Investigation of biochar amendments on odor reduction and their characteristics during food waste co-composting.

The odor emission such as ammonia (NH3) and hydrogen sulfide (H2S) during the composting process is a severe problem that adversely affects the environment and human health. Therefore, this study aimed to (1) evaluate the variation of physicochemical characteristics during the co-composting of food waste, and sawdust mixed biochar; (2) assess the efficiency of biochar-composting combined amendment materials for reducing odor emissions and their maturity. The raw materials including food waste (FW), straw dust (SD), and biochar (BC) were prepared and homogeneously mixed with the weight ranging from 120.0 kg to 135.8 kg with five treatments, BC0 (Control), BC1 (5 % biochar), BC2 (5 % distilled water washed biochar), BC3 (10 % biochar), BC4 (20 % biochar). Adding biochar could change physicochemical properties such as temperature, moisture, and pH during composting. The results indicated applying biochar-composting covering to minimalized NH3 and H2S aided by higher porous structure and surface functional groups. Among trials, biochar 20 % obtained the lowest NH3 (2 ppm) and H2S (3 ppm) emission on day 16 and stopping their emission on day 17. The NH3/NH4+ adsorption on large specific surface areas and highly porous micro-structure of biochar lead to reduced nitrogen losses, while nitrification (NH4+ ➔ NO2- ➔ NO3-) may also contribute to nitrogen retention. The H2S concentration decreased with increasing the biochar proportion, suggesting that biochar could reduce the H2S emission. Correlation analysis illustrated that temperature, moisture, and oxygen are the most critical factors affecting H2S and NH3 emissions (p <0.05). The physicochemical properties and seed germination index indicated that the compost was mature without phytotoxicity. These novelty findings illustrated that the biochar amendment is an effective solution to reduce odor emission and enhances the maturity of compost mixture, which is promising to approach in real-scale conditions and could apply in agricultural fields.

Nguyen MK ，Lin C ，Hoang HG ，Bui XT ，Ngo HH ，Le VG ，Tran HT ... -  《-》

Plant-derived biochar amendment for compost maturity improvement and gaseous emission reduction in food waste composting: Insight from bacterial community and functions.

This study assessed the impact of different plant-derived biochar (cornstalk, rice husk, and sawdust) on bacterial community and functions for compost maturity and gaseous emissions during the composting of food waste. Results showed that all biochar strengthened organic biotransformation and caused a higher germination index on day 12 (over 100%), especially for rice husk biochar to enhance the growth of Thermobifida related to aerobic chemoheterotrophy. Rice husk biochar also achieved a relatively higher reduction efficiency of methane (85.8%) and ammonia (82.7%) emissions since its greater porous structure. Besides, the growth of Pseudomonas, Pusillimonas, and Desulfitibacter was restricted to constrict nitrate reduction, nitrite respiration, and sulfate respiration by optimized temperature and air permeability, thus reducing nitrous oxide and hydrogen sulfide emissions by 48.0-57.3% by biochar addition. Therefore, rice husk biochar experienced the optimal potential for maturity increment and gaseous emissions mitigation.

Zhang L ，Yang Y ，Bao Z ，Zhang X ，Yao S ，Li Y ，Li G ，Wang D ，Li Q ，Yuan J ... -  《-》

Role of tobacco and bamboo biochar on food waste digestate co-composting: Nitrogen conservation, greenhouse gas emissions, and compost quality.

Anaerobic digestion is considered an environmentally benign process for the recycling of food waste into biogas. However, unscientific disposal of ammonium-rich food waste digestate (FWD), a by-product of anaerobic digestion induces environmental issues such as odor nuisances, water pollution, phytotoxicity and pathogen transformations in soil, etc. In the present study, FWD produced from anaerobic digestion of source-separated food waste from markets and industries was used for converting FWD into biofertilizer using 20-L bench scale composters. The issues of nitrogen loss, NH3 volatilization, and greenhouse gas N2O emission were addressed using in-situ composting technologies with the aid of tobacco and bamboo biochar produced at pyrolytic temperatures of 450 °C and 600 °C, respectively. The results demonstrated that the phytotoxic nature of FWD could be reduced into a nutrient-rich compost by mitigating nitrogen loss by 29-53% using 10% tobacco and 10% bamboo biochar in comparison with the control treatment. Tobacco biochar mitigates NH3 emission by 63% but enhances the N2O emission by 65%, whereas bamboo biochar mitigates both NH3 and N2O emissions by 48% and 31%, respectively. Overall, 10% tobacco and 10% bamboo biochar amendment could reduce total nitrogen loss by 29% and 53%, respectively. Furthermore, the biochar addition significantly enhanced the biodegradation rate of FWD and the mature compost could be produced within 21 days of FWD composting as seen by an increased seed germination index (>50% on dry weight basis). The results of this study could be beneficial in developing a circular bioeconomy locally with the waste-derived substrates.

Li D ，Manu MK ，Varjani S ，Wong JWC ... -  《-》

Mechanism of digestate-derived biochar on odorous gas emissions and humification in composting of digestate from food waste.

Emissions of odorous gases and prolonged composting duration are the key concerns in the composting of digestate from food waste (DFW). In this study, different amounts of biochar derived from DFW (BC-DFW) were introduced in the composting process of DFW to decrease the emissions of ammonia (NH3) and volatile sulfur compounds (VSCs) and composting duration. The addition of BC-DFW increased the temperature and germination index during DFW composting. The group with 25% BC-DFW exhibited a 30% smaller composting duration. Significant amounts of NH3 and VSCs emissions were observed in the initial phase of DFW composting. Dimethyl disulfide (DMDS) was a prominent contributor to the odor associated with VSCs. The addition of BC-DFW facilitated the adsorption of NH3 and VSCs, and the corresponding contents decreased by 5-21% and 15-20%, respectively. Moreover,the BC-DFW accelerated the transformation of ammonium-nitrogen (NH4+-N) to nitrate-nitrogen (NO3--N), thereby alleviating the NH3 volatilization. The addition of 25% BC-DFW minimized the NH3 emission and enhanced the generation of humic-acid-like matter, thereby promoting humification. Therefore, the addition of 25% BC-DFW was optimal for promoting the degradation of organic matter and humification and odor emission reduction (e.g., NH3, DMDS).

Wang N ，Huang D ，Bai X ，Lin Y ，Miao Q ，Shao M ，Xu Q ... -  《-》

Co-composting of food waste and swine manure augmenting biochar and salts: Nutrient dynamics, gaseous emissions and microbial activity.

The prominent characteristics of the biochar, high porosity, sorption capacity with low density improve the aeration, making it a desirable amendment material for composting process. The composting efficiency was analysed by the impact of rice husk biochar amendment (0, 2, 4, 6, 8 and 10%) in the presence of salts for the co-composting of food waste and swine manure, in composting reactors for 50 days. Results revealed that biochar amendment had improved the degradation rates by microbial activities in comparison with control. The final compost quality was improved by reducing the bulk density (29-53%), C/N ratio (29-57%), gaseous emissions (CO2, CH4, and NH3) and microbial pathogens (Escherichia coli and Salmonella sp.). However, 6% biochar amendment had significant improvement in compost quality, degradation rates and nutritional value which is recommended as the ideal ratio for obtaining mature compost from the feedstock, food waste and swine manure.

Ravindran B ，Awasthi MK ，Karmegam N ，Chang SW ，Chaudhary DK ，Selvam A ，Nguyen DD ，Rahman Milon A ，Munuswamy-Ramanujam G ... -  《-》