Ventilation is one of the most critical influencing factors in the homogeneous and efficient decomposition of organic matter during composting. Among them, the supplied air velocity of the perforation holes can dominate the airflow velocity in the pipe and the static pressure perpendicular to the pipe wall. Furthermore, the airflow direction from these perforation holes can often deviate towards the central axis of the pipe, leading to a ventilation-deficient zone in the proximal inlet area. The airflow direction can also be attributed to the relatively higher airflow velocity near the inlet. However, the insufficient ventilation can cause the low efficiency of the composting. In this study, the deflectors (0.75, 1, and 1.25 cm in height) were introduced behind the first perforated hole along the airflow direction. Computational Fluid Dynamics (CFD) analysis was employed to optimize the deflector height. A systematic investigation was also made on the impacts on the manure composting efficiency and microbial community dynamics. Results demonstrated that the optimal deflectors effectively mitigated the ventilation-deficient zone near the inlet. The height of the deflectors also dominated the airflow uniformity. Specifically, the deflector with a height of 0.75, 1, and 1.25 cm increased the average airflow velocity by 10.8%, 34.0%, and 34.2%, respectively, compared with the without deflector. In addition, there was no significant increase in the airflow speed with 1 and 1.25 cm deflectors. Finally, the height of the deflector was selected as 1cm, according to the cost and convenience. Two experiments were conducted to take the deflector-installed (1 cm) ventilation pipe as the treatment group (T), and the pipe without deflectors as the control group (CK). Compared with the CK, the T exhibited a 2.12 °C temperature increase during the thermophilic phase. While there was the decrease of 5.5%, 2.35%, 0.15 mS/cm, 7.4%, 0.1, 0.036 g/kg, 20.94% in the moisture content, the volatile solids (VS), the electrical conductivity (EC), the carbon-nitrogen ratio (C/N), the pH value (pH), the ammonium nitrogen (NH₄⁺-N), and the germination index (GI) at maturation period, respectively. High-throughput sequencing revealed that the deflector significantly enhanced the diversity of the microbial community. The airflow increased near the inlet, indicating the increase in the Chao 1 and Shannon index. At the level of the microbial phylum, especially during the thermophilic phase, the degradation of the macromolecular organic substances (such as the quick-acting carbon source substances) was promoted to increase the relative abundance of Firmicutes. The degradation of cellulose and lignin was promoted to increase the relative abundance of Actinomycetes and Proteobacteria in the cooling and maturing phases. Redundancy analysis indicated the positive correlations between Firmicutes and Temperature, as well as Actinobacteria/Proteobacteria/Bacteroidota and GI. While there was a negative correlation with the VS, C/N, NH4+-N. At the level of microbial genus. Especially in the thermophilic phase, the carbon consumption and heat release in organic matter were intensified to increase the relative abundance of Thermobifida and Bacillus. Redundancy analysis indicated the positive correlations between Thermobifida/Bacillus and temperature, while the negative with C/N ratio. Saccharomonospora/Parapedobacter showed a positive correlation with the GI, while a negative with the VS. Therefore, the deflector can be expected to increase the airflow volume near the inlet, thus promoting the degradation and maturity of the composting pile. This finding can provide the technical support to optimize the ventilation pipe during manure composting.

