Food waste (FW) storage influences its physical-chemical characteristics and anaerobic digestion (AD) performance. In this work we present the results of two weeks long experiment where two types of FW were stored in dedicated cells (10 L and 300 L). Air was evenly flushed on the top surface of the substrates and then analyzed to identify and quantify possible gaseous emissions. Solid and liquid fractions were also periodically sampled and analyzed for total solid, volatile solid, ammonia and VFA contents. Results showed that storage initiated a hydrolysis process that modified the physical structure of FW, leading to the production of gases (CH 4 , CO 2 and ethanol) and a partly liquefied FW. Depending on experimental conditions, a fraction between 61 and 70% of the initial substrate remained solid at the end of the storage period. In the liquid phase, a large proportion of lactic acid was measured with maximum contents of 5.9 and 14.8 g/kg vs for the small-scale experiments with two different FW types and 3.0 g/kg vs for the large-scale experiment, leading to inhibition of the biomethane potential (BMP) tests. In conclusion, this work showed that when storage of FW is needed before AD, the optimal time recommended to keep a high methane yield is one week.
To face the increase of waste production and meet the energy demand of urban areas, municipal waste management systems should be rethought. Innovative solutions such as decentralised small-scale anaerobic digestion could be developed. This work presents the design, operation and performances of a new micro-scale anaerobic digester (AD) developed to degrade food waste (FW) in urban areas i.e. highly compact and with low water and energy demand. To meet these objectives, the new micro-scale AD is a semi-continuous and two-stage process built vertically to take advantage of the gravity to mix and move the digested matter instead of using mechanical devices. The first stage consists in a tubular reactor fed weekly with FW and periodically watered with leachate from the second stage reactor located below the tubular reactor. Results show that AD performances were highly correlated to the efficiency of hydric transfer between the tubular reactor and the leachate tank. Indeed, pH, volatile fatty acids and microbial community analysis showed that the hydrolysis occurred in the tubular reactor, while the methanogenesis step occurred in the leachate tank. Overall, the average methane production was 143 ± 87 NL/kgvs with an average methane content of 44 ± 10% and the operation mode of the process has still to be improved.
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