Journal of Environmental Chemical Engineering 9 (2021) 105453

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Journal of Environmental Chemical Engineering

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Ultra-high temperature aerobic fermentation pretreatment composting:

Parameters optimization, mechanisms and compost quality assessment
Muhammad Ajmal a, Aiping Shi a, *, Muhammad Awais c, Zhang Mengqi a, Xu Zihao a,
Abdul Shabbir a, Muhammad Faheem a, Wei Wei a, Lihua Ye b, *
a
School of Agricultural Equipment Engineering, Jiangsu University, Zhenjiang 212013, China
b
School of Automotive and Traffic Engineering, Jiangsu University, Zhenjiang 212013, China
c
Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang 212013, China

A R T I C L E I N F O A B S T R A C T

Editor: Dr. G.L. Dotto Rapid treatment processing for agricultural waste is of the utmost importance with the boom in China’s agri­
culture sector. Ultra-high temperature aerobic fermentation pre-treatment process assisted composting (HTC) is
Keywords: superior to traditional composting (CCT) with enhanced compost maturity and accelerated organic matter
Agricultural waste degradation. This research aimed to optimize and investigate the change in the chemical composition of ultra-
Hyperthermophile composting
high aerobic fermentation pre-treatment (UHT-AF) during agricultural waste composting and compare the ef­
Process optimization
fects of HTC and CCT on physio-chemical and biological parameters for compost quality assessment. Taguchi
Chemical analysis
Structure analysis analysis based on physio-chemical parameters of pretreated-product provided experiment R5 (75 ◦ C, 15 h, 40 g/
Compost quality assessment kg) as optimal conditions. Comparative results revealed that HTC is superior to CCT with a shortened maturity
period of 24 days. HTC showed a very rapid increase in high temperature (96.02 ◦ C on the 3rd day) and a long-
lasted thermophile stage (day 1–20 ≥ 60 ◦ C). The C/N ratio reduced from 21.33 to 15.57, moisture content
60.5–35.5%, pH from 7.80 to 8.17, and compost showed GI ≥ 95%. The FTIR analysis of optimal pretreated-
product confirmed that the UHF-AF technique could promote lignocellulose degradation and lignin degrada­
tion in subsequent composting, and SEM images provided clear morphological evidence of lignocellulose
degradation. The study suggested UHT-AF pretreated (HTC) as a promising agricultural waste composting
technique for rapid degradation of organic matter and enhanced quality compost production.

1. Introduction advantages in the treatment of livestock manure, in the traditional

aerobic composting of livestock manure, the compost temperature must
With the development of intensive livestock production in China, be higher than 50 ◦ C, and the duration should be 5–10 days in order to
poultry waste with other agricultural wastes has increased tremendously meet the requirements of harmless sanitation of manure [5]. Moreover,
in recent years [1]. The amount of manure that this industry generates sometimes due to the physio-chemical characteristics of organic wastes,
every year has contributed to a rise in environmental pollution, such as conventional aerobic composting is not suitable for their decomposition
water contamination, odor, and even a great threat to human health. As [62]. These characteristics cause lower temperature increment in pro­
it is rich in organic matter (O.M.) and nutrients such as nitrogen, cess composting, which leads to poor sanitation of compost, insufficient
phosphorus, and potassium, livestock manure is also an important fer­ decomposition, and damage compost quality [63]. Along with the
tilizer resource in agricultural production [2]. Composting is an effective benefits of composting, conventional aerobic composting can also
way to utilize this resourceful livestock manure. Compared with other involve the production of many undesired substances and gases such as
treatment methods of agricultural waste, composting can not only NH3, H2S [6]. Moreover, it often takes a long time for organic materials
remove odor, toxic substances, and pathogens bacteria, but compost to be decomposed entirely on a large land area, and loss of organic
product can also be applied as soil amender, which enhances and carbon and nitrogen is large during the composting process. Conven­
improve the soil structure, increase the geochemical process of crop tional composting also lost a great amount of nitrogen resource in the
nutrients, and soil fertility level [3,4]. Although composting has many form of ammonia emission in the range of 70–88% [7]. However, it only

* Corresponding authors.
E-mail addresses: shap@ujs.edu.cn (A. Shi), yelihua@ujs.edu.cn (L. Ye).

https://doi.org/10.1016/j.jece.2021.105453
Received 5 February 2021; Received in revised form 16 March 2021; Accepted 6 April 2021
Available online 16 April 2021
2213-3437/© 2021 Elsevier Ltd. All rights reserved.
M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

