Enhancement of Sewage Sludge Bioconversion to Methane by the Addition of Exhausted Coffee Biowaste Liquid Fraction

Abstract

Anaerobic co-digestion of organic rich wastes and wastewater sludge has become an attractive economic possibility for water utilities as it enhances biogas production. The suitability of the organic rich waste depends on its biodegradability as well as on its synergetic effect on the anaerobic digestion process. The feasibility of sewage sludge (SS) treatment via co-digestion was studied in a semi-continuous mode at mesophilic conditions (36 ± 1 °C), with a hydraulic retention time of 17 days and an average organic loading rate of 0.94 ± 0.05 g VS L reactor day −1 , using the liquid fraction of pre-treated exhausted coffee biowaste (LECB) as a co-substrate. An anaerobic co-digestion trial (T1) was performed using as feeding mixture 80% SS and 20% LECB (v:v) and compared against a reference scenario of mono-digestion of SS (T0). The stability along assays was ensured by monitoring the digestate characteristics (pH, electrical conductivity, total alkalinity and ammonia content) and the specific energy-loading rate (SELR). Along the operation time of T1, methane yield and VS removal were significantly higher in comparison to mono-digestion of SS. Results showed that the addition of the co-substrate had a positive effect on specific methane production (3 times higher) and methane content (12% higher), indicating this is a feasible strategy towards self-sufficient wastewater treatment plants.

Recent Advance in Anaerobic Co-digestion Technology: A Review

“…The balance of the C/N ratio of the feedstock was shown to enhance the methane production of anaerobic co-digestion (Mozhiarasi et al, 2019) (Zealand et al, 2018) (Ngan et al, 2019). The proportion between carbon and nitrogen improves the buffering capacity and minimizes the effect of inhibitory compounds (accumulation of organic acids, ammonia, VFAs) (Elalami et al, 2019) (Fragoso et al, 2020) (Shen et al, 2019) (Sahoo & Rao, 2019).…”

“…And less famous, the Chen and Hashimoto model (Sukhesh & Rao, 2018) and the cone model (Achinas & Euverink, 2019) are also used for the kinetic analysis of the AD. Apart from the kinetics model, other methods including specific energy-loading rate where the reactor is stable below 0.4 day −1 (Fragoso et al, 2020), thermal analysis, and the differential scanning calorimetry are also used to assess the AD stability (González et al, 2019).…”

“…High ammonia concentrations could cause serious inhibition of specific enzyme responses and microbial growth in aqueous AD (Achinas & Euverink, 2019) (Wang et al, 2018) (E. Zhang et al, 2018). The recommended limit of the amount of ammonia 1.7-1.8 g.L −1 of the reactor was found (Fragoso et al, 2020) (Borowski & Kucner, 2019). Therefore, operating with suitable characteristics, porous biochar was used to absorb ammonia (Horan et al, 2018), decrease its inhibitory effect, and immobilize methanogenic microorganisms (Li et al, 2019).…”

“…The alkalinity parameter, also used for assessment and control of process stability of anaerobic digestion (Rabii et al, 2019) (P. Kumar et al, 2019), was recommended to be in the interval 1 500 and 6 000 mgCaCO 3 .L −1 of the reactor for assuring a stable process (Fernández-Rodríguez et al, 2019) (Fragoso et al, 2020) (Latifi et al, 2019).…”

In search of the optimal inoculum to substrate ratio during anaerobic co-digestion of spent coffee grounds and cow manure

“…Recent studies showed that the use of SCG as raw feedstock for biogas production emerges with interesting potential (Girotto et al, 2018; Orfanoudaki et al, 2019). Several studies have reported the anaerobic mono-digestion of SCG (Battista et al, 2016; Girotto et al, 2018; Valero et al, 2016) and co-digestion of SCG with other feedstocks, such as sewage sludge (Fragoso et al, 2018; Neves et al, 2006), cow manure (Codignole Luz et al, 2018), pig manure (Orfanoudaki et al, 2019) and others (Kim et al, 2017). In general, it was highlighted that SCG have high potential for biogas production; on the other hand, it can lead to high production of volatile fatty acids (VFAs) with a fast reduction of the slurry pH and, thus, cause a possible perturbation of the AD process (Codignole Luz et al, 2018).…”