- freely available
Sustainability 2014, 6(1), 112-122; https://doi.org/10.3390/su6010112
2. Materials and Methods
2.1. Pilot Plant Description
2.2. Pilot Plant Operating Conditions and Testing Methods
- Automatic daily average samplings of the raw wastewater and the treated effluent;
- Manual instantaneous samplings (at 8 AM, 12 AM and 4 PM respectively) at the sewage input.
- pH of raw sewage (fixed probe with automatic calibration, accuracy ±0.01 pH, ±1.8 °F/±1 °C);
- Dissolved oxygen (DO) in various parts of the reactors denitrification and nitrification-oxidation (fixed immersed electrochemical probes with resolution 0.01 mg L−1, automatic calibration and temperature compensation);
- Temperature of the mixed-liquor in denitrification (fixed probe, accuracy < 0.08%, Pt100 class A).
3. Results and Discussion
3.1. Sewage Quality
3.1.1. Average Daily Quality and Daytime Fluctuations in Sewage Quality
|Parameter||Time of sampling|
|Daily average (1)||Hour 8.00 (2)||Hour 12.00 (2)||Hour 16.00 (2)|
|CODin (mg·L−1)||248.0 (σ ± 59.3)||85.9 (σ ± 18.8)||397.0 (σ ± 130.2)||320.0 (σ ± 82.6)|
|BOD5in (mg·L−1)||132.0 (σ ± 42.0)||37.8 (σ ± 12.5)||215.0 (σ ± 65.0)||193.0 (σ ± 39.8)|
|TNin = TKNin (mg·L−1)||28.2 (σ ± 5.7)||19.20 (σ ± 3.8)||38.8 (σ ± 8.3)||26.7 (σ ± 5.0)|
3.2. Denitrification Efficiency
- The lower content of DO in the denitrification reactor in relation to higher F:M ratios, reduces the inhibition of the denitrification rate (higher effects at low F:M ratios). The inhibitory effects of DO on the kinetics of the process were postulated in 1975 by USEPA in its first report on the removal of nitrogen . In subsequent reports [5,6] USEPA highlighted this effect by inserting an inhibition factor K’0/(K’0 + DO) in the expression of the denitrification rate:
|rDEN||denitrification rate (NO3-N removal by dissimilation) [mg/(L·h)−1];|
|Y||etherotrophic bacteria synthesis yield (mgVSS/mg substrate consumed);|
|K||maximum specific rate of substrate utilization (h−1);|
|X||biomass concentration (mgMLVSS·L−1);|
|S||soluble degradable substrate concentration (mg·L−1);|
|Ks||substrate utilization half-velocity coefficient (mg·L−1);|
|NO3-N||nitrate concentration, as N (mg·L−1);|
|KN||nitrate half velocity coefficient (mg·L−1);|
|K’0||DO inhibition constant for nitrate reduction (mg·L−1);|
|DO||dissolved oxygen (mg·L−1);|
|η||fraction of etherotrophic bacteria that use nitrate in lieu of oxygen.|
- An anoxic-aerobic process, creating conditions of complete mixing in the anoxic stage so that some of the input load fluctuations can be absorbed;
- Simultaneous denitrification in which aerobic and anoxic zones are alternated in conditions of complete mixing. In this case the entire volume of the reactor helps to absorb the fluctuation of the input load.
Conflicts of Interest
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