takes 10–30 min to kill pathogens in animal manure by increasing the cycle. This goal can be achieved by combining above mentioned two
treatment temperature above 70 ◦ C [8]. approaches (hyperthermophilic pre-treatment & inoculation of hyper­
Aerobic composting is a self-heating process accomplished by func­ thermophilic microbial agent) to obtain rapid high-temperature and
tions of microbial communities [9]. These microorganisms are affected maintain a longer thermophilic stage. Thus, this research focused on
by the nature of composting organic material and process conditions like hyperthermophile pre-treatment composting of agricultural waste
pH, aeration, and temperature [10]. Besides, traditional composting can inoculated with hyperthermophile microbial agent for rapid and com­
be divided into three stages: warming stage, high-temperature stage, plete degradation of lignocellulose material. We named this new
and cooling and ripening stage [11]. Microbial activities progress can be pre-treatment process "Ultra-High Temperature Aerobic Fermentation
estimated by composting temperature phase. Temperature is considered (UHT-AF)" due to inoculation of microorganisms. To better understand
a vital parameter for the decomposition of organic matter. Lignocellu­ the impacts of this new approach on lignocellulose substance degrada­
lose accounts for a certain proportion of livestock manure, which is the tion in the pre-treatment process and subsequent In-vessel composting,
main limiting factor for the rapid stabilization of materials [12]. Ther­ the study on change in chemical composition and material structure is of
mophilic microorganisms degrade more than 65% of lignocellulose great importance.
substances in a high-temperature period [13]. To enhance organic The objectives of this study were to (i) optimize of UHT-AF pre-
matter decomposition, continuous high-temperature composting always treatment process, (ii) to evaluate the effect size of important pre-
desired. Thermophilic microorganisms tend to degrade more easily treatment parameters (temperature, time, inoculation rate) on physio-
degradable organic compounds such as protein and starch than meso­ chemical characteristics of pretreated-product, (iii) to investigate the
phile microorganisms [14]. Therefore, thermophilic microorganisms change in chemical composition and material structure of pretreated-
play a dominant role in the degradation of substrates’ fermentation product, and (iv) to explore effects of UHT-AF pre-treatment process
during the high-temperature period. Therefore, diverse disposal pro­ on physio-chemical and biological compost maturity parameters of
cesses using physicochemical and microbiological techniques are highly subsequent In-vessel composting and compare them with traditional In-
valued and widely used in livestock manure composting to obtain vessel composting.
thermophile temperature faster and for long-duration such as the
addition of bulking agent, ventilation control [15,16], and use of mi­ 2. Materials and methods
crobial agent at the initial stage of composting [17]. Control and
improvement in composting conditions such as pH, C/N ratio, and 2.1. Feedstock
aeration rate have shown a positive impact on microorganisms’ growth,
ultimately helping to attain the thermophile temperature stage [18]. Poultry manure was acquired from Lingtang Chicken Farm, Zhen­
To overcome traditional composting disadvantages, pre-treatment jiang, Jiangsu, China (32◦ N, 119◦ E). Corn straw was gathered from the
with a hyperthermophilic reactor followed by the traditional treat­ local field and first cut to 1 cm and then crushed. In order to finalize raw
ment (hyperthermophilic pre-treatment composting, HTPRT) was pri­ material ratios, lab-scale initial optimization experiments were per­
marily developed in previous studies [19–21]. The temperature of the formed. To make the C/N ratio of feedstock ~ 20, poultry manure and
hyperthermophilic reactor developed by Yamada [19] remains 100 ◦ C maize straw ratio was 8:1. A well-homogenized feedstock mixture was
for 2 h. Recently, Some other researchers [22–25] used a obtained by taking weighted amounts of poultry manure and corn straw
temperature-adjustable HTPRT reactor for pre-heating (85 ◦ C for 4 h) of and mixing them in a container. To reduce gases emission from the
various agricultural waste, and then the in-vessel composting process composting process, a small volume of superphosphate, widely used as
(up to 2 months) for mature compost production. The study on the fertilizer (5% of total feedstock), was mixed with the feedstock mixture.
physio-chemical characteristics showed that maximum temperature of The initial moisture content of this feedstock was adjusted to 65%.
subsequent in-vessel composting (67.4 ◦ C) was 13.6 ◦ C higher than that Table 1 shows some basic chemical and physical characteristics of
in the conventional in-vessel composting, and the thermophilic stage feedstock materials.
(≥50 ◦ C) lasted 2–3 days longer (total 13 days) during hyperthermo­
phile composting of chicken manure with rice straw, and the total
2.2. Inoculation
content of nitrogen (T.N.) and total carbon (TOC) of HTPRT compost
was higher at 9.7% and 11.3% than the control treatment, respectively
For inoculation, the complex enzyme is composed of Aspergillus
[22]. 13C NMR spectroscopic data showed a higher aromatics percentage
Usami, Trichoderma longibrachia, Candida tropicalis, Aspergillus
and earlier enrichment of aromatic structures in humus substances
fumigatus, Chaetomium globosum, and Bacillus decoctatum, it is
extracted from hyperthermophilic pre-treatment composting than con­
extracted from Bacillus thermophilus, Bacillus subtilis, Thermus ther­
trol treatment [26]. The hyperthermophilic pre-treatment composting is
mophilus, and Alcaligenes faecalis. Most of these bacteria are thermo­
superior in quality and efficiency of composting by accelerating com­
philic bacteria, which can survive at high temperatures above 70 ◦ C.
posts’ humification and shortening the maturation period [64]. This
novel composting technology of HTPRT also helped lower the emission
of malodor gases, such as NH3, H2S, and fast removal of antibiotic genes 2.3. Fermentation tank
and other mobile genetic elements during composting process [19,27].
On other hand, some scholars [28–31] used hyperthermophile bacteria An integrated laboratory-scale composter was used to conduct this
in organic waste composting, and found elevated temperature during experimental study with a capacity of 5 kg of feedstock (Length = 620
composting (90–100 ◦ C) and composting cycle was reduced by 15–25 mm, Diameter = 226 mm). The composter has been designed to give
days. Hyperthermophile bacteria inoculated compost showed a
20–30 ◦ C higher temperature and long thermophile stage than the Table 1
traditional composting, and the ultra-high temperature phase (≥80 ◦ C) Physical and chemical characteristics of the feedstock.
lasted for 5–7 days. It also accelerated the humification rate, reduced gas Parameter Poultry manure Corn straw
emission with some other pollution control measures. It can be
Moisture content (%) 26 9
concluded from the above discussion that if the composting process goes pH 8.12 6.36
beyond the warming period and the composting temperature is raised EC (mS/cm) 3.54 2.16
from the beginning to a higher temperature, and this high temperature TC (g/kg of dm) 40.5 423
lasts for a longer time, it is possible to realize the rapid degradation of TN (g/kg of dm) 2.6 8
C/N 15.58 52.88
lignocellulose waste, with enhanced quality compost within the short

