Anaerobic Digestion of Onion Wastes Using a Continuous Two-Phase Anaerobic Solids Digestion System

Abstract

The digestion of onion waste was conducted in a two-phase anaerobic solids digester. The digestibility of the onion waste was studied using batch and continuous digesters at mesophilic temperature (35° C). The C:N of onion waste was determined to be 20:1. The two-phase anaerobic digestion was first performed under batch conditions with 200 g (wet weight) of onion waste. Biogas yield of onion waste was 0.34-0.47 L CH4 / g VS fed, with methane yields ranging from 50-80%. Total solids (TS) and volatile solids (VS) reduction were 46% and 54%, respectively. The continuous digestion of onion waste was studied at three organic loading rates (OLR) from 0.5 to 2.0 g VS/L/d. The pH in the biogasification reactor was controlled above 7.0 by the addition of hydrated lime. The average methane yield was determined to be 0.35, 0.32, and 0.32 L CH4/gVS fed for OLR of 0.5, 1.0, and 2.0 g VS/L/d, respectively. The results were similar to the yields determined in the batch digestion study. The twophase system allowed the flexibility of adjusting the loading rate of organic acids to the methanogens, which made pH control possible without disruption of the continuous operation of the digester system.

Using Two-Phase Anaerobic Digestion for Organic Waste

“…JY Wang [14] compared the batch and semi-continuous feed of food waste treatment of solid-liquid two-phase digestion, and reached that the methane production, VS degradation rate, and methane content of semi-continuous feeding was higher than that of the batch feed. Rowena T [15] proposed that it could improve the reaction stability by regulating pH value in the two-phase matching coordinate control.…”