Introduction

Livestock production has markedly increased with increasing global population growth and demand for livestock. To take an instance from the global demand for pig meat, chicken meat and chicken eggs, it was predicted to grow by 32%, 61%, and 39%, respectively, up to 2030 [1]. According to Korean Statistical Information Service estimates, poultry breeding, mostly chicken, has increased by 306% [2] and South Korea has 72 million head of chickens [3]. The intensive chicken production systems have produced huge amounts of manure containing considerable nutrients, heavy metals and pathogens [4,5,6].

The composting reduced the volume of the manure wastes through the biochemical mineralization of the organic compound. The application of compost into soil could improve the soil fertility, provide nutrients, and minimize the risk of spreading pathogens and weeds [7,8,9,10]. Although composting is considered to have less environmental impact and wider applicability for various material [11], it inevitably emitted ammonia (NH3) and greenhouse gas (GHG) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), which not only reduced the nutrients in final compost but weakened environmental benefits of composting [12]. During composting, carbon is mainly lost by CO2 and CH4 through OM mineralization and reduction of acetic acid and CO2. Nitrogen is lost through NH3 volatilization and N2O emission from nitrification and denitrification, as a result, there is a loss of nutrients and microbial degradation. Substantial discharges of CO2, NH3, CH4, and N2O occurred [13]. The amount and characteristics of gases produced from composting process vary widely, which is highly related to the initial materials and the composting methodology.

Recently, several researches evaluated the effect of different raw material such as garden waste, green waste material, compost bedding of dairy farm and pig manure on composting process and compost quality [14,15,16,17,18]. These studies collectively demonstrated that the compost materials and combination method among them will be steadily diversified which resulted in different composting process and final compost quality. Since chicken manure has high nitrogen and low moisture content, co-composting with chicken manure could favor microorganisms to degrade different organic solid wastes into qualified compost [19]. Moreover, co-composting could dispose two or more kind of organic wastes. However, little is known about the combination effect of chicken manure on composting process such gases emissions, nutrient content and maturity.

This study aims to characterize the co-composting process of chicken manure with organic wastes. The specific objectives of the present study were (1) to study changes in gases (NH3, N2O, CO2, CH4) emissions during composting, (2) to investigate chemical characteristics of composts during composting, and (3) to assess relationship between gases emissions and compost quality.

Materials and methods

Composting materials

The composts were prepared manually by mixing chicken manure with cattle manure, swine manure, crop residue and spent mushroom medium. Sawdust was used to regulate the initial moisture content of the raw material, and it was adjusted to about 60%. The four treatments were labeled as OC (only chicken manure), CC (chicken + cow manure), CS (chicken + swine manure) and CRM (chicken manure + plant residue + spent medium), respectively. The detailed properties of raw materials are shown in Table 1.

Table 1 Properties of composting materials for this study (mean value ± standard deviation from triplicate measurements)
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Experimental design

The composting experiment was carried out using a conventional static chamber method for 107 days during winter-spring season. A plastic box 0.15 m3 in size (0.65 m × 0.44 m × 0.51 m) was used, which was covered with expanded polystyrene (5 cm thick) to prevent heat loss. The composting box was maintained open state during the experiment. The four treatments in this study were not replicated because the composting scale (62 L of volume) ensures the experimental reproducibility as well evidenced in other studies [10, 20, 21]. Air was supplied from the bottom into the composting chamber with a constant air flow (1–1.5 L min−1), which was fixed with a flow meter. The internal temperature of pile was continuously monitored in the fields using a data logger (EM50 Data logger, USA).

Measurement and calculation of gases emission

The closed chamber method was used to investigate flux of three greenhouse gases (CO2, CH4 and N2O) during the composting process [22]. The opaque chambers (D. 24 cm and H. 20 cm) was inserted into the compost pile to a depth of 15 cm only for sampling time. After sampling, these were removed and kept them next to compost reactor since every week compost piles should be turned and totally mixed to be properly homogenized and degraded. Gas samples were collected at 0 and 30 min after the chamber closure. Gases were sampled once a week and immediately transferred into air-evacuated vials (20 mL).

NH3 was absorbed by 0.1 mol L−1 sulfuric acid for quantification. The aqueous concentration of ammonia in the acid was analyzed by auto analyzer 3 (Bran Luebbe, Germany).

