Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

Wanderli Rogério Moreira Leite; Bruna Scandolara Magnus; Bárbara Albuquerque Branco de Moraes; Mario Takayuki Kato; Lourdinha Florencio; Rejane Helena Ribeiro da Costa; Paulo Belli Filho

doi:10.1016/j.jenvman.2023.117839

Mesophilic anaerobic digestion of waste activated sludge in an intermittent mixing reactor: Effect of hydraulic retention time and organic loading rate

J Environ Manage. 2023 Jul 15:338:117839. doi: 10.1016/j.jenvman.2023.117839. Epub 2023 Mar 30.

Authors

Wanderli Rogério Moreira Leite¹, Bruna Scandolara Magnus², Bárbara Albuquerque Branco de Moraes³, Mario Takayuki Kato⁴, Lourdinha Florencio⁵, Rejane Helena Ribeiro da Costa⁶, Paulo Belli Filho⁷

Affiliations

¹ Federal University of Pernambuco, Department of Civil and Environmental Engineering, Cidade Universitária, CEP 50670-901, Recife, PE, Brazil. Electronic address: wanderli.leite@ufpe.br.
² Federal University of Pernambuco, Department of Civil and Environmental Engineering, Cidade Universitária, CEP 50670-901, Recife, PE, Brazil. Electronic address: bruna.magnus@ufpe.br.
³ Federal University of Pernambuco, Department of Civil and Environmental Engineering, Cidade Universitária, CEP 50670-901, Recife, PE, Brazil. Electronic address: barbara.abmoraes@ufpe.br.
⁴ Federal University of Pernambuco, Department of Civil and Environmental Engineering, Cidade Universitária, CEP 50670-901, Recife, PE, Brazil. Electronic address: mario.kato@ufpe.br.
⁵ Federal University of Pernambuco, Department of Civil and Environmental Engineering, Cidade Universitária, CEP 50670-901, Recife, PE, Brazil. Electronic address: flor@ufpe.br.
⁶ Federal University of Santa Catarina, Department of Sanitary and Environmental Engineering, Campus Universitário Trindade, CEP 88.010-970, Florianópolis, SC, Brazil. Electronic address: rejane@ens.ufsc.br.
⁷ Federal University of Santa Catarina, Department of Sanitary and Environmental Engineering, Campus Universitário Trindade, CEP 88.010-970, Florianópolis, SC, Brazil. Electronic address: paulo.belli@ufsc.br.

PMID: 37003223
DOI: 10.1016/j.jenvman.2023.117839

Abstract

An anaerobic digester was operated at mesophilic temperature and with intermittent mixing conditions to treat waste activated sludge. The organic loading rate (OLR) was increased by decreasing the hydraulic retention time (HRT), and the effect on process performance, digestate characteristics and inactivation of pathogens was investigated. The removal efficiency of total volatile solids (TVS) was also measured by biogas formation. The HRT varied from 50 to 7 days, corresponding to OLR from 0.38 to 2.31 kgTVS.m^-3.d^-1. The acidity/alkalinity ratio remained within stable limits (lower than 0.6) at 50-, 25- and 17-day HRT; due to an imbalance between the production and consumption of volatile fatty acids, the ratio increased to 0.7 ± 0.2 at HRT of 9 days and 7 days. The highest TVS removal efficiencies were 16, 12 and 9%, which were obtained at 50-, 25- and 17 day-HRT, respectively. Intermittent mixing provided solids sedimentation greater than 30% for almost all HRT tested. The highest methane yields (0.10-0.05 m³.kgTVS_fed^-1.d^-1) were obtained when the reactor was operated at a higher HRT (50-17 days). At lower HRT, methanogenic reactions were likely limited. Zinc and copper were the main heavy metals found in the digestate, while the most probable number (MPN) of coliform bacteria remained below 10⁶ MPN.g TVS^-1. Neither Salmonella nor viable Ascaris eggs were found in the digestate. In general, increasing the OLR by decreasing the HRT to 17 days under intermittent mixing conditions provided an attractive alternative to treat sewage sludge despite some limitations due to biogas and methane yields.

Keywords: Biogas; Helminth egg; Intermittent mixing; Secondary sludge treatment; Stability.

MeSH terms

Anaerobiosis
Biofuels* / analysis
Bioreactors
Methane
Sewage*

Substances

Sewage
Biofuels
Methane