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  • 1.
    Lönnqvist, Tomas
    et al.
    KTH, Energi och klimatstudier, ECS.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. MDH.
    Espinosa, Cecilia
    Center for Promotion of Sustainable Technology (CPTS).
    Birbuet, Juan Cristóbal
    Center for Promotion of Sustainable Technology (CPTS).
    Silveira, Semida
    KTH.
    Dahlquist, Erik
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Persson, Per-Erik
    VAFAB Miljö AB.
    Lindblom, Sandra
    VAFAB Miljö AB.
    Khatiwada, Dilip
    KTH.
    The potential for waste to biogas in La Paz and El Alto in Bolivia2013In: 1st International Water Association Conference on HolisticSludge Management, 2013, Västerås Sweden, 2013Conference paper (Refereed)
    Abstract [en]

    In the cities of La Paz and El Alto, 573 tons of organic material are disposed in landfills every day. These residues can be used to produce biogas and recycle nutrients, thus alleviating environmental impacts related to waste management. Technical solutions are evaluated through a multicriteria analysis with the purpose of defining a strategy for implementing waste-to-biogas in the two cities. As a result, the development for waste-to-biogas-system is defined in three steps. Step 1 consists of an active extraction system of landfill gas in the already existing landfills. Step 2 implies the establishment of a dry-digestion biogas facility based on present waste collection practices, that is, not segregated waste. Step 3 consists of a biogas plant using dry digestion for processing source segregated bio-waste. The economic feasibility of these three steps is evaluated. Despite prevailing fossil fuels subsidies in the country, implementing waste-to-biogas turn out feasible in the country provided the digestate is commercialized as bio-fertilizer or erosion control material and additional services such as waste collection and deposition are computed in the total economy of the biogas production plant.

  • 2.
    Nordin, Annika C.
    et al.
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Vinnerås, B.
    Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Urea for sanitization of anaerobically digested dewatered sewage sludge2015In: Environmental Engineering Science, ISSN 1092-8758, E-ISSN 1557-9018, Vol. 32, no 2, p. 86-94Article in journal (Refereed)
    Abstract [en]

    When recycling sewage sludge to agriculture, the risk of disease transmission must be taken into account. Sanitizing treatment prevents disease transmission by reducing dissemination of pathogens early in the reuse chain. Sanitization is commonly achieved by heat treatment of sludge, for example, by prepasteurization before anaerobic digestion or by thermophilic anaerobic digestion. This study evaluated ammonia treatment of anaerobically digested dewatered sewage sludge at pilot scale (65 ton) by urea addition at 0.85% and 1.6% wet weight compared with storage without ammonia addition over 145 days of treatment during the Swedish winter, with ambient temperatures below 0 C. Addition of 1.6% urea reduced indicator organisms Enterococcus spp. and Escherichia coli to below the detection limit of 100 and 10cfu/g, respectively, within 3 months of treatment, whereas the 0.85% urea treatment did inactivate E. coli but not Enterococcus spp. within the study period (145 days). In the control, both indicator bacteria were still present at the end of the study period. Thus, 1.6% treatment with urea is a promising low cost on-demand option for sludge sanitization and can be performed at considerably lower cost than heat treatment.

  • 3.
    Nordlander, Eva
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Yan, Jinyue
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Simulation of energy balance and carbon dioxide emission for microalgae introduction in wastewater treatment plants2017In: Algal Research, ISSN 2211-9264, Vol. 24, no part A, p. 251-260Article in journal (Refereed)
    Abstract [en]

    A case study is described in which the activated sludge process is replaced with a microalgae-activated sludge process. The effects on the heat and electricity consumption and carbon dioxide emissions were evaluated in a system model, based on mass and energy balances of biological treatment and sludge handling process steps. Data for use in the model was gathered from three wastewater treatment plants in Sweden. The evaluation showed that the introduction of microalgae could reduce electricity and heat consumption as well as CO2 emissions but would require large land areas. The study concludes that a 12-fold increase in the basin surface area would result in reductions of 26–35% in electricity consumption, 7–32% in heat consumption and 22–54% in carbon dioxide emissions. This process may be suitable for wastewater treatment plants in Nordic countries, where there is a higher organic load in summer than at other times of the year. During the summer period (May to August) electricity consumption was reduced by 50–68%, heat consumption was reduced by 13–63% and carbon dioxide emissions were reduced by 43–103%.