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

heat to the feedstock mixture in a controllable pattern with a control Table 3

temperature unit, an aeration unit to meet the demand for oxygen in the Design of experiment by Taguchi method.
process of degradation, maintain the humidity level, and a guided Runs (#) Temperature (◦ C) Time (hr) Inoculation (g/kg)
agitator. Such systems provide the composting process with a semi-
R1 65 13 20
closed environment by monitoring various variables at values of R2 65 15 30
needed levels. The primary goal of such reactor-type composting sys­ R3 65 17 40
tems is rapid organic matter degradation under monitored conditions. R4 75 13 30
R5 75 15 40
R6 75 17 20
2.4. Methodology R7 85 13 40
R8 85 15 20
2.4.1. Optimization experiment of UHT-AF R9 85 17 30

The Standard L9 orthogonal array (O.A.) of the Taguchi Experiment

Design method has been applied for three variables with 3 levels.
Taguchi method and its application in the composting study have been Table 4
described in our previous study [32]. Table 2 shows the initial param­ Time distribution w.r.t temperature.
eters with levels. And compost C/N ratio was selected as a response Time Heating phase Thermal phase Cooling phase
parameter. L9 array generated 9 treatments with different temperatures, Hr. Hr. Temp Hrs. Hr.
inoculation, and time, as shown in Table 3. The total hours of each
13 ~1 65/75/85 8 ~4
treatment were divided into three temperature phases: the heating
15 ~1 65/75/85 10 ~4
phase, the constant temperature phase, and the cooling phase, as shown 17 ~1 65/75/85 12 ~4
in Table 4. a heating-up phase for almost one an hour to establish the
desired temperature, a constant thermophilic heating phase for 8–12 h
(For experiments R1 to R3 thermophilic phase temperature was 65 ◦ C, concentrated H2SO4 in the boiling water for 30 min. The digestate was
for R4-R6 it was 75 ◦ C, and for R7-R9 it was 85 ◦ C) and without heating a titrated by 0.2 M FeSO4. LSD tests for E.C., pH, M.C, T.C., and T.N. be­
cooling phase for the remaining 4 h. Throughout the composting pro­ tween several experiments were carried out on Minitab19 software. S/N
cess, batch agitation was applied. Continuously forced aeration at a rate ratio Analysis and Analysis of variance (ANOVA) were applied on
of 0.5 L min-1 kg-1 of feedstock was provided by an attached blower to Minitab19 described by [32].
the composter.
2.6. FTIR spectroscopy
2.4.2. Subsequent high-temperature composting process
After obtaining optimal conditions for the UHT-AF process, aerobic Nicolet 8700 IR spectrometer was used to perform the FT-IR analyses
high-temperature composting (HTC) was performed. Thus, the UHT-AF of feedstock and selected optimal compost (R5). For the sample prepa­
pre-treatment process was repeated for the same quantity of agricultural ration for spectroscopy, 3 mg of sample was ground in a vibrating puck
wastes by providing optimal conditions (temperature, duration, and mill with 300 mg of oven-dried KBr, then 150 mg of the mixture was
inoculation) in the fermentation tank. After the complete process of compressed under a hydraulic compressor into a translucent pellet. After
UHT-AF pre-treatment, moisture content was again adjusted 60% by that pellet sample was put on the holder and obtained spectrum between
adding water. This moisture content-adjusted pretreated material un­ 4000-400 cm-1, with a resolution of 4 cm-1 and 32 scans. For back­
derwent 24 days of high-temperature composting (HTC) in the same ground, spectra of pure KBr was used [33]. The main peaks were found
fermentation tank without providing heat from an external source (self- using OMNIC software (intensity and wavenumber). Spectra were
heating stage). To maintain aerobic conditions of the composting pro­ smoothed using a 30-point smoothing filter to highlight the emerging
cess, intermittence aeration was provided with the help of a blower at bands. Three reference points were used to correct the Spectra baseline:
the rate of 0.25 L min-1 kg− 1 of material without humification. Mixing of 4000, 1800, and 830 cm− 1, as zero absorbance points [34].
the material was performed twice a day by the agitator in the tank.
Control composting treatment (CCT) was also performed by following 2.7. Seed germination index
the same conditions in the same tank, without the UHT-AF process. CCT
treatment was inoculated with HTC compost (0.5% of dry matter). A water extract was prepared for the determination of the seed
germination index (G.I.). Fresh solid samples were mixed with deionized
2.5. Analytical analysis water at a 1:10 ratio (mass ratio) and shaken for 1 h, then centrifuged at
4000 rpm for 20 min and filtered through 0.45 um membrane filters. The
Total nitrogen (T.N.) and total carbon (T.C.) were measured by a G.I. was determined in triplicate using ten cucumber seeds and a water
Vario Macro CHNS Element Analyzer, the obtained value of T.C. and T. extract. Eight milliliters of the water extract were pipetted into Petri
N. were used to calculate the C/N ratio. For pH measurement, a distilled dishes (10 cm in diameter) packed with a piece of filter paper. Ten seeds
water-soluble extract 1:10 (w/v) was used with a DK0400 pH/E.C. meter were evenly scattered on the filter paper and incubated at 20 ± 1 ◦ C for
(Extech Instruments). The moisture content was obtained by Oven dry 48 h in the dark. Deionized water was used as a control. The G.I. was
method. Samples were put in the Oven dryer for 24 h with a constant calculated as follows:
temperature of 105 ◦ C. Total organic carbon (TOC) was measured by No. of seeds germinated in extract mean root length in extract
GI = ×
oxidation with a mixed solution of 0.8 M potassium dichromate and No. of seeds germinated in control mean root length in control
× 100%
Table 2
Initial factors and their levels.
3. Results and discussion
Level/ Temperature Time Inoculation (g/kg of
Parameter (◦ C) (hr) feedstock)
3.1. Evaluation of UHT-AF process
Level-1 65 ◦ C 13 20
Level-2 75 ◦ C 15 30 3.1.1. Optimization of UHT-AF process parameters with response C/N ratio
Level-3 85 ◦ C 17 40
For optimizing artificially applied temperature, permitted total