Gas (NH3, CO2, N2O and CH4) emission rate, Ea (μg dry kg−1 h−1) was calculated by Eq. (1) [22].

$${\text{E}}_{\text{a}} = \frac{C \times V}{M \times t}$$
(1)

where c is concentration of individual gas (μg m−3); V is the sum of the device and gas in a plastic composting box, (m3); m is the initial weight of the composting material (kg); and t is sampling time, (6 and 0.5 h for NH3 and other gases in this study).

The concentrations of CO2, CH4 and N2O were analyzed using gas chromatography (Shimadzu, GC-2010, Tokyo). Total fluxes of gases were calculated on an initial mass basis during composting process (g m−2) [23, 24].

$${\text{Total NH}}_{ 3} ,{\text{ CO}}_{ 2} ,{\text{ CH}}_{ 4} {\text{ or N}}_{ 2} {\text{O flux}} = \varSigma_{i}^{\text{n}} \left( {{\text{R}}_{i} \times {\text{ D}}_{i} } \right)$$

where ‘n’ is the number of sampling intervals, Ri is the gas emissions rate (mg−2 day−1) in the ith sampling interval and Di: the number of days in the ith sampling interval.

Analytic methods

Once a week, compost piles were turned and thoroughly mixed. After mixing, compost samples were collected using sampling core (diameter 5 cm × height 5 cm) at three different points (10–20 cm depth of compost pile). Fresh solid samples were dried at 65 °C for approximately 48 h and ground and sieved with 2 mm for chemical analysis. The total C and N concentration were analyzed by an elemental analyzer (CHNS-932 Analyzer, Leco.). The water extractable carbon (WEC), nitrogen (WEN) and hot-water extractable carbon (HWEC), nitrogen (HWEN), relatively labile organic compounds, were extracted by distilled water. The concentration was determined by TOC-5050A analyzer (Shimadzu Corporation, Japan). The nutrient (P, K, Ca, Mg, Na) contents were determined from digested samples using ternary solution (HNO3:H2SO4:HClO4 = 10:1:4, v/v/v) by spectrometry (ICP, Agilent) [25].

The compost samples were mixed with distilled water (1:20 w/w ratio) and shaken for 2 h. The pH and EC values were determined (Orion 3star, Thermo Electron Corporation, MA, USA). The extract was filtered through a 5 μm filter paper to evaluate the germination index (GI). The phytotoxicity and maturity level of compost pile were assessed by GI value [26]. Thirty radish seeds were distributed on filter paper in petri dishes (85 mm in diameter) and moistened with 5 mL of the compost water extract. Distilled water was used as a control. Three replicate for each sample were incubated at 25 °C, and the number of germinating seeds were counted after 72 h. They were again incubated and root length was measured between 120 and 125 h of incubation. The GI value was calculated by the following formula:

$${\text{GI }}\left( \% \right) = \frac{{\left[ {\text{Seed germination of treatment}} \right] \, \left[ {\text{Root length of treatment}} \right]}}{{\left[ {\text{Seed germination of control}} \right] \, \left[ {\text{Root length of control}} \right]}}$$

Mean values and standard deviations of triplicate measurements were shown in this study. The data were subjected to one-way analysis of variance (ANOVA), and identified the least significance variance (LSD) at P = 0.05 values by Statistical Analysis System (SAS 8.2). Determination of differences between parameters was performed via two-way ANOVA that included composting effect (initial and final compost product), treatment (different raw materials) and their interaction. The correlation coefficients were calculated using R software to determine the linear relationship between gases emissions and compost properties.

Result and discussion

CO2 and CH4 emission

The CO2 emission (Fig. 1) certainly presented the overall microbial activities and influenced the composting efficiency or degradation of organic matter [27, 28]. The CO2 emission was rapidly increased within the first few days in all treatments, the maximum CO2 emission 1574 (14th day), 1239 (7th day), 1385 (77th day) and 1016 (7th day) g kg−1 day−1 were observed in OC, CC, CS and CRM, respectively. Then CO2 emission was gradually decreased and dropped till the bottom after 30th day, then finally maturation phase was attributed with lowest CO2 emission. It indicated the stability of the end product or compost. CO2 emission trend is very similar with variation of temperature, and highly positive correlation was found between them (Table 2). The initial increasing trend of CO2 is because of rapid degradation of organic matter under high temperatures. But CS treatment showed high peak of CO2 at both initial and late stages, which reached highest CO2 flux (52 kg kg dw−1) while other treatments have similar CO2 flux values (38–40 kg kg dw−1).

