Ammonium Removal by Nitrifying Bacteria Biofilm on Limestone and Bioball Substrate Established in Freshwater Trickling Biofilter

Abstract

Ammonium, regarded as a major nitrogen pollutant in aquaculture, can be removed by biofilm formation in a biofilter. This research aimed to study ammonium removal on two kinds of substrates: limestone and bioball. Experiments were conducted through three consecutive steps: (1) Biofilter component set up (a trickling filter and substrate) of four groups; limestone substrate (LC), bioball substrate (BC), limestone substrate with nitrifying bacteria (LT) and bioball substrate with nitrifying bacteria (BT); (2) Monitoring biofilters performance for 15 days, where at day-0, 50 ppm ammonium was added into each system and at day-5 the ammonium level in all systems were adjusted to 70 ppm; (3) Enumeration of microbiome making up biofilm during biofilter conditioning period. In this current study, even though ammonium removal was observed in all experimental groups, inoculation of nitrifying bacteria significantly increased the ammonium oxidation rate. After 5 days, both treatment groups inoculated with nitrifying bacteria (LT and BT) degraded ammonium to 2.20-2.25 ppm, while the control groups (LC and BC) degraded ammonium to 12.38-16.59 ppm only. After ammonium adjustment, both treatment groups inoculated with nitrifying bacteria (LT and BT) degraded ammonium to 1.40-2.41 ppm, while the control groups (LC and BC) degraded ammonium to 17.06-23.53 ppm only. The total ammonium removal over 15 days of biofilter monitoring were 33.10% day-1 and 30.95% day-1 for LT and BT group, respectively, and 15.12% day-1 and 11.94% day-1 for LC and BC group, respectively. Biofilm formation on all groups showed the presence of ammonium and nitrite oxidizing bacteria (AOB and NOB) as well as heterotrophic bacteria. In the treatment groups AOB and NOB pioneered the biofilm formation, in contrast with the control groups where heterotrophic bacteria were the pioneer.