  • 4.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Co-digestion of microalgae and sewage sludge - A feasibility study for municipal wastewater treatment plants2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

  • 5.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Enhanced biogas production from municipal WWTPs: Co-digestion of microalgae with sewage sludge and thermophilic secondary digestion of mesophilic digested sludge2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.

  • 6.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Feng, Xin Mei
    JTI, Swedish Inst Agr & Environm Engn, SE-75007 Uppsala, Sweden .
    Ascue, Johnny
    JTI, Swedish Inst Agr & Environm Engn, SE-75007 Uppsala, Sweden .
    Gentili, Francesco G.
    Swedish Univ Agr Sci, Dept Wildlife Fish & Environm Studies, SE-90183 Umea, Sweden .
    Shabiimam, M. A.
    Indian Inst Technol, Ctr Environm Sci & Engn, Bombay 400076, Maharashtra, India.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Co-digestion of cultivated microalgae and sewage sludge from municipal waste water treatment2014In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 171, p. 203-210Article in journal (Refereed)
    Abstract [en]

    In this study two wet microalgae cultures and one dried microalgae culture were co-digested in different proportions with sewage sludge in mesophilic and thermophilic conditions. The aim was to evaluate if the co-digestion could lead to an increased efficiency of methane production compared to digestion of sewage sludge alone. The results showed that co-digestion with both wet and dried microalgae, in certain proportions, increased the biochemical methane potential (BMP) compared with digestion of sewage sludge alone in mesophilic conditions. The BMP was significantly higher than the calculated BMP in many of the mixtures. This synergetic effect was statistically significant in a mixture containing 63% (w/w VS based) undigested sewage sludge and 37% (w/w VS based) wet algae slurry, which produced 23% more methane than observed with undigested sewage sludge alone. The trend was that thermophilic co-digestion of microalgae and undigested sewage sludge did not give the same synergy.

  • 7.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Forkman, T.
    Swedish University of Agricultural Sciences, Sweden.
    Gentili, F.G.
    Swedish University of Agricultural Sciences, Sweden.
    Zambrano, Jesús
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Anaerobic co-digestion of sludge and microalgae grown inmunicipal wastewater: A feasibility study2018In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 77, no 3, p. 682-694Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Ma, Shabiimam
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Nehrenheim, Emma
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Thorin, Eva
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Co-digestion of cultivated microalgae and sewage sludge from municipal waste water treatmentManuscript (preprint) (Other academic)
    Abstract [en]

    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.

  • 9.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Philipson, M.
    Uppsala University, Sweden.
    Holmström, H.
    Uppsala Vatten Och Avfall AB, Sweden.
    Cato, E.
    Uppsala Vatten och Avfall AB, Sweden.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Energy efficient combination of sewage sludge treatment and hygenization after mesophilic digestion - Pilot study2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 61, p. 587-590Article in journal (Refereed)
    Abstract [en]

