Abstract
Bedded pack manure has long been considered an unsuitable feedstock for conventional anaerobic digestion systems due to its high solids content. However, solid-state anaerobic digestion (SS-AD) provides an opportunity to generate methane from such high-solids feedstocks. This study was conducted to determine the influence of moisture content on the digestion of bedded pack dairy manure using SS-AD. Mixtures of sawdust bedding and dairy manure were prepared with moisture contents (MCs) of 70, 76, and 83% and digested at 37 °C for 85 days. The performance of digesters containing manure at 83% MC was 1.3 to 1.4-fold higher than that of digesters containing 70% MC manure in terms of volatile solids (VS) reduction and biogas production. VS reduction rates were 55 to 75% and cumulative methane yield ranged from 64 to 90 NmL (gVS)−1. These values are lower than those from SS-AD of fresh manure and this is likely due to the partial decomposition of biodegradable materials during the two to three-month period before the manure was removed from the barn. However, in terms of efficient management of farm odors and providing a renewable energy source for heating, SS-AD of bedded pack manure offers a potential alternative to the conventional composting systems currently in use.
Highlights
Manure production from Korea’s 430,000 dairy cows was approximately 6 million wet tons in 2014 and constitutes about 13% of the country’s total animal manure production
The typical moisture content of bedded pack dairy manure collected on the farm ranges from 70 to 83% wet basis depending on the frequency with which the bedding is replaced
Our results showed that the technical digestion time (T95, the time needed to produce 95% of the methane potential) was significantly longer using feedstock at the lowest moisture content (Table 3)
Summary
Manure production from Korea’s 430,000 dairy cows was approximately 6 million wet tons in 2014 and constitutes about 13% of the country’s total animal manure production. Composting is an accepted method for treatment of dairy manure and bedding material mixtures, the majority of Korean dairy farms lack the resources and financial incentives to compost this material For this reason, most farms stack manure after collection and apply this untreated material to fields [2]. In 2013, seven full-scale liquid-phase manure digesters were in operation in Korea, mainly for handling high-moisture swine manure These systems are not suitable for treating manure containing low-moisture wastes such as dairy and beef manure collected from bedded pack barns. Results from previous studies suggest that the efficiency of SS-AD increases as feedstock moisture levels increase [18], there is no information on optimum moisture levels for SS-AD of dairy manure and sawdust bedding mixtures from bedded pack barns. It is very meaningful and important to develop an SS-AD technology for bedded pack dairy manure that can be used as an energy source as well as suggesting an alternative method of composting to that typically used
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