Abstract
Anaerobic digestion (AD) of chicken litter (CL) is a viable alternative to disposal. However, methane yields from this primarily organic waste are quite low when mono-digested. This paper discusses the effect of an enzyme cocktail, trace element (TE) supplementation and selenium (Se) addition in small-scale batch biomethane potential (BMP) assays to enhance the AD of CL. Eleven different assays were set up in triplicate including assays containing only inoculum (blank), only CL (negative control) and cellulose and inoculum (positive control). The results indicate that both enzyme treatment and trace element supplementation enhanced the biogas and methane yield. The highest specific biogas and methane yields were noted for 1% enzyme-treated CL of 835.2 L/kg volatile solids (VS) and 460.8 L/kg VS, respectively. Usually, mono-digestion of CL is low due to high nitrogen content and the presence of recalcitrant lignocellulosic material from the bedding material. Enzyme treatment performed better than the addition of the TE mix and Se.
Highlights
Animal manure is a rich source of minerals including, nitrogen (N), phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg), as well as organic matter
High carbon to nitrogen (C/N) ratios result in volatile fatty acid (VFA) accumulation, while low ratios lead to ammonia toxicity
The ammonia concentration and pH of both the inoculum and chicken litter (CL) were within the range at this time, it should be noted that a total ammonia concentration above 4 g/L can be inhibitory to the Anaerobic digestion (AD) process irrespective of the pH [28] (Table 3)
Summary
Animal manure is a rich source of minerals including, nitrogen (N), phosphorus (P), calcium (Ca), potassium (K) and magnesium (Mg), as well as organic matter. Inappropriate disposal of this waste stream can result in the contamination of ground and surface water and poses a risk to both animal and human health [1]. In Ireland, chicken consumption is high when compared to other poultry animals, which results in the generation of large volumes of chicken litter (CL) [2]. CL is carbon (C) rich when compared to poultry manure alone as it contains large amounts of bedding material which is primarily lignocellulosic in nature [4]
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