The use of composting for the treatment of animal by-products: Experiments at lab scale

Effect of C/N ration on disposal of pig carcass by co-composting with swine manure: experiment at laboratory scale

Disposal of animal carcasses by co-composting with animal waste usually selected conventional carbon to nitrogen (C/N) ratio around 25:1, in which the compost is widely used throughout the world. In this study, the pig carcass tissue blocks were sampled for composting at a laboratory scale to evaluate the effect of C/N ratio on the pig carcass compost. The time of thermophilic phase between 60 °C - 70 °C at a lower C/N ratio of 20:1 was significantly longer than that at the conventional C/N ratio, and it was the only one with the temperature beyond 70 °C that lasted for 2 days. Germination index and T value (the final C/N ratio / the initial C/N ratio) of the treatment with a C/N ratio of 20:1 were 94.67% and 0.69, respectively, meeting the standards of animal carcass compost. The degradation rate was 75.67%, and no significant difference was obtained as compared to the conventional C/N ratio groups. Organic fertilizer produced from the treatment with a C/N ratio of 20:1 was selected to evaluate the fertility by pot experiment of Cayenne pepper compared with chemical fertilizer. The results showed that organic fertilizer from this treatment could significantly improve the growth of Cayenne pepper. Overall, the use of the lower C/N ratio of 20:1 in the disposal of pig carcass by co-composting with swine manure could achieve the similar degradation rate as well as the maturity and stability of organic fertilizer as compared with the traditional C/N ratio at lab scale.

Full-Scale Composting of Different Mixtures with Meal from Dead Pigs: Process Monitoring, Compost Quality and Toxicity

ABSTRACT

Abundant by-products of large swine industries, such as slaughterhouse sludge and carcasses, require adequate treatment to prevent negative effects of their direct disposal in the open environment. This study is aimed to evaluate the efficiency of composting using meal from dead pigs through physicochemical analyses and phytotoxic assays. Five treatments were tested, all including 50% sawdust: T1, with 50% slaughterhouse sludge (control); T2, with 20% slaughterhouse sludge and 30% meal from dead pigs; T3, with 10% slaughterhouse sludge and 40% meal from dead pigs; T4, with 20% organic stabilizing compost and 30% meal from dead pigs and T5, with 30% organic stabilizing compost and 20% meal from dead pigs. The phytotoxicity assays used lettuce, cucumber, celia, soybean, rice and wheat as bioindicators. Inclusion of meal from dead pigs was related to reduction in pH, C/N ratio, humidity and temperatures inside the pile, although thermophilic peaks lasted longer than 50 days and the final composts showed high content of nitrogen and phosphorous. The germination of bioindicators was reduced in all tested treatments, compared to the control. The composts from treatments that included meal from dead pigs presented acceptable nutrient content, which may indicate their use as organic fertilizers. However, after 4 months, all bioindicators in contact with such composts presented impaired germination.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12649-021-01422-0.

Assessing the Economic Viability of an Animal Byproduct Rendering Plant: Case Study of a Slaughterhouse in Greece

Continuous human population growth has led to increased livestock production and hence large quantities of animal byproducts. One of the oldest and most efficient animal byproducts processing techniques is rendering, which facilitates the recovery of resources in the form of fat and protein flour. The purpose of this study is to provide data for the feasibility of rendering as a treatment method. The case of a Greek slaughterhouse is presented, regarding its animal byproduct treatment process through rendering and incineration. Three different waste management scenarios are compared, with rendering proving to have a lower operational cost (€51.80/ton) compared to incineration (€74.10/ton), and rendering followed by incineration (€72.13/ton). The rendering process is then compared with other established animal byproduct treatment methods like composting and anaerobic digestion through the analytic hierarchy process, in terms of environmental, economic, and technological efficiency, with rendering (having a final score of 72%) proving once again superior compared to composting (with a score of 54%), and anaerobic digestion (with a score of 55%).

Development of a model for food waste composting

Worldwide, large amounts of food are wasted every year. Reducing of food waste at European level is taken very seriously and it has been adopted even a target of reducing the amount of food waste in half until 2030. In many countries of the European Union, food wastes are composted, while in countries like Romania, the composting is too little used or not at all, but efforts are being made to apply this process. Food waste composting should take place both at the composting plants and housing level. An important step before starting the composting process is to establish an appropriate recipe. Therefore, the aim of this paper is to develop a composting recipe starting from investigation of food waste like peel and pomace of fruits (apple, banana, orange, and kiwi) and vegetables (potato, cabbage, and carrots) which are very common in waste generated at the housing level. The most important physical-chemical parameters were investigated in this study. Results show that pH of fruit waste is acid (4.0-5.0), while for vegetable waste, the pH is slightly higher (between 6.0 and 6.5). For all types of food waste, a very high moisture content (80-90%) was registered, while the nitrogen content is below 1%. Considering that C/N ratio is one of the most essential parameters, for the process to be carried out in good conditions, we have used regression analysis in order to determine the amounts of fruits and vegetable waste necessary to obtain different C/N ratios.