Fig. 1
figure 1

Emission rates and cumulative emissions of carbon dioxide (CO2) and methane (CH4) during composting. OC Only chicken manure, CC chicken + cow manure, CS chicken + swine manure, CRM chicken manure + plant residue + spent medium

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Table 2 Correlation coefficient (P value) between gases emissions and compost properties
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Methane was produced by methanogen using CO2 and acetic acid in anaerobic condition. Higher emission of CH4 could be indicated the unsuitable aeration during composting and improper density between raw materials [9]. Overall, low mean CH4 emissions were recorded. The emission patterns indicated that the anaerobic condition caused similar CH4 emission pattern, but concentration was different among the treatments. The CH4 emission increased within the 50 days (thermophilic and mesophilic phase) and then gradually decreased to an undetectable level for all treatment. The initially increased CH4 emission might be due to the largely consumed oxygen for organic matter decomposition during the thermophilic beginning phase. The highest accumulated CH4 was observed in OC, and its peak value was reached on the 42th day (32 g kg−1 initial matter day−1).

Microorganisms can rapidly degrade organic component, causing the consumption of oxygen supplied by aeration system in the thermophilic phase [29, 30].

NH3 and N2O emission

The changes in NH3 emission rates are shown in Fig. 2. The ammonia was emitted accompanied by the decomposition of N organic material during the early thermophilic phase. It happened because the compost reached the thermophilic stage and the organic acid began to volatilize rapidly in early stage (Fig. 2). This observation is different from that reported by Yang et al. [31], perhaps due to lower N content in food waste compared to chicken manure. After high peaks of ammonia volatilization, NH3 content of all treatments slightly declined between 4th and 5th week of composting, and then promptly elevated and finally stabilized. In this study, 40–75% of NH3 flux was emitted at initial stages (5th week of 15th week). These results agreed with the emission pattern previously described by Sommer [32], El Kader et al. [33], Ahn et al. [34], and Wang and Zheng [35]. Mixing with swine manure (CS) or plant residue plus spent mushroom medium (CRM) increased NH3 emission by 4.1 times compared with only chicken manure (OC). It is assumed that because of expended thermophilic phase and increased NH4-N content in both CS and CRM treatments (Fig. 3). Combination with cow manure was most effective to mitigate NH3 emission, only chicken manure as well. Reduced NH3 emission might improve nutrient of compost. It indicated that selection of combination materials could be a good practice to compost quality.

Fig. 2
figure 2

Emission rates and cumulative emissions of ammonia (NH3) and nitrous oxide (N2O) during composting. OC Only chicken manure, CC chicken + cow manure, CS chicken + swine manure, CRM chicken manure + plant residue + spent medium

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Fig. 3
figure 3

Changes in temperature, pH, NO3−N and NH4+-N of compost pile during composting. Values are the average of three repeats and error bars indicates the standard deviation. OC Only chicken manure, CC chicken + cow manure, CS chicken + swine manure, CRM chicken manure + plant residue + spent medium

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As shown in Fig. 2, N2O emission was observed after 60 days of composting in most of the treatments. Until middle of composting period, the conversion from organic nitrogen to NH4+-N was the dominant process, therefore the N2O emissions was not negligible. A low NO3-N concentration at beginning stage which is insufficient to emit N2O through denitrification during the thermophilic beginning phase. It might be due to incomplete denitrification/nitrification processes that change NH4+ into N gas [31, 33]. Conflicting with that result, some researcher reported that a high concentration of N2O was found at the initial stage of composting period [28, 34]. In our study, except N2O emission, all the gases were increased from beginning of the experiment. It might be adjusted suitable conditions of compost pile such as 50–60% of moisture content and < 25 of CN ratio that can rapidly degrade organic matters.

Nitrous oxide emission rapidly accelerated during the mesophilic and cooling phase, which is closely related with Han et al. [36] observation, who found that if the composting period was extended, N2O emissions during the cooling phase may have overran the mesophilic phase. Thus, temperature can be a major factor for controlling N2O emission during aerobic composting of chicken manure (P < 0.001) (Table 2).

Changes in temperature, pH and content of NO3 and NH4

The compost pile temperature is determined by the balance between heat production by organic matter degradation and heat dissipation of the pile [37]. Figure 3 showed consistent patterns with thermophilic, mesophilic and maturation stages in all four treatments. All treatments’ temperature rapidly rose, with temperatures above 60 °C at the initial stage, presented an appropriate initial ratio of compost [38]. The combination of chicken manure with other manure and residues might be favorable to microbial activity that produces heat. In the thermophilic phase, the temperature of all piles remained above 54 °C for 6–8 days, which secured reduction of pathogens to satisfy the maturity and sanitation requirements. The CS treatment had longer thermophilic phase. Huang et al. [39] observed that swine manure had the least O-alkyls and anomeric of carbohydrates, and thus it was more resistant to microbial attacks. The OC treatment most rapidly reached over 60 °C just 2 days after composting. It could be because of the highest concentration of water extractable C and N and hot-water extractable C and N in chicken manure, which is easily used for microbial (Table 1).

