Tertiary denitrification of the secondary effluent in wastewater treatment plants is necessary to control the eutrophication of receiving water bodies. Two denitrifying biofilters (DNBF), one packed with quart sand with sizes of 2–4 mm (DNBFS) and the other of 4–6 mm (DNBFL), were operated for tertiary denitrification under empty bed retention times (EBRTs) of 30 min, 15 min and 7.5 min, respectively. Under EBRTs of 30 min, 15 min and 7.5 min, the NO3−-N removal percentages were 93%, 82% and 83% in DNBFS, and were 92%, 68% and 36% in DNBFL, respectively. The nitrogen removal loading rates increased with decreasing EBRTs, and at the EBRT of 7.5 min, the rate was 2.15 kg/(m3·d) in DNBFS and 1.08 kg/(m3·d) in DNBFL. The half-order denitrification coefficient of DNBFS increased from 0.42 (mg/L)1/2/min at the EBRT of 30 min to 0.70 (mg/L)1/2/min at the EBRT of 7.5 min, while did not vary much in DNBFL with values from 0.22 to 0.25 (mg/L)1/2/min. The performance of both DNBFs was stable within each backwashing cycle, with the NO3−-N removal percentage variation within 5%. Better denitrification was achieved in DNBFS but with a slightly high decreased flow rate during the operation.

https://www.mdpi.com/2073-4441/6/5/1300/pdf

Tertiary Denitrification of the Secondary Effluent by Denitrifying Biofilters Packed with Different Sizes of Quartz Sand

A plastic raschig ring medium termed as a plastic medium was used to form dual‐media filters. This study was to evaluate the performance of dual‐media (anthracite‐sand and plastic‐sand) filters in terms of the filtrate suspended solids (SS), transparency, and color improvement. Results showed that the transparency was mainly affected by SS but color and the removal of SS from the filtrate can increase the transparency significantly. The removal of color was mainly affected by the pH during coagulation but the type of filter media. For both the anthracite‐sand filter and the plastic‐sand filter, the SS deposition patterns at pH 7 and pH 5 were surface filtration and in‐deep filtration, respectively. The anthracite‐sand filter exhibited rapid head loss development and SS breakthrough problems at pH 7 and pH 5, respectively. In contrast these problems did not occur in the plastic‐sand filter at pH 7. In addition, results based on the calculated filterability number showed that the plastic‐sand filte...

Filtration performance of a plastic‐sand dual‐media filter

Ii-142 - filtração terciária com pré-tratamento físico-químico em uma ete do tipo uasb + biofiltros aerados submersos

The study of filtration of three secondary effluents (activated sludge, rotating biological contactor, and trickling filter) is presented. It was found that filter effluent does not exceed, in average, 3 NTU for all the conditions studied. Activated sludge effluent has longer runs (6 to 27 h) than trickling filter (4 to 9 h) and rotating biological contactor (1 to 5.5 h). Best removals were achieved when treating trickling filter effluent (64%) compared to rotating biological contactor (51%) and activated sludge (55%). In all cases, the end of the run was caused by head loss rather than turbidity. Results showed that the behavior of each effluent varies widely under the same filtration and backwashing conditions and support the need for more experimental work to be conducted.

B. Jiménez

Papers

Comparison between Three Secondary Effluents in Tertiary High Rate Filtration