Divalent manganese stimulates the removal of nitrate by anaerobic sludge.

This study investigated the effect of different concentrations of Mn on the removal of nitrate by anaerobic sludge and changes in the microbial communities through batch experiments. The results showed that the addition of Mn promoted nitrate removal by anaerobic sludge; the nitrate was completely removed within 6 d in the treatment group with >5 mM Mn. With the increase in Mn, the concentration of nitrite and nitrous oxide increased in the first 4 d and then decreased to 0 μM after 8 d of incubation.

Compact Rb optical frequency standard with 10 stability.

We achieved a low-cost and small-sized Rb optical frequency standard based on Rb 5S → 6P transition with 10 stability, which is comparable with that of the best 532 nm I optical frequency standards. In this system, we directly lock the 420 nm diode laser on the 5S F = 3 → 6P F = 4 hyperfine transition line without an additional Pound-Drever-Hall pre-locking system. The signal-to-noise-ratio reaches as high as 350 000 when the averaging time is at 1 s.