In wastewater treatment, microorganisms are the real "cleaners." They break down organic matter and remove ammonia nitrogen—but only if they have a stable "home." Elastic fillers are precisely the carefully built "apartments" for these tiny workers. They allow microorganisms to shift from a suspended state to attached growth, greatly improving treatment efficiency and making them a core component of modern biofilm-based wastewater treatment systems.
I.What Are Elastic Fillers
Elastic fillers, also known as biofilm carrier media, are made from elastic filaments of polypropylene (PP), polyethylene (PE), or nylon, strung together on a corrosion-resistant center rope to form a sheet-like or bundle-like three-dimensional structure. Their defining feature is "elasticity"—the filaments spring back into place after being struck by water flow or air, so they don't tangle, mat together, or deform and fall off over long-term operation.
Compared with honeycomb fillers and corrugated plate fillers, the open structure of elastic fillers is less prone to clogging by aged biofilm that sloughs off, resulting in longer service life and lower maintenance costs.
II. Working Principle
The working process of elastic fillers is essentially the formation and metabolism of biofilm. As wastewater flows through the filler, microorganisms gradually attach to the surface of the elastic filaments, secreting extracellular polymeric substances to form a thin layer of biofilm. This film is enriched with bacteria, fungi, and protozoa, forming a complete microscopic ecosystem. Organic pollutants are adsorbed and absorbed by the biofilm, then decomposed into carbon dioxide and water through microbial metabolism.
Under the action of water flow and aeration, the elastic filaments continuously sway, allowing aged biofilm to slough off automatically while new film keeps growing, forming a dynamic balance. This "self-renewal" mechanism is the key to the long-term stable operation of elastic fillers.
III. Core Advantages
Large specific surface area, fast biofilm formation: The three-dimensional distribution of elastic filaments gives a specific surface area of 200–500 m²/m³, with biofilm formation typically taking only 3–7 days.
Resistant to clogging, long service life: The gaps between elastic filaments are large, making it difficult for suspended solids to accumulate. Normal service life can reach 8–10 years.
Strong resistance to shock loading: Biofilm has a strong buffering capacity against fluctuations in water quality and volume. When influent concentration suddenly rises, effluent quality remains stable.
Simultaneous nitrogen removal: The anoxic-aerobic micro-environment inside the biofilm favors the coexistence of nitrifying and denitrifying bacteria, enhancing nitrogen removal efficiency.
IV. Real-World Case: Elastic Filler Retrofit at a Dyeing Wastewater Treatment Plant
Dyeing wastewater is widely recognized as one of the most difficult industrial wastewaters to treat, with high organic concentration, poor biodegradability, and large water quality fluctuations. A dyeing park wastewater treatment plant in Zhejiang, with a design capacity of 20,000 m³/d, had an existing activated sludge system whose effluent COD fluctuated between 150 and 200 mg/L over the long term, failing to consistently meet the discharge requirement of COD ≤ 80 mg/L. During low-temperature winter periods, effluent COD even exceeded 250 mg/L, and sludge bulking occurred frequently.
Retrofit plan: Elastic fillers were added to the aerobic tank, converting the activated sludge process to a biological contact oxidation process. The front section of the aerobic tank was fitted with elastic fillers at a fill ratio of 50% of tank volume, made of PP with a specific surface area of about 300 m²/m³; the rear section retained the activated sludge process, forming a "biofilm + activated sludge" hybrid system. The aeration system was also optimized to maintain dissolved oxygen within the filler layer at 2–4 mg/L.
Operating results: After the retrofit, following 30 days of acclimation and biofilm formation, a yellow-brown biofilm about 0.5–1.0 mm thick formed on the surface of the elastic fillers. Continuous monitoring data over 6 months showed that effluent COD stabilized between 60 and 75 mg/L, with removal efficiency increasing from 75%–85% before the retrofit to 92%–95%; ammonia nitrogen dropped from 15–25 mg/L to below 5 mg/L; color decreased from 80–120 times to 30–40 times. The system's resistance to shock loading was significantly enhanced—when influent COD suddenly rose to 2,000 mg/L, effluent remained below 100 mg/L. During low-temperature winter periods (water temperature 12–15°C), effluent COD remained stable below 80 mg/L. Sludge bulking was effectively controlled, and excess sludge production decreased by about 30%.
Case insights: This case reveals the core value of elastic fillers in industrial wastewater treatment—they are not merely a "microbial carrier" but a stabilizer for the entire biological treatment system. When influent quality fluctuates widely and biodegradability is poor, the biofilm immobilized on elastic fillers has stronger shock resistance and environmental adaptability than suspended activated sludge. With a relatively limited filler retrofit investment, stable effluent compliance and reduced operating costs were achieved.
V. Selection and Maintenance Key Points
Material selection: PP offers acid and alkali resistance at low cost, suitable for general wastewater; PE has better flexibility, suitable for high-suspended-solids wastewater; nylon has the highest strength, suitable for high-load industrial wastewater.
Installation density: Typically 30%–60% of tank volume. Too low results in insufficient treatment; too high leads to clogging and oxygen deficiency.
Maintenance points: Regularly check aeration uniformity, observe biofilm condition (normal is yellow-brown; black indicates oxygen deficiency; too thick indicates insufficient scouring), check for broken or loose elastic filaments, and avoid shock from heavy metals and strong acids or bases.
VI. Application Scenarios
Elastic fillers are widely used in municipal wastewater treatment (anoxic and aerobic tanks in A/O, A²/O, oxidation ditch, and other processes), industrial wastewater treatment (dyeing, chemical, pharmaceutical, food processing), river remediation and ecological restoration (biological contact oxidation units for black-odor water bodies), and aquaculture water treatment (biological filter tanks in recirculating aquaculture systems).
VII. Development Trends
As environmental standards continue to rise, elastic fillers are developing toward functional modification (adding hydrophilic groups to accelerate biofilm formation), structural optimization (new filament arrangements to increase specific surface area), hybrid applications (combined use with suspended fillers and activated sludge), and intelligent operation and maintenance (integrated sensors for online monitoring).