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

duration, and inoculation for the UHT-AF process, the ideal carbon to both processes are strongly linked with permitted time and given tem­
nitrogen ratio (C/N) ratio was selected as the response factor. The perature [37]. Furthermore, their study supported experiments R5, R6,
required value of these criteria was based on the National Chinese R8, and R9. This part of our paper was completely supportive of the
Organic Fertilizer Standard. C/N ratio should be decreased from 20 to 25 findings of the Taguchi study. The E.C. assessment is shown in Fig. 2d. In
of feedstock to 15–18 of good quality and appropriate-cured compost. feedstocks, the initial E.C. value ranged from 3.8 to 4.3 mS cm− 1. In all
Compost having the best C/N ratio value should gradually mineralize experiments, E.C. values increased firstly, and this increment was
nitrogen with or without nitrogen immobilization [35]. directly proportional to the temperature applied. At the end of the
In order to assess the influence of the applied conditions on the heating process, E.C. values for treatments with temperatures of 65 ◦ C,
required C/N ratio value of the UHT-AF process, The S/N ratio response 75 ◦ C, and 85 ◦ C increased within the range of 5.5–6.0 mS cm− 1,
plots for the main effects were plotted by choosing the "nominal is the 5.9–6.4 mS cm− 1, and 6–6.8 mS cm− 1 respectively, followed by a steady
best" nature of the S/N ratio. Table 5 presented the S/N ratio for carbon decrease for all treatments up to the end of the cooling phase. The initial
to nitrogen (C/N) ratio. Delta value in this table defined that given value of E.C. was 3.8 mS cm− 1 during the fermentation process for R5
temperature and inoculation rate as being largely responsible for treatment, which increased to 6.3 mS cm− 1 at the end of the heating step
reducing the ratio of C/N for the feedstock relative to the time allowed. and decreased to 5.9 mS cm− 1 after 4 h. The pH assessment is shown in
The main graphs of the main effects of the S/N ratio are shown in Fig. 1. Fig. 2e. In all experiments, pH values first increased, which was directly
It showed the temperature, time, and inoculation rate levels that gave proportional to the applied temperature. At the end of the heating
maximum S/N ratios. According to this analysis, the middle level of process, pH values of treatments with temperatures of 65 ◦ C, 75 ◦ C, and
temperature and time level and the higher-level of inoculation level give 85 ◦ C increased within the range of 7.7–8.7, 8.2–8.7, and 8.5–9.1
the maximum S.N. ratio. Experiment R5 is a mixture of these stages, and respectively, followed by a steady decrease for all treatments until the
R5 was chosen based on as the optimal experiment based on this anal­ end of the cooling phase. The pH value decreased from 6.5 to 8.4 during
ysis. There are uniform effects on the S/N ratio of changes in tempera­ the process for the R5. The wet bulk density assessment is shown in
ture and time levels from low to medium and middle to high, but Fig. 2f. The wet bulk density value of all treatments has improved. In
changes in inoculation levels from medium to high are more successful feedstocks, the initial wet bulk density value ranged from 0.29 to
compared to low to medium levels. 0.32 g/mL. Wet bulk density values increased during the fermentation
An analysis of variance was conducted to determine the importance process in all experiments, and this increase was directly proportional to
of influencing variables with their percentage contribution to achieve the temperature applied. At the end of the cooling process, wet bulk
the desired C/N ratio value, and the results were presented in Table 6. In density values for treatments with temperatures of 65 ◦ C, 75 ◦ C, and
this study, the freedom-interaction effect of input factors for the non- 85 ◦ C improved within the range of 0.33–0.34 g/mL, 0.34–0.35 g/mL,
zero error degree was not included and eliminated in all remaining and 0.34–0.36 g/mL, respectively.
studies. It was very clear from the ANOVA table that the most important From these results, it can be concluded that ultra-high temperature
