Principles of Low Oxygen Biochemistry
Low oxygen biochemistry mainly achieves organic matter degradation and nitrogen and phosphorus removal by controlling the dissolved oxygen (DO) concentration in the reaction environment (usually 0.2-0.5mg/L) and utilizing the metabolic activity of microorganisms under micro oxygen or hypoxic conditions. Its core mechanism includes:
Microbial metabolic regulation: Low oxygen environment promotes the activity of denitrifying bacteria (anaerobic stage) and polyphosphate accumulating bacteria (anaerobic/aerobic alternating stage). Denitrifying bacteria use organic matter to reduce nitrate nitrogen to nitrogen, while polyphosphate accumulating bacteria achieve phosphorus removal through anaerobic phosphorus release and aerobic phosphorus uptake.
Inhibition of filamentous bacterial expansion: Low DO may induce filamentous bacterial micro expansion, but by controlling other parameters such as load and pH, the sludge settling performance can be maintained, while utilizing the large specific surface area of filamentous bacteria to improve organic matter degradation efficiency.
Energy metabolism optimization: Under low oxygen conditions, cells enhance energy generation through oxidative phosphorylation, while activating autophagy and antioxidant stress mechanisms, prolonging microbial activity.
The debugging process of low oxygen biochemistry
Sludge inoculation and domestication
-Add similar or identical activated sludge, with an initial concentration controlled between 1500-2500mg/L.
-In the initial stage, carbon sources such as feces and starch were added (COD 200-300mg/L), supplemented with nitrogen and phosphorus (BOD: N: P=100:5:1), and incubated under low pressure (air-water ratio 1:5-10).
-Determine sludge activity by observing the appearance of protozoa (such as nematodes and rotifers) through microscopic examination.
Load increase stage
-Initial stage: The volumetric load is 0.5-1.0kg COD/m ³ · d, and the influent COD is controlled at 1000-5000mg/L.
-Start up phase: Gradually increase the load to 50% of the design value (about 40 days), monitor the formation of granular sludge and gas production.
-Full load stage: Increase the load to 100% (30-40 days), adjust the aeration rate and reflux ratio to ensure that the effluent meets the standard.
Environmental parameter control
-Temperature: Medium temperature anaerobic (30-40 ℃) or low temperature (15-20 ℃), avoiding significant fluctuations.
-PH: Anaerobic section 6.5-8.0, aerobic section 7-8.5.
-Oxidation reduction potential (ORP): hydrolysis stage -100~+100mV, methane production stage -150~-400mV.
Operational management matters
Key parameter monitoring
-Dissolved oxygen (DO): 0.2-0.5mg/L in the anoxic stage and 1-3mg/L in the aerobic stage, to avoid excessive inhibition of denitrification or low levels that may cause sludge to float up.
-Carbon to nitrogen ratio (C/N): Maintain BOD5/TKN at 4-6, and add external carbon sources (such as acetic acid and methanol) when insufficient.
-Nitrate nitrogen: The nitrate nitrogen in the influent of the anoxic section is controlled at 10-20mg/L and adjusted by the internal reflux ratio (200% -400%).
EXCEPTION
-Sludge expansion: Micro expansion of filamentous bacteria (SVI ≤ 150) is acceptable. If excessive, it can be controlled by increasing DO, adjusting pH, or adding coagulants.
-Low denitrification efficiency: Check if the carbon source is sufficient, if the internal reflux is reasonable, or increase the HRT in the anoxic zone (2-4 hours).
Energy saving optimization
-Using frequency conversion aeration to control DO and reduce power consumption.
-Real time monitoring of denitrification status using ORP and dynamic adjustment of carbon source dosage.
Routine maintenance
-Regularly discharge sludge and maintain the sludge age (SRT) at 10-20 days.
-Monitor changes in biological phases and promptly detect abnormal microbial activity.
