Evaluation of the factors limiting biogas production in full-scale processes and increasing the biogas production efficiency

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Kouzi , A , Puranen , M & Kontro , M H 2020 , ' Evaluation of the factors limiting biogas production in full-scale processes and increasing the biogas production efficiency ' , Environmental Science and Pollution Research , vol. 27 , no. 22 , pp. 28155-28168 . https://doi.org/10.1007/s11356-020-09035-1

Title: Evaluation of the factors limiting biogas production in full-scale processes and increasing the biogas production efficiency
Author: Kouzi, Afamia; Puranen, Matti; Kontro, Merja H.
Contributor: University of Helsinki, Ecosystems and Environment Research Programme
Date: 2020-08
Language: eng
Number of pages: 14
Belongs to series: Environmental Science and Pollution Research
ISSN: 0944-1344
URI: http://hdl.handle.net/10138/320218
Abstract: Biogas production from sewage sludge volatile solids (VS) by anaerobic digestion slows down towards the end of the process, among inhibitory factors being pH increase upon ammonia accumulation, poorly digestible biomaterials, and high fixed solid (FS) content. The possibility of concentrating the digested sludge VS (41.7-56.6% on a dry weight basis) by surface and bottom layer separation with biogas post-production was studied. Furthermore, the potential to recycle concentrated VS and digested sludge back to the process after adjusting pH 7.0 to optimal for biogas-producing microbes and after acid, alkali, thermal, and sonolytic treatments was examined. In general, pH 7.0 control alone improved biogas production from the recycled digested sludge the most. An equally good improvement in biogas production was achieved by recycling the digested sludge, which had been heated until ammonia had evaporated and the pH dropped to 7.0 (1-2 h, 75 degrees C), and at the same time, VS was degraded. The biogas production from the sonicated and recycled sludge was almost as good as from the pH-adjusted, or heat-treated recycled sludge. After the acid and base treatments of the digested sludge, the recycled sludge yielded often the lowest biogas volume, as the added chemicals increased the FS concentration, which proved to be a more important inhibitory factor than poorly degradable VS. The high FS content significantly reduced the benefits of the treatments. By separating the surface and bottom layers with biogas post-production, the surface layer of VS was concentrated to 51.6-61.8%, while different compositions of the layers affected the biogas production.
Subject: Digested sludge
Post-treatment
Volatile solids
Fixed solids
pH changes
Layer separation
WASTE-ACTIVATED-SLUDGE
SUBSEQUENT ANAEROBIC-DIGESTION
METHANE PRODUCTION
HEAVY-METALS
MICROBIAL PROCESSES
PRETREATMENT
PH
DISINTEGRATION
ENHANCEMENT
HYDROLYSIS
1172 Environmental sciences
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