variable for changing the value of C/N ratio is given temperature and fermentation pre-treatment modified all physio-chemical characteristics
inoculation, that also in favor of the value of delta for the S/N ratio and of pretreated-product, which will accelerate the organic matter degra­
the number of ranks in the response table, and time is a non-significant dation in subsequent composting.
factor.
3.1.3. FTIR analysis of UHT-AF process
3.1.2. Evaluation of physio-chemical characteristics during UHT-AF Fig. 3a and b showed the FTIR spectrum of feedstock and R5 fer­
Following physio-chemical characteristics were monitored during mented compost, respectively. Both FTIR spectrums displayed almost
the pre-treatment process. It was observed that the size of the effect of identical absorption ranges, with spectral absorption intensity variations
different applied factors (temperature, time, inoculation rate) was and few peaks, comparable to findings of other authors. Fermented
different on physio-chemical characteristics. Fig. 2a showed the C/N compost spectrum interpretation is based on various studies, especially
ratios of the final products of all treatments. The groups of treatments with these cited researches [38–43].
with a higher temperature but at the same time and inoculation rate There occurred broadband between 3200 and 3360 cm-1 which
showed an improved C/N ratio. The overall C/N trend showed that the represented H− bond in O.H. groups. Peaks between 2960 cm− 1 and
degree of temperature and inoculation rate played a crucial role in the 2870 cm− 1 showed stretching of the C− H bond in aliphatic structures.
degradation of organic matter. As shown in Fig. 2b, this C/N ratio Peaks at 1650 cm− 1 and 1625 were ascribed to stretch of the C˭O bond
pattern for experiments with increasing temperature and time could be in amide groups (amide I), also the symmetric stretch of COO− groups.
described by the total carbon decreasing pattern. For the development of These peaks also comprehend the vibration of C˭O bonded conjugated
stable composts, experiments R3 and R5 were considered to be more carboxylic acids, ketones, esters, quinones, and the vibration of C˭C of
promising based on previous studies. During organic matter decompo­ aromatic compounds [42]. A peak at 1551 cm− 1 was allotted to aro­
sition, moisture has a critical role because it influences microbial ac­ matic ring vibration, and a distinct peak at 1410 cm-1 was assigned to
tivity [36]. Fig. 2c presented the moisture level variation in all the asymmetric stretch of C− O and deformation of O− H and C− O− H in
treatments during the UHT-AF process. It illustrated, with the passage of the carboxyl groups and COO− ions symmetric stretch [43]. 1375 cm− 1
time and increment in temperature, moisture level showed a decreasing was assigned to the stretching of N–O in nitrates, and 1245 cm− 1
pattern as excepted. Because of the output of microbial heat and attributed to carbohydrates and polyols [42,43]. Peaks at 1094 cm− 1
leachate, this decrease in humidity is associated with evaporation, and were attributed to the asymmetric vibration peak of C− O− C in the py­
ranoside bond [44]. The peak at 1160 cm− 1 was assigned to poly­
saccharides. The peak at 1030 cm− 1 is commonly attributed to the
Table 5 vibration of C− H during in-plane deformation and the stretch of C− O in
Response table for signal to noise ratios for C/N ratio. carbohydrates, polysaccharides, or polysaccharides-like components
Level Temperature Time Inoculation [45]. The sharp band at 875 cm− 1 can be attributed to the bending of
C–O during out-of-plane carbonates. A peak at 597 cm− 1 may be
1 29.14 27.96 29.68
2 34.73 34.31 27.79 assigned to bending of S-O of inorganic sulfates, and primary amine
3 27.98 29.58 34.38 groups (NH2 out-of-plane), secondary amine groups (N–H wag) [42].
Delta 6.76 6.35 6.60 Compared with the feedstock’s spectra, the band around 3280 cm-1
Rank 1 3 2 converted to a lower intensity band and moved toward a lower wave­
Nominal is best (10 × Log10 (Ybar^2/s^2)). number at 3200 cm− 1 in the spectra of the R5 fermented compost. The

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

Fig. 1. Main effects plot for SN ratio of C/N ratio.

