bottles where only sludge was used.
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| 4. |
- Olsson, Jesper, 1975-
(författare)
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Co-digestion of microalgae and sewage sludge - A feasibility study for municipal wastewater treatment plants
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increased emissions of anthropogenic greenhouse gases over the last 100 years is the reason for the acceleration in the greenhouse effect, which has led to an increase of the globally averaged combined land and ocean surface temperature of 0.85 °C between 1880 and 2012. A small fraction of the increased anthropogenic greenhouse gases originates from municipal wastewater treatment plants (WWTPs).This doctoral thesis was part of a larger investigation of using an alternative biological treatment based on the symbiosis of microalgae and bacteria (MAAS-process (microalgae and activated sludge)). This solution could be more energy efficient and potentially consume carbon dioxide from fossil combustion processes and also directly capture carbon dioxide from the atmosphere and thereby reduce the addition of anthropogenic greenhouse gases to the air. The objective of the thesis was to explore the effects when the microalgae-derived biomass from the biological treatment were co-digested with sewage sludge. The results from these experimental studies were then used to evaluate the effects on a system level when implementing microalgae in municipal WWTP. Microalgae grown from a synthetic medium improved the methane yield with up to 23% in mesophilic conditions when part of the sewage sludge was replaced by the microalgae. The microalgae grown from municipal wastewater showed no synergetic effect. In the semi-continuous experiments the methane yield was slightly reduced when implementing the microalgae. Furthermore the digestibility of the co-digestion between sewage sludge and microalgae were lower compared to the digestion of sewage sludge. The digestates containing microalgal substrate had higher heavy metals content than digestates containing only sewage sludge. This could have a negative effect on the potential to use this digestate on arable land in future, due to strict limits from the authorities. Filterability measurements indicated that the addition of microalgae enhanced the dewaterability of the digested sludge and lowered the demand for polyelectrolyte significantly. When a hypothetical MAAS-process replaced a conventional ASP-process the amount of feedstock of biomass increased significantly due to the increased production from the autotrophic microalgae. This increased the biogas production by 66-210% and reduced the heavy metal concentration in the digestate due to a dilution effect from the increased biomass production. The thesis demonstrates that microalgae in combination with bacteria from a MAAS-process can be a realistic alternative feedstock to WAS in the anaerobic digestion at a municipal WWTP. A few drawbacks need to be considered when choosing a MAAS-process as biological treatment.
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| 5. |
- Olsson, Jesper, 1975-, et al.
(författare)
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Co-digestion of microalgae, grown on municipal wastewater, and primary sewage sludge– : Pilot study in thermophilic and mesophilic conditions
- 2017
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Konferensbidrag (refereegranskat)abstract
- The most common biological treatment in a municipal waste water today is the activated sludge process (ASP). A possible substitution of the ASP could be the utilization of microalgae for the reduction and/or transformation of nutrients. The produced algal biomass can be converted to biofuel by anaerobic digestion. In the present study, co-digestion of primary sludge and microalgae are studied in semi-continuous tests at mesophilic and thermophilic conditions. Two reactors fed by waste activated sludge and primary sludge are used as reference. The results show that thermophilic digestion of microalgae and primary sludge is less attractive since the methane yield is approximately the same as the mesophilic digestion. In mesophilic conditions the results are approximately the same in the two pilot reactors and also comparable with the mesophilic full-scale digesters in Västerås, Sweden.
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| 6. |
- Olsson, Jesper, 1975-, et al.
(författare)
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COMPARATIVE STUDY – PHARMACEUTICAL RESIDUES IN WASTEWATER AND SLUDGE FROM A MICORALGAE PLANT AND AN ACTIVATED SLUDGE PROCESS
- 2016
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Konferensbidrag (refereegranskat)abstract
- This study explores the possibility of using a microalgae based activated sludge – process (MAAS-process) to increase the reduction of pharmaceutical residues in outgoing wastewater, compared to a conventional wastewater treatment plant with activated sludge process. In an on-site study, residual sludge from four pilot scale digesters fed with primary sludge and waste activated sludge or microalgae were sampled and analysed for pharmaceutical residues. The aim of the study was to compare the reduction efficiencies of a microalgae based process with a conventional biological treatment and also to explore the reduction of the residues in the different process steps including the sewage sludge thickening before the anaerobic digestion, the digestion and the secondary treatment with the sludge dewatering process. The results show that the total reduction of pharmaceutical residues in the water phase appears to be significantly higher in the MAAS-process. The substance diclofenac was not degraded in any of the biological processes in the study. The reduction of pharmaceutical residues in digested sludge seems to be higher in mesophilic conditions compared with thermophilic conditions.