    Biogas production is probably the most feasible way of utilizing sewage sludge as energy source, simultaneously with nutrient recovery by recycling the biogas digestate (i.e. The residue) to arable land. However, the sludge commonly contains high amounts of human pathogenic bacteria excreted in faeces and urine. To use sludge as fertilizer on food producing land is therefore a controversial issue, partly because of the risk of spreading diseasecausing pathogens. The Swedish environment protection agency (SEPA) pre-approved two hygenization methods for the treatment of the sludge due to their positive effects on the sludge quality. One of them, conventional pasteurization (70 °C, 1 h), was investigated for its feasibility in Uppsala, Sweden, and it was found that the heat consumption was very high. The other method has the advantage of potentially increase the produced biogas. This hygenization method has been investigated in the present study through a pilot experiment where thickened mesophilic digested sludge is digested once more at thermophilic conditions (55 °C). The aim of the study was to investigate the possibility to develop this self-sufficient (in heat and electricity) hygenization method. The results showed an increase in the gas production from 430 dm3/kg VSin to 610 dm3/kg VSin by adding the thermophilic step. This increase gave an energy balance with an excess of both heat and electricity. Sludge hygenization was sufficient with the method and another important result is the significant decrease digestate volume.

  • 10.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Co-digestion of microalgae, grown on municipal wastewater, and primary sewage sludge–: Pilot study in thermophilic and mesophilic conditions2017Conference paper (Refereed)
    Abstract [en]

    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.

  • 11.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Mesophilic and thermophilic co-digestion of microalgal-based activated sludge and primary sludgeIn: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732Article in journal (Refereed)
  • 12.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Microalgae as biological treatment for municipal wastewater - Effects on the sludge handling in a treatment plant2018In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, ISSN 0273-1223, Vol. 78, no 3, p. 644-654Article in journal (Refereed)
    Abstract [en]

    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. 

  • 13.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Shabiimam, MA
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Sustainable Development of Society and Technology. Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    CO-DIGESTION OF CULTIVATED MICROALGAE AND SEWAGE SLUDGE FROM MUNICIPAL WASTE WATER TREATMENT2013Conference paper (Refereed)
    Abstract [en]

    The demand for biogas is continuously growing and the biogas substrate, such as food waste, may soon become limited and it is therefore important for biogas producers to expand the range of substrates. One way can be to use microalgae in co-digestion with sewage sludge.

    The present study explores the possibilities to use harvested microalgae from Lake Mälaren, as a co-substrate to sewage sludge in biogas production under mesophilic and thermophilic conditions. The aim is to investigate if co- digestion of microalgae and sewage sludge is more efficient for biogas production compared using the sludge alone. The study has been carried out as a BMP-experiment (Biochemical Methane Potential) in batch fermentation bottles. The substrate was undigested sludge where 0%, 12 %, 25 % and 37 % were replaced with the cultivated microalgae. The results showed that the use of an algae/bacteria community, cultivated in prior to digestion, can serve as a biomass substrate for biogas production together with municipal wastewater sludge. Co-digestion of microalgae and sewage sludge can be more efficient for biogas production compared to using the sludge alone under mesophilic conditions. It can also be concluded that thermophilic co-digestion between the microalgae and sludge give lower biochemical methane potential. 

  • 14.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    TRANSITION OF MESOPHILIC TO THERMOPHILIC DIGESTION OF SEWAGE SLUDGE2016In: TRANSITION OF MESOPHILIC TO THERMOPHILIC DIGESTION OF SEWAGE SLUDGE, 2016Conference paper (Refereed)
    Abstract [en]

    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.

  • 15.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Juszkiewicz, Agnieszka
    Mälarenergi AB, Sweden.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    COMPARATIVE STUDY – PHARMACEUTICAL RESIDUES IN WASTEWATER AND SLUDGE FROM A MICORALGAE PLANT AND AN ACTIVATED SLUDGE PROCESS2016Conference paper (Refereed)
    Abstract [en]

    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.