3400M, Japan). Samples were prepared, and their SEM examination was
Table 6
done according to the method described by Powell.
ANOVA on C/N value.
In the fermented compost of this study, lignocellulose was mainly
Source DF Adj SS Adj MS F-value P-value derived from corn straw, which is consisted of cellulose (34%), hemi­
Temperature 2 17.4331 8.71655 10.17 0.001 cellulose (37.5%), and lignin (22%). SEM analysis for feedstock and R5-
Time 2 0.0681 0.03407 0.04 0.961 compost were shown in Fig. 4a and b, respectively. There were signifi­
Inoculation 2 17.8476 8.92378 10.42 0.001 cant discrepancies between the mixed raw waste and the final fermented
Error 20 17.1342 0.85671
Lack-of-fit 2 8.1221 4.06107 8.11 0.003
compost in SEM observation images of feedstock and compost product.
Pure error 18 9.0121 0.50067 The final compost product had a looser structure relative to the compact
Total 26 52.4830 microscopic morphology of feedstock, with the location of apparent
microbial communities. Microorganisms played a significant role in
reducing the particle size and improving the porous structure of the final
band around 2925 cm− 1 in feedstock was broad with less intensity, but it
products, as demonstrated by gaps and holes in the fermented compost
became sharp in spectra of R5 compost, and two small peaks 2960 and
[48,49]. Overall, SEM analysis supported our fermentation approach for
2870 cm− 1 appeared in compost spectra, might because of aliphatic
poultry manure and corn straw feedstock.
structures preferential biodegradation [46]. Noteworthy increment in
peaks at 1651 cm− 1 attributed to assigned to alkenes or aromatic ring
modes and 1245 cm− 1 attributed to phenols or aryl ethers were detec­ 3.2. Evaluation of subsequent composting
ted. The increment in such peaks showed higher production of aromatic
components during the fermentation process, signifying compost sta­ 3.2.1. Changes in temperature
bility. An increase in the peak at 1551 cm− 1 in compost spectra Temperature reflects the microbial activity in the composting pro­
compared to feedstock spectra indicated the degradation of lignin at cess and is also the most important parameter affecting the microbial
higher temperature composting [47]. Two small peaks at 1375 cm− 1 growth and composting process. Fig. 5 shows the changes of high tem­
and 1160 cm− 1 disappeared in compost spectra, but a new small peak at perature composting (HTC) and control composting treatment (CCT),
1094 cm− 1 appeared. The bands at 875 cm− 1 and 597 cm− 1 were and ambient temperature during the composting process was room
distinct in the spectra of R5 compost but weaker in feedstock spectra. temperature (Average 25 ◦ C). At the beginning of composting, the
These bands are preferentially assigned to vibrations in temperature of HTC increased rapidly, reached the highest temperature
proton-substituted aromatic rings. Overall, higher absorbance in­ of 96.02 ◦ C on the third day, then decreased slowly to 60.53 ◦ C from the
tensities were observed in compost spectra compared to feedstock 5th day to the 20th day then decreased rapidly to 32.55 ◦ C on the 24th
spectra, indicating the maturity of compost. day, and finally stabilized. According to the change of reactor temper­
Furthermore, the FTIR analysis results confirmed that our UHT-AF ature, the HTC process can be divided into four stages: (1) heating stage;
strategy for poultry manure with maize straw may promote the degra­ 0–1 day (≤80 ◦ C). (2) ultra-high temperature stage 1st to 9th day
dation of lignocellulose and particularly promote the degradation of (≥80 ◦ C). (3) high-temperature stage, 10th to 21st day (50–80 ◦ C) (4)
lignin during the thermophilic composting stage. stabilizing stage for remaining days (<50 ◦ C). According to the tradi­
tional composting process, the high-temperature stage (including ultra-
3.1.4. SEM analysis of UHT-AF process high temperature stage) of ≥50 ◦ C in HTC lasted for 21 days, in contrast,
Microstructures of feedstock and treatment R5 compost samples the temperature of the CCT pile increased slowly and reached the high-
have been found through electron microscope scanning (HITACHI S- temperature stage (50 ◦ C) on the 7th day, and then fluctuated around
50 ◦ C, and then reached maximum temperature 58.25 C on 15th day

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

Fig. 2. Variation in (a) C/N ratio (b) TN & TC (c) moisture content (d) EC (e) pH (f) Wet bulk density during UHT-AF process of all treatments.

6
M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

Fig. 4. SEM image (a) feedstock (b) pretreated-product of R5 treatment.

