Stabilization of source-separated urine by biological nitrification process: treatment performance and nitrite accumulation.

A laboratory study on nitrification of high-strength source-separated urine was conducted by means of sequencing batch reactors (SBR) and membrane bioreactors (MBR). The highest influent ammonia concentration for SBR and MBR reached more than 2,400 and 1,000 mg N/L, while the maximum pH was about 9 and 8.9, respectively. The ammonia oxidizing efficiency in both SBRs and MBRs was around 50%, which was restrained mainly by the deficiency of alkalinity in bulks. Meanwhile, the nitrite accumulation did also dominate in these two systems, and the major factor to inhibit the nitrite oxidization was thought to be the high free ammonia and free nitrous acid content in bulks. Hence, an ammonia nitrite solution was achieved with concentration ratio of 1:1; after that ammonia oxidation was restrained owing to the deficiency of alkalinity in urine. The temperature and influent ammonia content have no great influence on the nitrification process in both kinds of bioreactors. The nitrification can be progressed under a solids retention time (SRT) longer than 30 d; however, termination of ammonia oxidization was observed as the SRT fell below 20 d. The nitrifier biomass showed an excellent settleability, such that the suspended solids (SS) in effluent was of a low average, about 60 mg/L. This study on the stabilization of human urine will be useful to understand the process of urine separation from source.

A qRT-PCR-based method for the measurement of rrn operon copy number.

AIM: To develop a convenient and accurate method for estimating the rrn operon copy number (Y(rrn)) in cells of pure prokaryotic cultures based on quantitative real-time polymerase chain reaction (qRT-PCR). METHODS & RESULTS: Using Escherichia coli, the Y(rrn) of which is known to be 7, as a reference, the rrn concentrations of target species and E. coli in sample solutions were measured based on their respective threshold cycle numbers (C(t)), whereas the cell concentrations of both species were measured by microscopic counting after staining. The Y(rrn) of the target species was then calculated from the initial cell concentrations and the rrn concentrations of the target species and E. coli. Using this method, the Y(rrn) values of four species, i.e. Xanthomonas campestris, Staphylococcus aureus, Aeromonas hydrophila and Pseudomonas fluorescens, were estimated as 1.80, 4.73, 8.58 and 5.13, respectively, comparable to their respective known values of 2, 5, 10, and 5, resulting in an average deviation of 8%. CONCLUSIONS: The whole cell qRT-PCR based methods were convenient, accurate and reproducible in quantification of rrn copy number of prokaryotic cells. SIGNIFICANCE AND IMPACT OF THE STUDY: qTR-PCR is a fast and reliable DNA quantification approach. Compared with previous qTR-PCR based methods measuring rrn copy number, the present method avoided the prerequisite for the information on genome size and GC content of target bacteria or a gene with known copy number, thus should be more widely applicable.

Autotrophic denitrification in nitrate-induced marine sediment remediation and Sulfurimonas denitrificans-like bacteria.

A group of autotrophic sulfide-oxidizing denitrifying bacteria was identified from an aged anthropogenic marine sediment treated by nitrate for the removal of recalcitrant organic residues. Based on 16S rDNA similarity, they were most closely related to Sulfurimonas denitrificans which oxidizes sulfide to sulfate using nitrate as electron acceptor. This group of bacteria was one of the eleven operational taxonomy units (OTUs) identified using a universal primer set for Eubacteria, but it was accounted for 69% of the total nitrate reduction. Using a primer set designed specifically for S. denitrificans, six new S. denitrificans-like OTUs were identified by cloning-sequencing. They had over 97% similarity with S. denitrificans and its relatives, including Thiomicrospira sp. strain CVO, Thiomicrospira sp. clone HKT806 and Campylobacterales clone DS169.