  • 16.
    Olsson, Jesper
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Tova, Forkman
    Uppsala Universitet, Sweden.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    CONTINUOUS CO-DIGESTION OF MICROALGAE AND REPRESENTATIVE MIX OF SEWAGE SLUDGE: -2014Conference paper (Refereed)
    Abstract [en]

    A natural mix of microalgae grown on wastewater was co-digested with a representative mix of sewage sludge in a semicontinuous pilot digester system. The share of microalgae in the mix were 37 % calculated as VS-content. The organic loading rate was 2.4 kg VS (volatile solids) m-3d-1 and the hydraulic retention time was 15 d in a reference reactor, with just a representative mix of sewage sludge, and a digester where microalgae were added. The results from the three retention times showed that the addition of the microalgae enhanced the methane yield with 39 % for every gram reduced VS in the reactors. The specific methane yield for every gram added VS to the reactors were 9 % lower in the digester where microalgae had been added. Less sludge was degraded when microalgae were added, but more methane was produced for every gram VS reduced. CST-measurements indicated that the addition of microalgae enhance the dewaterability of the digested sludge.

  • 17.
    Thorin, Eva
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Biogas from Co-digestion of Sewage Sludge and Microalgae2017In: Energy Procedia, 2017, Vol. 105, p. 1037-1042Conference paper (Refereed)
    Abstract [en]

    Microalgae cultivated in waste water could contribute to increased biomass production at municipal waste watertreatment plants. The biomass could be utilized for biogas production when co-digested with sewage sludge. In thispaper previous published results on co-digestion of sewage sludge and microalgae are summarized and remainingknowledge gaps are identified. The available batch tests in literature mostly concern digestion at mesophilicconditions. Some of those tests indicate a synergetic effect for the co-digestion. Investigations at thermophilicconditions and of semi-continuous processes are scarce. The available results show good possibilities for co-digestionof sewage sludge and microalgae. Further investigations are needed to find optimal conditions for biogas production.

  • 18.
    Thorin, Eva
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Olsson, Jesper
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Schwede, Sebastian
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Nehrenheim, Emma
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Co-digestion of sewage sludge and microalgae: Biogas production investigations2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 227, p. 64-72Article in journal (Refereed)
    Abstract [en]

    In municipal wastewater treatment plants (WWTPs), algae could be utilised for cleaning the water and, at thesame time, produce a biomass that can be used for energy. Through anaerobic digestion, microalgae can contributeto biogas production when co-digested with sewage sludge. In this paper, previous published results onthe co-digestion of sewage sludge and microalgae are summarised and reviewed, and any remaining knowledgegaps are identified. The batch tests currently documented in literature mostly concern digestion under mesophilicconditions, and studies investigating thermophilic conditions are less common. The average biochemicalmethane potential (BMP) for 29 different mixtures co-digested under mesophilic conditions is 317 ± 101 N cm3CH4 gVS−1 while the result for 12 different mixtures investigated under thermophilic conditions is a BMP of318 ± 60 N cm3 CH4 gVS−1. An evaluation of the heat required for increasing the temperature from mesophilicto thermophilic conditions shows that increased methane production under thermophilic conditions can beenough to create a positive energy balance. For a full-scale WWTP, using thermophilic digestion on sludge, or acombination of sludge and microalgae could therefore be of interest. This is dependent on the demands onsanitation of the sludge and the possibilities for heat recovery.Most of the mesophilic investigations indicate a synergetic effect for co-digestion, with enhancements of up toalmost 70%. However, the results are uncertain since the standard deviations for some of the BMP tests are in thesame order of magnitude as the identified enhancement. Neither of the presented publications provide an understandingof the basic mechanisms that led to higher or lower BMP when microalgae were mixed with wastewatersludge. We, therefore, call for care to be taken when assuming any effects related to the specification ofsubstrates. Microalgae and wastewater sludge have several similarities, and the specific results of BMP in themixtures relate more to the specifics of the respective materials than the materials themselves.Investigations into semi-continuous processes of co-digestion of microalgae and sludge are scarce. The yieldsfor three co-digestion studies show high variation, with an average of 293 ± 112 N cm3 gVSin−1. The availableresults show strong potential for co-digestion of sewage sludge and microalgae. Further investigations are requiredto identify optimal conditions for biogas production, and analysis of microalgae implementation onwastewater treatment at a system level is also needed to identify the total mass balance of substrate and nutrientrecovery.

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