Fig. 3. FTIR spectra of (a) feedstock (b) pretreated-product of R5 treatment.

and then decreased to 52.81 ◦ C on 24th day of composting. This high

temperature of C.T. on the 24th day shows that the CCT process needs
more time to make the stable product as the microbial activity is still
going to decompose organic matter. But high temperature (50 ◦ C) of
both processes indicated that these two processes had a good killing
effect on pathogens. However, the temperature of HTC with a large
amount of rapidly increasing ultra-high temperature lasted longer than
that of CCT, and the maximum temperature was significantly higher
than that of CT by 30–40 ◦ C, indicating that the microbial activity of
HTC compost was significantly higher than that of CCT compost, and
same temperature behavior was seen in studies of hyperthermophile
composting technology for sludge by [27,30] and high temperature
pretreated chicken manure with rice straw composting without inocu­ Fig. 5. Changes in temperature during subsequent composting.
lation by [50]. Therefore, it also means that microorganisms in the HTC
process may need to consume more organic matter and generate more 3.2.2. Changes in moisture content and pH values
heat to support the reactor to achieve ultra-high temperature. This During composting, the moisture content directly affects the
high-temperature difference between HTC and CCT compost indicates fermentation rate and compost maturity. The moisture in the reactor is
that UHT-AF shaped the microbial community that released more usually reduced by evaporation in the form of water vapor due to the
metabolic heat during the fermentation process. combined effect of heat and ventilation. It can be seen from Fig. 6a that
the overall change trend of HTC and CCT moisture content is decreasing,

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

CCT increased from 7.80 to 8.21 and from 7.32 to 8.20 during the first
12 days of composting, respectively. After the 12th day, the pH of CCT
kept increasing up to 8.65 on the 24th day, but the pH of HTC decreased
to up to 8.17 on the 24th day, this decrement was very low, almost
unchanged. The alkaline pH of both composts could be explained by the
release of ammonia by mineralization of organic nitrogen and decom­
position of organic acids by microorganisms [53]. Compared with T.C.,
HTC could stabilize compost rapidly.

3.2.3. Changes in TOC, TN, and C/N ratio

The changes of carbon and nitrogen during composting can be used
to evaluate the maturity of the composting process. Total organic carbon
(TOC) can represent the content of easily degradable organic matter in
the composting material. After UHT-AF pre-treatment, the Total carbon
content reduced from 335 to almost 320 g/kg of dry matter. It can be
seen from Fig. 7a that the TOC content changes in HTC and CCT pro­
cesses are similar, both of which decrease first and then tend to remain
unchanged in HTC. However, the TOC content in the HTC reactor is
faster and significantly lower than that in the CCT reactor, reaching
222.44 g/kg of dm on the 18th day, and decreased very slowly up to the
24th day (almost unchanged). TOC in CCT showed little decrement rate
from 6th to 12th day, and then decrement rate increased, showing that
CCT compost still needs more time for maturity. As shown by previous
studies [25,26] It can be seen from this study that HTC can accelerate the
decomposition of organic matter and the mineralization of organic
matter as compared to CCT [54].
During UHT-AF pre-treatment, T.N. content reduced from 16.75 to
almost 15 g/kg of dry matter. Fig. 7b shows the change of T.N. during
high temperature composting. In the HTC process, T.N. started to
decrease in the early stage of composting, and this decrement was
obvious in the first three days, and then decrement rate was very low
(almost unchanged) up to the 12th day and then started to increase up to
13.85 on 24th day. Whereas in the early stage of the CCT process, T.N.
reduce drastically from 16.75 to 13.85 g/kg of dry matter up to the 6th
day of composting, and after that reduction rate was very low up to the
24th day. This drastic reduction in T.N. could be explained by the pro­
duction of NH3 by microbial degradation of protein substances and its
volatilization due to high temperature and composting mixing opera­
tion. In the later stage of HTC, lower increment or unchanged T.N.
content can be explained by mineralization of organic matter, and
reduction in dry matter due to evaporation of water. It can be seen that
Fig. 6. Changes in (a) moisture content (b) pH, during subsequent composting. although the UHT-AF pre-treatment of poultry materials increases the
temperature of the compost, it does not increase the loss of nitrogen in
but the difference between their decreasing rate is very significant. As the compost as compared to CCT. This saving can be explained by lower
the temperature of HTC material increased rapidly, the moisture content production of NH+4 in HTC compost as compared to CCT compos, as
of HTC compost decreased rapidly to 44.3% on the 12th day, during the NH+4 is the main source of ammonia volatilization [55]. This little
18th to 24th day, the moisture content of the HTC pile decreased slightly increment in T.N. may also be explained by research results of [25],
up 35%, which may be due to the water vapor produced by organic ultra-high temperature pre-treatment has a negative impact on ammo­
matter decomposition was difficult to volatilize due to the low tem­ nification activity of microbes, lower ammonification rate, lower urease
perature of HTC process. However, the moisture content decrease rate of activity as well as protease activity than traditional composting. These
CCT in 0–18th days was very low and then decreased until the water enzymes are important in the N cycle as they catalyze hydrolytic re­
content of the reactor decreased to 47.3% on the 24th day. These results actions to generate NH3. These negative effects could be explained by
show that the moisture content in the HTC reactor decreases faster and the temperature profile of the HTC compost. Although it has been re­
the quantification effect of composting material is more significant. ported that higher temperature promotes mineralization of organic
Faster reduction of moisture reflected that raw materials dewaterability compound [56], the optimum temperature for the conversion of organic
characteristic could be enhanced by UHT pre-treatment [51]. N to ammonium N and protease activities can range from 40 ◦ C to 60 ◦ C
pH is an important factor affecting the growth and reproduction of according to laboratory studies [55,57]. Compared with CCT, HTC not
microorganisms during composting. When the pH value is 7~8, the only accelerated the degradation of organic matter but also had a certain
microorganism grows and propagates quickly, and the organic matter effect on nitrogen retention, also showed by [58].
degradation efficiency is high. The change of pH value during com­ C/N ratio is a common index to evaluate compost maturity. Gener­
posting in this experiment is shown in Fig. 6b. The pH value of UHT-AF ally speaking, the C/N ratio decreased from (25− 30):1 to (15− 20):1
pretreated compost was a little higher than that of CCT raw materials at during composting, indicating that the compost has been decomposed
the initial of subsequently composting. This difference could be related enough. As can be seen from Fig. 7c, As can be seen from Figure 17, C/N
to the presence of organic acids produced during the process of UHT-AF in the HTC process, showed a significant decreasing trend, which de­
pre-treatment by lignocellulose material [52]. The pH value of HTC and creases rapidly from 21.33 to 16.93 on the 12th day and then tends to be
stable, and finally reached the value of 15.50 on 24th day. while C/N in

