Pretreatment of poultry manure for efficient biogas production as monosubstrate or co-fermentation with maize silage and corn stover Tam  as B € ojti a , Korn  el L. Kov  acs a, b, c, * , Bal  azs Kakuk a , Roland Wirth a ,G  abor R  akhely a, b , Zolt  an Bagi a a Department of Biotechnology, University of Szeged, K€ ozep fasor 52, Szeged 6726, Hungary b Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, Temesv ari krt. 62, Szeged 6726, Hungary c Department of Oral Biology and Experimental Dental Research, University of Szeged, Tisza L. krt. 64, Szeged 6720, Hungary article info Article history: Received 4 February 2017 Received in revised form 20 March 2017 Accepted 24 March 2017 Available online 27 March 2017 Handling Editor: Kornel L. Kovacs Keywords: Anaerobic digestion Chicken manure Co-fermentation Maize silage Corn stover abstract Water extraction of raw chicken manure elevated the carbon-to-nitrogen ratio 2.7-fold, i.e. from 7.48 to 19.81. The treated chicken manure (T-CM) thus became suitable for biogas fermentation as mono- substrate. Improved methane production was achieved in co-fermentations with either maize silage (24% more methane) or corn stover (19% more methane) relative to T-CM monosubstrate. The standardized biogas potential assay indicated that the methane yields varied with the organic loading rate between 160 and 250 mL CH 4 /g organic total solid (oTS). Co-fermentation with maize silage was sustainable in continuous anaerobic digestion for at least 4 months. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The poultry industry is growing rapidly along with human consumption, which results in large quantities of animal wastes to be treated. Inappropriate management of manure may cause numerous undesirable consequences such as odor problem, attraction of rodents, insects and other pests, release of animal pathogens, groundwater contamination, surface water runoff, deterioration of biological structure of the soil, etc. [1,2]. NH 3 and greenhouse gases, CH 4 and CO 2 , emitted from the waste storage units cause air pollution problems [3]. Anaerobic digestion (AD) is a commonly employed process for treating animal manure and biogas production is widely studied and practiced [4e7]. Chicken manure (CM) is generally considered a problematic substrate for AD [8,9]. CM has a high nitrogen content, which is in two main forms: uric acid and undigested proteins, representing 70% and 30% of the total organic nitrogen, respectively. AD of these components is accompanied with the production of inhibitory concentrations of unionized NH 3 and NH 4 þ ions [10,11]. Accumu- lation of these toxic products does not allow fermentation at higher total solids (TS) loadings. The recommended substrate concentra- tion is less than 5% TS and a decrease in biogas production rate has been observed when TS was further increased [12,13]. Stripping of the liquid phase is an efficient way to avoid the accumulation of NH 3 during biogas fermentation. The removed NH 3 can be reacted with sulfuric acid (H 2 SO 4 ) to form ammonium sulfate ((NH 4 ) 2 SO 4 ). Addition of H 2 SO 4 increases the operational costs but in exchange, (NH 4 ) 2 SO 4 can be utilized as a fertilizer [14] and accelerates the recycling of nitrogen because farms can handle the slurry or solid fertilizer more easily than the residue after wet AD [15,16]. In alternative approaches, CM was treated anaerobically after dilution with water either in a semi-solid form, i.e. 10e11.5% TS content, or in a wet form (0.5e3% TS) [17] or the high N-content was extracted with water and ammonia recovered by stripping (Nie et al., 2015). Other endeavors to reduce the inhibitory effect of NH 3 involved adsorbing onto zeolite or clay [18,19]. * Corresponding author. Department of Biotechnology, University of Szeged, K€ oz ep fasor 52, Szeged 6726, Hungary. E-mail addresses: bojti.tamas@bio.u-szeged.hu (T. B€ ojti), kovacs.kornel@bio.u- szeged.hu (K.L. Kov acs), kakuk.balazs@stud.u-szeged.hu (B. Kakuk), wirth@bio.u- szeged.hu (R. Wirth), rakhely.gabor@bio.u-szeged.hu (G. Rakhely), bagi.zoltan@ bio.u-szeged.hu (Z. Bagi). Contents lists available at ScienceDirect Anaerobe journal homepage: www.elsevier.com/locate/anaerobe http://dx.doi.org/10.1016/j.anaerobe.2017.03.017 1075-9964/© 2017 Elsevier Ltd. All rights reserved. Anaerobe 46 (2017) 138e145