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Identification of thermochemical pathways for the energy and nutrient recovery from digested sludge in wastewater treatment plants
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-4932-7368
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-5014-3275
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-3485-5440
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-6279-4446
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2019 (English)In: Energy Procedia, Elsevier Ltd , 2019, Vol. 158, p. 1317-1322Conference paper, Published paper (Refereed)
Abstract [en]

There are several restrictions and limitations on the emissions and disposal of materials and pollutants related to wastewater treatment plants (WWTPs) emphasizing improvement of current processes and development of new methods. Process integration is one way to use all fractions of waste for improved efficiency. WWTPs produces sludge which is usually anaerobically digested to produce biogas and a byproduct called digestate. Digestate is an organic material that contains macro and micronutrients such as nitrogen, phosphorous, and potassium and also contains heavy metals. Digestate is mainly used for agricultural applications because of the presence of nutrients. However, digestate also contains energy in the form of carbon and hydrogen which can be harnessed through various processes and integrated with nitrogen recovery process. This study aims to recover the energy and nutrients from digestate through thermochemical treatment processes. Combustion, pyrolysis, and gasification are assessed and compared in this work. An ammonia stripping method is assumed to recover nitrogen from digestate. The thermochemical processes are heat integrated with ammonia stripping through modeling and simulation. Results show that almost half of the energy present in digested sludge is required for its drying. Moreover, nitrogen recovery also requires much energy. The combustion and gasification of digested sludge give better results than pyrolysis. The heat integration becomes feasible when the auxiliary biogas is also burned along with products from the thermochemical treatment of sludge.

Place, publisher, year, edition, pages
Elsevier Ltd , 2019. Vol. 158, p. 1317-1322
Keywords [en]
Combustion, Digestate, Gasification, Pyrolysis, Wastewater treatment, Ammonia, Anaerobic digestion, Biogas, Heavy metals, Nitrogen, Nutrients, Reclamation, Sewage pumping plants, Waste incineration, Wastewater disposal, Water treatment plants, Carbon and hydrogens, Macro-and micronutrients, Model and simulation, Process integration, Thermo chemical process, Thermochemical treatments, Wastewater treatment plants
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-43184DOI: 10.1016/j.egypro.2019.01.325ISI: 000471031701105Scopus ID: 2-s2.0-85063872188OAI: oai:DiVA.org:mdh-43184DiVA, id: diva2:1307162
Conference
10th International Conference on Applied Energy, ICAE 2018, 22 August 2018 through 25 August 2018
Available from: 2019-04-26 Created: 2019-04-26 Last updated: 2020-09-04Bibliographically approved
In thesis
1. Waste-integrated biorefineries: A path towards efficient utilization of waste
Open this publication in new window or tab >>Waste-integrated biorefineries: A path towards efficient utilization of waste
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Waste-management systems have progressed from landfilling and dumping to waste prevention, recycling and resource recovery. In state-of-the-art waste-management industries, waste is separated into various fractions and treated with suitable processes. The non-recyclable organic fraction of waste can be incinerated for combined heat and power (CHP) production, while biodegradable waste can be converted to biomethane through the anaerobic digestion (AD) process. Thermochemical processes such as gasification and pyrolysis provide alternative methods for treating various fractions of waste. This thesis aims to design energy-efficient and cost-effective waste-integrated biorefineries by integrating thermochemical processing of waste with existing WtE technologies.

A system analysis of five process-integration case studies have been performed. The first case assesses the limitations and operational limits of thermochemical processes retrofitted in an existing waste-based CHP plant. The second and third case studies evaluate the feasibility of the current waste-based CHP plant to shift from cogeneration to polygeneration of biofuels, heat and power. In the fourth case study, a new process configuration is presented that couples AD of biodegradable waste with pyrolysis of lignocellulosic waste. The last case deals with the handling of digested sludge from WWTPs by the integration of thermochemical processes.

The findings suggest that waste-integrated biorefineries can utilize infrastructure and products from existing waste industries through process integration and improve the overall process efficiencies and economics. Existing waste-based CHP plants can provide excess heat for integrated thermochemical processes; however, the modifications required are different for different gasifiers and pyrolyzers. Similarly, refuse-derived fuel (RDF) — processed from municipal solid waste (MSW) — can be utilized for production of various biofuels alongside heat and power without disturbing the operation of the CHP. But biomethane and dimethyl ether (DME) showed higher process feasibility than methanol and drop-in biofuels.

The integration of pyrolysis with the AD process can almost double biomethane production compared with a standalone AD process, increasing efficiency to 67% from 52%. The integration is an attractive investment when off-site — rather than on-site — integration of pyrolysis and AD is considered.

Drying of sludge digestate from wastewater treatment plants (WWTPs) is a bottleneck for its post-processing by thermochemical processes. However, waste heat from the existing CHP plant can be utilized for drying of sludge, which can also replace some of the boiler feed through co-incineration with waste biomass.

The economic performance of waste-integrated biorefineries will depend on the volatility of market conditions. Finally, assessment of the effects of uncertainty of input data and process parameters on metrics of technical and economic performance is vital for evaluation of overall system performance.

Place, publisher, year, edition, pages
Västerås: Mälardalen University, 2020
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 322
Keywords
Gasification; Pyrolysis; Anaerobic digestion; Process integration; Aspen Plus; Ebsilon; Techno-economic analysis
National Category
Energy Engineering
Research subject
Energy- and Environmental Engineering
Identifiers
urn:nbn:se:mdh:diva-49878 (URN)978-91-7485-476-3 (ISBN)
Public defence
2020-10-23, Beta + (Online, Zoom), Mälardalens högskola, Västerås, 09:00 (English)
Opponent
Supervisors
Available from: 2020-09-04 Created: 2020-09-03 Last updated: 2020-09-23Bibliographically approved

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Salman, Chaudhary AwaisSchwede, SebastianThorin, EvaLi, HailongYan, Jinyue

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