Aerobic composting is one of the primary steps for the resource utilization and harmless treatment of rural kitchen waste. The treatment device of food waste is ever increasingly needed for single or multiple households, as the development of separate waste collection and promotion of on-the-spot organic waste disposal and utilization. In this study, an aerobic composting device was designed to consider segmented fermentation for composting material, precise aeration and turning control, and multi-function integration. According to the four-stage aerobic composting, four chambers of sequential fermentation were utilized to achieve the separate fermentation of materials in different stages for the harmless treatment of the product. This integrated system also incorporated the agitation apparatus, aeration equipment, control devices, leachate collection mechanisms, and odor control systems. Continuous feeding was employed to introduce the kitchen waste and sawdust daily at a wet-to-weight 10:3. The aeration strategy was set at one minute of aeration every 10 min, and an aeration rate of 10L/min. The stirring frequency was positive for 4 min, reverse for 6 min, and stop for 240 min. The mixing performance simulation and composting experiment were conducted using kitchen waste and pine sawdust as the feedstock. In the simulation test: a fermentation tank and material particle model were constructed and calibrated the simulation parameters of kitchen waste and pine sawdust. The mixing state was simulated to explore the effect of kitchen waste and pine sawdust in four fermentation tanks using the discrete element simulation software EDEM. The mixing degree was calculated for the two kinds of materials in the fermentation tank using the coefficient of variation. The working performance of the equipment was verified in the test. In the composting experiment, solid samples were collected on days 21, 23, and 25 of the composting process, termed as the feeding port (P1), discharge port (P6), and the mid-sections of the first to fourth fermentation tanks (P2 to P5). Physical and chemical properties were determined for the maturity indices of the fermented products. The gas samples were analyzed using portable gas detectors to measure the concentrations of ammonia (NH₃) and hydrogen sulfide (H₂S) within the first, second, third, and fourth fermentation chambers, as well as at the outlet of the deodorization unit (P7). The results show that the mixing uniformity of materials in the fermentation bin was about 94%, which fully met the requirement that the mixing degree of fermentation materials reached 90%. Furthermore, the color of the fermented material was gradually darkened, the unpleasant odor gradually dissipated, and the fermented material was loose and granular after aerobic fermentation. The compost experienced a high-temperature phase exceeding 55 °C reached 5 d, and following 20 d of continuous fermentation. The number of fecal coliforms reached the hygienic safety standard. And egg mortality rate reached 100% for Ascaris lumbricoides. The seed germination index was 73%, fully meeting the requirements of the National Standard for Organic Fertilizer (NY/T 525-2021). In summary, continuous composting and independent fermentation control can be expected to effectively enhance the quality of the fermentation product in different stages. This research can also provide technical references for local resource utilization, fertilizer application, and harmless disposal of kitchen waste in rural regions.

Northeast China is the main grain production base with a large planting land for the cash crops of corn, soybean and rice in China. Animal husbandry can also be the promising potential to the waste territory, rich feed resources, and environmental carrying capacity. However, the livestock manure is difficult to be returned to the farmland nearby, due to the relatively simple planting structure of crops. It is very necessary to fully utilize the organic fertilizer for the soil organic matter, in order to avoid the degradation of agricultural ecological function. This study aims to explore the application status of livestock manure treatment and utilization modes in Northeast China. A field investigation was selected from the 272 livestock and poultry farms in Heilongjiang, Jilin and Liaoning provinces. A systematic analysis was performed on the breeding livestock and inventory, the volume of livestock excrement, as well as the treatment technologies, facilities and equipment. The parameters of manure returning to farmland were finally summarized to evaluate the utilization modes of livestock manure. The results showed that dry-dung cleaning was the main cause of manure collection, accounting for 94.35% of all the modes. Composting was dominated in the treatment technology of solid manure, accounting for 86.93% of the field tests. The proportion of manure composting time of more than 30 d accounted for 92.86%, which fully met the requirements of technical specifications for livestock manure composting. The area of feces storage facilities for all kinds of livestock also met the high requirements of construction specifications for the feces resource utilization facilities of large-scale livestock farms. The liquid manure was mainly treated by manure storage, accounting for 68.18% of the investigated farms. The storage time of liquid manure from pig and poultry farms was close to 90 d, where more than 80% of dairy farms reached 180 d. The storage capacities of dairy farms were less than the standard requirements of construction specifications for the feces resource utilization facilities of large-scale livestock farms. The storage capacity should be considered from the liquid manure production volume and storage time. Corn was dominated in the planting crop in the study area, accounting for 78.13% of all crops. There was a lower area of farmland matching for manure returning at present, compared with the demand area of livestock manure land carrying capacity. The application mode of solid manure was the most in the artificial fertilization, accounting for 88.00% of the total. The application modes of liquid manure were the two most in flood irrigation and sprinkler irrigation, accounting for 54.17% and 37.50% of the total, respectively. The time of manure returning to farmland was focused mainly on two periods, March to April and September to October. The volume of manure fertilization was less than 150 m³/hm². On the whole, the technical mode of the manure resource utilization was dominated by the dry-dung cleaning with solid manure composting and liquid manure storage. The findings can provide a strong reference for the promotion and policy-making of manure treatment and resource utilization in Northeast China.