Although pH is an indicator for state of composing, pH values in all treatments showed a similar trend with small changes. Increasing trend in the thermophilic phase were found. That trend could be attributed to the degradation of acid compounds and the increase of ammonia.

The nitrogen is firstly converted into NH4+-N and easily volatilized as NH3 in the thermophilic stage, due to the high temperature and slightly alkaline condition resulted from the decomposition of compost. The NH4+-N is converted into NO3−N through aerobic nitrification and anaerobic denitrification, during which the N2O and N2 produced. The NO3−-N concentration was low at the initial stage of the composting and increased sharply in the second mesophilic/maturation phase.

Changes in compost quality

Table 3 shows the concentration of carbon (C), nitrogen (N), C/N ratio, phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), electricity productivity (EC) and pH in all treatment at initial (0 week) and final (15 week) stages. Composting cycle significantly increased C/N ratio, P, Ca, Mg, K, Na, EC and pH, specially Ca content of final compost was greatly increased by 1.4–3.0 times over that of initial compost (P < 0.001). Total N concentration was decreased by 20–31% at final stage except CC treatment, where emitted the lowest NH3. Only total C and Ca concentration was not affected by composting process, while other properties were considerably changed by composting process. Total carbon concentration slightly increased despite carbon losses. This might be due to the influence of sawdust used as a bulking agent. Considering the total mass reduction, total C of compost definitely decreased as shown in Table 4. The compost types showed significant difference in all parameters analyzed (P < 0.001) (Table 3).

Table 3 Characteristics of initial and final compost (mean value ± standard deviation from triplicate measurements)
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Table 4 Carbon and nitrogen balances during composting
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C/N ratio is main indicator to present the stability of composting and the maturity of final product [29]. Similar with previous studies [40, 41], the C/N ratio slightly increased at thermophilic stage, it might be due to the N loss caused by ammonia volatilization. The final C/N ratio values of four treatments were less than 25, which is indicated the maturity (Fig. 4).

Fig. 4
figure 4

Changes in carbon, nitrogen, C/N ratio and germination index (GI) of compost pile during composting. Values are the average of three repeats and error bars indicates the standard deviation. OC Only chicken manure, CC chicken + cow manure, CS chicken + swine manure, CRM chicken manure + plant residue + spent medium

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The EC of all treatments increased at the beginning of the composting process due to the decomposition of complex organic matters into dissolved components [42, 43]. Slightly higher EC value was observed in CC treatment than others. The EC values in final products of all treatments OC, CC, CS and CRM were 3.21, 3.93, 3.62 and 3.17, respectively (data graph was not shown). Awasthi et al. [9] previously reported that less than 4 dS m−1 of EC value will not cause any phytotoxicity to apply. Thus, the final compost product of all treatments were allowed for non-phytotoxic limit.

The GI values gradually increased with composting in all treatments (Fig. 4). This changes of GI were similar with previous studies [44, 45]. A more rapid increase in GI was found in OC and CC treatments, whose GI reached and maintained above 80% from 60 days of composting. It might be attributed to relatively low NH3 emission during whole composting period. At the final stage, GI values attained more than 80%, indicating the maturity of compost in all treatments [46]. Thus all four composts could be safely applied in agricultural soil without any phytotoxic effects.

The present study indicates the importance of co-composting material to control gases emissions and compost quality during chicken manure composting. The chicken manure had the greatest amount of labile organic matter such as WEC, WEN, HWEC and HWEN. Therefore, OC treatment most rapidly reached the highest temperature immediately after composting and, showed the highest CO2 emission at beginning of composting. Mixing this chicken manure with other organic wastes brought different carbon and nitrogen losses. The CS and CRM exhibited relatively longer thermophilic phase, which leaded degradation of acid type compound and increase in NH3. On the other hand, CC treatment didn’t show specific increases in gases emissions. The OC and CC showed slightly faster maturation, it should be due to the smaller amount of NH3 generated in OC and CC than that in CS and CRM. Our findings suggest that sole chicken manure or combination with cow manure could be effective strategy to improve compost quality and minimize gases losses for chicken manure composting.