Waste Management through Composting: Challenges and Potentials

Composting is the controlled conversion of degradable organic products and wastes into stable products with the aid of microorganisms. Composting is a long-used technology, though it has some shortcomings that have reduced its extensive usage and efficiency. The shortcomings include pathogen detection, low nutrient status, long duration of composting, long mineralization duration, and odor production. These challenges have publicized the use of chemical fertilizers produced through the Haber–Bosch process as an alternative to compost over time. Chemical fertilizers make nutrients readily available to plants, but their disadvantages outweigh their advantages. For example, chemical fertilizers contribute to greenhouse effects, environmental pollution, death of soil organisms and marine inhabitants, ozone layer depletion, and human diseases. These have resulted in farmers reverting to the application of composts as a means of restoring soil fertility. Composting is a fundamental process in agriculture and helps in the recycling of farm wastes. The long duration of composting is a challenge; this is due to the presence of materials that take a longer time to compost, especially during co-composting. This review discusses the proper management of wastes through composting, different composting methods, the factors affecting composting, long-duration composting, the mechanism behind it, the present trends in composting and prospects. The extraction of mono-fertilizers from compost, development of strips to test for the availability of heavy metals and pathogens as well as an odor-trapping technique can go a long way in enhancing composting techniques. The addition of activators to raw materials can help to improve the nutritional quality of compost. This review further recommends that degradable organic material in which composts slowly should be assessed for their ability to mineralize slowly, which could make them advantageous to perennial or biennial crops. Viricides, fungicides, anti-nematodes, and anti-bacterial of plant or organic sources could as well be added to improve compost quality. The enhancement of composting duration will also be useful.

The microbiota structure in the cecum of laying hens contributes to dissimilar H2S production

Background Host genotype plays a crucial role in microbial composition of laying hens, which may lead to dissimilar odor gas production. The objective of this study was to investigate the relationship among layer breed, microbial structure and odor production. Results Thirty Hy-Line Gray and thirty Lohmann Pink laying hens were used in this study to determine the impact of cecal microbial structure on odor production of laying hens. The hens were managed under the same husbandry and dietary regimes. Results of in vivo experiments showed a lower hydrogen sulfide (H2S) production from Hy-Line hens and a lower concentration of soluble sulfide (S2−) but a higher concentration of butyrate in the cecal content of the Hy-Line hens compared to Lohmann Pink hens (P < 0.05), which was consistent with the in vitro experiments (P < 0.05). However, ammonia (NH3) production was not different between genotypes (P > 0.05). Significant microbial structural differences existed between the two breed groups. The relative abundance of some butyrate producers (including Butyricicoccus, Butyricimonas and Roseburia) and sulfate-reducing bacteria (including Mailhella and Lawsonia) were found to be significantly correlated with odor production and were shown to be different in the 16S rRNA and PCR data between two breed groups. Furthermore, some bacterial metabolism pathways associated with energy extraction and carbohydrate utilization (oxidative phosphorylation, pyruvate metabolism, energy metabolism, two component system and secretion system) were overrepresented in the Hy-Line hens, while several amino acid metabolism-associated pathways (amino acid related enzymes, arginine and proline metabolism, and alanine-aspartate and glutamate metabolism) were more prevalent in the Lohmann hens. Conclusion The results of this study suggest that genotype of laying hens influence cecal microbiota, which in turn modulates their odor production. Our study provides references for breeding and enteric manipulation for defined microbiota to reduce odor gas emission.

Biochemical Changes and Biological Origin of Key Odor Compound Generations in Pig Slurry during Indoor Storage Periods: A Pyrosequencing Approach

Production of odors is a complex process. Many bacterial species are involved in the production of an extensive array of key odor compounds in stored pig slurry. Understanding of basic microbial communities and their role during storage periods is an essential way to control and prevent the odors generations. In this aspect, the pig slurry samples were taken directly from deep pits of finisher pig building every two weeks, their biochemical changes were analysed, and the indigenous bacterial communities that involve in offensive odor producing compounds were identified. The SCFA, BCFA, phenols, and indoles levels altered drastically in the slurry during storage periods. The COD, BOD, SS, P2O5, TKN, and NH4-N were increased in the stored slurry. Bacterial ecology indicatesFirmicutesandBacteroidetesphyla were dominantly found in pig slurry. Odorants produced in pig slurry were correlated with bacterial communities. Phenols, indoles, SCFA, and BCFA productions were positively correlated with bacteria species which comes under phyla ofFirmicutesandBacteroidetes.It seems that bacterial species underFirmicutesandBacteroidetesphyla play an important role in the offensive odor compounds production. Taken together, the prevention of these phyla bacterial growth and early discharge of pig slurry might reduce the offensive odor production.

Methods for controlling stored urine odor in resource-oriented sanitation

Urine odor is a major challenge in the development of resource-oriented sanitation (ROS). One common solution to overcome odor issues is to use energy-consuming ventilation practices. However, historically ancient Koreans practiced separation of urine and feces, followed by the collection and utilization of gathered sanitary matters. Furthermore, ancient Persians developed solutions to urine odor issues. This study investigates the role of NH3 concentration on odor production in stored urine using the standard threshold odor number (TON) measurement. Trends in pH and NH3 production, as well as their interactions with TON, were investigated by simulating ancient Korean practices that stored urine under anaerobic conditions at different temperatures. The results show a direct relationship between the concentrations of NH3 and TON. Storing urine under anaerobic conditions leads to the production of NH3, which intensifies as temperature increases. The effect of pH and NH3 concentrations on the TON of stored urine explains the ancient Persian approach, given that additives, such as acetic acid and sodium bicarbonate, are effective for removing urine odor. Such approaches can be successfully applied to ROS systems.