Evaluation of the disintegration of linen fabric under composting conditions

In recent years, about 10% of the total wastes generated around the world were fabric wastes and, due to the large volume of these wastes, should be well managed. Among the various types of fabrics, some have greater biodegradability and can be decomposed at the acceptable rates under controlled conditions. In this study, the disintegration of linen fabric was investigated under composting conditions. During the composting process, temperature, moisture, and aeration were controlled. According to FTIR spectra of linen fabrics during the composting process, the disintegration of linen fibers was identified as the breakdown of carbonyl groups and hydrogen bonds of cellulosic chains. Regarding the SEM images of linen fabrics, the composting process in the first 45 days led to the breakdown of the fibers, and in the second 45 days of the process, most of the fibers were degraded. Since in the second 45 days of the process, the compost pile temperature is always between 39 and 44 °C and 65-70 °C, it can be concluded that the rate of microbial disintegration of the linen fabric is higher at these temperatures. At the end of the test, the disintegration value of the linen fabric was 55% and the weight loss due to organic matter conversion was 61%. The samples weight loss showed that linen fabric has high biodegradability under composting conditions. The germination index (GI) of the resulting compost was 73.88%, which indicates the produced compost is mature.

Influence of N-rich material in valorization of industrial eggshell by co-composting

Industrial eggshell (ES) is an animal by-product (ABP) involving some risk if not properly managed. Composting is a possible treatment approved for its safe use. This study aims to assess the influence of using N-rich material (grass clippings (GC)) to improve co-composting of ES mixtures for reaching sanitizing temperatures imposed by the ABP regulation from the European Union. Two sets of mixtures (M1 and M2) were investigated, each containing industrial potato peel waste, GC and rice husks at 3:1.9:1 and 3:0:1 ratios by wet weight. In each set, ES composition ranged from 0% to 30% (w/w). Co-composting trials were performed in self-heating reactors for 25 days, followed by maturation in piles. Results showed that only M1 trials attained temperatures higher than 70°C for nine consecutive hours, but N-losses by stripping on average were four- to five-fold higher than M2. In the absence of N-rich material, biodegradability of mixtures was 'low' to 'moderate' and organic matter conversion was impaired. Physical, chemical and phytotoxic properties of finished composts were suitable for soil improvement, but M1 took 54 more days to achieve maturity. In conclusion, co-composting ES with N-rich materials is important to assure the fulfilment of sanitizing requirements, avoiding any additional thermal treatment.

Effect of temperature on bacterial emissions in composting of swine manure

Swine manure was subjected to laboratory scale composting in order to quantify bioaerosols, i.e., airborne culturable bacteria and endotoxin, in the exhaust gas, which provided details on the effect of temperature on bacterial emissions. The concentration of airborne bacteria reached 31,250 colony-forming units (CFU)/m(3) during the thermophilic stage of composting, and positively correlated with the temperature profile of the compost pile. Initially, the endotoxin concentration was 1820 endotoxin units (EU)/m(3), but it decreased exponentially as the composting process proceeded. The temperature can be an excellent indicator of bacterial emissions during the composting process, indicating that the composting process requires a consistently high temperature to ensure sanitization of both compost and bacterial emissions. The cumulative emission data showed that emission factors was 11.2-13.5 CFU/g dry swine manure and that of endotoxin was 0.5-0.9 EU/g dry swine manure. The bacterial diversity in the bioaerosol was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis, revealing the presence of various gram-negative bacterial consortia.

Potential of chicken by-products as sources of useful biological resources

By-products from different animal sources are currently being utilised for beneficial purposes. Chicken processing plants all over the world generate large amount of solid by-products in form of heads, legs, bones, viscera and feather. These wastes are often processed into livestock feed, fertilizers and pet foods or totally discarded. Inappropriate disposal of these wastes causes environmental pollution, diseases and loss of useful biological resources like protein, enzymes and lipids. Utilisation methods that make use of these biological components for producing value added products rather than the direct use of the actual waste material might be another viable option for dealing with these wastes. This line of thought has consequently led to researches on these wastes as sources of protein hydrolysates, enzymes and polyunsaturated fatty acids. Due to the multi-applications of protein hydrolysates in various branches of science and industry, and the large body of literature reporting the conversion of animal wastes to hydrolysates, a large section of this review was devoted to this subject. Thus, this review reports the known functional and bioactive properties of hydrolysates derived from chicken by-products as well their utilisation as source of peptone in microbiological media. Methods of producing these hydrolysates including their microbiological safety are discussed. Based on the few references available in the literature, the potential of some chicken by-product as sources of proteases and polyunsaturated fatty acids are pointed out along with some other future applications.

Biochemical changes and GHG emissions during composting of lignocellulosic residues with different N-rich by-products

Nitrogen availability plays a critical role in the biodegradation of organic matter during composting. Although the optimal initial C/N is known to be around 25-30, the chemical form in which N is present influences microbial activity and therefore degradation rate and gaseous losses. This study was conducted to evaluate the influence of N availability on the composting of a mixture of lignocellulosic materials. Three composting piles were made of a mixture of wheat straw and cotton waste, each pile containing different N-rich animal by-products. The evolution of the main physico-chemical parameters was monitored (temperature, pH, electrical conductivity, C/N, NH(4)(+), NO(3)(-), water soluble C and N) as well as the enzymatic activity related to the cycle of the main nutrients (β-glucosidase, protease, alkaline phosphatase and fluorescein diacetate hydrolysis). Additionally, fluxes of CO(2), CH(4) and N(2)O emitted from the composting piles were measured by the closed-chamber technique. Cumulative CO(2) emissions were fitted to five different kinetic models with biological significance to C mineralization data. The application of the different N-rich residues had a significant effect on the C and N dynamics during composting. However, most enzymatic activities followed similar patterns in the three piles. The major CO(2) fluxes were recorded during the thermophilic phase, showing a direct relationship with temperature peaks. No CH(4) fluxes were detected for any of the composting piles during the whole trial, whereas low N(2)O emissions were found at the early beginning and during the maturation stage.