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ผู้เขียน หัวข้อ: Nitrification in moving bed and fixed bed biofilters treating effluent water fro  (อ่าน 1543 ครั้ง)
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« เมื่อ: มิถุนายน 26, 2014, 09:52:55 AM »

Nitrification in moving bed and fixed bed biofilters treating effluent water
from a large commercial outdoor rainbow trout RAS
K.I. Suhr, P.B. Pedersen *
Technical University of Denmark, DTU Aqua, Section for Aquaculture, The North Sea Research Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark

A B S T R A C T

The nitrification performance of two fixed bed (FB) biofilters and two moving bed (MB) biofilters was evaluated. They received the same cold (8 8C) influent water from a commercial outdoor RAS facility producing rainbow trout (average density 32 kg m3). The filters were constructed as four identical 5.5 m3 tanks with different filter media inside and tested simultaneously in duplicate. FB filters were filled with 4.2 m3 polyethylene netshaped cylinders (Bioblok1, 200 m2 m3), and MB filters with 2 m3
polypropylene carriers (Biomedia, 850 m2 m3). Nitrification rates were measured 31/2 months after start-up, and inlet water was supplemented with ammonium chloride in order to determine maximum nitrification rates (0-order kinetics). The filters were conditioned at an inlet TAN concentration of 2.89  0.1 mg l1 and water in-flowranging from 1 l s1 to 4 l s1. Expressed as volumetric total ammonia-N (TAN) removal rate, the MB filters had significantly higher removal rate (231  17 g N1 m3 d1) compared to the FB filters (92  2 g N1 m3 d1). Expressed as surface specific TAN removal rate MB filters had significantly lower removal (0.27  0.02 g m2 d1) than FB filters (0.46  0.01 g m2 d1). When conditioned to a higher inlet TAN concentration (6.27  0.39 mg l1) for 2 weeks, the FB filters increased the removal rate (146  3 gm3 d1 or 0.73  0.01 g m2 d1) while the MB filters had unaltered performance. The results indicate, that the more heterogeneous and stratified biofilm to be expected in FB, can react more flexibly when challenged with changes such as differences in TAN loading. The effect of dissolved oxygen level on FB filter nitrification rates was additionally tested at TAN 5.35  0.06 mg l1. Below approximately
60% saturation (7.1 mg O2 l1) measured at the filter outlet, nitrification rates started decreasing rapidly. An exponential expression (y = 10.05 + 10.48(1  e0.0798x), R2=0.96) was found to model the whole data range
from 40% to 80% DO saturation well.

Keywords: Nitrification RAS Biofilter Moving bed Fixed bed filter
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