Influent Hydraulic Retention Time Research Articles

Effect of seeding biofloc on the nitrification establishment in moving bed biofilm reactor (MBBR)

In recirculating aquaculture systems, nitrification is usually accelerated by inoculating nitrifier or mature biocarriers. In this study, the performance of the establishment of nitrification in the MBBR according to three different strategies: conventional method (Control group A), inoculation with biofloc recovered from a tilapia biofloc culture system (Group B), and addition with extra nitrite (Group C) in the Moving bed biofilm reactor (MBBR) was compared. Among them, the biofloc-inoculated group considerably accelerated the nitrification process in the MBBR (38 d), which is roughly 18 d faster than the control group (A) (56 d) and 21 d faster than group C (59 d). Less ammonia (8 mg/L NH4+-N, 10 mg/L in other groups) and external nitrite (2 mg/L NO2−-N) in the influent caused effluent ammonia to drop more slowly (5 d slower than the control group, 8 d slower than the B group), which is detrimental to the nitrification process' development. Notably, the influent's hydraulic retention time (HRT) was reduced from 12 h to 6 h following the successful establishment of nitrification. During the adaptation to reduced HRT, the MBBR inoculated with biofloc experienced short-term changes in the water quality index of the effluent water, whereas the other groups did not. The biofilm seeded with biofloc had the highest mean gray value ratio (1.42) of live/dead cell fluorescence, which grew better and could cover the entire groove under multiple microscope observations. However, the other groups did not demonstrate a similar trend. In summary, the research found that seeding biofloc use as nitrification bioaugmentation into the MBBR of the recirculating aquaculture system (RAS) to greatly speed up the nitrification process.

Ammonium conversion in liquid organic fertilisers

Liquid organic fertilisers allow growers to abandon the use of conventional de novo (mined or synthesised) fertilisers without major technological adaptions to the cultivation system. In prior experiments the conversion by aerobic substrate born bacteria of ammonium into nitrate was plant growth limiting. To improve the formulation of a commercial liquid organic fertiliser by increasing the nitrate concentration, a simple bench scale moving bed bioreactor of 20 L volume was constructed and used in continuous mode. The objective was to convert 80% or more of the organic N present in the original liquid organic fertiliser into nitrate. In the bioreactor we used naturally occurring aerobic nitrifying soil bacteria. Bacterial material from a soil sample was multiplied in vitro in selective media. The bioreactor was inoculated with ammonia and nitrite oxidising bacteria. Bacteria were maintained on a bio-carrier with a high specific surface area and a low specific mass. The bioreactor was aerated from below which allowed the bio-carrier to float and fertiliser solution could freely reach all bacterial mass. After initial inoculation, bacteria established themselves on the bio-carrier over a three week period after which accumulation of nitrite ended and stable production of nitrate as an only product of nitrification started. The nitrate production was monitored for several months during which it produced continuously. The bioreactor was supplied with fertiliser solution containing 6 mmol L-1 (total N, no nitrate). Over 90% of nitrogen supplied was converted to nitrate. Influent hydraulic retention time in the bioreactor was around 12.5 h. In conclusion, in line continuous conversion of liquid organic-N fertiliser into nitrate can be achieved for over 90% by a simple and reliable technique. The technique may be used by growers supported by the fertiliser industry or may be scaled to pre-treat commercial liquid organic fertilisers before marketing.