Reducing the composting time of broiler agro-industrial wastes: The effect of process monitoring parameters and agronomic quality

Does the initial C/N ratio interfere with the performance of sewage sludge composting and cotton waste?

The effects of the initial C/N ratio on the composting of sewage sludge and cotton residues are not reported in the literature. Understanding the main composting control parameters is essential for the good stabilization of these wastes. Therefore, this study sought to evaluate different initial C/N ratios for the composting of sewage sludge and cotton waste, aiming to find the ranges with the best performance for the process and quality of the final organic compost. In this sense, five mixtures of sewage sludge (S) and cotton residues (C) were prepared and composted with three replications for each treatment in a completely randomized design. Physicochemical parameters were evaluated during composting and in the final organic compounds. A Multivariate Principal Component Analysis (PCA) was applied to evaluate the agronomic quality of organic compounds. The thermal behaviour of the mixtures presented differences. The treatments 90C10S, 80C20S and 67C33S showed the highest EXI² index (3566.64, 3448.39 and 2738.89), longer duration of thermophilic phase (12 and 13 days) and better potential for maximum degradation (A) of organic matter (67.5, 61.2 and 65.6%C). The final compounds of 90C10S and 80C20S showed higher pH values (7.9 and 7.5) and higher CEC (123.6 and 114.0 meq/100 g OM). PCA showed similarity in the agronomic quality of organic compounds for 90C10S, 80C20S and 67C33S. The treatment 28C72S (initial C/N ratio of 16.6) presented final pH of 5.3 and did not meet the minimum limit required by Brazilian regulations. Initial C/N relations between 24.9 and 35.2 showed better stabilization of waste and final organic compound with better agronomic quality.

Slaughterhouse by-products composting: can microorganisms inoculum addition mitigate final compost odor emission?

Small slaughterhouses generate biowaste, which for economic reasons, is generally destined for composting. Inoculating appropriate microorganisms can improve biodegradation efficiency and mitigate odor generation during the composting process and can give rise to composts with neutral or pleasant odors. Therefore, the aim of this study was to compare the odor intensity reduction of compost generated with and without a formulated inoculum (Saccharomyces cerevisiae, Bacillus subtilis, and Rhodopseudomonas palustris). A set of experimental data was collected and analyzed according to the German "Verein Deutscher Ingenieure" odor protocol. The results showed that adding microorganisms was effective in reducing unpleasant odors in all three composts generated from swine, cattle, and poultry slaughterhouse by-products during both summer and winter seasons. Additionally, soil odor was predominant in composts that were inoculated in the two tested seasons (i.e., summer and winter). On the other hand, composts without inoculation had odors similar to peat for swine compost, ammonia for cattle compost, and manure for poultry compost, regardless of the season tested. Overall, composting process with appropriate inoculum can help in the correct disposal of slaughterhouse wastes by transforming organic matter into composts, which can have economic and environmental value as a soil conditioner and/or fertilizer.

Response characteristics of Flax retting liquid addition during chicken manure composting: Focusing on core bacteria in organic carbon mineralization and humification

To explore the applicability of flax retting liquid (FRL) addition, the physicochemical properties, microbial community structure and function, carbon conversion and humus (HS) formation were assessed during chicken manure (CM) aerobic composting. Compared with the control group, the addition of FRL increased the temperature at thermophilic phase, while the microbial mass carbon content (MBC) in SCF and FRH groups raised to 96.1±0.25 g/Kg and 93.33±0.27 g/Kg, respectively. Similarly, FRL also improved the concent of humic acid (HA) to 38.44±0.85 g/Kg, 33.06±0.8 g/Kg, respcetively. However, fulvic acid (FA) decreased to 30.02±0.55g/Kg, 31.4±0.43 g/Kg, respectively and further reduced CO₂ emissions. FRL influenced the relative abundance of Firmicutes at thermophilic phase and Ornithinimicrobium at maturity phase. Additionally, FRL strengthen the association among flora and reduce the number of bacteria, which was negative correlated with HA and positive with CO₂ during composting. These findings offer powerful technological support for improving agricultural waste recycling.

