Effect of acclimatization rate on biogas production from anaerobic digestion of biodiesel waste products

Digester acclimatization can improve the efficiency of anaerobic digestion (AD), a potentially sustainable process for generating biogas from the biological decomposition of organic byproducts from biodiesel production. This study examined the impact of acclimatization rate on biogas production and conversion efficiency in laboratory digesters using inocula from a wastewater treatment plant digester and from an agro-industrial waste digester. The results showed that co-digestion of crude glycerol and biodiesel wastewater at high organic loading rates, up to 6.8 g chemical oxygen demand (COD) L-1 day(-1), is possible without the addition of other substrates or pretreatment. Higher organic loading rates were achieved in the digesters using inocula from the agro-industrial waste digester than in the digesters using the wastewater treatment plant digester, indicating that an inoculum with similar physical characteristics may be most appropriate for the AD of biodiesel waste. Of the two acclimatization rates studied, the slower rate improved the cumulative biogas production for both inocula. Both inocula also exhibited higher maximum daily efficiencies with a slower rate of acclimatization, up to a maximum average daily biogas yield of 621 mL biogas g(-1) COD added. This implied that the rate of acclimatization can impact the ability of the digester to adapt efficiently to a new substrate.