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

3.2.4. Changes in germination index

Seed germination index (G.I.) is the most commonly used index to
evaluate the biological toxicity and maturity of compost. The change of
G.I. during HTC and CCT process is shown in Fig. 8. Zucconi [59] re­
ported that the G.I.≥ 50% represents the maturity of composts produced
from manure. HTC, as well as CCT processes, showed an increasing trend
of G.I., in HTC, G.I. reached 60% on the 12th day of composting,
whereas it took 12 extra days to reach 60% in the CCT process. The
increment rate of G.I. in HTC was higher than that of CCT. Low germi­
nation index could be explained by the production of small molecular
substances that are toxic to plants such as NH3 and organic acids from
rapidly degradable organic matter with the development of composting
process [60]. After the 12th day, the content of organic matter in the
compost decreased, so the content of small molecular substances with
toxicity to plants gradually decreased, and the compost rapidly
increased. On the 24th day, the G.I. of HTC reached 95.6%, which was
much higher than the composting maturity standard of G.I. ≥ 80%,
proposed by [61]. While the G.I. of CCT reached 60.3% at the end of
composting. The results showed that HTC compost could reach compost
maturity after 24 days of fermentation, while CCT compost could reach
compost maturity after some more days of fermentation according to
Riffaldi.

4. Conclusion

UHT-AF pre-treatment of chicken manure & corn straw for a short

time modified the physio-chemical characteristics of pretreated-product
for rapid degradation of organic matter in subsequent composting. UHT-
AF pre-treatment combined with aerobic composting increased the
heating rate and maximum compost temperature, prolonged the high-
temperature period, shortened the composting cycle, and saved com­
posting time. HTC produced mature compost after 24 days, CCT process
was still ongoing. The compost pretreated by UHT-AF degraded the
organic matter more thoroughly. The total N content in compost prod­
ucts is also higher than the CCT process, which indicates that this
method provided higher-quality compost products. Moreover, the
reduction rate of total N was also higher in CCT compared to HTC, with a
final reduction of 20% and 9%, respectively. However, due to the high
energy consumption cost caused by external heating in the pre-
treatment process, it is necessary to further study the methods to
reduce the energy consumption cost, such as utilizing the heat released
from high-temperature composting in the later stage. For the compre­
hensive utilization of agriculture wastes, this research work could act as
a good example and provide valuable guidelines to researchers and

Fig. 7. Changes in (a) TOC (b) T.N. (c) C/N ratio, during subse­
quent composting.

CCT increases from almost 20–21.92 on the 12th day, and gradually
decreases to 18.91 on the 24th day. During HTC, it can be seen that C/N
reduced rapidly during the ultra-high temperature stage, and then
reduced gradually. Due to fluctuation in T.N. value during the CCT
process, C/N showed inconsistency between HTC and CCT.
Fig. 8. Changes in Germination Index during subsequent composting.

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M. Ajmal et al. Journal of Environmental Chemical Engineering 9 (2021) 105453

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Muhammad Ajmal: Conceptualization, Methodology. Zhang
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Declaration of Competing Interest [23] Y. Huang, D. L, G.M. Shah, W. Chen, W. Wang, Y. Xu, H. Huang,
Hyperthermophilic pretreatment composting significantly accelerates humic
The authors declare that they have no known competing financial substances formation by regulating precursors production and microbial
communities, Waste Manag. 92 (2019) 89–96.
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The authors would like to acknowledge Jiangsu University for its
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support in providing experiment station and labs, and the scholarship Spectroscopic evidence for hyperthermophilic pretreatment intensifying
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