Semi-soft packing, combined packing and shield packing — structure, features, parameters and applications for biological contact oxidation.
← Back to Combined Packing MediaCombined packing combines the advantages of semi-soft and soft fillers, and is suitable for wastewater with lower biodegradability and lower concentration. The structure presses a plastic disc onto a double large plastic ring, and presses acetal fibre or polyester filament onto the ring so the fibre bundles are evenly distributed; the inner ring is a snow-flake plastic branch, which both supports biofilm and effectively cuts air bubbles, raising the oxygen transfer rate and utilization, so that gas, water and biofilm exchange fully and organics are treated efficiently.
Combined packing overcomes the drawbacks of soft filler — scattered strands knotting, uneven tensile strength, easy breakage in operation, fibres hard to spread horizontally in water, uneven distribution and deviation, biofilm agglomeration, low actual surface area and short service life.
It suits aerobic treatment of industrial wastewater (printing & dyeing, papermaking, pharmaceutical, wool, carpet, cotton, silk, chemical, petroleum) and domestic sewage, as well as anaerobic treatment of high-strength wastewater (ramie, alcohol, sugar, papermaking, food fermentation). Its advantages: easy film formation and no clogging, with a film-forming time about half that of other media — reaching full-load operation in 6–7 days at 18–30 ℃ with a set carbon/nitrogen nutrition, strain and gas-water ratio.
| Model | Ring size / mm | Mass / g | Bulk density / kg/m³ | Porosity / % | Surface area / m²/m³ |
|---|---|---|---|---|---|
| LF-150-40 | 150 | 4.8–5.2 | 6.2–6.7 | >96 | 12012 |
| LF-150-60 | 150 | 4.8–5.2 | 4.6–5.0 | >96 | 8743 |
| LF-150-80 | 150 | 4.8–5.2 | 3.6–3.9 | >96 | 6449 |
Widely applicable to domestic sewage and industrial wastewater treatment in petrochemical, light papermaking, food, brewing, sugar, textile, printing & dyeing, tanning and pharmaceutical industries; used with contact oxidation towers, tanks and troughs, and is a biological carrier for both biological contact oxidation and anaerobic fermentation wastewater treatment.
Shield packing is independently developed in China — Zhou Chigu applied for the shield-combinational packing patent in 1987. A semi-soft component is designed at the centre of the packing to support the soft fibre bundles outside; its plane resembles a shield, hence the name. It consists of fibre bundles and a centre rope; the fibre bundle consists of fibre and a plastic support with a hole to pass water and air; a plastic tube is embedded in the centre rope to fix distance and support the fibre bundle.
It uses the chemical properties of aldehyde-acetal vinylon fibre in soft fibre packing (acid- and alkali-resistant, ageing-resistant, biodegradable-resistant) and the physical properties of large specific surface area, light weight and good biofilm adhesion, while giving play to the semi-soft packing advantages of easy biofilm shedding, no agglomeration, high gas-water redistribution capacity, light weight and high mass-transfer efficiency.
Parameters: specific surface area 1000–2500 m²/m³, porosity 98%–99%; under normal hydraulic load COD removal 70%–85%, BOD₅ removal 80%–90%; the shield fibre packing reactor has a maximum load of 8.0 kg COD/(m³·d), and at 90% COD removal the reactor load is 7.0 kg COD/(m³·d). Specific surface area can reach 2500 m²/m³ with porosity 98%–99%.
Combined packing types continue to increase with water treatment progress. Common arrangements use a plastic ring skeleton (double ring / plum blossom ring) with aldehyde-acetal vinylon or polyester filament; typical diameters include Φ150 / Φ180 / Φ200 mm, and the media are often strung on a centre rope and suspended in contact oxidation tanks or integrated biological units. It provides a high biomass for efficient organic removal, and is a cost-effective choice for municipal and industrial wastewater treatment and upgrading.
Compiled per Water Treatment Packing & Filter Media (3rd Edition) §2.7.3, with supplementary reference notes. Actual parameters to be confirmed against the specific product.