Parameter optimization and performance of backwashing in biological aerated filters

The backwashing optimization, which included gas washing, water washing and water rinsing, was carried out in three biological aerated filters with zeolite, ceramic particle and carbonate media. The recovery of headloss and treatment efficiency in the biofilters after backwashing were also investigated for deeper understanding of the relationship of headloss and backwashing in BAF. The results showed that the COD and SS increased in effluent just after backwashing but could be recovered in 2 hours. The concentration of ammonia nitrogen in effluent almost did not change and recovered quickly. All of three BAFs have a promising backwashing performance and operational stability after backwashing. The backwashing procedure of upfollow BAF is suggested as follow: Firstly, air washing 2-3min with air flow rate of 10 L m
^-2
s
^-1
, then air and water washing 3-5min with both air and water flow rate of 10 L m
^-2
s
^-1
, and finally water rinsed for 9-11min with water flow rate of 10 L m
^-2
s
^-1
.