Recovery of organic resources from sewage sludge of Al-enhanced primary sedimentation by alkali pretreatment and acidogenic fermentation

• Published in: Journal of cleaner production Vol. 172; pp. 3334 - 3341
• Main Authors: Lin, Lin, Li, Ruo-hong, Li, Xiao-yan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 20.01.2018
• Subjects: Chemically enhanced primary sedimentation (CEPS); Polyaluminum chloride (PACl); Resource recovery; Sludge fermentation; Volatile fatty acids (VFAs); Volatile fatty acids (VFAs); Polyaluminum chloride (PACl); Sludge fermentation; Resource recovery; Chemically enhanced primary sedimentation (CEPS)
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2017.11.199

Primary sludge from wastewater treatment is of rich organic contents that can be resource for recovery. However, the sludge derived from the chemically enhanced primary sedimentation (CEPS), especially using Al-based coagulants, features a rather low biodegradability and treatability due to the agglomeration of solid matters by the coagulant. In the present study, alkali pretreatments by three chemicals (NaHCO3, Na2CO3 and NaOH) were applied to disintegrate Al-based CEPS sludge (Al-sludge) aggregates and improve its hydrolysis and biodegradability for fermentation and organic recovery. Results showed that alkali pretreatment significantly reduced the Al-sludge particle size and accelerated the release of the enmeshed organics. NaHCO3 exhibited the best pretreatment result. At ambient temperature, the yield of volatile fatty acids (VFAs) of the Al-sludge pretreated by Na2CO3 (initial pH 10) was improved by four times compared to the untreated sludge, resulting from both the improved abiotic and biotic hydrolysis effects. The effect of alkali pretreatment on Al-sludge was found to be mainly attributable to the pH adjustment rather than the alkalinity increase. Illumina MiSeq sequencing revealed that protein-fermenting bacteria Treponema and Bacteroides became dominant during fermentation of the alkali pretreated sludge. By PACl-based CEPS and enhanced sludge acidogenesis, around 17% of organics in municipal wastewater can be recovered, mainly in the form of VFAs, which is significantly greater than 6% by the conventional primary sedimentation and sludge fermentation. [Display omitted] •PACl dosing for chemically enhanced primary sedimentation (CEPS) produced Al-rich sludge.•PACl coagulant in Al-sludge inhibited the hydrolysis and biodegradability of the sludge.•Alkali pretreatment disintegrated Al-sludge particles and enhanced organic hydrolysis.•About 17% of organics in wastewater was recovered by enhanced sludge fermentation.