Effects of carbon-based additive and ventilation rate on nitrogen loss and microbial community during chicken manure composting

Aerobic composting is a sustainable method for recycling of chicken manure, while its unsuitable porosity and carbon to nitrogen ratio limit the oxygen supply, which must result in high nitrogen loss because of anaerobic micro-zones in the materials. Treatments with five carbon-based additives and two ventilation rates (0.18 and 0.36 L·min-1·kg-1 DM) were set in chicken manure composting, to investigate their effects on biodegradation process, ammonia (NH3) emission, nitrogen loss, physiochemical properties and microbial community. The additives and ventilation rates influenced the CO2 production from the 2nd week, meanwhile varied the physiochemical parameters all the process. No inhibitory effect on the maturity were observed in all treatments. With woody peat as additive, the NH3 emission amount and nitrogen loss rate were shown as 15.86 mg and 4.02 %, when compared with 31.08-80.13 mg and 24.26-34.24 % in other treatments. The high aeration rate increased the NH3 emission and nitrogen loss, which were varied with different additives. The T-RFLP results showed that the additives and the ventilation rates changed the microbial community, while the prominent microbial clones belonged to the class of Bacilli and Clostridia (in the phylum of Firmicutes), and Alphaproteobacteria, Deltaproteobacteria and Gammaproteobacteria (in the phylum of Proteobacteria). Bacillus spp. was observed to be the most dominant bacteria in all the composting stages and treatments. We concluded that woody peat could improve chicken manure composting more than other additives, especially on controlling nitrogen loss. 0.18 L·min-1·kg-1 DM was suitable for chicken manure composting with different additives.


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Due to the rapid development of chicken farms in China, the output of chicken manure has risen 39 sharply in the past decades, which was nearly 102 million tons (dry weight) in 2016 (Jia et al., 2018).

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The over production and accumulation of untreated chicken manure has caused a series of 41 environmental and social problems (Shi et al., 2018). Recycling the chicken manure to arable land 42 as fertilizers has been recognized as a sustainable utilization method, for chicken manure has high    were used in vegetable wastes or sewage sludge composting. When the ventilation rate was 140 increased to 0.36 L‧min -1 ‧kg -1 DM, less CO 2 emission amount were observed in S1, S3 and S5( Fig.   141 2B), suggested that the ventilation rate of 0.18 L‧min -1 ‧kg -1 corresponded to a higher biodegradation than 0.36 L‧min -1 ‧kg -1 DM in the current study. Significantly differences were observed after the  for almost every treatment, followed with a stable value till the end ( Fig. 3C and 3D). The carbon 175 additives influenced the EC variation, while they were always in the safe range, except 4.37 mS·cm -1 176 in T1. For more biodegradation happened in T1, which was indicated by the CO 2 production and 177 temperature. Woody peat used in T2 reduced the EC in the whole process, because of the absorption 178 caused by its rich humic acid. The rapid emission of gases and volatile organic acids in treatments 179 with high aeration rate also reduced the EC value caused.

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To avoid the toxic effects on plant growth resulted from the toxic substances, such as short-chain 181 fatty acids, GI is always used as an important index to evaluate whether compost is mature enough.

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A minimum value of 80% is considered to indicate the compost mature at an extraction ratio of 1:5

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(compost: water wet w/v). As shown in Fig. 3E and Fig. 3F, the GIs increased with the 184 decomposition of toxic materials, especially in the 1 st week. Nearly all the GIs were higher than 80% in the treatments, except T4 in series Ⅰ, and S1 and S3 in series Ⅱ. Then the GIs keep slightly  with the same compost materials, S1 had significantly higher cumulative NH 3 losses (by 117.70%) 209 compared with T1, S3 (by 25.55%) with T3, and S5 (by 38.14%) with T5. Which suggested the 210 increased aeration rate led to higher cumulative NH 3 losses.

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During the composting, the TN always increase from the initial to the end, because of the 212 concentration effect caused by the significant organic decomposition (Chan et al., 2016). In current 213 study, most of the treatments were consistent with this theory, except T5 and S5, in which the peanut 214 hull was used as carbon additives (Table 3). For their NH 3 emission were really high when compared 215 with other treatments, shown as 69.79 mg and 96.41 mg (Table 3). What's more, less matter loss 216 resulted from less organic decomposition decreased the concentration effect, for a high ratio of

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N in treatments T3 and T5 than S3 and S5 (shown in Table 3), suggested high aeration rate helped 227 to transfer NH 4 + -N into NH 3 ventilation, so that more NH 3 ventilation were observed in Fig.5 and Table 2. Meanwhile the total nitrogen loss rates were higher in treatments with high aeration rate 229 resulted from high NH 3 ventilation.

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3.4 Structure of microbial community 231 Compared with the normal additive corn straw. woody peat, saw dust and pine bark increased the 232 biodiversity at the beginning while peanut hull increased it at the 3 rd day (Fig. 5(A)). At the 233 beginning, the most abundant T-RF was 85bp, with the ratio of 100%, 56%, 53%, 44% and 47%, in all the three treatments ( Fig. 6(B)), even it occurred in the first 7 days in S1 and S5 while in later 244 two weeks in S3.

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The species distribution of bacteria in composting system can be better understood by constructing 246 bacterial clone library. In this experiment, five of the compost samples in different treatments were 247 selected to construct the clone library. Library analysis showed that the 247 sequences belonged to 248 9 different phyla, among which Firmicutes, Proteobacteria, Bacteroides and Actinomycetes account for 85.83% in the total sequences ( Fig. 6(A)). Nearly 70 of the 247 sequences were Bacillus spp.,

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The biodegradation process and the pH, EC and GI values were influenced by the five carbon-based 267 additives used in our experiment, while no inhibitory on composting maturity were observed. The 268 aeration rate of 0.18 L‧min -1 ‧kg -1 DM was more suitable than 0.36 L‧min -1 ‧kg -1 DM for chicken 269 manure composting. Woody peat had shown better effect on reducing NH 3 emission and nitrogen loss, while more NH 3 emission and nitrogen loss were observed when the aeration rate was higher.

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The