Humification evaluation and carbon recalcitrance of a rapid thermochemical digestate fertiliser from degradable solid waste for climate change mitigation in the tropics

Indiscriminate, unhygienic and unscientific disposal of solid wastes poses significant risks leading to soil, water and air pollution. Abiotic and nonenzymatic rapid thermochemical processing technology provides a solution for the management of degradable solid waste at the source, converting it to organic digestate fertiliser within a day, thus overcoming the main drawback of the long time span required for composting. A study was performed to evaluate the maturity parameters and the extent of humification of the thermochemical digestate fertiliser and the raw biowaste substrate. We made an objective assessment of the recalcitrance efficiency of the added thermochemical digestate fertiliser on tropical Ultisol soil grown with two cycles of tomato and amaranthus crop sequences. Unlike the raw biowaste substrate, the thermochemical digestate complied with the threshold standards of compost maturity parameters and humification indices. Soil application of the thermochemical digestate fertiliser brought significant additions to the labile, microbial biomass and recalcitrant fractions of soil organic carbon within a year after four cycles of crop growth, as revealed by principal component analysis. Linear regression analysis revealed a strong and significant fit of the labile and microbial biomass carbon fractions with the total dry biomass of amaranthus and tomato. The thermochemical digestate fertiliser imparted a recalcitrance index of 85.57 % and enhanced the soil carbon stock by 4.81 % over the compost-based treatments with a superior soil carbon sequestration rate. The study confirmed that thermochemical digestate fertiliser is a fairly humified, high-resource organic fertiliser input with enhanced agronomic biomass production and recalcitrance efficiency, favouring soil carbon sequestration in Ultisol soils of the tropics.

Agroindustrial wastes as a substrate for the cultivation of Eruca sativa Miller seedlings: physical-chemical and phytometric parameters assessment

Evaluation was made of the use of organic substrates obtained from the composting of poultry industry wastes, together with crude glycerin, for the production of arugula seedlings (Eruca sativa Miller). The raw materials included hatchery waste, chicken litter, and flotation tank sludge, in combination with other materials such as tree pruning, sugarcane bagasse, crude glycerin (at 0, 1.5, 3.0, 4.5, and 6.0%), and boiler charcoal. Analysis of the organic substrates included determination of nitrogen, phosphorus, and potassium (NPK), pH, electrical conductivity, functional groups, and carboxylic acids. Physical parameters determined were water retention capacity, solids volume, porosity, density, and granulometry. For the arugula seedlings, determinations were made of the ease of removal of the root ball from the tray, the effect of free drop on the root ball, phytometric parameters, and total phenolic compounds. Decreased concentrations of carboxylic acids, together with the presence of aromatic functional groups, indicated maturation/stabilization of the organic substrates. The phytometric measurements indicated that the use of the organic substrates with addition of 3.0, 4.5, and 6.0% of crude glycerin favored arugula production and led to higher contents of total phenolic compounds in the seedlings, with values of 3657.54, 3602.13, and 3232.92 mg GAE g^-1, respectively. The results demonstrated that the use of these organic substrates with the addition of crude glycerin provided satisfactory development of arugula seedlings.

Composting of swine production chain wastes with addition of crude glycerin: organic matter degradation kinetics, functional groups, and carboxylic acids

Little is known about the effect of adding crude glycerin (CG) as a carbon source during the composting of agro-industrial residues, such as those generated in the swine production chain, especially concerning the impact on organic matter humification. Therefore, the aim of this work was to study the effect of adding crude glycerin during the composting of organic swine waste, using appropriate analyses to determine the degree of maturation of the organic material. The experiment was performed using composters constructed from pallets. The variables considered were temperature, mass, volume, organic matter, functional groups, carboxylic acids, pH, electrical conductivity, total organic carbon, total Kjeldahl nitrogen, total phosphorus, potassium, basal respiration, and germination index. For all the CG concentrations tested, thermophilic temperatures were reached, while higher amounts of CG (4.5 and 6.0%) maintained temperatures above 55 °C for longer periods (28 days). Fourier transform infrared spectroscopy analysis showed the presence of an aromatic stretching vibration signal at 1620 cm^-1, confirming mineralization of the organic matter, while the decrease of carboxylic acids at the end of the composting period indicated stabilization. The organic composts presented high nutrient contents and absence of toxicity, indicating that they could be safely used in agriculture.