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| 7. |
- Olsson, Jesper, 1975-
(författare)
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Enhanced biogas production from municipal WWTPs : Co-digestion of microalgae with sewage sludge and thermophilic secondary digestion of mesophilic digested sludge
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Biogas is produced when organic material is broken down in oxygen-free (anaerobic) conditions. This process is called anaerobic digestion and is used in most large and medium-sized municipal wastewater treatment plants in Sweden. In the wastewater treatment sewage sludge is obtained, from the mecanical-, biological and chemical treatment step, which contains decomposable organic material. The sludge is pumped into a digester, which is an airtight container. In the digester raw biogas, consisting of methane and carbon dioxide, is produced. The material that comes out of the digester is a nutrient rich residue (digestate) which can be used as a fertilizer or soil conditioner. The purpose of this study was to explore ways to increase the biogas production that takes place at the municipal wastewater treatment plants by either co-digestion of sewage sludge with microalgae from a possible future biological purification steps or to use two digestion stages in series with different operating temperatures, mesophilic (37ºC) followed by a thermophilic digestion (55ºC). The challenges with these methods, which are also taken into consideration in the studies, were changes in the dewaterability of the digestate, system efficiency regarding electricity and heat consumption, the ability to recycle nutrients, changes in the carbon footprint from the treatment plant, change of the pollution level in the digestate and the ability to create a sanitization method for the digestate.The results from the first part showed in both batch digestability tests and continuous anaerobic digestion experiment that microalgae cultivated on wastewater can be a feasible feedstock for anaerobic co-digestion with sewage sludge. Microalgae improved the biogas production in mesophilic conditions but not in thermophilic digestion. In the semi-continous experiment, with the addition of a natural mix of microalgae grown from wastewater to sewage sludge, the specific methane production was enhanced with 39 % for every gram organic matter reduced. The specific methane production for every gram added organic matter to the reactors were 9% lower in the digester where microalgae had been added. When microalgae were added the total digestibility was reduced compared to the reference digestion with only sewage sludge. Filterability tests indicated that the addition of microalgae enhanced the dewaterability of the digested sludge. Heavy metal levels in the microalgae substrate were much higher than in the sludge which could restrict the utilization of the digestate on arable land in a possible future full scale application.The results in the second part showed that the process solution could be a self-sufficient sanitation method. The highest organic loading rates tested in this study were in the range causing an unstable process due to high ammonia levels The thermophilic digestion gave the sludge worse dewaterability. However, a subsequent aeration step could improve the properties again.
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| 8. |
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| 9. |
- Olsson, Jesper, 1975-, et al.
(författare)
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Microalgae as biological treatment for municipal wastewater - Effects on the sludge handling in a treatment plant
- 2018
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 78:3, s. 644-654
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Tidskriftsartikel (refereegranskat)abstract
- A mix of microalgae and bacteria was cultivated on pre-sedimented municipal wastewater in a continuous operated microalgae-activated sludge process. The excess material from the process was co-digested with primary sludge in mesophilic and thermophilic conditions in semi-continuous mode (5 L digesters). Two reference digesters (5 L digesters) fed with waste-activated sludge (WAS) and primary sludge were operated in parallel. The methane yield was slightly reduced (≈10%) when the microalgal-bacterial substrate was used in place of the WAS in thermophilic conditions, but remained approximately similar in mesophilic conditions. The uptake of heavy metals was higher with the microalgal-bacterial substrate in comparison to the WAS, which resulted in higher levels of heavy metals in the digestates. The addition of microalgal-bacterial substrate enhanced the dewaterability in thermophilic conditions. Finally, excess heat can be recovered in both mesophilic and thermophilic conditions.
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| 10. |
- Olsson, Jesper, 1975-, et al.
(författare)
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TRANSITION OF MESOPHILIC TO THERMOPHILIC DIGESTION OF SEWAGE SLUDGE
- 2016
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Ingår i: TRANSITION OF MESOPHILIC TO THERMOPHILIC DIGESTION OF SEWAGE SLUDGE.
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Konferensbidrag (refereegranskat)abstract
- In this comparative study two types of temperature transition strategies from mesophilic to thermophilic conditions in anaerobic digestion was explored. Both strategies used a rapid increase from 37 to 55°C with a constant organic loading rate (2.4 kg VS m-3 d-1) and hydraulic retention time (14 d). The two digesters used the same mesophilic inoculoum but in the second digester a small share of thermophilic digeastate was also inoculated. A comparative dewaterability study between the fullscale mesophilic digestate and the thermophilic digestates were also performed as part of the study. The results showed a stabilization in both digesters within 14 days (1 Hydraulic retention time). The digester where a small share of thermophilic inoculum was introduced had a higher methane production compared to the control reactor where just mesophilic inoculum was used. The comparative dewaterability study showed a deterioration of the dewaterability in both digesters when thermophilic conditions was established.
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