1. Filling Media (Filling Media Phase)
(1) During media filling, observe whether accumulation occurs. If accumulation is observed, stop filling and resume on the next day after further observation.
(2) During media filling, intermittent aeration should be adopted. Continuous aeration can be maintained at night, but the aeration rate should be reduced.
(3) After 24 hours of operation, introduce continuous inflow for 2–3 hours, then resume the aforementioned aeration. After 48 hours of operation, observe the biofilm formation on the media. Increase the inflow rate and extend the inflow duration, while monitoring the dissolved oxygen (DO) level in the tank, which should ideally be maintained at 1.5–2.0 mg/L. After 72 hours of operation, initiate continuous inflow and gradually increase it to the design level. Monitor (conventional) influent and effluent water quality indicators. It is expected that the design water quality requirements will be met within approximately 7 days.
2. Biofilm Cultivation Phase
Biofilm cultivation refers to the process of promoting the growth and accumulation of microorganisms in the treatment system to achieve a certain thickness of biofilm on the media. The main methods include static cultivation and dynamic cultivation.
(1) Static Cultivation
Static cultivation aims to prevent newly formed microorganisms from being washed away by water flow, thereby maximizing the contact time between microorganisms and the media layer. To accelerate biofilm formation, during the initial stage, nutrients such as urea, diammonium phosphate, and白糖 (sugar) are added once daily at a ratio of C:N:P = 100:5:1 to avoid nutrient deficiency in the wastewater.
First, inoculate sludge (10% of the effective biochemical volume) and wastewater are pumped into the biochemical tank, followed by the initiation of aeration cultivation. The filling volume of media in the biochemical tank should account for 35%–40% of the effective tank volume. Allow the system to stand without aeration for 4–5 hours to facilitate the attachment of fixed microorganisms to the media. Then, aerate for 1 hour, followed by another 2 hours of standing, and then aerate for 1 hour. Repeat this operation. After 4–5 days, the media surface should be fully covered with biofilm. On the 6th day, begin continuous low-flow influent introduction.
(2) Dynamic Cultivation
After 6 days of sealed aeration cultivation, a thin layer of yellowish-brown biofilm will have formed on the media surface. Switch to continuous inflow for dynamic cultivation. Adjust the inflow rate and control the dissolved oxygen (DO) level between 2–4 mg/L (measured using a dissolved oxygen meter). After approximately 15 days, protozoa such as amoebas and Litonotus (observed under a biological microscope) will appear on the media. The media will feel sticky and slippery to the touch. After 20 days, flagellates, Vorticella, Paramecium, and free bacteria will emerge. After another 20 days of cultivation, metazoans such as rotifers and nematodes will appear, indicating that the biofilm has fully developed. Continuous industrial operation can then commence.
3. Biofilm Acclimation Phase
The purpose of acclimation is to select microorganisms adapted to the actual water quality conditions and eliminate non-useful microorganisms. For treatment processes with nitrogen and phosphorus removal functions, acclimation ensures that nitrifying bacteria, denitrifying bacteria, and polyphosphate-accumulating organisms (PAOs) become the dominant microbial communities.
The specific approach is to maintain normal operation of the process while strictly controlling process parameters. The average dissolved oxygen (DO) should be maintained between 2–3 mg/L, and the aeration time in the aerobic tank should be no less than 5 hours. During this process, daily measurements of various water quality indicators and control parameters should be conducted. When the average biofilm thickness reaches approximately 0.2–0.5 mm, the biofilm cultivation is considered successful. The process continues until effluent indicators such as BOD₅, SS, and COD₆ᵣ meet the design requirements.