Community structure and population dynamics of ammonia oxidizers in composting processes of ammonia-rich livestock waste.

This study investigated the relationship between the population dynamics of ammonia-oxidizing bacteria (AOB) and archaea (AOA), and changes in the concentrations of nitrogenous compounds during ammonia-rich livestock waste-composting processes. The data showed that ammonia in beef and dairy cow livestock waste-composting piles was slowly oxidized to nitrite and nitrate after approximately 21-35 days under thermophilic or moderately thermophilic and mesophilic conditions. Real-time quantitative PCR (qPCR) assays showed a relative abundance of betaproteobacterial AOB during ammonia oxidation but did not detect AOA in any composting stage. Furthermore, real-time qPCR and terminal-restriction fragment length polymorphism (T-RFLP) analyses for the AOB in two composting processes (beef and dairy cow livestock waste) out of the three studied found that thermophilic or moderately thermophilic uncultured betaproteobacterial AOB from the "compost AOB cluster" contributed to ammonia oxidation during hot composting stages. Non-metric multidimensional scaling analyses of the data from T-RFLP showed that only a few analogous species predominated during composting of beef, dairy cow and pig livestock wastes, and thus, the AOB community structures in the three composting piles operating under different conditions were similar. AOB-targeted clone library analyses revealed that uncultured members of the "compost AOB cluster", which could be clearly distinguished from the authentic species of the genus Nitrosomonas, were the major constituents of the AOB populations. These results suggested that a limited and unique species of AOB played a role in ammonia oxidation during the composting of ammonia-rich livestock waste.

Successions of bacterial community in composting cow dung wastes with or without hyperthermophilic pre-treatment.

Comparative analyses of bacterial community successions in the composting materials were done for a conventional windrow post-treatment (WPOT) process with the hyperthermophilic pre-treatment (HTPRT) and simple windrow composting (SWC; without the HTPRT). Multidimensional scaling profiles based on data of terminal restriction fragment length polymorphisms of the bacterial population in the samples of every 7 days composting material and analyses of the 16S rRNA gene-based clone library of the 7 and 21 days composting materials suggested that bacterial communities of the composting materials differed much between these two processes until the 35 days of composting, whereas that they were closely related to each other at the final composting stage (42 days of composting). Detailed phylogenetic analysis clarified that all WPOT clone libraries contained many clones of the lineages of aerobic bacteria (for example, bacilli). However, the most abundant clones retrieved from all SWC materials were affiliated with a clone cluster closely related to identified and classified members of the phylum Firmicutes that have strictly anaerobic metabolism pathways. From these results, we conclude that the HTPRT process contributed to easily establish an aerobic ecosystem from the early stage to the final stage of WPOT composting with plowing the materials only once a week.

Composting cattle dung wastes by using a hyperthermophilic pre-treatment process: characterization by physicochemical and molecular biological analysis.

To solve malodorous odor problems by ammonia emission in composting of cattle dung wastes, we developed an alternative composting method consisting of a hyperthrmophilic pre-treatment reactor (HTPRT) (first step) combined with a general windrow post-treatment system (WPOT) (second step). In this study, physicochemical and microbiological differences in compost materials during the HTPRT-WPOT process and a simple windrow composing process (SWC) were investigated. The HTPRT-WPOT process removed excess ammonia in the compost materials by physical ammonia stripping, and controlled the malodorous ammonia emission. The organic matter evolution index showed that the HTPRT-WPOT process also contributed to accelerate formation of humic acids in composting. Quantitative real-time PCR analyses using Bacterial-, Archaeal- and fungal-protozoan-specific primer sets showed that small subunit ribosomal RNA (SSU rRNA) gene copy numbers differed much between composting materials of these two processes. Particularly, the SSU rRNA gene copy of eukaryotic microbes (fungi-protozoa) in the HTPRT-WPOT process was much higher than in the SWC process. From these results, we conclude that the HTPRT-WPOT process has great advantages for the control of malodorous odor problems caused by ammonia emission, and for high rate of composting evaluated by the humification rate and microbial characterization of the composting materials.